Anritsu MS2651A repair (need service manual) - Page 1
Forum section: electronics / repair

author: jimon
author_rank: Regular Contributor
timestamp: March 30, 2016, 09:07:37 pm
content: Hi, got a broken unit from ebay, hoped it will just work, but not so fast ... so my first repairlet's see what we can do.Symptoms so far :- no/very small signal (was unable to track anything reliably from rigol dg4102, don't have any other reliable signal sources atm, anything I can buy cheaply for it?)- huge (like 50db or more) amplitude level difference between 0-3GHz full span and 0-100MHz span, when spectrum analyzer in full spane mode picture looks like normal (with noise level on -70db or so), in 0-100MHz mode noise is somewhere around 0db, no idea whats going on there, is there even a different path for different frequencies?- no other visible issues- cpu board shows self check is ok.Looks like there is no internal test signal to check if this thing works, 'cause I've tried to disconnect whole RF stage and there were no complains on a screen.Checked input DC block and attenuator - they seem to be fine. Checked almost all test voltage points - they look fine.Does anyone have an idea where to look for service manual ? Tried to google it, but was not so lucky.And any tips what to check next ? and maybe how IF should look like on oscilloscope ?

author: nidlaX
author_rank: Frequent Contributor
timestamp: March 30, 2016, 09:16:14 pm
content: Quote from: jimon on March 30, 2016, 09:07:37 pmIf you haven't already, I recommend watching some of Shahriar's spectrum analyzer repair videos to get an idea of how the input stage typically works and where you might have a problem. If you have a scope, have you tried following the signal from your Rigol through the input stage?

author: jimon
author_rank: Regular Contributor
timestamp: March 31, 2016, 07:08:23 pm
content: Not really sure what's wrong with that unit, I've tried to bypass input attenuator and put 1Mhz -40 dBm into input of RF front end ... and I found nothing at with oscilloscope all around first mixer. Also nothing shows-up on output of LO ... it might be the same as herehttp://www.antiqueradios.com/forums/viewtopic.php?f=8&t=274605Will I even be able to see LO output on 100 MHz oscilloscope ? Or should I look for whatever driving LO ? (there is probably some sort of PLL for it)

author: sherlock
author_rank: Contributor
timestamp: April 02, 2016, 07:56:23 pm
content: I don't have that analyzer, however I had bought an Advantest SA a few years back that didn't display any signals on the screen. In my case the mixer diodes were shot, along with a couple of burned resistors in the attenuator. I too had questions about the LO circuit working. You're correct in that a 100 MHz scope won't show anything. Since I was mostly interested to see if the LO was working or not, and not on frequency at this time, I used an old radar detector for the car that I had lying around. I powered it from a small 12 volt supply and used the detector as a probe. In my case I was able to pick up the microwave LO signal so I knew it at least worked. You might have to remove some shielding to pick up anything. You can also check if you have the large "spike" at the left side of the screen (0 MHz). Or set the center frequency for zero Mhx, full frequency span, and see if you get a zero indication in the center of the screen. If you get that, then the LO and mixer is probably working. Then you can troubleshoot where the input signal is getting lost. Good luck with your purchase.

author: jkf1000
author_rank: Regular Contributor
timestamp: June 11, 2016, 11:49:26 am
content: Hi Jimon, did you manage to get any further with your analyzer? I have just purchased the "B" model of the same analyzer as a spares or repair unit. The fault with my unit is a display issue, the LCD displays nothing but vertical lines, I have scoped the ACRTC chip and have found signals are missing for the Vsync and Hsync and have ordered a new PLCC chip for it. It appears as if it is functional as far as the RF circuits are concerned as I can get the unit to run its own self cal. routine by pressing the shift-cal-F1 while monitoring the IF out on the scope.Did you manage to get hold of any service data for your unit as I have found nothing online and Anritsu UK could only supply the user manuals!!Given that we are looking at 2 completely different faults we may be able to help each other out given the lack of supporting manuals. Karl

author: kanuk
author_rank: Contributor
timestamp: June 12, 2016, 01:52:53 am
content: Does anyone have an idea where to look for service manual ? Tried to google it, but was not so lucky.And any tips what to check next ? and maybe how IF should look like on oscilloscope ?Look here:https://www.anritsu.com/en-US/test-measurement/support/downloadsGood Luck.

