Repair: HP 5328A part 1

As I do not have as much time as I would like to repair this counter I will write a number of posts while I continue to diagnose and repair this instrument.

Symptom: the instrument doesn’t turn on.

This isn’t exactly right as a part of the power supply works as long as the instrument is plugged in. I suppose this is so to keep the optional OCXO at a constant temperature.

However this matters not because as soon as someone turn on the switch the F1 fuse on the power supply board blows.

I tought that something is shorted to ground so I disconnected the power supply board from the main board (to do so you need a soldering iron) and I also disconnected the four power transistors which are conveniently socketed.

The power transistor that blows the fuse is A2Q1 which means that I have to check it and the associated circuitry.

Luckily I have the schematics but there are different versions of the power supply boards so it took me a bit of time to find the service manual with the correct schematics.

That’s all for this post.


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One Response to Repair: HP 5328A part 1

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