ft-901dm ham radio repair. - Page 1
Forum section: electronics / repair

author: drforbin
author_rank: Regular Contributor
timestamp: December 08, 2015, 03:03:23 am
content: Hi guys. I don't know if this is the proper place to ask for help related to ham radio repair, but I thought I'd try anyway.I am currently trying to repair a ft-901dm ham radio.I'm having problems if transmitter power output.When turned up on 160, 80,20 I'm getting close to full power on 20m I'm getting only 10 watts.I tracked it down to ALC circuit (this circuit is pretty simple. If anyone wants schematics I can provide them) It seems that on some bands, 20m in particular the ALC is preventing the PA from reaching full power. I tested all the caps and traced the circuit, even going as far as changing most of the caps associated with the ALC. NO good. I really cannot figure out whats going on. I really need some help or suggests to put me on a new path.Ok thank you all for reading.any suggestions will be welcome.Drforbin.PS. I have neutralized the tubes.

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 02:39:08 am
content: Hi,Been a while since working on one of these but i would download this service manual first and start there (if you dont already have it).http://www.radiomanual.info/schemi/FT901DM_serv.pdfIts an excellent manual and covers all sections in detail. And includes a trouble shooting section as well as modifications and updates.The ALC is not band specific so any faults on it would effect all bands. So i dont think its that. It just reduces TX drive throughout.Some questions:Does the Receive side work on all bands? Use the Marker switch and check all bands. Eg (from the manual) 14.2Mhz should read as S9+10 on the meter. Are all the bands able to receive ok? If not, its a clue.Is it only the 20m band not transmitting well? Do all other bands peak ok up to the correct power? into a 50ohm dummy load of course never ant!!If the receive side is all ok, and fault is purely 20m TX power low, then i would be looking at the Band Switch wiring to Tank Coil. Check for dry joints. This is also mentioned in the manual.Other 20m only things to check are the Xtal board (20m xtal and coil can) and VCO unit (coil can). These may be out of adjustment or an actual faulty component. But if the RX side works ok, this is unlikely.hope this points you in the right direction.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 02:49:08 am
content: Hi..I have the service manual. The radio seems to be working on RX on all the other bands.I'm getting small ALC on 160,80 bands and a great offset on 40m.What I mean is this. With ALC disconnected I get over 100 watts on dummy load on 40m when connected I get 10 watts.ALC does not seem to be working at all on 20m at all.The ALC seems to be cutting in to early. I checked the entire ALC circuit cannot find anything wrong.

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 02:59:46 am
content: Hi,And on 20m with ALC disconnected, are you able to get 100watts there too? So is the problem getting worse the higher the band selected? Whats 10m like?

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 03:10:30 am
content: Yes. I get full power on 20m with alc connected or disconnected.On 10m same.On 80m and 160m I can get close to full power.Measuring ALC line it's producing a small offset on 80m and 160m.Enough to attenuate power alittle. On 40m it attenuates so much that it cuts power to the 10 watts as stated.Some others have had same problem...but no one has posted a solution.please see reference.https://forums.hamisland.net/showthread.php/17415-Yaesu-FT-902DM-ALC-problem

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 03:22:06 am
content: Ok i see. So the real problem is occurring at 40m. Not 20 as i read it in your first post.Slight power reduction on 160 and 80m, 40 is very low and all other bands are good. I think thats the summery?The link you posted suggests the Mode Switch. But how would that effect the ALC / Band selected.i'll take a look at the diagram. Will get back if i see anything.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 03:25:40 am
content: The mode switch is not it. I checked it.I do get full power on 40m on all modes accept SSB. that is why the poster logically suggested that it was the mode switch. It is not. The reason why the other modes work and SSB does not is because the mode switch grounds ALC for ALL modes except SSB operation.

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 04:54:32 am
content: Well, looking at the Rect A Unit, the ALC is derived from the grid bias (unit pin 5) from the final PA. That signal is then rectified and filtered to produce the ALC line (out on pin 3) which then feeds to the NB/Proc unit to reduce tx signal. And yes it clearly shows the mode switch grounding the ALC on all other modes other than SSB as we mentioned.That said, its odd that only 40m seems to be having a bad effect on the ALC operation. Maybe some of the ALC rf filtering is not working (looking at that 2M2 resistor, c12 , c11 area).. And its become 'tuned' to 40m. Did you check that area on Rect A? Some small pf caps, they will need testing. Other than that, something else causing the ALC to change badly on 40m, possibly a PA fault / tuning issue. Could even go as far a needing a re-alignment procedure (especially 40).

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 05:00:49 am
content: Firstly...thank you for helping me.Ok...I checked and even changed the rec 'a' caps associated with ALC. so we are on the same page.I realigned everything including 40m. I also have new Tubes. All this has been done.You see...it's quite a perplexing problem.FYI with finals removed ALC signal stops. With Finals in place even with filaments not lit. Problem persists.I also have neutralized tubes.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 05:10:16 am
content: FYI..Alittle bit of theory. I believe the finals are suppose to be CLass B amps.which means that they should always be negatively biased. The theory of operation best I can tell of the ALC is the peaks which positively bias the grid draw current (of course) where as negative bias (and signal donot). It's these positive excursions which the alc is looking for thus indicating a over drive condition. The problem is I looked at it on a oscilloscope and even when I attenuate the signal enough for it to be entirely neg biased I still get alc on 40m and some on the other bands (i.e. 160,80) as before.It doesn't make any sense.

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 05:39:05 am
content: 'With Finals in place even with filaments not lit'There's only two things i can think of that could cause that. Inter plate capacitance or faulty valves/tubes. uk here so its valvesEither way, its doing bad things to the ALC , as you are painfully aware of.Yes, the PA stage is biased with a negative grid to keep them in their linear region, turning the valve ON. And the bias - Ic (I current) is set by the user with a preset and panel meter. The ALC looks like its simply detecting anything ac from the bias voltage. I guess that's distortion or clipping of RF at the grid. That looks like its then rectified and produces a negative ALC line (to turn off the dual gate FET at the NP/Proc unit). Now if you have distortion at 40m for some reason, it may show as excess ALC.

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 06:07:51 am
content: Oh, just correct myself there. Rather than detecting distortion, of course this is SSB and the RF rectified would be from a speech envelope of RF. So its detecting the levels of carrier as you speak. Makes more sense.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 06:13:06 am
content: yep..that's what I thought "inter plate capacitance" But everything has been neutralized and I even went as far as to change alot of the caps on driver and finals board.I know i'ts not the correct way to fix something is to throw parts at it but I'm desperate.Ok..you mentioned distortion. Coming out of the rf unit where the signal and vco are heterodyned the wave is jumping around alot. It not fully stable. well maybe a problem??I'll make a video of it and post it to my youtube channel. Would you mind giving me your opinion at that point?

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 06:19:47 am
content: FYI..As I said I'm at the end of my rope. The ALC circuit is pretty simple and I really think it is function correctly. Also I changed just about everything or tested it on both driver and PA sections. The only thing I have not test is the resistance values of the parasitic chokes off the plate. but I think they are ok. so, again thanks for brain storming with me.I'm new to ham radio. If you wann have a look at my youtube channel I have fixed spectrum analyzers. tds540 oscilloscopes etc. and this rf stuff has me pulling out my hair.https://www.youtube.com/user/seaman6661/videosWhat I thinking of doing is isolating the driver and PA from the rest of the radio and sending a 7 Mhz 3.5 P-P waveform into the driver and see how the ALC and power output respond. Problem Is I currently donot have a function generator.HUmmm what would dave do?

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 06:27:19 am
content: You are certainly welcome to post a video of the signal going in. And if you can, sniff some of the RF out and see if thats a clean sinewave. Hopefully you can see 7Mhz on your scope.Oh its a tricky one! haha,

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 06:31:52 am
content: I've looked at it already. The vco is clean and the signal is clean the heterodyned signal coming from the rf unit is alittle strange. I just didn't think that could be the problem. Your telling me it may be? I'm get the video done by tomorrow for you to look at.Thank you again.

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 06:09:23 pm
content: I am suggesting that taking a look at the RF output (sniffed at dummy load) may give a clue. Just key down for a few seconds for a clean constant carrier. Another thing, if you have access to a spectrum analyser, take a look at the RF out and check for spikes or parasitic oscillations. Again this could be clue and compare 40m with a known good band like 160m.At this stage, anything that shows up may direct you to finding the fault. Because it sounds like all the likely faults have been dealt with already. Time to start looking for the not-likely onesoh, i need to ask, sorry, but are the output valves the exact correct type? 6146B's if i remember correct.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 06:15:24 pm
content: Well. Sniffing at the output of the PA is a problem do to the power. Don't want to blow my test equipment. I will have the video for you tonight sniffing at rf unit output and input.I have two sets of tubes one set are the B versions and the other the W versions.Again...thanks for help.As a said. I did this test already I just will commit it to video.The output of the rf unit is very jittery. I would like you to have a look at the waves form once I have it on video and see what you think. I didn't think it could matter but who knows.

author: AF6LJ
author_rank: Unknown
timestamp: December 10, 2015, 06:32:54 pm
content: Don't know what you have for test equipment...Replacing all those caps may have introduced your current problem.You need to check what you replaced and make sure it is the proper value. also a way to check if the PA is properly nutralized is to place the transmitter in tune on a band such as 20 or 15 meters tune for max into a dummy load. (let the tubes rest for a minute) then with the radio's meter in the IC position verify that the peak output point agrees with minimum (the dip) in IC reading. If they don't occur at the same point the PA is not properly neutralized. It has been 25 years since I worked on one of those, so I am a little rusty...

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 08:09:20 pm
content: 'Sniffing at the output of the PA is a problem do to the power. Don't want to blow my test equipment'Just wrap some wire around the coax to the dummy load, its safe. Not a direct connection!. The term 'sniff' means loosely coupled, a small sample of the larger RF energy. Just a few turns. Not much. Just enough to see the carrier. (assuming your scope can handle 7Mhz.).

