Electronics > Repair
53131A OCXO timebase cal failures - simple fix.
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naimns:
I've had an Agilent (MYxxxxxxx) 3CH 53131A sitting on my bench for a while needing attention. Working fine with the failed OCXO disconnected. OCXO p/n 10811-60160 (OPTION 010) .
Problems with the OCXO were located down to a blown E1 ferrite and blown L2 inductor. Both easily replaced. Not sure how this was caused.
The next issue was a little confusing. The unit wouldnt pass the timebase cal. 10MHz signals looked fine. I used a standard GPSDO and waited for 24H for the 53131A OCXO to stabilize.
After several fails, I checked the OCXO DAC serial port on a LA and monitored the DAC vout, all fine and no problems with the interface. While checking the DAC, I noticed that the cal always failed when the DAC output was at max (+5v). You can watch the vout shift as the unit tries to trim the OCXO.
The problem was located to the OCXO internal trim (labelled FREQ. ADJ.) being too far off for the DAC to compensate. A few attempts at shifting the trim resolved the issue (several turns).
The timebase cal does pass without the OCXO having being run for long (a few hours).
Generally quite some noise on the +5v/-12v/+12v, possibly needs some caps replacing.
coromonadalix:
if something as blow up sure you have or had problems, and yes others here would say check all you caps and redo them if needed,
your ocxo section was at fault, and maybe it's a matter of time before the same problem happens again ? maybe some spikes in it's supply ??
naimns:
yes, possibly some past life issue. power supplies measure fine, min/max/rms as expected.
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