Radio stopped working - Hitachi KH-1190E - Page 1
Forum section: electronics / repair

author: martfoxy
author_rank: Regular Contributor
timestamp: January 28, 2021, 12:03:55 pm
content: My radio (Hitachi KH-1190E) stopped producing any sound when I was using it.I have tested the supply voltage from the batteries (4 x 1.5) to the pcb and is about 5.8v. The mains fuse inside the radio is also ok. The radio makes a slight noise when I turn it on.I have tested with a DIN lead connected to my stereo and get very quiet sound from the radio if turn the volumes up to maximum. Also if a plug in earphone I get soft white noise.Can anyone help with this? I have a multimeter and a capacitance meter. The capacitors don't look swollen.I have attached a schematic - its not brilliant.

author: Renate
author_rank: Super Contributor
timestamp: January 28, 2021, 08:52:40 pm
content: Hi.Is the audio low for both AM & FM?The DIN output is the takeoff point, the speaker and the headphone go from there.If both AM & FM are low check the voltages on Q10. The voltages are on the schematic.It could be something as simple as a wonky switch on the DIN socket. Try exercising it.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 09, 2021, 03:09:17 pm
content: Thanks for replying apologies it took me so long to answer.I measured Q10 and only got 0.02v on the base and 0v on collector and the emitter.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 09, 2021, 03:25:51 pm
content: I got a paper copy of the service manual and took a photo of the schematic which I have attached. Hopefully cleared than previous pdf.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 09, 2021, 03:32:16 pm
content: There is no sound on both AM and FM.Only time I got a very quiet sound was when I connected my hifi to the DIN socket - that was on maximum volume on both - plus it was distorted (that was input from hifi).I tried exercising the DIN socket but that hasn't fixed it.Thanks

author: Renate
author_rank: Super Contributor
timestamp: February 09, 2021, 06:17:30 pm
content: Well, we may have hit a good debug spot there.There should be ~2.5V on Q10 collectorThat gets fed from C45 is the extra filtering for the audio.That gets the 4.7V zener D5 that gets fed from the 6V.Something is wrong around there. Shorted cap? Shorted zener? Open resistor?(C45 & D5 are right on the crease of the schematic.)

author: Audiorepair
author_rank: Frequent Contributor
timestamp: February 09, 2021, 07:02:48 pm
content: I was looking at that.If D5 or the capacitors across it were short, the power supply would be shorted, probably a fuse would blow, or the batteries would be flat.So more likely a short the other side of R18.Or maybe R18 just failed open as you suggest.C45 could short without taking R18 out, Q10 could be shorted without taking R18 out.Quote from: Renate on February 09, 2021, 06:17:30 pm

author: Renate
author_rank: Super Contributor
timestamp: February 09, 2021, 07:11:52 pm
content: Quote from: Audiorepair on February 09, 2021, 07:02:48 pmD5 is fed by 150ΩA dead short is only 1/4 W on that resistor.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: February 09, 2021, 07:34:40 pm
content: Ah, didn't see that, the schematic is rather hard to follow.Silly me, there HAS to be a resistor before the zener.So maybe best to meter for a short across D5 and C45 and see what that turns up.Edit: And measure R18 and R37 in circuit at the same time.That should give enough clues.Quote from: Renate on February 09, 2021, 07:11:52 pm

author: martfoxy
author_rank: Regular Contributor
timestamp: February 10, 2021, 04:57:30 pm
content: Thanks for your replies.R18 measures 218 Ohms. The zenor diode D5 measures 21 Ohms when the power switch is switched on and 1.2 Ohms when turned off. I took the zenor diode out to test and is not shorted out of circuit.R37 measures 156 Ohms.C45 measures 219 Ohms in circuit.