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 09:03:59 pm
content: Hi..thanxs for your input.The radio was doing this before I changed anything.All caps were changed using values read from old caps and from schematics.As for neutralizing what I do is run some RF through the PA with the finals filaments not lit.Using a sensitive DMM I adjust from dummy load for a minima at 29Mhz.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 09:08:44 pm
content: voltz, cool! great idea thanks..I have a 500MHz tds540.so basically just use inductive coupling right?

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 09:15:04 pm
content: Yes. Maybe start very loose, 1 turn, then proceed to increase as needed. Do it 'by feel' .

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 09:16:42 pm
content: wrap it around the coax to dummy load?

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 09:28:46 pm
content: somewhere between transmitter and dummy load, its not really important. Around the outer coax plastic, a loose turn.. Increase power slowly, watch the scope, adjust the Y amp.. etc. Until you get a decent trace. The loose turns should be enough to pick up stray RF on the coax. Put your probe across the wire loop. Start small, build it up as needed.

author: Mr Simpleton
author_rank: Unknown
timestamp: December 10, 2015, 09:51:08 pm
content: Beeing a proud owner of a 901DM I find this problem interesting... I even dug out my old service manual as one really need the paper versionYou say you do get the ALC to prevent full output on some bands. The ALC is broadband, i.e. rectified RF from the finals and then applied to NB PCB where the transmitter IF is attenuated. ALC voltage is found at ACC socket pin 7 where and external amplifier may take control of the ALC. If you have not measured the ALC here you do have an easy access point here.If your BIAS is set to 50 mA the final amp should be running linear and the ALC would work OK. Now if you have a messed up neutralizing circuit your tubes may oscillate... I would check this first!! Look at the Ic and see if it is higher than normal for the power output. The dip at Ic should be pretty much spot on max power output, and adusting the load shoul not be "nervous" to the measured Ic.Finally do not forget to measure the RF output at the phono jack at the rear this is a low power output and should be equal amplitude regardless of frequency, this is from the driver,a nd should work with PA filament switched off! This will tell if the driver and circuits are OK.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 10:02:46 pm
content: Thank you for your interest.I have measured the ALC. It's near -4 volts going into pin 16 on nb unit. This is on 40m.I have neutralized the tubes as per my last message. I have not checked rf of finals due to power output.But thanks to voltz suggestion of inductive coupling I will tonight.I have checked driver output. On the 100p mica cap I'm getting about 170 to 200 volts P-P depending on band.

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 10:07:50 pm
content: 'As for neutralizing what I do is run some RF through the PA with the finals filaments not lit.Using a sensitive DMM I adjust from dummy load for a minima at 29Mhz.'drforbin, i am not familiar with that procedure of neutralisation. Is this a correct way to neutralise the PA? Other posters (and myself) do it the proper way by matching Ic dip with power out peak. Could you try it that way? Its in the book of course too.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 10:08:41 pm
content: By the way. neutralization should only be a problem at higher freqs 29Mhz for example.On lower freqs the reactance of the caps coupling is high thus blocking oscillation.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 10:10:28 pm
content: I will try other way. But supposedly using the dmm and rf pass through is a superior method.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 10:12:05 pm
content: Kenwoods use pass through method all the time.

author: Mr Simpleton
author_rank: Unknown
timestamp: December 10, 2015, 10:16:44 pm
content: When you check the low level RF output, and haviing the filament switched off, you say you have pretty much the same RF voltage out. That is interesting as it appears as if it is the driver RF that is recitified and creates the ALC voltage!What happens if you reduce power with the control knob? If you press the tune button, this will give lower output on all bands, is it still misbehaving on 40 meter??

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 10:22:57 pm
content: Yes..that's what's crazy. On 20m for example I can drive the input to the finals at ~176 P-P with NO ALC being produced. on 40m I have to reduce the amplitude to around 80 volts P-P to result in near 0 ALC.

author: AF6LJ
author_rank: Unknown
timestamp: December 10, 2015, 10:25:58 pm
content: Quote from: drforbin on December 10, 2015, 10:08:41 pmThat is true unless it is way out.I wonder if enough RF energy is getting through both driver and final to preform the neutralization properly. When I worked on the 901DM I did I had removed screen voltage from the final and left the heater switch on, and did neutralization that way.Mr. Simpleton is spot on

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 10:28:41 pm
content: 'That is interesting as it appears as if it is the driver RF that is recitified and creates the ALC voltage!'Yes it is, see diagram. It only feeds the final PA grids. (Rect A Board to -100v Bias).

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 10:30:54 pm
content: Yes. I seem to get enough. I have quite a sensitive Dmm u1272a and I definitly see the dip when I tune the neutralizing cap. What I will do tonight is run the thing with inductive coupling on 40m and see if I get a really clean sin wave.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 10:32:29 pm
content: Yes..it's the driver which is rectified on rec board 'a' and is then cleaned up and feed back to mosfet on NB board. As I said...it's a real neat problem.

author: Mr Simpleton
author_rank: Unknown
timestamp: December 10, 2015, 11:02:16 pm
content: Let's recap, with heaters on PA off, you have proper signals on low level RF output and the ALC behaves "normal" on all bands. Now swtiching on the heater and run full power you do get funky ALC on 40 meter. Now as the PA is really out of the ALC loop this sounds like the PA tubes magically upsets the ALC... I would start with fresh 6146B tubes. Then start look at components i.e capacitors at the final tube grids, But I would first look at the output specturm with my spectrum analyzer to verify no self oscillation.-.-. ...-.-

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 11:13:24 pm
content: No....kinda. To recap.Final tubes on or off does not seem to effect the alc.Which is logical considering the alc is derived from the driver. If I pull the tubes (finals) alc seems to go away.I am getting no alc on 20m no matter how hard I drive it. on 160 and 80 the alc is offseting alittle about -2 volts. On 40m it offsets so much that at full power with alc disconnected I get over 100 watts with it connected I get 10 watts. I just did voltz's inductance check. I guess I have really good coax because the shielding was such I could get anything by wrapping wire around coax.I did wrap a wire around the wire going to plug for coax and got a good signal. The freq was correct and the wave form looked very clean. So there seems to be no self oscillation.I have two sets of tubes. The strange behavior is on both sets. It's not the tubes.

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 11:22:36 pm
content: Glad that worked, at least now you have the ability to see the RF output. Its also a good technique for spectrum analysis. Which is the next question, as we mentioned before, do you have one?Other things left to try, text book style neutralisation. If anything, to rule this out as a possible problem.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 11:24:28 pm
content: yes..I used the tds540 scope on it.I have a 8590a SA which I repaired. I'll have a look with it.What am I looking for harmonics?

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 11:32:37 pm
content: Hmm, well yes there will be harmonics but they should be tiny in comparison to the fundamental. If you see anything wondering around, free running oscillations, thats bad!.. Just take a good sweep plus and minus of the carrier.. Ideally, it should only be one major spike.

author: Mr Simpleton
author_rank: Unknown
timestamp: December 10, 2015, 11:47:13 pm
content: Ho-hum....So only running the driver, having the finals idle, you still have the 40 meter ALC problem... That sounds pretty odd. Likely a rotten cap then.Look and see how the transmitter tunes on 28 MHz... if smooth on both side of the Ic dip, it should be properly neutralized.

author: drforbin
author_rank: Regular Contributor
timestamp: December 10, 2015, 11:50:29 pm
content: ok..just used SA on PA. I used a 30Mhz span to capture at least two harmonics.I'm getting a perfect peak at 7Mhz nothing else.I'll put all this on video tonight for you guys.So you can see what I'm talking about.

author: voltz
author_rank: Frequent Contributor
timestamp: December 10, 2015, 11:55:52 pm
content: Ok, that was a good test. Sounds clean. Just try to re-neutralise as per the manual.

author: drforbin
author_rank: Regular Contributor
timestamp: December 11, 2015, 07:17:56 am
content: Ok guys..heres a quick video showing the problem.I'll get the test video up soon.

author: voltz
author_rank: Frequent Contributor
timestamp: December 11, 2015, 10:09:17 am
content: Nice. I see what you did with the sniffer wire at the socket. Plenty of RF there.Yep, thats pretty much how I saw the ALC reacting after talking in depth about it. Its really odd as the other bands do not show that high level of ALC.Out of interest, how are you driving the SSB audio? signal generator at the mic, or does the Tune button work by injecting a tone. I cant remember. Because the ALC is only activated in SSB mode so just trying to understand that.Good work so far, quite sure you will get to the bottom of it in time. My favorite mantra at times like these is 'There is always a reason for it'.. Just a solution that hasn't been found yet.

author: drforbin
author_rank: Regular Contributor
timestamp: December 11, 2015, 05:16:23 pm
content: Thank you. I really do appreciate your help.I will do some more tests tonight and post them. Tonight I'll show vco signal, driver signal and result from rf unit on tds540. I will also post rf signal on tds540.I later will do SA as well and post that for you guys.I did notice that the SA results were alittle strange on 40m. But perhaps I am projecting (you know looking for an answer where there is now. Something I have been doing my whole life!)As for driving the signal. The tune button uses CW freq and injects that just as a straight carrier for tuning purposes.I just bought a function generator (wavetek) it should be here by next week.What I'm thinking of doing is isolating the entire driver/finals section and injecting a 7Mhz signal at proper amplitude into it. If the ALC behaves itself than I know it's something with the signal.When I post the tds540/SA results have a look at them.The output of the RF unit is quite jittery. I'm not expert enough it know if that's ok or is a sure sign of danger.thanks guys!

author: AF6LJ
author_rank: Unknown
timestamp: December 11, 2015, 08:24:00 pm
content: Looking forward to seeing the spectrum analyzer and scope images.I have a theory and will keep it to myself for now.

author: drforbin
author_rank: Regular Contributor
timestamp: December 12, 2015, 03:24:49 am
content: Oh the subject of neutralization, I just wanted to post these two links for informational purposes.http://www.k4lmp.org/downloads/Cold_Neut.txthttp://www.w8ji.com/neutralizing__amplifier.htmWill have videos by tonight.Thanxs guys.