author: jimon
author_rank: Regular Contributor
timestamp: June 12, 2016, 07:49:52 am
content: jkf1000, awesome that you only had LCD issue! nice score!I only found service manual for MS2601A version, I believe they should be similar in RF part. I played with it for few days, was unable to detect if LO1 is present or not (meh I just don't have any tools for that), maybe I should revisit it.jkf1000, if you have any tools for that, would you please measure what kind of signal is going on from RF block (from port X3) to LOCAL-B board. I suspect it's just 2nd IF after 2nd mixer, but my oscilloscope doens't pickup anything. If it's indeed 2nd IF I wonder if I can just inject something to LOCAL-B board and see if it works.Also would you mind to check if you noise level changes if you change RBW? My noise level jumps from ~-80db to ~-30db when I change from 3 MHz to 1 KHz RBW :/ I wonder if integrator is fine there.

author: eeadata
author_rank: Contributor
timestamp: June 12, 2016, 08:15:27 am
content: Check all RF mixer diodes in mixer sections.

author: jkf1000
author_rank: Regular Contributor
timestamp: June 13, 2016, 12:21:13 pm
content: Mine is still a work in progress unfortunately, I still have no display and without any documentation I am still a little lost as to which direction to go. I am trying to draw out a block diagram of the CPU board by following the traces on the board but it is at least 4 layers thick which makes it quite time consuming. what I have established so far is that the signals from the Toshiba processor pass through a pair of 3 state octal transceivers before the ACRTC video controller chip. To further complicate matters the output signal line from the ACRTC then go into the Altera Max PLD device which I am guessing is handling some of the video processing before feeding the LCD display. Unfortunately video signals are new to me as I am more into radio diagnostics.Jimion, I will see what signals I can find at various points the next time I pull the unit apart but at the moment it is waiting for parts to be delivered so is all boxed back together.It would be so much easier with some real documentation to follow. Karl

author: jimon
author_rank: Regular Contributor
timestamp: June 13, 2016, 07:58:19 pm
content: If you want me to trace some signals - just ask, in my case screen subsystem is perfectly fine.

author: jimon
author_rank: Regular Contributor
timestamp: June 13, 2016, 09:01:03 pm
content: So finally took time to make photos of RF module, unfortunately the very first part between input (X1) and 1st LO is hidden behind a board and really hard (desoldering) to get to.1) Photo of top of RF module2) Close in on 1st LO-ish part3) This is the closest thing between YiG and input ... but is it really 1st the mixer? It sure doesn't look like one :/

author: jimon
author_rank: Regular Contributor
timestamp: June 13, 2016, 09:05:17 pm
content: 4) Bottom of the RF module, looks like 2st LO is there!5) What this thing might beIt was even pressed firmly by a cover, and looks like after I removed the cover (or poked into something else) I started to get 0dbm+ peak on 45 MHz instead of 0 Hz (stupid me)6) PLL, wonder where control frequency comes from, maybe I should poke that7) Output board, 100 MOhm resistor O_o, but looks like it outputs 10-20 MHz signal (based on manual for MS2601A)PS. So where the infamous mixer diodes are?

author: jkf1000
author_rank: Regular Contributor
timestamp: June 13, 2016, 09:59:51 pm
content: Hello again Jimon, have you looked at the block diagrams in the version 1 operators manual? Have a look from around page 201 to 211 and it gives you quite a good idea of the signals you should be looking for. As a side note all the high frequency appears to be only in the 3Ghz unit, all the IF and mixer frequencies look to be a lot lower which you should be able to sniff out with a scope if you can go upto around the 100Mhz range.If you want a simple and cheap higher frequency sniffer have you tried one of the cheap SDR dongles as a wide frequency receiver? The one I use can cover from 24Mhz to over 1.5Ghz and can make a simple spectrum analyzer with software such as SDR# but the resolution is only around 3.5Mhz bandwidth but still makes a useful tool. Karl

author: jkf1000
author_rank: Regular Contributor
timestamp: June 19, 2016, 10:08:37 pm
content: Jimon, (or any one else that may have the same spectrum analyzer) Considering the fact that I am not able to see any information on my LCD screen, can you list in sequence the button press order to enable the composite PAL output at the rear of the analzer in the menu settings? I have read through the manual but it assumes that you can follow the onscreen prompts.Many thanks, Karl

author: jimon
author_rank: Regular Contributor
timestamp: June 21, 2016, 07:36:01 pm
content: jfk1000, please find a video here(with instruction in the video description)Not sure if this what you need, because looks like my analyzer doesn't have TV-out option (this is what it prints when I try to enable it), though it does have "composite out" on back panel. If I plug oscilloscope to "composite out" channel I'll get some signal by default without doing/pressing anything. On a board itself it marked as "Y output", and X and Z are not populated.