author: Renate
author_rank: Super Contributor
timestamp: February 10, 2021, 05:16:52 pm
content: Quote from: martfoxy on February 10, 2021, 04:57:30 pmWell, you're confusing me with this talk of power switch on.You shouldn't be measuring resistance with the power on, or did you just mean the switch without batteries in?Measuring resistance might go to a low reading for a short time but then rise to a steady value if there are capacitors around.It might even show negative resistance if one of the capacitors are charged.C45 should not measure 198 ohms if it is out of circuit and the probes are on the right direction.It sounds like R18 is burned out, double check it out of circuit.Check voltage on R37, R18, D5 with the radio on.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 10, 2021, 05:59:08 pm
content: Sorry for confusion I was getting confused myself and modified my message a few times. Please ignore the messages about switch on/off.I tested R18 out of circuit and it measures 219.Also measured C45 out of circuit and it measures open. Also tested on meter measures 258uF.The voltage on one end of R37 measures 5.2v and the other end 0.02v (where D5 is connected).On R18 0.02v at the D5 end and 0v at the other end.D5 measures 0.02v and 0v.

author: Renate
author_rank: Super Contributor
timestamp: February 10, 2021, 06:34:06 pm
content: Ok, we're getting somewhere.Something is shorted to ground in the whole area of D5.That's probably C29, directly to the right of D5 on the schematic.I'm going blind looking at that thing.You can pull C29 and check the D5 voltage without it in circuit.It won't harm anything, just noisier operation.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 10, 2021, 07:57:48 pm
content: I have pulled C29 and still getting 0.02v on D5. Have you got the second image of the schematic I sent - it is clearer.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: February 10, 2021, 08:35:19 pm
content: C31 and C85 are also in parallel with C29, might be one of them.C22 and C26, if shorted, would also give a low resistance path to ground at this point, but probably not zero volts.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: February 10, 2021, 09:01:22 pm
content: C27 would short this to ground also, but only if FM is selected.C4 would short via 100 ohms, but again only if FM selected.Maybe try unselecting FM to see if the situation changes.Ok, just saw you already did that.

author: Renate
author_rank: Super Contributor
timestamp: February 10, 2021, 09:31:37 pm
content: Quote from: Audiorepair on February 10, 2021, 08:35:19 pmTrue, but they're little ceramics, I wouldn't suspect them first.Most of that line is connected through higher resistors and caps.You might try removing D5, the voltage is low enough it won't harm anything.I'm not sure we can trust the previous checking of it.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: February 10, 2021, 10:28:19 pm
content: I agree, it really isn't possible to check a zener is good with a multimeter.Quote from: Renate on February 10, 2021, 09:31:37 pm

author: martfoxy
author_rank: Regular Contributor
timestamp: February 10, 2021, 11:11:22 pm
content: I tested C31,C85,C22 and C26 but not shorted.C27 and C4 are also not shorted.I tried unselecting FM but makes no difference to the situation.Thanks for your ideas though.I will try removing D5 tomorrow to see if that makes any difference.

author: perieanuo
author_rank: Frequent Contributor
timestamp: February 11, 2021, 10:00:29 am
content: R37 then R18 gets the static polarisation point for Q10 if I see well your schematic, have you checked them?(also R65 ? near Q10)you get those 6V on IC1maybe DIN socket is not OUTPUT but INPUT

author: martfoxy
author_rank: Regular Contributor
timestamp: February 11, 2021, 12:20:14 pm
content: I disconnected one leg of D5 and I have a component tester and it recognised it as a zenor diode 4.3v. The voltage on the rail was 0.02v still.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 11, 2021, 12:28:44 pm
content: perieanuoYes tested R37 and R18 they seem to be ok.Just tested R65 and is 3.2kI get 6v on pin 1 on both ics.I am not sure if the DIN socket is output or input to be honest or both.Thanks for your reply.

author: Renate
author_rank: Super Contributor
timestamp: February 11, 2021, 12:40:06 pm
content: Well, you do have a short to ground on that D5 bus.We've already suggested the most probable nearby components.The other components on the bus seem to be isolated by large enough resistors to make them seem unlikely.Hook up your ohmmeter using clips on the D5 bus (without batteries or power plug).You said that it measured 1Ω.Is there anything that changes this value?Check all the switches and even the positions in between the clicks.