author: drforbin
author_rank: Regular Contributor
timestamp: December 12, 2015, 05:01:27 am
content: Ok.As promised here is latest video.Let me know what you all think!

author: voltz
author_rank: Frequent Contributor
timestamp: December 12, 2015, 01:07:31 pm
content: Well i have to say it looks pretty clean to me. The jittery waveform on 40m would be the result of the mixing process before its filtered. Input A and B of a mixing signal always finds its way out of the mixer. Thats just how mixers work. Its not just the wanted mix frequency out.I think you are seeing some of the 15Mhz input superimposed on the 7 (about double period). Of course, the output of the mixer is then filtered at the RF driver and so on to result in a pure 7. So this looks ok to me. And without a comparison 901DM, i would say this is expected.EDIT, sorry i had to change this after posting-->This is shifting the focus.. I now suspect something has become resonant at the PA final grids. There are a few components but two stand out. L02 with 56R choke coil and L03 also with 56R at the grids. Suppose one of those damping resistors went open?. You get a self tuned circuit (high impedance rejector). Now also suppose thats at 40m.. The ALC is going to react badly and would block RF to the final. It also explains why the PA valves (even with heaters off) effects the ALC problem. Those few pf extra are changing the resonant frequency of the tuned (problem) circuit. Its a theory! There's also a chance that with only one final valve removed it would have an effect on the ALC fault. Narrowing down to one choke or another. But its hard to say if this is a safe test with only one PA running, i would suggest this is only safe at low power levels, not driving to max. Never had to do that before, so some caution there.Any chance of checking those?

author: AF6LJ
author_rank: Unknown
timestamp: December 12, 2015, 04:29:18 pm
content: A common trap for those who may not be too careful is to have the 40 meter coils tuned ot the 8.9MHZ signal and not the difference frequency between the VCO and the 8.9MHZ signal. A number of radios that use an IF in that frequency range. (most commonly 9MHZ) fall into the same trap.All the coils for 40 meters should be set for Max inductance and carefully tuned for the first peak, move in the decreasing inductance direction.In theory this is what could be happening.EDIT:What you see as jitter is not; it is both the 8.9 signal and the 7.0 MHZ signals.As I said above the 40 meter band coils are misstuned.

author: drforbin
author_rank: Regular Contributor
timestamp: December 12, 2015, 08:14:08 pm
content: Again thank you all. I thought it looked pretty clean as well.Voltz, That was one of my initial ideas as well, resonance !I already removed and checked those resistor/inductor pairs.The wire is wrapped around the resistor, so I had to carefully cut the wire, check the resistance and resolder.AF6LJ, thanks for helping?What coils are you talking about?I believe I realigned everything properly, but I could be wrong.here is a schematic of the driver/PA and general schematic.Could you tell me what your talking about.

author: AF6LJ
author_rank: Unknown
timestamp: December 12, 2015, 08:52:51 pm
content: Your 40 meter mixer and driver coils.If you start with them at max inductance and tun for max you can't go wrong.

author: drforbin
author_rank: Regular Contributor
timestamp: December 12, 2015, 09:48:00 pm
content: They only have trimmer caps.

author: drforbin
author_rank: Regular Contributor
timestamp: December 12, 2015, 09:49:45 pm
content: There is a whole procedure for alignment. I've gone through it at least 5 times.I sometimes even used a scope to peak everything.No change.

author: AF6LJ
author_rank: Unknown
timestamp: December 13, 2015, 12:11:03 am
content: Quote from: drforbin on December 12, 2015, 09:48:00 pmThat's right they are only trimmers.Okay good enough.I still wonder why there is so much IF feedthrough on 40..

author: drforbin
author_rank: Regular Contributor
timestamp: December 13, 2015, 03:57:54 am
content: With all due respect I donot see how this could interact with the ALC. As observed on the scope I am not getting run away amplitude.

author: AF6LJ
author_rank: Unknown
timestamp: December 13, 2015, 12:59:11 pm
content: Quote from: drforbin on December 13, 2015, 03:57:54 amFix the problem and see if you still have ALC issues, it needs to be fixed anyway.My Tempo-One isn't even that dirty.

author: AF6LJ
author_rank: Unknown
timestamp: December 13, 2015, 02:05:21 pm
content: I might add;On 40 meters you could have more 8.9mhz feedthrough than you have actual 7.0MHZ signal. The PA could be swamped with that signal, and during the tuning process you might have tuned the mixer, driver in and plate caps to that frequency.I can't find it in the schematic (that copy of the manual is really bad) but there should be a couple of 8.9MHZ traps, and the manual won't tell you how to adjust them, that is typical for Yaesu, their documentation is marginal at best. Your spectrum analyzer will show a fairly large amount of 8.9MHZ on the output. This can interfere with ALC operation on 40 meters, because that circuit sees all, not just the 40 meter energy.As for the driver tuned circuits filtering that 8.9MHZ energy out; I wouldn't count on it.To prove my point on the documentation;you may have noticed there is no alignment procedure for the VFO.Well...My 75 meter sked is starting up....Be back later.

author: drforbin
author_rank: Regular Contributor
timestamp: December 13, 2015, 07:14:46 pm
content: So you think the signal is dirty?I'll do a spectrum analysis tonight and post it.Also I have a function generator on the way.it'll be here Tuesday. Going to isolate the driver/final section inject a 7Mhz signal and see what happens.

author: AF6LJ
author_rank: Unknown
timestamp: December 13, 2015, 07:19:24 pm
content: Quote from: drforbin on December 13, 2015, 07:14:46 pmI don't think it is dirty; I know it is, I could see it on your scope.QuoteThat might be helpful but not necessary.

author: drforbin
author_rank: Regular Contributor
timestamp: December 13, 2015, 07:43:46 pm
content: ok great....Was it dirty coming in the rf unit or after rf unit?Remember I showed the vco/signal and the result from rf unit.I think the vco and signal looked clean.The only jitter was after the rf unitVoltz what you think?

author: voltz
author_rank: Frequent Contributor
timestamp: December 13, 2015, 07:51:24 pm
content: Its certainly worth investigating.However my questions would be, if 40m was tuned to the IF rather than the wanted 7Mhz, how is the TX stage able to still achieve full power on the correct 40m band?. Also, i guess the VFO would not work, due to it being tuned to a fixed 8.9Mhz IF?. And lastly, does this explain the action of when the PA finals are removed, the ALC recovers, even with heaters off. To me it does not add up. The spectrum analysis will be interesting to see. I have no answers, only questions at this time.

author: Mr Simpleton
author_rank: Unknown
timestamp: December 13, 2015, 08:14:24 pm
content: An odd problem indeedNow that you do have access to a spectrum analyzer it should help to nail down the problem. I would run full output on 7 MHz and study the signal with your SA.There are only two things that can show this kind of troubble... i.e. self oscillation close to 7 MHz, or that a stage has developed higher than normal amplification on 7 MHz. You may even find something if you look at the signal that goes to the driver stage, making sure it is clean enough. Maybe the band selector has developed a problem on one of the switches and select wrong or multiple resonators....

author: drforbin
author_rank: Regular Contributor
timestamp: December 13, 2015, 08:32:14 pm
content: Yeah..Leave it to me to get the really hard problems.The TDS540 scope I just fixed took me 6 months.It had some of the craziest problems.look on youtube (my channel) if your interested.As for the ft-901 thanxs all for helping.I know I keep saying that but it is much appreciated.I will run the SA analysis tonight and post.

author: AF6LJ
author_rank: Unknown
timestamp: December 13, 2015, 09:07:53 pm
content: I don't think it is a self oscillation I have seen this before, and it is easy enough to fix.QuoteAs to the VFO working it would depend on how much of the wanted signal made it through VS the unwanted (IF) signal.These tuned circuits are fairly broad and the PA can be tuned to operate on 8.9MHZ with just the front panel controls. on the 40 meter coil tap.Like I stated above this is an easy mistake to make in tuning and even easier if someone has been in there before and mistuned one of the 8.9MHZ (or 9.0MHZ) Yaesu was famous for using to get by the shortcomings of their designs.

author: drforbin
author_rank: Regular Contributor
timestamp: December 13, 2015, 10:18:11 pm
content: Ok then...what is the procedure for tuning this thing.I have followed the procedure as outlined in the manual with NO luck.

author: AF6LJ
author_rank: Unknown
timestamp: December 13, 2015, 10:58:22 pm
content: Quote from: drforbin on December 13, 2015, 10:18:11 pmHere is what I would do;Use the spectrum analyzer in place of the watt meter.Loosly couple it to your dummy load tune it to 7MHZ (they say 7.2 in the book as I remember) and tune the two trimmers for max out.Then see if your output power is correct.I can say with a high level of confidence nothing is wrong with the ALC circuit.I can also say with a high degree of confidence that your transmitted signal is not clean on the 40 meter band.What I can also say is; having spent half an hour looking on line I cannot find a decent copy of the manual, but hay... I guess we get what we pay for.

author: drforbin
author_rank: Regular Contributor
timestamp: December 13, 2015, 11:09:12 pm
content: Here is link for manual.http://www.foxtango.org/ft-library/FT-Library/FT101ZD-901-902/FT-101ZD-901-902.htmAs for peaking fine. But I have done that alrdy multiple times. Peaking I mean.I did not use the SA. In fact it's not possible to peak the 40m with the ALC connected because it's fighting you the whole time. I do agree with you. I believe there is nothing wrong with the alc circuit.It's very simply and I have checked all the possible fault modes.You said the signal looked dirty, I request again, which part?The vco input to rf unit, the signal input to rf unit or the resultant output of rf unit?The PA output looked real clean to me but it's been filtered alot by that time.thanxs for your time.

