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Hi group!

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New member here. I have an 8920B here that I repaired some time ago (power supply failure) and considered it working.

But the other day used it to test a transmitter and no Tx frequency! Found the Receiver Synth has no PLL lock. (hopefully that's the only issue)

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I have repaired a few ESA Series SAs with this error and in all cases, it was a failed divider. I see from the 8920 schematic that it uses a similar scheme as the ESA series. (VCO to dividers to Frac-N divider)

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Looks like a bear to troubleshoot w/o extender cards. Has anyone seen this before? (divider failure)

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Thanks!

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Mark

Cool! I looked at Amtronix and did not see 08920-61020 but did see some others. Not sure of any compatibility issues.

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OK. Took me a while but finally have the correct # for my Rx Synth: 08921-61020

Will call Ric on Monday.

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

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Jim

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.

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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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..

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

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

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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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.

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.

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.

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.