Advantest R3765AH and R3765BH Network Analyzer (RF Source board Repair)

[anupong1983]

Hello Anyone,

I've bought used ADVANTEST R3765AH and R3765BH network analyzer but both units were found defective on RF Block (THD128A) (no RF output signal level and frequency) and Rch board assembly (BLL-021116).
just now, I cannot find which defective component have to be replacement or where I can buy spare part for replacement.
If anyone has service manual, service diagram or other document about repair would like share to me, I will so appreciated.

Thank you.

[tmbinc]

Probably not much help, but I had a defective R3765AH as well. Symptom was "random" measurements (essentially just noise) regardless of input to A/B, no RF from Source. YTO was "good" (output frequency was, as far as I could measure, coupled to input voltage), RF block was seriously misbehaving so I first suspected it to be dead, but replacing the RF block with a mixer (which it essentially is: mixer + pga) didn't result in any visible change. Turned out - it was much simpler.

In the end, it was just that all capacitors were dead (truly dead, as in: no measurable capactity). From the outside, they all looked fine. This resulted in SYNTHE board not outputting anything useful (basically the - now unfiltered - power supply ripple caused the power sequencing to reset itself continously), which resulted in the PLL being unlocked all the time; the YTO was never driven with a stable voltage (even with Span=0, which apparently is how you calibrate it). After replacing the capacitors, it's mostly good again, though I'm seeing some excessive noise at some frequencies that I still have to track down.

Can you post pictures from the R3765BH directional coupler?

I don't have any service manual; would be very interested to have one, though.

I also wonder if retrofittinghacking the 8GHz option would be possible as it's essentially just a bypass for the mixer; I could live without the power being adjustable.

[anupong1983]

Hi tmbinc,

Thank you for your sharing!
I have a good RF Block (THD128A) and Rch board assembly (BLL-021116) (from other R3765BH) and I have swapped between good part & defective part.

Then I found two parts above on defective unit were dead (RF Block (THD128A) is short circuit) and Rch board assembly (BLL-021116) is high level noise.
When I measured signal from Output Source, the resulted is always Zero (0 dBm) that mean some component on RF Block short circuit. I suspected a part in Red box on RF Block it to be dead (compare with a good RF Block).

Please advice where I can buy all capacitors with exactly spec or type?
Think I have to do adjustment after repair but I also do not know what to do!

Please find the pictures from the R3765BH directional coupler in attached.

 

[tmbinc]

Thank you for posting the pictures!

When you say "is always zero (0dBm)", do you mean there is no output at all, or that there is constant 0dBm output regardless of power setting and just the attenuation isn't working?

My RF section looks a bit different (probably older one), maybe related to the 8GHz option (which is not present, but seems to go into the empty space).

Now I'm curious how the RF section of the 8GHz model looks like...

[tmbinc]

Regarding capacitors, I've used https://www.reichelt.de/Elkos-SMD-Low-ESR-105-C/VF-33-35-P-D/3/index.html?ACTION=3&GROUPID=4001&ARTICLE=109216 (german link, sorry, but  you should be able to extract the relevant parameters). You need 35 of these, I think.

[anupong1983]

Thank you for posting.

I mean no output at all while I measured Test PORT 1 and RF Block OUT port (THD128A) . I measured from both port and when I have swapped with a good RF Block (THD128A) from other unit (R3765AH) the defective unit is working.

Regarding to posted picture.