author: voltz
author_rank: Frequent Contributor
timestamp: December 13, 2015, 11:40:28 pm
content: From reply #43:"ok..just used SA on PA. I used a 30Mhz span to capture at least two harmonics.I'm getting a perfect peak at 7Mhz nothing else."guys, its clean... and tuned. Otherwise there's no way the TX would achieve 100 watts at that frequency. (with ALC disconnected). no?Whatever is coming out of the RF mixer (jiggle on scope) is just the result of mixing. You can see 'jiggle' on your scope at 20m too. And is then filtered out at the following driver stage. Its all working as it should! Power and frequency wise. Its just the ALC is 'seeing' something wrong. Thats the mystery. That is my current thinking of it. It might all change when we see this SA result!

author: Mr Simpleton
author_rank: Unknown
timestamp: December 13, 2015, 11:45:43 pm
content: IF the ALC is working as it should, i.e. reducing the power to a max predetermined power.. question is where is the power?Now if you cannot have full output on 7 MHz, and the ALC is at full blast, there MUST be energy on some other frequency.... simple as thatThe spectrum analyzer should show where...Load cap should be around 3-5 if I recall correctly and you should see a max ouput on plate and that would also be a shallow dip in Ic, if you have less load the dip will be narrower. Bit it seems you cannot see this and the PA seems to be making a lot of power on a magic frequencyIF transmitter is OK without the ALC loop closed. It points a big fat finger to the loop it self. Carefully look at the circuit around driver and how the RF voltage is sampled. It may be you have a resonance at 7 MHz creating far too much ALC applied.Good Luck hunting it down

author: voltz
author_rank: Frequent Contributor
timestamp: December 14, 2015, 12:05:42 am
content: "IF transmitter is OK without the ALC loop closed. It points a big fat finger to the loop it self. Carefully look at the circuit around driver and how the RF voltage is sampled. It may be you have a resonance at 7 MHz creating far too much ALC applied. "Yes Mr Simpleton. The transmitter does appear to be fully working without the ALC loop connected (or with PA valves removed). We did discuss resonance around the ALC rectifier circuit some posts back. But with no result. Components were tested/changed.I still believe this is a resonance related issue effecting the ALC detector. It could even be a simple Valve type issue. After reading some docs about various types of 6146. It seems the 6146B is not always compatible with earlier 6146 / A valves. It also states some of the problems in changing to 6146B's are 'differences in inter-electrode capacitance and spurious parasitic oscillations..' hmm, sound familiar?

author: drforbin
author_rank: Regular Contributor
timestamp: December 14, 2015, 12:26:40 am
content: Voltz is correct. I originally thought it may be a resonance issue. I still have not ruled that out.My attack plan is as follows.I will post Sa results tonight.When Function generator shows up I will run a 7Mhz about 3.5vP-P signal through the driver/FinalsIf I still get a ALC then AT least we have isolated the problem to the driver/finals.If the problem remains it has SOMETHING to do with the signal because my function generator presumably is a clean wave form.any comments?Voltz, it's my understanding you think the waveforms as presented on tds540 to be clean, is that correct?Our other watchers donot agree. Any comments?

author: retrolefty
author_rank: Super Contributor
timestamp: December 14, 2015, 12:38:48 am
content: Quote from: voltz on December 14, 2015, 12:05:42 amSounds familiar. I have owned a Kenwood TS-520S hybrid forever it seems (idle in a closet) that used the Japanese version of the 6146/6146A, S-2002 I think I recall. I too recall reading that mixing between 6146/A/B some of the older hybrid transceivers can be tricky.

author: voltz
author_rank: Frequent Contributor
timestamp: December 14, 2015, 12:47:28 am
content: "Voltz, it's my understanding you think the waveforms as presented on tds540 to be clean, is that correct?"Yes. But let me define 'clean':The jiggle you are seeing is the expected result from the mixer. Its not clean in the classic sense of the word, ie a pure sine wave, but i believe it is correct and should not cause a problem to the ALC.If i'm wrong but your radio gets fixed, its still a great result because your radio got fixed!

author: drforbin
author_rank: Regular Contributor
timestamp: December 14, 2015, 12:49:38 am
content: I agree....Just wanted to clarify

author: voltz
author_rank: Frequent Contributor
timestamp: December 14, 2015, 01:07:30 am
content: Your plan of attack sounds good. Divide and conquer.But, what types of valves do you have there at your disposal? Final PA valves. Can you change them. And compare ALC levels.The biggest thing that stuck in my mind was your finding about pulling out the finals and curing the ALC. Thats just weird and we're back to finals again. See my 6146 types post earlier.. What do you think?.

author: drforbin
author_rank: Regular Contributor
timestamp: December 14, 2015, 01:12:52 am
content: Well, there is a difference between the a/b/wThe B tubes should be used. The W version is a militarized version(Us Americans love our military you know).I have both the B and W versions available. Both produce the same results.

author: voltz
author_rank: Frequent Contributor
timestamp: December 14, 2015, 01:19:43 am
content: I read that B and W types are basically the same with different branding letters. But the earlier 6146 and 6146A are more stable and not the same. Are we sure this radio was designed for B types?Im getting my information from here:http://www.foxtango.kc9foz.com/FT101ZD-901-902/FT-901DMsg.pdfpage 25 of the pdf.EDIT: no, B and W are not the same, after reading again, but W types can be any type. Only the date stamp gives it away.

author: drforbin
author_rank: Regular Contributor
timestamp: December 14, 2015, 01:28:11 am
content: This is from service manual.

author: voltz
author_rank: Frequent Contributor
timestamp: December 14, 2015, 01:34:25 am
content: Indeed.But something is wrong here. Maybe a version change at some point? Its sounds 'out there' doesn't it.

author: drforbin
author_rank: Regular Contributor
timestamp: December 14, 2015, 01:36:04 am
content: I know...that's why I needed (need) and appreciate you guys help.It's a nutty..will post SA analysis a bit later.

author: voltz
author_rank: Frequent Contributor
timestamp: December 14, 2015, 02:31:56 am
content: Seems like there were at least two versions of the 901dm. An early version and a later one. Yours appears to be an earlier version (looking at your trimmer board colour). But i cannot find any references to what finals were used in the earlier type. Can anyone comment on that?.

author: drforbin
author_rank: Regular Contributor
timestamp: December 14, 2015, 02:45:56 am
content: yes. you are correct, mine is an early model. The finals and driver are the same.You can download the ft-901 survival guide from tango foxtrot and it will detail the difference between versions of all components.

author: AF6LJ
author_rank: Unknown
timestamp: December 14, 2015, 03:56:18 am
content: Quote from: drforbin on December 13, 2015, 11:09:12 pmThe signal going into the driver should have been cleaner than it was.

author: AF6LJ
author_rank: Unknown
timestamp: December 14, 2015, 03:58:30 am
content: Quote from: voltz on December 13, 2015, 11:40:28 pmYou are looking too far out.You want to look within 5MHZ of the 7MHZ signal.QuoteNot if you are looking so far out.See above...\

author: AF6LJ
author_rank: Unknown
timestamp: December 14, 2015, 04:02:31 am
content: Quote from: drforbin on December 14, 2015, 01:12:52 amIf you are getting a hundred watts out on the other bands your tubs are good, you are barking up the wrong tree.

author: AF6LJ
author_rank: Unknown
timestamp: December 14, 2015, 04:03:30 am
content: Quote from: voltz on December 14, 2015, 01:34:25 amSomething is wrong but it is not in the PA.

author: drforbin
author_rank: Regular Contributor
timestamp: December 14, 2015, 05:30:24 am
content: Ok guys...here is SA! What do you all think?span is 5 Mhz to 50Mhzresolution BW 1 Khz

author: voltz
author_rank: Frequent Contributor
timestamp: December 14, 2015, 01:36:10 pm
content: Yep, pretty much what you expect to see from a wide band mixer output with no filtering. And it would look similar on all bands.Looking at the RF unit circuit PB1702, there is no filtering at all to terminal T2 out (pin 6). Its totally wideband. Only when it hits the driver board does filtering start. Which is what i was saying some posts ago.Ok, since the valve type theory and various others have so far lead nowhere, i think AF6LJ's suggestion of getting in closer to 7Mhz is a good one.Say take a look within a few Mhz only +- of 7. If there is any unwanted energy next to it, you would need to get in close to see it.But looking at your SA, you can actually see the IF at 9Mhz and its very low in comparison to the wanted 7. So thats correct.

author: voltz
author_rank: Frequent Contributor
timestamp: December 14, 2015, 03:18:29 pm
content: It would be interesting to see SA at the RF Out phono jack a the back of the unit. This is a convenient connection to the actual grids the ALC is monitoring. If there is a tuning issue or resonance happening, surely we would see it there. It should be quite pure 7Mhz at that point. After driver filtering.

author: AF6LJ
author_rank: Unknown
timestamp: December 14, 2015, 03:55:16 pm
content: A few things that need to be said..The mixer output is not designed to work into 50 ohms.I had asked to see close in to the carrier (+ / - 5 MHZ)Well since I am not getting the data I need to see.Let us all know what you find when you finally fix it.Take CareI am done with this thread.

author: drforbin
author_rank: Regular Contributor
timestamp: December 14, 2015, 06:40:18 pm
content: AF6Lj,I'm sorry. I really donot remember you stating you wanted a up close of carrier.Thank you for trying to help though.

author: AF6LJ
author_rank: Unknown
timestamp: December 14, 2015, 07:57:09 pm
content: Quote from: drforbin on December 14, 2015, 06:40:18 pmFirst you need to understand that none of those cables in that radio represent a 50 ohm system. So when you plug one into a a 50 ohm device such as a spectrum analyzer the readings are meaningless. Plus you risk putting DC on the input of the SA, that's bad.With that said;Build yourself a sampling loop.Take a BNC cable and cut the connector off one end and strip back the outer jacket about 2", and all but a quarter inch of the shield, slide a piece of heat shrink over the cable.Strip a quarter inch of insulation off the center conductor and solder it to the shield forming a loop. Bring the heat shrink tubing up over the joint to insulate it and shrink the tubing... Now you have a sniffing loop.This is what you use to sense RF in circuits where your gear will load the circuits downWhat you are looking for are relative signal levels, this loop is good enough and you won't load down the circuits in question and you won't damage your SA.The only signals you are concerned with are those within a few MHZ of 7.0MHZ, so looking at the second, third, harmonics will do nothing to lead to finding the fault.Here is what you want to do;Tune the radio up on 7.0 MHZ with the ALC connected. (that's right)With your sniffing placed near the bottom of the driver tube look at the spectrum display. Set your frequency span to 1 or 2 MHZ per horizontal division.What you will most likely find is your IF signal (over at 8.9MHZ) is nearly as strong as your desired signal, While you are transmitting...While you are looking at the analyzer (and in transmit mode) rock the preselector control back and fourth. Look to see if the frequency of any of the signals on the display are changing in frequency, The desired and IF frequencies will change in amplitude... Rotate the preselector and see where the desired signal peaks...See if that is where the manual says it is suppose to be at or is it further counterclockwise from that position.Because the IF 9.8MHZ is close to the desired frequency 7 MHZ it is easy to misalign.There ya GO.

