Advantest R3172 Repair - Accidental 18V DC Injection on RF Input(Low Band Issue)

[lbrazil]

Hi everyone,

I am currently troubleshooting an Advantest R3172 Spectrum Analyzer that was unfortunately damaged due to an operator error. A DC voltage of approximately 18V was accidentally applied directly to the RF input jack.

Current Symptoms:

The instrument turns on normally, but it can no longer read/measure signals on low frequencies (low band).

High band signals seem unaffected/less impacted, but the low band path appears to be completely dead or heavily attenuated.

After opening up the unit and doing some troubleshooting on the RF front-end, I managed to isolate the failure down to the specific module shown in the attached picture (the TOP2301 XK High Band / YIG Mixer module).

Since this module handles the low-band pass-through routing as well as the high-band mixing, it seems the 18V DC injection fried the input stage or a protective switching diode inside it.

Has anyone dealt with a similar DC injection failure on this specific Advantest module? Is there any known internal schematic available for the TOP2301, or is it a completely sealed hybrid that cannot be repaired at component level?

Thank you in advance for your help!

Best regards,