author: jdragoset
author_rank: Frequent Contributor
timestamp: February 11, 2021, 12:44:12 pm
content: Might as well check C 16, as it is also across 4.5 volt bus to ground bus

author: Renate
author_rank: Super Contributor
timestamp: February 11, 2021, 01:46:43 pm
content: Quote from: jdragoset on February 11, 2021, 12:44:12 pmC16? Are we playing "Where's Waldo?"C16 under Q3? That's kind of isolated.

author: jdragoset
author_rank: Frequent Contributor
timestamp: February 11, 2021, 01:58:15 pm
content: There is another C-16 by D-10 and T-6

author: Renate
author_rank: Super Contributor
timestamp: February 11, 2021, 02:28:57 pm
content: Quote from: jdragoset on February 11, 2021, 01:58:15 pmOh,thatC16.

author: perieanuo
author_rank: Frequent Contributor
timestamp: February 11, 2021, 02:58:46 pm
content: Quote from: martfoxy on February 11, 2021, 12:28:44 pmin this case, you got 6V on the upper leg of R18, R65 is ok, so why Q10 have 0V in collector? check voltages on this path, which 'polarise' Q10 from DC point of view.Q10 emiter is ground (check this), Q10 collector gets voltage via R18 = 220 > R37 = 3k3 > R67 = 560k if I see well... so check this DC voltage resistor by resistor (maybe R67 is dead?)

author: martfoxy
author_rank: Regular Contributor
timestamp: February 11, 2021, 03:18:58 pm
content: I did the test with the resistance - none of the knobs being altered made any difference to the value. I did notice a fine piece of wire coming out of one of the silver boxes. I have attached a photo - not sure how that happened. I moved this and this made no difference either.I also repaired a bit of the pcb near the ferrite rod - with jumper wires as a piece had broken off, but this was after the radio had already stopped working. I took the repair off and this didn't make any difference either.

author: perieanuo
author_rank: Frequent Contributor
timestamp: February 11, 2021, 03:32:38 pm
content: if you modified the 'knobs' I sugest you buy another radio, the adjustments for the RF part are NOT convergent

author: martfoxy
author_rank: Regular Contributor
timestamp: February 11, 2021, 03:45:26 pm
content: No I didn't modify the knobs just turned the volume, tone and band select as Renate suggested whilst measuring the resistance.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 11, 2021, 03:49:04 pm
content: Also tested C16 near D10 it isn't shorted.Also top of R18 is about 0v.

author: perieanuo
author_rank: Frequent Contributor
timestamp: February 11, 2021, 04:03:02 pm
content: I retract all I said, if you don't have voltage on  C29 positive terminal, quickest way to find the 'short' to ground is not to disassembly all your radio, is to inject voltage directly on C24 from a variable DC supply and let the current protection on some high setting like 2A or more (in laptops I used 20A, yes 20 amps !!!)the defective component will get hotthat's how I spotted shorted caps on motherboards, tooked some seconds

author: perieanuo
author_rank: Frequent Contributor
timestamp: February 11, 2021, 04:06:42 pm
content: you can check ALL capacitors parralel with  C29 if you don't wont to inject voltage on C29, by injecting if C40 is shorted you risk to burn T5 for examplesuspects: C31 C85 C29 C16

author: Renate
author_rank: Super Contributor
timestamp: February 11, 2021, 04:20:26 pm
content: Quote from: perieanuo on February 11, 2021, 04:03:02 pmYeah, that is how to do it when you're ready to give up.Unless you have an good thermal camera it would be too easy to burn up one of the little RF transformers.Other people put isopropyl alcohol on and wait for the dry spot.But all the goop on this, I wouldn't want it to all run into the air capacitors.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 11, 2021, 04:25:16 pm
content: Ok thanks I haven't got a bench power supply so not sure I can do this.I have a variable power block that has output 1.2A.I think I have tested all the capacitors you mentioned C29,C31,C85 and C16.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: February 11, 2021, 05:05:48 pm
content: T5 shorted primary to secondary could short out the rail, don't know how likely that actually is.Unless there's a stray piece of wire underneath it.