author: jkf1000
author_rank: Regular Contributor
timestamp: June 23, 2016, 09:12:05 pm
content: Thanks for uploading the video but unfortunately it does not help much. I don't have the tv option installed only the rear composite out which I am unable to activate without a screen. Looking at my user manual the setting is in the system menu 3, composite mode-composite-PAL-return.I finally had chance to do some measuring for you (assuming my unit is working ok on the RF side of things) on the coax to connector X3 on the 3Ghz unit there is no output, just an input from the Local board of around 96Mhz which matches the info on my block diagram. It list the local signal on X3 to be from 94 to 106Mhz I measured the signal on my 100Mhz DSO at around 3.56v Peak to Peak.On your scan board with the "Y" output board I have 3 flashing LEDs, on yours are they flashing or constantly lit as I suspect mine are showing a fault condition relating to my failed display condition?

author: jimon
author_rank: Regular Contributor
timestamp: June 24, 2016, 09:38:49 am
content: So X3 is an INPUT not outputwoah thanks for the info! that explains a lot ... especially why I was not getting anything out of X3On my board all three leds are flashing on a same time with frequency around 2Hz. If I connect a scope to Y output I get something like on the screenshot.

author: jkf1000
author_rank: Regular Contributor
timestamp: June 25, 2016, 07:06:17 am
content: I don't know what technical differences there are between your A model when compared to my B model. Do you have the block diagram available? In the absence of any sort of in-depth technical documentation or schematic it will at least give you an idea of what signals to scope for and the direction of the LO and signal paths. As I mentioned previously, apart from inside the 3Ghz convertor, all other signals should be low enough in frequency to trace with your Rigpl DSO.Just as a long shot, but if yours is just a level error have you tried running the full auto calibration routine within the menu. Also check the backup battery for 3v just in case it is not able to retain its stored values.Not made any progress with mine as yet but cleared most of the other jobs off the bench so should get back to it later. So far I have confirmed digital communication between the processor and the video chip but no sync output between the video chip and the CPLD. Without the Vsync and Hsync signals there will be no timing signals for the LCD module. I will try and source another video controller chip first and take it from there, A process of elimination without the schematic and I am in unknown territory trying to to trace and understand digital signals.Let me know if you make any progress, Karl.

author: jkf1000
author_rank: Regular Contributor
timestamp: June 25, 2016, 10:54:05 pm
content: Just done a quick google search for you and to see what differences there are in the models and I found a manual specific to the "A" models. Unfortunately it is too large to attach here but it was easy to find with google, I just searched MS2651a and it was one of the first results. Download it and check around page 181 for the block diagrams which gives you the signal paths and frequencies. Karl.

author: jimon
author_rank: Regular Contributor
timestamp: June 26, 2016, 07:27:48 pm
content: Found it, awesome, thanks!I'm still a bit busy with other stuff so had little time to do anything with it. Looks like their internal connectors represent PATA-ish pitch. Need to make a small cable extension so I can run RF module and be able to access back side of it (where 2nd mixer is).

author: jkf1000
author_rank: Regular Contributor
timestamp: June 27, 2016, 08:16:25 pm
content: Post back when you have more time spare or anything more you need me to measure. I have questions about the signals around the ACRTC chip which you could scope for me when time permits, Karl.

author: jimon
author_rank: Regular Contributor
timestamp: June 27, 2016, 09:02:49 pm
content: Sure, I'll do it tomorrow evening, anything in particular you want to know? I've tried to look for ACRTC-ish chip/marking, but can't find it ... board next to LCD mostly contains 74-ish chips and CPU board doesn't look like have this marking. So where I should look?

