Wiltron / Anritsu 69147A 20 GHz Sweep Generator - Error 113 YIG Loop Osc Failed

[John_ITIC]

Hello, I'm going over my test instruments to bring bad ones back to life. This Wiltron 69147A was purchased on Ebay in 2019. The unit had some lock error but that was repaired before I purchased the unit. I have used the unit only a few times over the years and it started (a couple of years ago) having issues with the YIG locking over approximately 11 GHz (Error 113). When taking it out of storage this week, I noticed that the issue happened over many other bands. After having had the units on some time for trouble-shooting, the issue seems now permanent, except the first 10 seconds after turning it on. I'm suspecting something gets hot and fails somehow. And whatever it is, seems to degrade over time - even when the unit is not in use.

The closest service manual I could find is "Anritsu_Wiltron_680XXB_681XXB_SYNTHESIZED_CWSWEEP_GENERATORS_Service_Manual-10370-10262.pdf", here: http://ftb.ko4bb.com/getsimple/index.php?id=manuals&dir=Anritsu-Wiltron

That manual describes the Error 113 and has trouble-shooting diagrams. But, I noticed that my card layout is not the same as the 68xxxB units. So, before starting the trouble-shooting, I was wondering if anyone happens to have the proper 69xxxA service manual?

Note that the A4 block has a different style than the other blocks. Is this correct? Or was the A4 swapped out by the seller before I purchased the unit?

Thanks,
/John.

[John_ITIC]

Attached is the ERR 113 self test result.

[John_ITIC]

I may have a clue what is going on. Per the attached images and PDFs, the A4 "course loop" module should output a frequency in the range 219.5 MHz to 245 MHz range, that varies with the configured output frequency. It does. But it also outputs many multiples of this frequency with such high amplitude that my frequency counter has a hard time locking onto the base frequency.

When looking through the maintenance manuals for similar units it is not quite clear whether these harmonics should be there.

The MG369xB maintenance manual states (see attached block diagram too):

One input to the YIG loop is the 219.5 to 245 MHz signal from the coarse loop. This signal is amplified to drive
the step-recovery diode (located on the A7 PCB). The step-recovery diode produces harmonics of the coarse loop
signal (≥ 1.9755 to > 20 GHz). These harmonics are used by the sampler.

The 680XXB/681XXB maintenance manual states:

The coarse-loop oscillator has a programming (tuning)
range of 439 to 490 MHz (219.5 to 245 MHz for
units with serial number 512001 and above) and a
resolution of 1 MHz. This provides harmonics from
1.9755 GHz to >20 GHz. This allows any YIG tuned
oscillator output frequency to be down converted
to a YIG IF signal of 21.5 to 40 MHz.

My unit is architecturally newer than the 68XXXB but older than the MG369xB. I have not been able to locate a maintenance manual for a 69xxxA unit.

I believe the wording of the newer document for the MG369xB  is closer to the truth. Both the attached block diagrams shows that the harmonics 1.9755 to 20 GHz are drawn after the SRD (Step Recovery Diode).

So, it looks like a low pass filter in my A4 Course Loop block is bad, such that all these harmonics are let through?

Thanks,
/John.

[John_ITIC]

Does anyone happen to know whether the signal paths in the YIG loop are supposed to carry spectrally pure sine waves or whether it is only the zero crossing interval that matters (i.e. distorted sine waveform is okay)? I measured the output from the A3 (10 MHz and 100 MHz references) and A4 (course loop). Only the 100 MHz signal has a clean sine wave, the other two are distorted sine waves. in particular, the A4J2 output resembles a square wave, which explains the many harmonics in the frequency domain.

Thanks,
/John.

 

[John_ITIC]

I managed to find the 69147A maintenance manual here. The link says user manual but it is the MM.
https://docs.alltest.net/manual/Alltest-Anritsu-69177A-UserManual-2266-.pdf

I was very happy to find the correct MM tonight as neither the 68XXB or MG369xB matches exactly my unit.

Thanks,
/John.

[metrologist]

Ah, I was going to post that link. It might just be the YIG driver - top of YIG, or a regulator circuit if voltages are not correct. YIG loop was always a little tricky to TS.

And there will be harmonics on the lower loop outputs. Anyway, report back what you find working through the procedures.