Shaun Merrigan's Information Pages

Tag: Electrolytic Capacitors

Racal 9478: Widespread Electrolytic Capacitor Failure

Posted by Shaun Merrigan in Electronics, Restoration, Troubleshooting. Comments Off on Racal 9478: Widespread Electrolytic Capacitor Failure

25th May

The Racal Dana Model 9478 Frequency Distribution System has an internal precision, oven-controlled crystal oscillator, or it can be phase locked to an external signal derived from a GPSDO or other master oscillator.  The system will automatically lock to an external signal above 100 mV, and with a standard frequency of 1, 5 or 10 MHz.  “In Lock” indication is provided.

I recently repaired two Racal 9478 units. What I found was widespread electrolytic capacitor failure such as I had never encountered before. A summary of the issues found in both units follows:

Virtually all electrolytic capacitors in both units (nearly 90 in all) had failed, showing either very low capacitance and/or very high ESR. Interestingly enough none showed short circuit failure.All the failed electrolytic capacitors were made by Philips in late 1980’s The -15v regulator was originally bolted … Read More »

HP 3245A Capacitor Replacement

Posted by Shaun Merrigan in Electronics, Restoration, Test Equipment. Comments Off on HP 3245A Capacitor Replacement

4th January

The HP3245A Universal Source (datasheet is copyright HP/Agilent) is a precision AC/DC voltage and current source that can provide a wide range of precise and repeatable voltages and currents up to +-100vdc and 100mA dc. It can also provide sine, square and arbitrary waveforms up to 1Mhz and 200vpp. Such an instrument is extremely useful in the lab for calibrating meters, driving current and voltage amplifiers and checking equipment. The particular units I have were built in 1992/1993 which means the electrolytic capacitors are approaching 30 years of age. I had decided to replace the RIFA line filter capacitors in (documented here) both my units and performed routine power rail voltage and ripple checking as part of that. For example:

+5.0840 4.4mv+15.194 30mV+18.625 29mV-18.691 28mV

The other power rails and HV Amp power supply also measured good, using an … Read More »