author: Renate
author_rank: Super Contributor
timestamp: February 11, 2021, 05:17:14 pm
content: Quote from: Audiorepair on February 11, 2021, 05:05:48 pmHa! I was just about to post that!Everything else has resistors or teeny caps or it goes through the band switch.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 11, 2021, 09:54:50 pm
content: I removed that stray wire and unfortunately no difference!I couldn't get it to conduct on the meter either.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: February 11, 2021, 10:14:10 pm
content: Probably enamelled wire, insulated.Someone must have been poking around in there at some point then.The plot thickens.

author: Renate
author_rank: Super Contributor
timestamp: February 11, 2021, 10:46:59 pm
content: Quote from: martfoxy on February 11, 2021, 03:18:58 pmWell, when, how did this break? Was the unit dropped?You should look further for mechanical damage.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 11, 2021, 11:07:02 pm
content: Yes I have knocked the radio over before but it still carried on working. I will have a good look tomorrow to see if anything else is mechanically broken and blow out anything that I can - in case there is anything else lurking in there.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: February 11, 2021, 11:11:07 pm
content: I don't know much about radios, but it looks like the tuning capacitor is designated as a 4 gang capacitor RV1 - RV4.Each connected to the shorted rail.If this tuning capacitor is somehow shorted to ground, this will give the symptoms here.

author: jdragoset
author_rank: Frequent Contributor
timestamp: February 11, 2021, 11:20:52 pm
content: Put a current across D-5 to produce a 0.2 volt drop.Use a DMM on 250 mV scale across all components and +4.5 V and -V traces and find where the voltage drop is minimum.

author: perieanuo
author_rank: Frequent Contributor
timestamp: February 12, 2021, 08:20:18 am
content: Quote from: Renate on February 11, 2021, 04:20:26 pmwell, when you repair 20 motherboards per day in a repair shop, you cannot aford to search some capacity for 2 hours, that's not economicbut our friend can choose to dig 2 days, it's his choice

author: perieanuo
author_rank: Frequent Contributor
timestamp: February 12, 2021, 08:22:33 am
content: Quote from: Audiorepair on February 11, 2021, 05:05:48 pmnever seen one shorted primary to secondary on those voltage levels. it's not a smps transformer manipulating watts or classic supply step-down voltage transformer.but who knows

author: perieanuo
author_rank: Frequent Contributor
timestamp: February 12, 2021, 08:24:44 am
content: Quote from: jdragoset on February 11, 2021, 11:20:52 pmyep, this type of thing can be the short everyone is looking for

author: martfoxy
author_rank: Regular Contributor
timestamp: February 12, 2021, 09:10:10 am
content: Thanks for all your suggestions!

author: martfoxy
author_rank: Regular Contributor
timestamp: February 12, 2021, 09:32:42 pm
content: I attached batteries 4.5v across the shorted rail. T5 got warm. So I took it out and the short has gone.The three pin side is shorted to the two pin side.Does that mean there is nothing I can do to repair it?Thanks

author: Renate
author_rank: Super Contributor
timestamp: February 12, 2021, 09:40:06 pm
content: Yes, you can sort of repair it.Leave T5 out.If you connect on the left (three terminal side) the middle connection (that goes to D5 and the power) to the top terminal (that goes to the FM detector) you should be still able to get FM radio just fine.Just a short piece of wire in the PCB.There is a resistor already on the collector of the transistor so nothing will be harmed.Kind of amazed that it was T5.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 13, 2021, 11:59:37 am
content: Thanks very much I will try that in a while. Plus there wasn't a wire underneath shorting anything!!Just got to get a few components I was testing back in again as well.

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 13, 2021, 02:52:56 pm
content: Does it have a black 'screw'? Just get another one from a donor AM radio and it will be fine.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 13, 2021, 06:11:40 pm
content: Yes it does. Does it have to be turned to the correct position to work properly?

