Re: 8935 Restarts Randomly

I just fixed my power supply! That 47uF cap was down to 12 uF. Whoever figured this one out is a genius.

Many thanks.

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Re: FS: HP 8920A Service Monitor

I think that FF picture might be forthcoming; before Michael's FS post was even posted I was discussing with him how his initial batch of pictures?could be shown to better advantage (better resolution).

This may take a few days to get sorted out.

Hank

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On Wednesday, December 25, 2024 at 02:33:31 AM EST, Dave wrote:

Any pictures of the entire front face .??

Re: FS: HP 8920A Service Monitor

#1148

Any pictures of the entire front face .??

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FS: HP 8920A Service Monitor

#1147

Mates,

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I have available an HP8920A.? Unit appears to be in great shape, but of course, is not new.? Has options 001, 004, 013, 020, 102, 103.? Or at least, that's whats listed on the tag.? There is a screen shot of the option list below.? I can't tell you the last time it was calibrated.? I followed Amtronix's instructions to check the units operation, and everything passed.? There is some burn in, but the screen appears to be bright and readable.? I did some minor testing with my recently calibrated Mot. 2670, and all measurements were extremely close.? I have replaced the bumpers with high quality 3D printed parts.? Please note, I don't have the covers for the handle hinges, and I believe the springs are not present, so one must pull out the hinges in order to lock the handle.??

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Looking for $1500.00 obo.? I can ship at your expense.? I am located in Los Angeles, California.? I would prefer to to sell in person, but am willing to ship at your expense (though I will cover insurance.)

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Here are some pics:

Re: 8920B Receiver Synth "Out of Lock"

#1146

I do same loop back as a check on power on. The recovery is pretty quick. Maybe the steering line voltage needs to be bumped one way or another. It fixes itself too quickly to determine exactly way frequency it falters. Been this way since I bought it decades ago.

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Has anyone changed the lithium battery in theirs? I have a new battery but hesitant to tear this down.

Re: 8920B Receiver Synth "Out of Lock"

#1145

I have never seen that and usually use the SA tracking GEN in full sweep looped back through a cable to verify the RF I/O alignament.

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Level should be close to the Trk Gen Level and relatively flat across the full span.

Re: My last 3 Problems on my HP 8920A repair

#1144

开云体育

Thanks Adam.?

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I am determined to get this done myself and learn the instrument.? I have a lot of bench time over a lot of years. ?This is not my first Rodeo as they say. And having the complete schematics is a major bonus.

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By the time I am done, I will know the instrument well and have it working as well as I can.? There are a lot of smart people on here to help me.

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Thanks for the note.

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Best.

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Ronnie

VE3NLS

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From: <[email protected]> on behalf of "VE6WMR via groups.io" <akuzych@...>
Reply-To: <[email protected]>
Date: Sunday, December 8, 2024 at 12:10 PM
To: <[email protected]>
Subject: Re: [HP8920/8935 Family] My last 3 Problems on my HP 8920A repair

?

It seems like a few problems there, Ron. Maybe there's someone on here who would take yours on as a repair and return. Best of luck.

Re: My last 3 Problems on my HP 8920A repair

#1143

Hi John. Thanks for the reply.

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First of all, I replaced the A23 as the input Divider on the old one was damaged.? Burnt SMT resistors, and I don't know what else.? it has always not been right since I got the instrument years ago. For sure someone transmitted into it 100W when it was set to the RX test mode.??

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The replacement was from a good 8920A.? I never expected that the Firmware in the PROM would be different if the A23 was from another 8920A.? However, I am not an expert on these so I will do what you suggested and take it apart and repair the damage I find, and install it again and run the diags.??

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Yes that would be the A2 Audio Analyzer board.? Sorry for the incorrect terminology. I will run the tests again on it and report back the exact failures.

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I will do a 12dB SiNAD test today and see if this is my error. I just don't recall ever seeing it pinned before I started replacing Audio Boards etc.

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The Output Assembly will also get tested again. That failure (Output Assembly Low) was from the DIAGS.

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This instrument sits on my bench 100% of the time.? Once warmed up it is pretty accurate therefore the reason for installing the High Stab unit.? It never goes in the field.?

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I primarily service Amateur Radio Equipment and it works well for me.??

?

Thanks for your help, I will be back in a few days with some results.

?

Ronnie

VE3NLS

Re: My last 3 Problems on my HP 8920A repair

#1142

It seems like a few problems there, Ron. Maybe there's someone on here who would take yours on as a repair and return. Best of luck.

Re: My last 3 Problems on my HP 8920A repair

#1141

OK HUGE red flag to me is swapping the A23 Input Assembly.

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Unless you moved the calibration EERPOM over from the processor board? that's just about always going to fail on the receiver test if you have the SA option installed? ( which is fairly typical for most users )

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Also you can not swap the calibration EEPROM between an 8920A and 8920B.

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I would only repair the A23 modules for use in the same unit or move the EEPROM? ( which may cause some other complications )

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Not sure what an AA2 is ...is that the A2 Audio Analyzer board ?? ?What test is failing? Is it in the Audio Diags and the failure message.

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Also on the SINAD meter being pegged ...normal if there is no o signal present? with a 1Khz tone ...maybe an operational issue there.

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On the Output assembly low? is that from the RF diags? or operational .? If it's from the diags please provide the full failure descption.

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Best thing is to take one problem at a time .

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I would start with the RF diagnostics and getting those to pass.

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I would go back to you original A23 and calibration data? and go from there.