author: jkf1000
author_rank: Regular Contributor
timestamp: June 27, 2016, 11:35:31 pm
content: The ACRTC is the HD63484 on the main processor board. It is the main process chip for the display. What I need to know is what if anything is happening on your Hsync and Vsync lines which are pins 13 and 14. I was expecting to see cmos level timing signals to control the display timing but not getting any thing like it. I am still trying to diagnose the root of my display issue but not making much progress so far. Karl

author: jimon
author_rank: Regular Contributor
timestamp: June 28, 2016, 04:54:17 pm
content: Thanks for the waiting, here hsync and vsync signals. Please let me know if you want me to probe more!

author: jimon
author_rank: Regular Contributor
timestamp: June 28, 2016, 10:17:07 pm
content: jkf1000, do you have IF 110.695 MHz anywhere ? I was poking all around RF block ... and meh .. sure I found 100 MHz from getting from X3, and than it's was all over RF traces (was poking around 2nd mixer and VCO) with level around -30 dBm. Looks like it was leaking to VCO output trace with level around -35 dBm.Looks like 110.695 MHz should go through backplane, but I cannot find anything with oscilloscope going through RF block connector to backplane :/ I would really appreciate if you poke there and check if IF is present.

author: jkf1000
author_rank: Regular Contributor
timestamp: June 28, 2016, 10:34:22 pm
content: Thanks for checking that for me. exactly the signals I expected to see if measured from pin 13 and 14. ( On a working machine ) Time for me to order a new chip as I have no regular pulses on my unit so no timing control for later stages. The other possibility with mine is corrupted data from the CPU or bad 3 state transceivers between the CPU and the ACRTC chip. I am flying a little blind on this without data so its a process of elimination based on best guess and logical signal paths. I will report back with any progress but it may take a while to source the parts.I just hope that if or when I restore my display there are no further issues with my machine lol.Did you check your backup battery and run a full calibration sequence with your machine as I suggested earlier? It may give you more of a direction to go in if it does not resolve your level problem. If I can return the favour with measurements from my unit let me know and report back with any findings and progress you make. Karl.

author: jkf1000
author_rank: Regular Contributor
timestamp: June 28, 2016, 10:42:36 pm
content: I will check the IF for you but it wont be until tomorrow evening at the earliest. Please bear in mind also that until my display issue is resolved I cannot determine that my machine is working 100% Karl

author: jimon
author_rank: Regular Contributor
timestamp: June 28, 2016, 11:06:29 pm
content: Self cal doesn't do much, either mixers are completely dead or either something is really strange.Basically my current situation is just crazy:- Did "All Cal", it went fine. And actually I've checked what happens if you just remove cal input from main attenuator - the device doesn't care, there is simply no "calibration failed" errors (or I was not able to trigger them any way possible)- Did preset -> All, and I'm getting straight line over 0 dBm on whole spectrum- Device reports >+4 dBm (sometimes +300 dBm) over all spectrum- If I provide some input signal, spectrum around this signal jumps down to ~-50 dBm- Noise level (can you really even say +4 dBm is a noise level???) jumps between different levels when I switch between different RBW.- Backup battery is doing fine, minor level of oxidation is present though.Not having tools to properly test 1st and 2nd mixers (I don't even understand wiring of them) makes me sadFor now I just want to know what works and what doesn't.

author: jkf1000
author_rank: Regular Contributor
timestamp: June 28, 2016, 11:19:37 pm
content: Study and try and understand the block diagrams in the manual. They are our only source of information at the moment. Assuming that my unit is functioning 100% as far as the RF stages is concerned, between both our units we should be able to resolve both units as both appear to have completely unrelated faults. Karl

author: jkf1000
author_rank: Regular Contributor
timestamp: June 29, 2016, 07:27:12 am
content: One other thing you can try is to hold in the Preset button for 5 to 10 seconds while powering up which boots the unit into a default condition according to the manual. Karl.