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 13, 2021, 07:30:08 pm
content: Yes, tune in on an AM station and turn for best audio. Don't touch the other transformers.Be very careful, these ferrite tuning slugs are very easy to break.

author: Renate
author_rank: Super Contributor
timestamp: February 13, 2021, 07:52:44 pm
content: Quote from: PA0PBZ on February 13, 2021, 02:52:56 pmWell, you've got a better idea than I do how standardized those things are.Still, I think that bypassing T5 just to see if everything else is working first is what I'd do.

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 13, 2021, 08:02:54 pm
content: Oh sure, but I guess that TS wants to restore full functionality. If bypassing doesn't get the FM part back to life there's bigger problems.And yes, this stuff is pretty standardized.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 13, 2021, 09:21:12 pm
content: BRILLIANT FM is working - thanks so much for all the help everyone has given.I will try and get hold of a replacement for T5 I don't know if available on Ebay.Also need to get a replacement for D3 as I broke it when testing.Thanks again.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: February 13, 2021, 09:55:19 pm
content: Note this advice well, this is very important.The first time you try and adjust a ferriite tuning slug, you WILL break it.And then you will be in the shit.So if you are going to get one of these on ebay, I would get at least more than one, so you can practice how to adust it and find the right tool to do so, without turning the slug into powder in the process.Been there, done that.Quote from: PA0PBZ on February 13, 2021, 07:30:08 pm

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 14, 2021, 09:26:27 am
content: Search for "455 Khz transformer" and note they come in different sizes, this one is 7 mmhttps://www.ebay.co.uk/itm/265005552490

author: perieanuo
author_rank: Frequent Contributor
timestamp: February 15, 2021, 02:25:00 pm
content: Quote from: martfoxy on February 12, 2021, 09:32:42 pmfinally, the method worksn isn't it, someone here laughed beforeglad you 'extracted' the bad apple

author: martfoxy
author_rank: Regular Contributor
timestamp: February 19, 2021, 11:30:06 am
content: I got another AM coil and now working on AM, however FM volume is quiet on the lower end 88MHz for Radio 2 I have to put volume at max to hear it, but louder at 100Mhz.I did replace D3 with a 1N60 I got from Ebay - supposed to be germanium but not sure it is. Would this cause the volume problem?

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 19, 2021, 11:43:59 am
content: 1N60 is germanium and I don't think it can cause the effect you mention anyway.Try to carefully adjust CT1 to see if it gets any better.

author: martfoxy
author_rank: Regular Contributor
timestamp: February 19, 2021, 09:50:53 pm
content: Thanks for the advice. However I tried radio on mains and is much louder. The batteries must be run down!

author: martfoxy
author_rank: Regular Contributor
timestamp: March 28, 2021, 05:02:00 pm
content: Once again just soft white noise but there isn't a short like before - I get this on mains or battery.I noticed if I connect two tracks together the radio works. I have attached a diagram to show these on the pcb.I have tested the nearby transistor Q5 and the voltages seem to match the specified ones.

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 28, 2021, 06:26:16 pm
content: Are you saying that bridging R16 makes the radio work? How did you find out, bridging random points until something happened?What do you measure on Q5 with and without connecting the tracks together?

author: martfoxy
author_rank: Regular Contributor
timestamp: March 28, 2021, 08:53:46 pm
content: Thanks for your reply.It was just chance I bridged the two tracks and it started working.I tested Q5 without bridging the two tracks.

author: martfoxy
author_rank: Regular Contributor
timestamp: March 29, 2021, 09:03:01 am
content: I was testing voltages and accidentally bridged those two tracks with the probes.

author: martfoxy
author_rank: Regular Contributor
timestamp: March 29, 2021, 08:54:36 pm
content: The voltages measured on Q5 are B 1.098v C 3.82 E 0.8Specified as B 1 C 3.3 E 0.35v

author: Renate
author_rank: Super Contributor
timestamp: March 30, 2021, 12:04:14 pm
content: Quote from: martfoxy on March 29, 2021, 08:54:36 pmDid you ever replace D5, that zener that you said you broke?If not, that's why the collector is high-ish.I suspect something with the AGC (maybe when you changed T5?)It gets its bias from R36 (at the bottom, near the DIN connector).The bias gets "stolen" off the AM detector and smoothed by C30 (near D5 & company).Get D5 in there first if it isn't.

