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HP 3245A Capacitor Replacement

Posted on January 4th, by Shaun Merrigan in Electronics, Restoration, Test Equipment. Comments Off on HP 3245A Capacitor Replacement

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 in calibration Keysight U1253B.

Several years ago when I first acquired a 3245A/option 2 I checked the xdevs website to see what issues he had documented with his 3245A. In fact, xdevs had found leaking capacitors on the HV Amplifier (A3) board. The same family (Nippon Chem-icon LXF) of electrolytic capacitor was used on the A6 board. I replaced those capacitors on the A3 board of my 3245A and continued to use it. My recent investigation and documentation of failed RIFA line filter capacitors caused me to revisit xdevs findings. This was reason enough to remove the LXF capacitors from the A6 board:

C1 and C11 removed from A6 board: Corrosion found under C11.

I found a corroded trace and alkaline deposits (via pH test) under C11, a 680uF@50v Nippon Chemi-con LXF series capacitor. The leaking C11 capacitor fell within specification for every test I performed on it: capacitance, ESR (120 Hz), dissipation factor, leakage current at 55vdc. And the corrosion was completely invisible with the original capacitor in place. C11 is a filter capacitor on the output of the 5v regulator.

Pad under C11 shows corrosion damage (post neutralizing and cleaning)

After taking appropriate steps to neutralize and clean the corroded pads, I replaced all the electrolytic capacitors on the A1 and A6 boards (the A3 board had be serviced previously).

A6 Board all electrolytic capacitors replaced

Rechecking all the voltage rails on each of the A1, A3 and A6 boards showed no significant change from my initial voltage and ripple checks. Although the leaking filter capacitor was still functioning correctly, it is certainly best practice to replace it (and its brethren) once found.

Thanks for reading.

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