author: Falkra
author_rank: Regular Contributor
timestamp: June 29, 2016, 09:18:01 am
content: Quote from: jimon on March 30, 2016, 09:07:37 pmIs this what your are looking for ?http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Anritsu/MS2601A_J_SM.pdf

author: jimon
author_rank: Regular Contributor
timestamp: June 29, 2016, 10:48:03 am
content: Quote from: Falkra on June 29, 2016, 09:18:01 amMS2601 is a bit close, but different:- Modules layout is different, 2651 have almost everything RF related in one block, with external local oscillator board.- 2651 uses 4.xxx GHz between 1nd and 2st mixer when 2601 is uses 2.5214 GHz- 2651 IF is 110.695 MHz and 2601 is 21.4 MHz- YTO \ VCO controls looks to be different- etc

author: jkf1000
author_rank: Regular Contributor
timestamp: June 29, 2016, 03:35:41 pm
content: If your unit is responding to an input signal, assuming that it is displaying the correct signal frequency, that suggests to me that it is not a mixer issue and is more likely to be a leveling issue. Maybe a failed AGC or ADC. Does it display your input signal at around the right signal position on screen? Does the signal level displayed on screen match the output level of your generator?

author: jkf1000
author_rank: Regular Contributor
timestamp: June 29, 2016, 10:27:06 pm
content: I have had a probe around the RF board and not been able to find the 110.7Mhz signal but there are 16 pins on the connector that I am not able to probe. There is a very good chance that it will be on one of the unreachable pins. I found the 100Mhz reference and the 12Mhz mixer signal (on the connector marked X2) but that was all.I find it very strange that they would choose to route a high frequency signal through a 0.1 header then on via a board to board interconnect. I can only guess that it has very effective guard traces around it or it is buried in one of the inner board layers between ground planes.The only way you will see more is by making some sort of extender cable as you suggested before using an ATA type connector. One thing I did notice is that from the 32 0.1 header connections, at least 17 of them are just ground which leaves only 15 for supply, signal and control signals.If there is anything else I can check for you just ask. Karl.

author: jimon
author_rank: Regular Contributor
timestamp: June 30, 2016, 08:20:16 am
content: Hm it's strange that you have 12 MHz around X2 (Looks like it's directly coupled to YIG), I don't think it's a reflection from the mixer ... or it might be?I got the extension cable, and indeed top pins are mostly ground and power, will check lower ones.

author: jkf1000
author_rank: Regular Contributor
timestamp: June 30, 2016, 02:18:33 pm
content: I have ordered a new chip for the video circuit, unfortunately none available locally so will take a few days from the USA. I no longer trust the HongKong/China marketplace for anything branded, I have had too many fakes in recent months. In the meantime I will pull the old chip and just fit a PLCC socket to make life easier. There is still the possibility that it may be one or both of the octal transceivers between the CPU and video chip so may change those as a matter of course while waiting.Jimon, I will update with any progress. and let me know if you need anything from me as far as measurements. the 12Mhz was found by scoping the back of the X2 multi connector not at the X2 coaxial connector, sorry if that caused any confusion. Karl

author: jimon
author_rank: Regular Contributor
timestamp: June 30, 2016, 05:34:28 pm
content: Ok good news, AGC is f**cked after CAL procedure, so full reset (by holding preset button on power up) helps a lot! Basically SA is unusable after CAL.Some bad news, something somewhere is f**cked as well, by default I get a peak in 48 MHz when nothing is connected :/ And when I provide 100 MHz on input - I get peak at 148 MHz ... well at least mixing works somewhat, so what is it? YIG or VCO out of tune?

author: jkf1000
author_rank: Regular Contributor
timestamp: July 01, 2016, 07:59:05 pm
content: I have no idea about the 48Mhz, I can only guess that it is a mixing product but dont have the block diagram to hand to look at the frequencies involved. It may be you have a failed filter or similar. I will look into the block diagrams and see if I can work it out for you but it does look as if you are heading in the right direction with what you have learned so far, Karl

author: khach
author_rank: Contributor
timestamp: July 04, 2016, 03:10:43 pm
content: Quote from: jimon on June 13, 2016, 09:01:03 pmYes, thats is a star mixer. IF input of mixer is RF input of analyzer.