author: martfoxy
author_rank: Regular Contributor
timestamp: March 30, 2021, 02:05:33 pm
content: It was D3 I snapped in half and have replaced that. D5 was ok when I tested it last.I have found R36 and C30 on the circuit diagram.The radio did work for a while after I changed T5 but sadly died again.Thanks

author: Renate
author_rank: Super Contributor
timestamp: March 30, 2021, 02:47:04 pm
content: Q5 sounds blown.The voltage measurements don't make a lot of sense, it should be: b ~= e + 0.65 VOk, if you had a strong signal tuned in the IF waveforms could confuse a DVM.You tested Q5?Check the voltage on C30.Try thowing a 5k or 10k from C30 to ground.

author: martfoxy
author_rank: Regular Contributor
timestamp: March 30, 2021, 07:16:31 pm
content: Tested Q5 component tester says NPN hFE=91 Vbe=780mV Ic=6.0mAI also tested zener D5 says Uz=4.33VChecked the voltage across C30 it’s 0.710VHaven’t tried the resistor to ground yet.

author: martfoxy
author_rank: Regular Contributor
timestamp: March 31, 2021, 08:20:20 pm
content: I took out C30 to test it. However now the old fault of shorted rail has come back.I tested T5 and the 2 pin side is shorted to the 3 pin side.Not sure what is making this happen.

author: Renate
author_rank: Super Contributor
timestamp: April 01, 2021, 02:05:31 am
content: Wow, that is really weird.Did you do a post-mortem on the first dead one?This thing is 6 V, it couldn't have arced over unless you were running a kite in a thunderstorm.More likely there is some intermittent that is overheating one side and causing it to melt to the other side?

author: martfoxy
author_rank: Regular Contributor
timestamp: April 01, 2021, 08:54:30 am
content: Just took the first one apart. I wonder if its where they are twisted together - if you can see on the photo?

author: Renate
author_rank: Super Contributor
timestamp: April 01, 2021, 12:25:58 pm
content: I can't see a thing.Do the windings look "crinkly, sugar coated" or nice and smooth?If you think that you found the spot you can snip it out and see.You still have one end of each winding connected so that you can verify.When you were fixing the problem to start with T5 was not shorted, the collector of Q5 had 3.8 V.The only thing that I can think of would be an intermittent short in T3 on the bottom pin to ground (the case or the lower secondary).This would cause lots of current in the primary of T5, melting it and causing a short to the secondary of T5.With T5 removed, check to see the resistance from the line between T5 & T3 to ground.You can try bypassing T5 again (once you check that T3 is not shorted).This is one for the weird stuff book.

author: martfoxy
author_rank: Regular Contributor
timestamp: April 02, 2021, 08:19:49 pm
content: I unwound the coil and there is section where the wire looks black.Tested for a short on T3 and didn't find one. So I put the bypass wire back in and can get FM if I short the tracks mentioned before.Thanks for your help.

author: Renate
author_rank: Super Contributor
timestamp: April 03, 2021, 01:45:01 am
content: Quote from: martfoxy on April 02, 2021, 08:19:49 pmWait, by shorting tracks you mean Q5 base to emitter?That besides T5 blowing up again you still have the problem with it not working?Without T5 you have no AGC.Check the voltage on C30 and try throwing resistors across it.Try weak and strong stations.

author: martfoxy
author_rank: Regular Contributor
timestamp: April 03, 2021, 08:01:10 pm
content: No I am shorting across R16 which means Q5 emitter is connected to 0v.I tried various resistors across c30 but did not get any radio output.I measured the voltage across C30 and it is 0.73vThanks

author: Renate
author_rank: Super Contributor
timestamp: April 04, 2021, 12:11:39 pm
content: Is R16 actually 330Ω?I think it's open or disconnected?Check R17 also for 1k.You should be able to get a decent reading on both without unsoldering.

