Partial Re-cap of H7109-C PSU for a VAXstation 4000 VLC

Recently I had occasion to dig out one of my VAXstation 4000 VLC machines. Before using it I decided it was prudent to check the power supply, a H7109-C, to make sure there were no leaking or bulging capacitors.

It was a good job I did, because one of the capacitors had leaked. So I took the opportunity to check all the electrolytic capacitors and found several that had a high ESR. I have now replaced them all and cleaned up the leak. I also noticed that a ceramic disk capacitor was split (see photo). This capacitor did not measure a stable capacitance, so I replaced that too.

In the photos below I have numbered the replaced capacitors and give their values here:

  1. 39uF 16V
  2. 330uF 25V
  3. 330uF 25V
  4. 470uF 25V, this is the one that leaked
  5. 330uF 25V
  6. 330uF 25V
  7.  3.3nf Ceramic Disk, this is the one that is split.

After replacing the capacitors I powered on the machine and it worked fine. The ripple was about 50mV on both the 5V and 12V outputs.

Here is the machine with the cover off:

VAXstation 4000 VLC (VLC3)

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