author: jimon
author_rank: Regular Contributor
timestamp: July 06, 2016, 04:05:49 pm
content: Got delivery today ... jeez I would say having the right tools for the job is a number one requirement everywhere ... so looks like X4 output (top of RF module) is coupled directly to ... I don't even know what to .. looks like unfiltered output of second mixer or something, and good news are my new epic EIP 545a is able to pick it up!Bad news are:- the screw on pic is a fine tune for resonant frequency of VCO ... I'm getting range a bit around 3.95 - 4.08 GHz- I have no idea which frequency should be there, I guess either 4110.695 MHz as specified (but the screw doesn't go that far), or 3999.995 if it's direct VCO output (4110.695 - 110.7).UPD: from X4 there is 1 strong signal around 4.0xx GHz and another one around 8.0xx GHzUPD: managed to get readings from X2 in zero span mode:cf 3ghz = 6985.03 MHzcf 100mhz = 4166.53 MHzcf 0hz = 4070.67 MHzcf -100mhz = 4008.9 MHzSounds correct regarding the diagram (4.1 - 6.6? GHz), but I don't know if margins are ok, 6985.03 - 3000.0 = 3985.03 MHz on first IF when there is a filter for 4110.695 ... :/

author: jimon
author_rank: Regular Contributor
timestamp: July 06, 2016, 08:44:00 pm
content: khach, woah thanks, first time see mixer like that! =)

author: jimon
author_rank: Regular Contributor
timestamp: July 06, 2016, 09:18:15 pm
content: Ok, I've finally found where the IF out from RF module! This is LND11 port visible from one side of a module. This output is barely amplified (there a pot on other side), noise level is around 50 mVpp, and 0dbm is around 120 mVpp.

author: jkf1000
author_rank: Regular Contributor
timestamp: July 06, 2016, 10:12:35 pm
content: It looks like our RF boards are pretty much identical but there is a difference in part numbers so not sure what if anything may be different in the operation. Mine is a Anritsu A1001 322U12943b (Y2)Just measured mine from the same LND11 point and this is the wave form that I got on a single shot capture. It was a real pain to get it to trigger as there seems to be a lot of noise and other signals at that point. I have the trigger set just at the top of one of the peaks. If I just let the scope run the signals on screen are very messy.I am still waiting for the video chip for mine which should be here in the next few days so have not really done anything with it, but it is still open on the bench if you need measurements. Karl

author: jkf1000
author_rank: Regular Contributor
timestamp: July 15, 2016, 10:00:42 pm
content: My video chip finally arrived (HD63484CP8) but unfortunately made no difference, still no HSYNC/VSYNC control signals so still no display. It looks as if either the information being sent to the chip is being corrupted by a peripheral chip or the CPU itself is not generating the correct data to be sent to the video chip in the first place. I have done a lot of measuring with the scope and DMM and found several ICs on and in the path of the video chip so not sure which direction to go next. I am thinking of starting a seperate thread just for help on the display problem as I am now out of my comfort zone as far as diagnosing further on the digital signals.. Karl

author: jimon
author_rank: Regular Contributor
timestamp: August 16, 2016, 05:25:03 pm
content: Got some time to tinker with that big boy, so I learned how to tune and measure : second LO, IF, and now I'm getting 118.7 MHz there!Apparently first LO was 100 MHz off and is not locking correctly, if I set CF to 200 MHz and than go to 0 Hz with 20-50 MHz increments - it works. If I set to CF to 1-3GHz and than suddenly jumps to 0 Hz - YTO locks (? not sure if it locks at all) around 50 MHz off ... which kinda explain random crap I observed and why DC was off by ~40-90 MHz. Thanks my stupid brain was smart enough not to touch cavity filter screws because I don't have tools to calibrate that at all.Now I need to understand how the heck YTO PLL is working there, and where the hell are lock signals if any. MS2601 supposedly have LEDs to represent this, and looks like MS2651 have none.

author: jkf1000
author_rank: Regular Contributor
timestamp: August 16, 2016, 10:43:26 pm
content: Still no further with mine but not had much time due to other projects/repairs. I have fitted new SRAMs as they are a known failure point but that made no difference, next stop is probably the video RAM which I found reasonably cheap but a real pain to fit. I have found more information about them at (http://www.ko4bb.com/getsimple/index.php?id=manuals). Download the service manual for the MS2665C model which is very close to what we have and gives a lot more information on the signal paths and board to board connections. There is also a file named MS2650 service manual which contains bits of service info. Let me know how you progress.. Karl