author: martfoxy
author_rank: Regular Contributor
timestamp: April 04, 2021, 01:55:21 pm
content: R16 and R17 measure close to what they should be.Thanks

author: Renate
author_rank: Super Contributor
timestamp: April 04, 2021, 04:48:18 pm
content: How about jumping R16 with a cap?

author: martfoxy
author_rank: Regular Contributor
timestamp: April 08, 2021, 10:16:47 am
content: Doesn't seem to work with a cap jumping R16.I have ordered 4 replacement IF transformers for T5 to see if this fixes the issue. I suppose I am just going round in circles on this it will probably burn out again!

author: Renate
author_rank: Super Contributor
timestamp: April 08, 2021, 11:22:08 am
content: I don't get it.If Q5 is good and a high beta then the drop over R17 should be three times the drop on R16.Since Q5 emitter is measuring 0.8 V that means the drop over R17 should be 2.4 VDouble check the voltages on Q5 and the high end of R17.Any chance that you put Q5 in backwards after pulling it?Q5 emitter is reading too high, but the base doesn't seem to be reading high enough to justify this.OK, the AGC is deactivated without the AM detector, which would make Q5 base a bit higher.

author: martfoxy
author_rank: Regular Contributor
timestamp: April 08, 2021, 02:40:05 pm
content: Took Q5 off to test it to see which pin is collector and emitter - and to see if I had it in the right position. Unfortunately one of the legs fell off must have bent them too many times.I will try and get a replacement its marked 9018.Thanks

author: Renate
author_rank: Super Contributor
timestamp: April 08, 2021, 03:18:43 pm
content: Quote from: martfoxy on April 08, 2021, 02:40:05 pmOops, sorry.As long as it's out, check the voltages on what would be CBE.Are we missing something?Any decent modern NPN should mostly work there. (But check the voltages first.)

author: martfoxy
author_rank: Regular Contributor
timestamp: April 08, 2021, 04:14:44 pm
content: B 1.07vC 3.72vE 0.77vI am not sure why both ends of R17 (1k) measure the same voltage.

author: Renate
author_rank: Super Contributor
timestamp: April 08, 2021, 05:55:05 pm
content: Quote from: martfoxy on April 08, 2021, 04:14:44 pmBecause there is no current going though there.Are these measurements with a new transistor or with nothing installed?

author: martfoxy
author_rank: Regular Contributor
timestamp: April 08, 2021, 07:20:15 pm
content: Nothing installed. I have found a BC337 which I have now installed. Voltages are nowB 1vE 0.65vC 3.61vRadio works but only if short across R16 again.

author: Renate
author_rank: Super Contributor
timestamp: April 08, 2021, 07:29:16 pm
content: Something is screwy here.With Q5 removed R16 can't have any voltage across it.Are you using some funny reference point for ground? It's the same as the low end of R16.Is something shorted/contaminated/something?I'd pull Q5 and double check where/what the low end of R16 is connected to and what the high end is misconnected to.We're missing something here.Edit: C22 is leaky. Pull it and put something else in.

author: martfoxy
author_rank: Regular Contributor
timestamp: April 08, 2021, 08:15:13 pm
content: Sorry for the confusion. I was using the negative on the battery supply for ground.If I measure across R17 I get 0v.

author: martfoxy
author_rank: Regular Contributor
timestamp: April 08, 2021, 09:24:15 pm
content: I have taken c22 out and is acting as a resistor of 1.4K. So will replace when I can find another one.

author: Renate
author_rank: Super Contributor
timestamp: April 08, 2021, 09:48:20 pm
content: Wow, so C22 is really leaky?Just put anything in there for now.

author: martfoxy
author_rank: Regular Contributor
timestamp: April 09, 2021, 09:00:26 am
content: Brilliant the radio is now working. I tried it without C22 I will order a replacement.Thanks for all your help on this.Hopefully T5 won't burn out again when I replace it.