author: drforbin
author_rank: Regular Contributor
timestamp: December 14, 2015, 09:13:30 pm
content: Hi..thanxs....I tested for dc before using SA and I coupled with a high cap thus eliminating dc. Anyway. I think your input is great and thank you so much.As I said before I really didn't remember you asking for a specific test.I'd be happy to do what you ask for.I did wish to bring you all up to date.I just got finished performing my test.I isolated the driver/pa from the rest of the unit and used my new (old) wavetek 288 to inject a 7Mhz signal into the driver.I had my DMM connected to ALC output.Using the signal from the wavetek or the signal from the radio I GET the same ALC offset.This to me clearly means the signal leading to the driver/final is fine.What do you all think?If you still wish me to conduct any test let me know and I shall do it.

author: voltz
author_rank: Frequent Contributor
timestamp: December 14, 2015, 09:42:37 pm
content: Firstly, congratulations on getting a fine function generator like that. Nice piece of kit.If you're taking requests for tests, i would like to see the RF Out phono jack socket at the back with SA please. Tuned on 40m. ALC on. +- sweep.Thanks.

author: drforbin
author_rank: Regular Contributor
timestamp: December 14, 2015, 09:50:51 pm
content: Ok voltz...I'll do it.What do you think about my test?any comments?

author: voltz
author_rank: Frequent Contributor
timestamp: December 14, 2015, 10:01:41 pm
content: I have to agree, it removes any chance of IF being injected, or any other unwanted frequencies for that matter. But the fault remains a mystery at this time.I am hoping the RF Out jack will show us something interesting. It is sensing the exact same point the ALC does. So we should see something! Its hard to guess the sweep range this time, if this is resonance, it could be anywhere.. So sweep away and have a good look around, up and down, then close in on 7. Thanks for doing these tests.

author: Mr Simpleton
author_rank: Unknown
timestamp: December 14, 2015, 10:11:03 pm
content: Guess we are narrowing in.... I would open up the ALC before the rectifying diode, and look at the RF with a scope.First try with transmitter on 7 and 14 MHz to see what levels you have, It if is way more RF on 7 MHz, the problem is still there and we may carry on from there.Do not remember if you still have the high ALC with PA tubes pulled??

author: voltz
author_rank: Frequent Contributor
timestamp: December 14, 2015, 10:33:25 pm
content: The ALC returns to normal once the PA's are pulled.And a resonance could easily be amplitude related bang on 7Mhz, rather than other RF energy at a different frequency. I agree with Mr Simpleton, that checking the amplitude between bands at the detector would help further narrow in. +1 on that.

author: drforbin
author_rank: Regular Contributor
timestamp: December 15, 2015, 02:46:54 am
content: ok guys.here is that exact same problem.But no solution was ever posted.http://www.foxtango.org/phpBB2/viewtopic.php?p=3133uploading tests now!

author: drforbin
author_rank: Regular Contributor
timestamp: December 15, 2015, 03:21:25 am
content: ok...here is latest video enjoy.ALL comments welcome...thanxs

author: voltz
author_rank: Frequent Contributor
timestamp: December 15, 2015, 11:48:32 am
content: A few points here:Was that test showing RF from the main ANT socket (sniffed with your loop)? Because the test i wanted to see was from the RF OUT socket (small phono at the back on the unit). Its much better suited because it connects directly to the ALC grid point in question. Sorry if you already did that.That second harmonic looks way large from the finals at full power with ALC OFF. But that would be because the PA finals are not being controlled with alc feedback and will be distorting. So thats expected. It was clean enough when you connected the ALC ON.If i understand what you said later on in the video correctly, you have already tried an SA right at the ALC point in question and you found it clear of all other frequencies. But the 7Mhz rf was very large?.. If that is correct, then this has to be amplitude related and most certainly some kind of resonance on or around 7Mhz.. It explains all the symptoms perfectly, and it also explains when valves are removed the ALC clears because the inter electrode capacitance is being removed and the 'bad' tuned circuit is being either changed or removed entirely.

author: AF6LJ
author_rank: Unknown
timestamp: December 15, 2015, 01:49:40 pm
content: Just because you can explain away the problem in what appears to be a rational manner, doesn't mean you are right.Good luck everyone, you will need it.

author: drforbin
author_rank: Regular Contributor
timestamp: December 15, 2015, 07:18:18 pm
content: That is from the phono jack as you requested.I used the scope not SA at the alc rectification point. It looked clean.But the amplitude did peak at when the alc peaked. As I said the freq was the freqs of the primary.

author: drforbin
author_rank: Regular Contributor
timestamp: December 15, 2015, 07:54:21 pm
content: I will do a spectrum analysis of signal right before rectifier tonight.You understand I will not be able to sniff it. Generally what U do is first use the scope and turn the signal down enough that it does not harm the SA and then use the SA.I'll tune everything up. show with finals in place and removed.Thanxs for all your help guys.ps...did you read the post from fox tango? Very similar problem.

author: voltz
author_rank: Frequent Contributor
timestamp: December 15, 2015, 08:08:11 pm
content: Oh ok, i saw the sniffer loop and thought that was the pickup point. Sorry for my misunderstanding of the setup. My bad.So yes, there appears to be no other frequencies involved. Thats clear now.Mr Simpleton suggested taking a look at the ALC point with rectifier disconnected and comparing the amplitude from 7 to 14 Mhz. I believe we should be seeing a huge difference in the level of RF there. But i don't want to over step someone else's comments here, so please read his post and maybe go that way.May i just add (sorry this even has to be said); Make no mistake, this will get resolved! Just takes time and patients. And a logical approach. Which is exactly what we have all done so far. Things needed to be explored, ruled out, ruled in. Thats just how it works. Its not an easy problem, we are 'ALL' clueless at this time as to the actual component fault. Luck does not come into it. Its a procedure. And its getting closer all the time. I suppose the real question is how much time are we all prepared to spend on this. Personally, i run my own electronics business so i can find time to log in and read posts on this forum as i operate on my own timetable. So count me in!Right enough said... Back to the problem finding and less of the personal stuff. Which is irrelevant.Yes, i did read the post on FoxTango. Not convinced about it, he didn't mention anything about it being band specific. It sounded like a general ALC failure. I guess its not the same issue. He was getting just mW rather than your 10 watts too.

author: drforbin
author_rank: Regular Contributor
timestamp: December 15, 2015, 08:20:30 pm
content: thanxs...Yes..it was not band specific in the case of the post.thanxs again.

author: voltz
author_rank: Frequent Contributor
timestamp: December 15, 2015, 08:36:26 pm
content: "You understand I will not be able to sniff it. Generally what U do is first use the scope and turn the signal down enough that it does not harm the SA and then use the SA. I'll tune everything up. show with finals in place and removed."I don't think its necessary to use the SA any more, Your scope is fine for these amplitude tests from now on. Its a clean signal, we are now just interested in level.

author: drforbin
author_rank: Regular Contributor
timestamp: December 16, 2015, 04:35:15 am
content: Exciting news guys! Have a look.

author: voltz
author_rank: Frequent Contributor
timestamp: December 16, 2015, 11:25:13 am
content: Great!. Just a quick response for now, and i will get back later, this was what we predicted.Having ruled out spurious oscillations occurring (using SA) we were left with a resonance (increased amplitude at 7). Your scope clearly shows that. Notice how at 8Mhz it was actually attenuated? and 9 is almost gone completely..Two things this could be: after the resonance point its common to see a dip. And there it is. It means its not a clean damped resonator. It has a tail off with varying amplitude. OR this could be a 9Mhz IF trap as its suspicious that the dip seems to be at 9Mhz.I was going to suggest doing exactly what you did haha, power OFF and inject the stage manually with your wavetek! you beat me to itOk, now its all about isolating to the component.. It means soldering iron at the ready. And now there's no power on, its totally safe.[usual warning notice here, sorry if you already did this] Please physically REMOVE the big mains plug from the back of the unit and take it away from the bench.. Seriously, you know im not kiddingQuick one, try pulling one PA at a time - while the test is running at 7Mhz - live. Pull out, Push in, one side then the other. Are both PAs having the same effect or is this one sided?.. and do the anode caps have any effect?.More later.

author: voltz
author_rank: Frequent Contributor
timestamp: December 16, 2015, 01:07:24 pm
content: More questions / tests,did the Band Switch have any effect? You tested the Preselect, how about the band selector rotary.

author: drforbin
author_rank: Regular Contributor
timestamp: December 16, 2015, 07:49:35 pm
content: I didn't try the band selector, I will, but it should not make any difference all the band selector stuff for the finals is to the right in the circuit (not connected to this segment). I agree with with your suggestion. The only problem is I have changed all the caps in that area. I already checked the two parasitic chocks (resistors and inductors).That's why this problem has been so difficult, the first thing I thought of was resonance and checked all that stuff.But it's clearly resonance of some kind and the voltage is really to low to be moving electrons around in the tube themselves, so this potion of the circuit should be isolated.more to come.will do your suggestions.