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I would have avoided upgrading the internal reference since that has issues in the field with warm up time and on the bench an external GPSDO would be a better option.

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My last 3 Problems on my HP 8920A repair

#1140

Good day to all.? ?I am a newcomer to the site and need some help on these last 3 problems. I have ready many threads and? I have done searches but came up empty.??

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I will preface this with a comment.? Rick at Amtronix sent me a new set of Audio cards, and a new Reference module at a very good price.? At that time I was having a terrible time with my email from my domain. It was so bad that I think Rick may have not even received half of what I sent. So Rick, I know you are on this FORUM , no harm no foul. I know you probably tried to reach me Rick,? but it was bad for 2 months back in the summer.? I basically just gave up trying to reach you.?

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I have done a complete rebuild on the PSU. All voltages are perfect and clean.? I upgraded the Standard Reference module Rick sold me to the High Stability one and calibrated that.? All good. I have also replaced the Input Assembly A23 with a known good unit. All other tests pass with the exception of the following.

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On to the problems.

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#1.? AA2 assembly fails. My original module would not pass the diagnostic.? Tests 9 thru 14 fail on BOTH my card and the one Rick sent.? So, is this a card problem or should I be looking elsewhere?? Hard to believe that 2 cards are bad but I guess that could be. Can this card be repaired and if so what am I looking at here?

#2.? My SINAD meter is PEGGED? on Power on.? I have no idea why or where to look?? Is this the AA2 or do I now have a problem with the Receiver module?

#3.? Output assembly? low failure.? Not sure why or where to look for this.? I did take the Attenuator out and apart and it tested just fine.? 50.4 ohms input and 50.4 ohms output to the Input assembly module. No smoked or damaged parts inside it.? There is NO mention of an Output assembly in the manual that I can find.? I suspect that is just the A24 module.

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I am in Canada and I do have a source of parts now for my instrument.? I have a second one on the way that needs some help and I purchased it.??

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Thank you all for any help in advance.

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Ronnie

VE3NLS

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Re: 8920B Receiver Synth "Out of Lock"

#1139

FYI the manual says to let the analyzer warm up for 15 minutes before running any tests. I find that my synthesizer is out of lock at around 350 MHz and 700 MHz if I run a wide sweep in the spectrum analyzer tracking generator mode (with a cable to in and out). It has always done this and I think normal as it resolves in a couple minutes.

Re: 8920B Receiver Synth "Out of Lock"

#1138

the difference in the reference is due to the CLIP being for the standard version and you having the low noiseversion.

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usually what I do is open the VCO steering line and insert my own tuning voltage to get the VCO on frequency.

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This? tells you if an issue in the divider? phase detector or VCO.

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If you can tune the VCO with a reasonable voltage it should be OK. Normally I sweep the voltage across the entire range and monitor the output level for flatness.

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If the VCO is correct and the divider output is at the reference or close than those are are OK which leaves the phase detector.

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That design of the phase detector is still in use today in later service monitors like the Viavi 3920 ...they added some switching around the output filters to allow for the SA functionality.

Re: 8920B Receiver Synth "Out of Lock"

#1137

Well this has proved frustrating, mostly due to the CLIP being (all) wrong! Take a look here:

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This says it's the Sig Gen Synth (not the Rx Synth) but that it IS in fact A17 (the Rx Synth) and I cannot find anything on a 08920-60220. What is that?

The parts list says 08920-68127 so who knows. Also, look here:

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This signal to the Phase Detector is indeed for the Sig Gen Synth. So much for the CLIP! However, I was able to determine that TP4 and TP5 are the inputs to this Phase detector.

The "SGS_200KREF" is a nice steady 1MHz. The input from the FRAC-N DIVIDER is around 2.3MHz and bouncing around quite a bit. Not sure what circuits are between the two

so stuck again. But sure looks to me that the dividers or something in between is broken. (unfortunately, non-standard parts)

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Re: 8920B Receiver Synth "Out of Lock"

#1136

I found a node at J46-17. Measures 43V so that looks OK.

Re: 8920B Receiver Synth "Out of Lock"

#1135

Is there an easy spot to check the PS rails? (w/o extender cards) This thing is really buttoned up.

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Re: 8920B Receiver Synth "Out of Lock"

#1134

On 8924's that I've repaired with OOL LED (out of lock) on any module it has been the power supply 40V (I think) rail - normally pulled low by faulty electrolytic cap. Uses same modules as 8920/8921..

Re: 8920B Receiver Synth "Out of Lock"

#1133

John - Yup. You are right. I have an 8921 Sig Gen Synth card and the High Stability Reference card installed.

I think that's a good sign.

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The tag on the back lists options 001, 004, 031 and 102.

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Mark

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Re: 8920B Receiver Synth "Out of Lock"

#1132

those are the low noise synthesizers and you should have a matching GEN synthesizer with an 08921 prefix as well.

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Those need a specific reference module as well ...usually that low noise option comes with an optional high stability reference ...should show on the options display as 001 IIRC.

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The option 50 low noise synthesizer will not show in the options display ...only on the rear tag if fitted at the factory.

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short version is that all three parts need to match in the unit as far as part numbers ...you cannot use a standard synthesizer or reference unless all three parts are replaced.

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The reason I mention this is someone may have swapped in the wrong synthesizer module unless you are sure the unit passed the RF diags previosuly.

Re: 8920B Receiver Synth "Out of Lock"

#1131

Rick & Amtronix are great to deal with. They helped me with my 8924C

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Jim