Tag: Electrolytic Capacitor Failure
Analysis of Sprague 672D Capacitor Failures in vintage HP Test Equipment
28th November
Shaun Merrigan investigated Sprague 672D Electrolytic capacitor failures in the HP 70000 MMS test equipment. He found that due to thousands of hours of running time and high internal temperatures, many capacitors have failed. The capacitors made before 1990 are highly prone to failure, while those made between 1990-1999 show signs of aging. He replaced the faulty capacitors with Chemi-Con KYA and KZN series capacitors and all modules are now functioning properly.
Apple IIe Power Supply Rebuild
2nd September
The Apple IIe personal computer was manufactured from January 1983 through November 1993. I purchased an Apple IIe several years ago and put it into storage at the time. I recently pulled it out from storage and began the process of refurbishing it. Part of that process was rebuilding the power supply, which I will describe here.
The power supply appeared to be original to the computer with a date code of 47th week, 1985.
Apple II PCB Removed from case. Original capacitors in place. Build Date 47th week, 1985.
Examining the circuit board showed that the electrolytic capacitors were superior quality United Chemi-con.
Original Capacitors in place, output side.
By contrast, the line filter capacitor was a RIFA film capacitor of a type known to fail. Cracks were clearly visible in the outer case of the … Read More »
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 »