author: voltz
author_rank: Frequent Contributor
timestamp: December 16, 2015, 09:06:38 pm
content: One thing further. Was the driver wire disconnected at the PA finals (feeding C01, 100pf) when you did your tests? If not, i would try de-soldering it and check again. This is because the resonance may be at the driver side (PB1092 trimmer board for example). It really is about disconnecting stages and testing to get closer to the problem. This may take a few iterations.Just to recap:PA finals, unplug one at a time test - any difference between them or both the same?Anodes off one at a time - any effect?bandswitch - any real effect?Disconnect drive wire to C01. retest for resonance. Is it still there with driver stage disconnected?That should help isolate the problem.thanks.

author: drforbin
author_rank: Regular Contributor
timestamp: December 17, 2015, 04:38:19 am
content: ok guys...I need your opinion. Here are results and surprise!

author: AF6LJ
author_rank: Unknown
timestamp: December 17, 2015, 05:24:11 am
content: That coil is part of a 8.9MHZ trap, The trap keeps IF from feeding through when you are on 7.0MHZ. Remember that dirty looking signal you saw on the scope???I told you about that also.I told you there was one, someone misstuned it to 7..MHZ (more or less).I just wanted to say I told you so, but y'all were not going to listen.

author: drforbin
author_rank: Regular Contributor
timestamp: December 17, 2015, 05:46:42 am
content: I am listening. I'm sorry you think I am not.From what I can tell it has nothing to do with tuning. it seems dead.Am I wrong?

author: drforbin
author_rank: Regular Contributor
timestamp: December 17, 2015, 06:11:29 am
content: FYi I like the picture of your cat.I'm a cat lover too.

author: voltz
author_rank: Frequent Contributor
timestamp: December 17, 2015, 11:22:14 am
content: Ok, so that red wire disconnection takes us left, back to the driver direction.You remember the scope did actually DIP at 9Mhz (not 7)? It was a clear dip with fairly hi Q.Well, as said, if it was either a resonance at 7 with an overshoot tail off OR a 9Mhz Trap at work, then that scope test the other day would suggest its working at the desired 9Mhz frequency and not 7.So i'm afraid from me, i'm still not convinced [that its a faulty coil].Some things here:Testing an RF choke may not show correctly if you test it with a general tester at audio frequencies. If its a dust iron core (and it probably is) then you may get the wrong reactance showing. To test the coil, put it in a tuned circuit with a capacitor in parallel and work out a where it should resonate. [fo = 1/ (2pi root LC) ]Then check that with your signal generator and scope for a dip across the coil. The calculated resonance point and measured point should be the same, if not, the coil is faulty.It should be easy to rule this choke in or out, simply short it out in the circuit. If this is a misaligned trap, the resonance will stop.

author: voltz
author_rank: Frequent Contributor
timestamp: December 17, 2015, 12:11:49 pm
content: Oh guys, 4 cats here!! We are all cat people lol.AF6LJ - we are listening my friend, please dont think we are not. Its an open forum, anyone can comment.. Please do. But it would be really helpful to focus on what the actual fault could be. Did you get a good look at the diagram? Is this the coil you believe to be the IF trap and you believe to be faulty? That would be interesting. Its too broad a statement to say 'its an IF trap'.. where?

author: AF6LJ
author_rank: Unknown
timestamp: December 17, 2015, 05:17:02 pm
content: Quote from: drforbin on December 17, 2015, 05:46:42 amIf it is mistuned you will have low output on forty.

author: AF6LJ
author_rank: Unknown
timestamp: December 17, 2015, 05:17:47 pm
content: Quote from: drforbin on December 17, 2015, 06:11:29 amShe was my best friend for over thirteen years.

author: AF6LJ
author_rank: Unknown
timestamp: December 17, 2015, 05:42:22 pm
content: In these designs that use this type of conversion scheme, IF feedthough is a problem on the 7.0 MHZ band, for one thing without a properly tuned IF trap somewhere after the mixer but before the PA input it becomes possible for an operator to tune up the transmitter to operate on the IF frequency, that would get said operator in trouble.The ALC circuit is seeing more signal than it should, and doing what it does best, provide a signal to lower the gain of a stage or stages in the transmitter chain.Before I had a spectrum analyzer and all the pads and directional couplers, sniffing loops and DC blocks you need to take meaningful measurements I would use a sniffing loop with an adjustable attenuator connected to a receiver tuned to the transmitter IF frequency and use the receiver as a selective volt meter.Works great for tuning those traps and general troubleshooting.Which is why I know what that coil is used for. (notice the manual doesn't provide alignment instructions for that coil Yaesu manuals Suck deeply.)And i will mention this again. None of those circuits internal to that radio are designed to work into a fifty ohm load such as your spectrum analyzer, which is why I suggested using a sniffing loop. Nobody back when that radio was being built was designing their subsystems to work into fifty ohms, nobody making amateur radio gear that is. So when you plug one of those cables into your SA you alter how that circuit works.At this point you should be able to put that coil back in, place the radio in transmit on 40 meters and tune it through its range and observe the change it has on the transmitter's output. That coil does have to be tuned to 8.9MHZ to notch out the IF signal, you might find things working a whole lot better.Good luck.

author: drforbin
author_rank: Regular Contributor
timestamp: December 17, 2015, 08:00:20 pm
content: Thanxs for reply. I tried tuning it while in circuit it did nothing.This was done before I removed it. As I showed with the lcr meter it seems bad.It manual calls for 300 uH all I can get out of it is 5.6 uH.The manual does say something about tuning the l09 but as you said the manuals are very unclear.I find Alot of mistakes in the manual.Sorry to hear about kiddie. I have two which are aLittle over 12 years right now.

author: AF6LJ
author_rank: Unknown
timestamp: December 17, 2015, 09:03:49 pm
content: Quote from: drforbin on December 17, 2015, 08:00:20 pmDouble check the listing in the manual, make sure you have the right part.

author: drforbin
author_rank: Regular Contributor
timestamp: December 17, 2015, 09:08:28 pm
content: I have triple checked it. It's l09 main chassis. I have a very good LCR and as I said i'm getting about 5.4 uH on it.

author: voltz
author_rank: Frequent Contributor
timestamp: December 17, 2015, 10:17:52 pm
content: Hi all,Been looking at the diagram again and it looks like L09 is actually just a preselector extender for the 160 and 80m bands. If you look at wafer S1-J (i think it is) this coil is shorted out for all bands except 160 and 80. Its just allowing the preselect coil to cover these bands more easily and improve the position on the dial.The other thing is, and if anyone is interested, the FT101ZD which has a very similar PA circuit does not have any coil like this in it. I guess when they did the 901 later, they extended the range of the preselect using this coil.My guess is, there is no real adjustment to do with it, other than make sure 160 and 80 are covered on the preselect dial. I think!Like i said before, your very fine LCR meter (which it is) may not be able to accurately measure inductance of dust iron RF coils. RF coils should be tested at RF, not audio like 1khz.. Its a different world and my theory in advanced magnetics is limited... Maybe the manual value is even a mistake. Either way, simply short it out and rule it out. Just like the 101 does.Take care everyone.Sorry for your loss AF6LJ, i know what its like, like loosing family isnt it.. Had so many pets over the years.. Now these four are a real handful, around 10 months old and a mother cat

author: drforbin
author_rank: Regular Contributor
timestamp: December 17, 2015, 10:43:58 pm
content: You have four kiddies? Great. I agree maybe the meter is not working at high freqs.But it does measure the other values accurately. I will short it and see what it does.

author: drforbin
author_rank: Regular Contributor
timestamp: December 17, 2015, 10:49:51 pm
content: I remember when I was in England last (during the 90's) what impressed me is how many shops you could walk into and there was a cat or dog roaming about!Could you send pictures of kiddies?

author: voltz
author_rank: Frequent Contributor
timestamp: December 17, 2015, 10:58:02 pm
content: Thats true! we do have cats and dogs in some shops, the smaller shops that is, obviously not the larger stores.. My partner is German, and she had a shop with a cat on the counter for many years.. So not just the UK it seems.Got wayyyy too many cat pictures!!! but i'll see if i can fine something small enough to post. Dont want to go crazy.How about you, you have two catties?

author: drforbin
author_rank: Regular Contributor
timestamp: December 18, 2015, 02:18:43 am
content: ok....thanxs so much for your cat pictures. I have four of them, older kitties.They are also my best friends.I think your correct. The lcr meter just can't measure the the inductance because it's not at RF.Ok I put it back together and peaked everything including l09 and I'm getting REALLy good power on everything except 40m when the alc is connected AGAIN.I just can't figure this out.Perhaps I could ask this. What is the theory of operation of the ALC?it's my understanding it should only register peaks where the excursion of the waveform is positive.

author: AF6LJ
author_rank: Unknown
timestamp: December 18, 2015, 04:02:53 am
content: Quote from: drforbin on December 18, 2015, 02:18:43 amI told you what to do about the 8.9MHZ trap L09ALC stands for Automatic Level Control.Its function is to keep the PA from being overdriven which would cause flattopping of the signal and result in excessive distortion products known as splatter.

author: drforbin
author_rank: Regular Contributor
timestamp: December 18, 2015, 06:02:37 am
content: AF6LJ, along with everyone else. I just wanted to thank you all.Firstly I do know what ALC means I was just asking the theory of operation for a class 'B' which is what I believe this unit uses.ok, here is update.I resoldered the choke and realigned everything again,This time messing with L09 in the process.It's alittle to soon to tell but it looks like I'm staring to get more power on 40m.I did nothing different than this time fiddling with l09.So it seems AF6LJ may be correct.AF6LJ, I would like to ask this if you donot mind.I understand your statement about using direct connect at the 50 ohm, but if you look at my video where I was sniffing the phono jack there was no direct connection and I did not see a 8.9Mhz pass through. Now it appears you may very well be correct that the ALC is seeing another signal and responding to it, but we did not see a 8.9Mhz signal on SA. Any idea why?And in order for the ALC to be attenuating the desired signal too much would the amplitude of this unwanted signal had have to have been larger than the desired signal.Thank you for bearing with my ignorance. My background is in digital electronics and programming. This is my first attempt at RF and I obviously have alot to learn.thank you all.