author: ducus
author_rank: Newbie
timestamp: April 18, 2020, 12:50:35 pm
content: Hi there,Did you manage to fix your spectrum analyzer? I have an Anritsu MS2668C with same behaviour like yours. It wass working an suddenly it being to do stange things with amplitude. After recalibration noise flor it is around-20 dbm. Before it was a problem with power supply but i fixed. Do you have maybe the pinout or voltage frim power supply?Thanx

author: jkf1000
author_rank: Regular Contributor
timestamp: April 18, 2020, 01:14:37 pm
content: Not able to offer any further information for you unfortunately. It does sound like you may have a failed amplifier or attenuator stage. I ended up selling mine as a parts unit. I managed to resolve the display issue which turned out to be a 74 series IC which sat on the data lines from the main CPU so was corrupting pretty much everything else. Turns out that mine had other issue which I don't have the tools needed to diagnose the various stages. Basically you need a working analyser to be able to trace issues on a faulty one.One thing I have learned from the time spent with mine is not to buy another Anritsu device. There is just not enough service and repair information out there, even for long discontinued products. Karl

author: ducus
author_rank: Newbie
timestamp: April 18, 2020, 02:06:33 pm
content: Tanks for reply. It is possible to be one amp, but is more an challenge to fix it. If it will be to sell parts from it i will get more money than i spend buying this one.

author: jkf1000
author_rank: Regular Contributor
timestamp: April 18, 2020, 03:55:58 pm
content: It all comes down to how cost effective the time and potential parts cost will make the repair. No doubt a good analyser when working but when you compare it to a budget Siglent or Rigol unit with 12month minimum warranty and more features it very quickly becomes beyond economic repair. Karl

author: Pacotech
author_rank: Newbie
timestamp: January 05, 2022, 05:34:13 pm
content: Hi there, just to explain whats inside the 1st mixer..once desoldered all the wires, below the closed area there were a central pin to upper side ( 2 double diodes and probably 4 Resistors) IN MY CASE THE ATTENUATOR z1 is opened in input, so need to change them with a 4 / 5 dB ATTENUATOR.tHE INPUT 10-20-30-40- dB ATTENUATOR IT HAS BEEN REPAIRED WITH SMD RESISTORS 0,1%.Now waiting the new smd to change the Z1.For all you guys , with the doubth .. what's inside... here the pics..

author: Cwvto
author_rank: Newbie
timestamp: March 30, 2022, 05:54:00 pm
content: Hi all,Because the cov19, I finally have time for playing with my MS2665C SA.After looking around for the service manual, I finally come to this post here.My unit look pretty much the same symptoms like your guys said and the RF board look very similar to jimon posted.So may be I can share what I had found, may be someone someday need these information.Lets share my story.I got my unit from the china online second hand shop.The display level is over 0 dbm over the whole frequency range. The level cal cant help, but the displayed level will change after each level cal.The interesting thing is that if I connect a external signal, say 5GHz 0dbm to the input while doing level cal, the level seems more reasonably normal, at least I can see the spectrum peak response on the correct frequency. I suspecting the cal signal cant switch in to the RF path, but confirm I am wrong after a simple check.I study the block diagram, and check if the signal can reach before the IF output, when operating at zero span. Luckily, IF level follows the SG level change.I check all LO that I can reach on the RF assembly, they area. 3.5-7.5GHz 1st L.O,b. 100MHz Ref,c. 94-106MHz for SAMPLER.They all seems fine and in lock. When I look closer to the spectrum line, the peak seems swinging, and a pulse like signal shown when the C.F below 3GHZ.I wondering may be the level cal process referenced to a wrong level because some LO drifted at the sampling instant?One LO I can not check at the beginning is the 2nd LO, which operating at 4GHz inside the 3GHz converter. I don't want to touch every single screw I see, coz experience tell me this ack may end up to a tragedy.The missing 4GHz was found when I figuring out which screws holding the 3GHz assembly, it is moving like sweeping. This signal should be a CW signal at exactly 4GHz for 2nd mixing, moving around definitely abnormal.The 4GHz can be check on the SMA connector shown in Signal Flow.png.Since no schematic is available, the only way to fix is trial and error. After probing around the pcb trace, I confirm the 4GHz VCO is controlled by "N5" - SOP8 IC marked as 812. The -11V is controlling the VCO freq. on N5's pin 4. May be adjust the R22 and R40 can make it lock on again.So I started my iteration, I adjust R22 a little bit and install it back and check the 2nd LO. I am so lucky that the signal now not swinging any more. Then I adjust more to find if there is another sweet spot and check the test point LND15 (-11V), which is accessible when the module installed back, with oscilloscope A.C couple mode to find a spot the amplitude of the "noise like" signal, which is the error voltage of VCO, is minimized.Finally, the problem is fixed, and the cal status are all zero which means every thing is good. The minor issue is when using a very small span, 20kHz, a FM like signal is observed but actually a CW signal is feeding. May be this is the phase noise of 4GHz or other L.O, but its good enough for me and I don't want to create new problem while hunting for the minor problem.Forgive my long article, I just finish the repair and so happy to share the information with all you guys.

