need help repair my 53131a

[f14]

Hi All,
I have problems with my 53131a. it show QSPI and INTERP fail in power on self test
I open it and check A4 power supply board . it okay with power output in specs. then I check a A1 mainboard. I see something strange in C60 C61 cap. votage not stable (changing ~2v <->5v) .  and the U42 (LM337) it hotter than U48(LM337) a lot
thank you

[m k]

Since it's still pumping the regulator is not the first suspect.

What else is hot?

It seems to be an over current situation.

[Wallace Gasiewicz]

I agree with the over current statement.
I am not familiar with repair of that unit.
However some HP units have a current sense and the supply will cut out if there is a failure on another section of the unit or another board.
Could be something simple like one of the smaller filter caps for the ICs....

[f14]

thanks for your reply
This is first time I repair frequency counter ,. I have no exp with this device before
after few day. I found C60 C61 with voltage changing from ~2 to 5V seem normal because the frequency same with two blinking status leds (channel 1&2). and U42 and U48 working properly. my 53131a serial above MY470000. so I can't use old service manuals from agilent
btw I use a Printer ON via RS232 to see more details about this error and I have 4 line:
-Interpolator : A , MRC mode Fail
-Interpolator : B , MRC mode Fail
-Interpolator : B , CC mode Fail
-QSPI : HEX DAC Fail

[madao]

Hi

I have  a  53131A with bad PSU .
After fixing of bad PSU, it works again with QSPI:FAIL  and INTERP:FAIL message.


It was only  U4,  MC14410DW, hex DAC  with SPI interface..
I have raped  a 53181 skeleton and pull their U4 and place it into  53131A

It works again with no Error Message.

Regards
matt