author: voltz
author_rank: Frequent Contributor
timestamp: December 18, 2015, 09:57:43 am
content: We seem to be going in circles here.. L09 is short circuit at 40m [EDIT: this comment was wrong, see later]. Its that simple really. It cannot be an IF trap at 40m.Besides, its not a tuned circuit. Its just a coil without a cap. A trap it is not. There's no doubt about it.As said, its just a preselector range extender for 160 and 80. Most likely to improve RX TX prselector tracking on those bands.There is next to no 8.9Mhz on the SA because there is none. 50 ohms has nothing to do with it, that would only load the mixer slightly but not effect its resultant frequencies - its a low impedance mixer output (source/drain output and a forward biased switching diode) so any effect is negligible.And if when you do the short circuit coil test it DOES have an effect, then your band selector wafer s1-J is defective. Maybe check that it IS short circuit at 40, it should be according the the diagram, and locate the damaged wafer point.

author: drforbin
author_rank: Regular Contributor
timestamp: December 18, 2015, 10:38:04 am
content: I agree. I donot see any 8.9Mhz signal. In fact I checked again tonight.BUT, you should check the schematics again. The choke is only shorted 20m and higher freqs.160,80,40 it is in effect. It's crazy, I donot know what it's doing BUT.I realigned fully and I'm getting pretty much full power now on 40m.I will make a video detailing everything.In fact when I turn the choke I can reproduce the 10 watt problem I was having on 40m,so something is going on. The real question now is what.As I said I checked the SA again (sniffing this time) and I'm a 7Mhz signal and two harmonics.Each harmonic lower than to prior. This is not want is effecting the ALC.Could it be that the choke is somehow damping the feedback. notice the plate of the finals is feedback.I'm at a loss.I really would like to understand this.Thank you.

author: voltz
author_rank: Frequent Contributor
timestamp: December 18, 2015, 10:46:38 am
content: Look at S1-J again. I agree its not exactly clear how it operates but the default position shown is at 160m. So with that, follow the positions and shorting of L09 starts at 40m. Well, according to my eyes.

author: voltz
author_rank: Frequent Contributor
timestamp: December 18, 2015, 11:03:26 am
content: As a clock face, i see contact 11 o'clock as closed on 160m .. then its two clicks clockwise and then its 1 o'clock short. Thats 40m.They have drawing the inner common contact in a slightly ambiguous way. I guess the best way to resolve this is to manually examine the wafer with a spy glass.

author: drforbin
author_rank: Regular Contributor
timestamp: December 18, 2015, 11:04:14 am
content: it rotates counter clockwise and the bias for the driver plate flows through it, and through l09.look at the full schematics it has arrows showing rotation.I have also confirmed this with dmm

author: voltz
author_rank: Frequent Contributor
timestamp: December 18, 2015, 11:10:25 am
content: Hmm, well there's no arrows on the final PA diagram and its clearly shows the band positions in the key at the bottom! Which is clockwise.Your DMM may show as 40 open, but according to this diagram, that's a fault. Can you visually inspect the wafer. Whats actually true?

author: drforbin
author_rank: Regular Contributor
timestamp: December 18, 2015, 11:14:57 am
content: no..look at this (attached).It rotates counter clockwise.three clicks counter clockwise would find it on 20m and shorted at that point.This in fact make sense. 20m and above were working.160,80,40m were having varying degrees on ALC anomaly.The question is how.

author: voltz
author_rank: Frequent Contributor
timestamp: December 18, 2015, 11:31:22 am
content: Dammit our diagrams are different!!! Thats not what I have here. No arrows and a band select wafer key.Ok, so yours at least has a arrow for direction, thats clearer than what i have.So yes, you are correct it starts at 20 and L09 is operational at 160, 80 and 40. However, its still not a trap. It simply means the preselect coil is extended at 160, 80 and 40. All other bands its shorted out. I was 1 click out.When you adjust L09, you will see an effect on 40, its peaking the preselect alignment on TX. So just peak it. Then re-check RX is peaking is at the same point.

author: drforbin
author_rank: Regular Contributor
timestamp: December 18, 2015, 11:37:59 am
content: I don't think it is a trap. But somehow when peaked it's fixing my problem.I'll do a video later.I'll also sniff it on the SA for everyone.

author: voltz
author_rank: Frequent Contributor
timestamp: December 18, 2015, 11:41:34 am
content: Exactly. Just peak it - but please do re-check the preselect tracking between TX and RX is correct. Both should obviously peak at the same time. L09 will effect tracking on 160, 80 and 40m.So if i read you correctly, did this resolve the issue and you have full power on 40 with ALC correct?

author: drforbin
author_rank: Regular Contributor
timestamp: December 18, 2015, 11:47:01 am
content: It seems so...I'll double check everything later and do a video.I reconnected the ALC it seems to be working.I just don't know why it's working.

author: voltz
author_rank: Frequent Contributor
timestamp: December 18, 2015, 12:01:29 pm
content: Excellent!Its working because L09 was indeed out of alignment. But not because of not rejecting any IF signal, its wasn't tuned to an IF - there was no IF present, but because the energy was being rejected back to the C01 Rf input pin. Rather like a bad SWR with reflected energy. This caused the amplitude to be magnified (like a resonance) and that boosted the ALC rectifier voltage way too much cutting back the power.So that simple alignment had a knock back all the way back to the ALC.Its always easy to say after an event i know, but it does make complete sense.Some things have been learned:Yeasu diagrams are misleading! Compare different versions.LCR meters are not very good when it comes to measuring RF coils (dust iron cores for sure) Make a tuned circuit.Stay calm and logical. We all did. Well done everyone.RF sniffer loops are your friend in the RF world.

author: drforbin
author_rank: Regular Contributor
timestamp: December 18, 2015, 12:07:38 pm
content: Well...I thank all you guys. You all were great. I will do a wrap up tonight..I'm pretty sure it's correct.So you think the signal being delivered to the finals was to high, and the alc was picking up on that?Yes, the manuals is quite bad.In fact the alignment procedure has to be interpreted in places.must be translation problems.

author: voltz
author_rank: Frequent Contributor
timestamp: December 18, 2015, 12:13:28 pm
content: "So you think the signal being delivered to the finals was to high, and the alc was picking up on that?"Yes. because of the reflected energy from the miss-aligned coil.Look forward to your wrap up videoIts quite possible this thread could become a reference to others with the same problem. No its not the mode switch!!!

author: drforbin
author_rank: Regular Contributor
timestamp: December 18, 2015, 12:23:53 pm
content: Yeah....This is quite a strange problem.I hope we can keep in touch.You too AJ.As I said, when I tune the l09 I can reproduce the effects I was seeing.If your correct I suppose it should mean the finals are not being driven as hard.I was getting about 185-200volt p-p on on the other side on c01 coupling cap.I'll test and see what I'm getting now.Man this RF stuff is crazy! O0

author: drforbin
author_rank: Regular Contributor
timestamp: December 18, 2015, 11:32:06 pm
content: Hi guys.Just wanted to publish a few links for how Class 'B' amps work and how ALC is suppose to work. Also attached is somewhat less than stellar explanation of how the ALC works in Yaesu ft-101 series radios. The circuit is almost exactly the same as my ft-901dm.Please let me know what you think.http://www.duncanamps.com/technical/ampclasses.htmlhttp://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/hr/1984/08/page40/index.htmlhttp://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/radcom/1995/07/page61/index.htmlhttp://www.somis.org/D-amplifiers1.htmlhttp://www.astrosurf.com/luxorion/qsl-amplifier-principle4.htmhttp://www.biasking.com/qa_biasing.htmhttp://www.w8ji.com/cb_amplifiers_convert_ham.htmI hope these references help someone.I still donot understand why this problem on my ft-901 was present.I will be posting more videos tonight showing some more experiments.thank you all.

author: drforbin
author_rank: Regular Contributor
timestamp: December 19, 2015, 04:08:49 am
content: ok guys..here is latest video.Let me know what you all think!Thank you.https://youtu.be/yaADlmZqI40

author: voltz
author_rank: Frequent Contributor
timestamp: December 19, 2015, 12:53:08 pm
content: Hi, Well firstly, the radio seems to be working and you appear to be getting near full power on 40 with the correct ALC showing. Pretty sure with some further careful alignment including L09 you should get 100 watts. Did you check all the other bands for full power too? Everything should be tested including RX for preselector tracking to TX. The works.So all that being true then you could put the case lids back on and walk away!! What i am saying is, maybe you are looking too hard?, or did you want to take the thread into an educational direction rather than a repair.Ok, some comments, rambling on, just generally putting it out there..Your SA looks correct, but we already did this test quite some posts ago. Its basically showing 7Mhz fundamental, 2nd and 3rd harmonic. Thats because its before the finals which then filters further and results in a near pure 7. So thats correct.The ALC is really easy. Some RF from the final grid bias is first decoupled to remove the -V, then rectified to create a negative control voltage related to the amplitude of the RF at the grid. Thats it. So as RF increases, the -V control line goes more negative. That signal is then fed to the NB/Proc board to reduce carrier level as needed. The whole thing forms a negative feedback loop to control the PA finals which keeps them in the linear range avoiding distortion and harmonics. So as you talk, the SSB speech envelope whos peak power is much higher than you see on the PO meter is the signal used by the ALC. The very idea of ALC is to remove final distortion.I'm pretty sure you already know all that, we covered this very early on. It seems to be working as it should.As you talk, with a low mic gain setting, the ALC should not kick back and stay at full scale. There is a separate preset somewhere to set full scale (FSD). As you increase the mic gain to higher levels and talk louder, the ALC should just start to kick back. At that point the audio mic gain is sufficient to activate some ALC. Go further and really drive it hard and the ALC will really kick back as it tries its best to keep the finals limited (clean). Without any ALC, the finals would distort and clip - a major problem for transmitters, its against the law to transmit like that and cause all sorts of problems with TVI etc.. ALC is our friend.As said, L09 was simply out of tune. L09 forms part of a tank circuit in series with the preselect variable inductor and the whole thing in parallel with the capacitor trimmer board. Classed as a 'rejector' circuit or tuned tank. Its called a rejector because it rejects current at its resonant point. If there's no current at resonance, then there is high impedance and therefor high voltage across the tank. This is exactly how a crystal set radio works. Its just a rejector circuit then rectified by a diode. When tuned, the voltage across it is maximum. All other frequencies are minimum.Series tuned circuits are called 'acceptor' circuits because they accept current when tuned.Your L09 / preselect coil / Trimmer board combo is exactly that. A big, band select-able tank circuit. So when tuned, the current through it is minimum = impedance is high = voltage across it is maximum. in other words - peaked.ok, Since L09 was NOT tuned correctly (the actual fault) current was flowing in the tank at 7Mhz and that leads to some pretty strange effects. Its not a resistive current path, its reactive. Things go out of phase and it goes complex. Some tuned circuits react differently to others especially where there are resistors involved (effecting Q) or other reactive components like L and C.. Remember that its not just a LC tank, there are other components in the circuit right back to the finals (remember pulling the finals had an effect?). What i suggested earlier on was that because of the mis-alignment of L09, you actually got a rise in 7Mhz amplitude but because of the complex phase nature of the tank, it was similar to a bad SWR where much of the power becomes reflected back. That then caused the problem with the ALC level.I think if you REALLY want to see what happened in detail, you'd need to enter in the exact values from the circuit into something like a SPICE modelling simulator to get the result. So there are some assumptions here but on the whole, i'm pretty confident its correct.EDIT: or set up a real tracking generator and sweep through the tuning range while viewing your SA and adjust L09.Sorry that was a long post.