author: JohnnyS
author_rank: Newbie
timestamp: January 15, 2023, 10:15:14 am
content: Quote from: Cwvto on March 30, 2022, 05:54:00 pmHi all,I got from my company junk an Anritsu MS2665C spectrum analyzer, it was supposed to have problem with the input attenuator and 3GHz up-converter, but when I try to power on I discovered that the power supply is not working.The power supply unit is the Anritsu 34Z112975 fitted in the SA series MS266x, the schematic is not available, it blows the fuse at power on, the input stage is ok, no burned component, so it is very difficult for me to repair. I'm thinking to replace with external unit, but there aren't voltage labels on the connector, so I'm trying to find the pinout and the voltage levels.This is what I find:A BV1 1 1 V1V1 2 2 GNDGND 3 3 GNDV5 4 4 V5V5 5 5 GNDGND 6 6 GNDV3 7 7 V3V3 8 8 V3V3 9 9 GNDGND 10 10 GNDGND 11 11 GNDV2 12 12 V2V2 13 13 GNDGND 14 14 GND? 15 15 ?? 16 16 GNDFor sure V3 is +12V and V5 is negative.Any help will be appreciated.

author: JohnnyS
author_rank: Newbie
timestamp: January 20, 2023, 08:04:33 am
content: After some reverse engineering of the PSU schematic, I was able to find a faulty MOSFET of the PFC circuit. I removed it, since it's not strictly necessary and the PSU restart to work. Now a stand-by voltage is present on a pin of the interface connector.I will check the rest of the PSU and finally connect back into the instrument, going on with the rest of the instrument.I will try to put in clear the schematic of the power supply, for every one that may need it.

author: dannyx5321
author_rank: Newbie
timestamp: April 11, 2023, 11:32:52 pm
content: Hello,I've been reading for a while through this post since a won an Ebay auction for the same Anritsu analyzer and in hindsight I think I'm going to regret it. For a couple of hundred dollars more I could have got a working HP. The one I bought has power supply issues and so far no schematic is to be found. I'm hoping that you'll post that diagram when you have a chance,Thanks, Daniel

author: Halcyon
author_rank: Unknown
timestamp: June 12, 2023, 07:03:01 am
content: Not sure what it is about this thread, but why are we getting pointless reports to moderators? Spam bots perhaps?

author: hansgt21
author_rank: Newbie
timestamp: May 25, 2024, 11:47:55 pm
content: Hi JohnnyS, All,I have MS2661C with a defective power supply.I have replaced the AN8032 controller chip and a blown 10 ohm resistor.All other parts seem to check out ok so far.However, when powering up the supply with my current limiting bulb it blinks periodically.Currently waiting for a high power differential probe for some safe measurements with my scope.Have you had a chance to publish the re-engineered schematic of the power supply ?Any idea whether there is a chance to identify the main controller chip ( black square plastic package ) ?Thanks for any help !

author: johnbaker26
author_rank: Contributor
timestamp: August 03, 2025, 03:45:55 pm
content: Hey guys I'm troubleshooting the same power supply. I found a faulty MOSFET k2371 and the same blown 10 ohm resistor. Please help me with what is the problem when this happens. Thanks!

author: maxniz
author_rank: Contributor
timestamp: September 22, 2025, 07:56:29 pm
content: Good evening, can you tell me something about the mixer's components? What are the diode codes and resistor values? When I measure them, I get values ​​from 15 to 50 ohms!!!