author: drforbin
author_rank: Regular Contributor
timestamp: December 20, 2015, 09:24:43 am
content: Hi..thank you so much for your reply.Just to cap everything off.I am going to do another FULL Alignment and post the results.Voltz, I want to let you know I did some further research and you are correct.There are two 8.9Mhz traps in early models like mine (please see attached).But it is not at all that clear they were all that useful or even used for the purpose stated by some posters. Please refer to the attached schematic. It is TC07 and T02.The TC is mislabeled TC2506. One band pass filter is connected to input of the driver section, it is then grounded. In effect creating a band stop filter. So it filters out any 8.9Mhz signal which I guess maybe left after mixing in the RF unit. So AJ was right is this regard, but this filter was removed in later models with the new mixer sections so it could not have been that useful, or maybe the new mixers are just cleaner. The other tank circuit is TC07 and T02 on board 24 (RX trimmer board) it is used to filter any unwanted 8.9Mhz signal in RX section. So you were correct the L09 is just a follower.The TRAPS are located elsewhere.I hope this information helps someone.Also The Alignment procedure is very convoluted as detailed in the manual.I have managed to figure it out and will scan my annotated procedure upload to forum for all to share.thank you all again.

author: voltz
author_rank: Frequent Contributor
timestamp: December 20, 2015, 11:13:22 am
content: You are absolutely right, TC07 (TC2506 on diagram) and T02 form a series resonant 'acceptor' circuit, the exact opposite of a tank coil circuit (parallel). So at resonant frequency (8.9), current through it is maximum = voltage across it is minimum. Now that is a TRAP. And it goes to ground so this is a sharp 'notch' filter if you like, to remove the 8.9. It should be fairly easy to adjust. Simply inject 8.9 and adjust for minimum RF. Notch it out so to speak. It probably already is.I had spotted that trap some time ago but didn't mention anything as i wasn't sure exactly what frequency it was tuned to. Well that CAP sheet from fox tango clears that upI'm sure if you put together a better alignment sheet for the 901DM, others would benefit from it. And i agree, things are misleading or simply missing from the Yeasu manual.Lets see if you manage to squeeze the proper 100watts from 40m.. It should be able to. (dont forget to neutralize again too)Great job.

author: drforbin
author_rank: Regular Contributor
timestamp: December 23, 2015, 03:44:15 am
content: Not really repair but I thought it would be nice to post me calibrating the carrier unit on the ft-901. Then I will re-align it.

author: voltz
author_rank: Frequent Contributor
timestamp: December 23, 2015, 08:31:07 am
content: Watching with interestIm sure the moderators will let you know if this isn't the right place.

author: drforbin
author_rank: Regular Contributor
timestamp: December 23, 2015, 09:05:13 am
content: Thank you so much for your support Voltz, and everyone else!

author: drforbin
author_rank: Regular Contributor
timestamp: December 30, 2015, 10:13:20 am
content: Ok guys, sorry about the delay. Here is tune up at 40m band.Enjoy!Anyone who wants alignment procedure contact me and I will send it to you.

author: voltz
author_rank: Frequent Contributor
timestamp: December 30, 2015, 12:32:30 pm
content: Hey, hope you had a good Christmas!. Its good to take breaks from projects. Clears the mind.Well, it looks pretty good but i 'think' you should actually be getting 100 watts. I remember my Ft101ZD mk3 could reach 100, maybe even more than that. Is this a common thing with the 901 perhaps?.I remember you said you were going to peak everything in your alignment procedure. Did you get a good peak with L09 and at the same time peaking the preselector?. Its a back and fourth situation until it can't peak any more. Then check the preselector is still tracking correctly on RX (using the marker switch). Maybe you did all that.. Just checking.Out of interest, i did some SPICE modelling on the the PA. I ended up almost doing the entire driver and PA section. And sure enough adjusting L09 effects PA output on 40m and has an effect on ALC when detuned. What i also noticed during the simulation was how critical Trimmer board B and C are with respect to the Preselector coils. Everything has to be bang on before you get 100 watts. In some cases just 1pf either way reduced power by 5-10 watts. Simulations are never perfect models, they are only as good as the data going in, but i am getting 100 watts (slightly over that actually) on 40m. So it looks reasonably close.Oh and btw, remember when you measured L09 and thought there was a problem? Well turns out your LCR reading was correct. The sim works when L09 is just a few uH. Its not 300uH, the book is misleading. There is no data for it published. So, its fine, but we already knew this otherwise you would not be getting high outputI wish i could measure or find data on the preselector coils. There's nothing out there.. Armed with that data, I could separate the preselector coil values from their fixed series coils and deduce L09. But its low, around 0.5 - 4uH.

author: drforbin
author_rank: Regular Contributor
timestamp: December 30, 2015, 01:18:02 pm
content: Wow...could you send me spice file?drforbin6@gmail.com

author: Radio Tech
author_rank: Frequent Contributor
timestamp: December 30, 2015, 01:23:33 pm
content: Good to see it is working much better than before.Most radios I have seen of this era have no issues producing 100 watts on top band (80, 40, 20) and will drop off a bit on 10. So that does concern me a bit with the below 100 watt mark on 40.Also I caught a glimpse of your dummy load. Is that salt water load?Again, good to see it is working and once you get it on the air then the real test beginsI am going back to my Kenwood TS-940 today. It has the PLL issues, wire connector issues and is possessed. When testing one day and if you do not like the results it changes the nextLink to first repair attempt:https://www.eevblog.com/forum/other-blog-specific/18-kenwood-ts-940-dot-on-display-chasing-down-the-rabbit-hole-pt-1/

author: drforbin
author_rank: Regular Contributor
timestamp: December 30, 2015, 01:26:01 pm
content: No...it's oil dummy load. Hum I tried realigning three times and that's about the best I can get.Dunno what to do at this point.

author: AF6LJ
author_rank: Unknown
timestamp: December 30, 2015, 03:37:52 pm
content: Adjusting the 8.9MHZ trap for max is not the answer.You have a spectrum analyzer use it.

author: voltz
author_rank: Frequent Contributor
timestamp: December 30, 2015, 03:45:09 pm
content: L09 is not a trap. Its a preselect series coil to extend its range on 160, 80 and 40m. There is a 8.9Mhz trap in the PA, but thats not it.

author: AF6LJ
author_rank: Unknown
timestamp: December 30, 2015, 03:51:35 pm
content: Quote from: voltz on December 30, 2015, 03:45:09 pmPerhaps so, the docs online are so crappy I don't see how anybody can read them.The one I worked on I actually had a real manual for instead of the shit online that passes for a manual.

author: voltz
author_rank: Frequent Contributor
timestamp: December 30, 2015, 04:23:27 pm
content: I had to print sections out and tape them together in order to make sense of it all. The worst problem during reverse engineering this was the lack of inductor values. Most of them I had to calculate and cross check. Its almost as if they didn't want engineers to really know how it worked. But, given enough time, it does make sense now. And i have values in the sim where there manual does not. So i agree with you, the diagrams are less than perfect (being polite lol).

author: Radio Tech
author_rank: Frequent Contributor
timestamp: December 30, 2015, 04:33:33 pm
content: I agree with online manuals being crap. So far I have downloaded 3 version of the 940 manual. Then you get the scans of a scan.I did get lucky and found the original 2 page fold outs for the 940. One of my viewers sent them to me.

author: drforbin
author_rank: Regular Contributor
timestamp: December 31, 2015, 09:40:53 am
content: Hi all.Found this post on Fox Tango as related to Power output of ft-901.Now the manual does call for 100watts across the board BUT?"Postby n5hny » Sun Apr 23, 2006 6:37 amDan, WimThanks for the reply. I got out the old dummy load and here is what the rig is doing when you hit the tune button.Band Emission Output Power (Watts)160 SSB 110160 CW 15080 SSB 18080 CW 18040 SSB 7540 CW 15020 SSB 12020 CW 12015 SSB 6015 CW 6010 SSB 11010 CW 110As you can see, the numbers don't add up so to speak. Sometimes 40 and 15 are lower than the numbers posted here.Also, I have to readjust the preselect to get the drive to respond even though I just changed modes, not frequency.Thanks for the replys. I was beginneing to think I wasn't going to get any. HI HI.73Vance"

author: AF6LJ
author_rank: Unknown
timestamp: December 31, 2015, 02:00:03 pm
content: I totally disagree.Not to mention the figures are way over what those tubes will do.The most you can get out of a pair of 6146s series tubes is 120W without doing damage to the tubes.