HP 6296A DC power supply restoration advices

[aviv_zl]

Hello everyone.

I picked up HP 6296A from the scrap yard. It is in a relatively nice shape and even seems to be in a working condition (just from a very quick test). I would like to fully restore it an gonna need some advices.

First question, regarding electrolytic / film caps- is the general recommendation to replace them all regardless of any meassurments I can do or something else?

Attached some photos.

Thanks!

[factory]

With my own stuff I don't usually change the electrolytics, unless the seal is cracked, it's leaking electrolyte, or measures bad i.e. open circuit. Then smallest one in the last picture is a hermetic sealed tantalum, these are very high quality/expensive caps.

Very unlikely to have a problem with any of the plastic film caps.

Only caps you haven't mentioned are RIFA metallised paper caps, these are often found in later HP TE, usually as part of the mains filtering, these are a change on sight component and might even be the reason it was thrown out, people see the smoke escape & think it's terminal.

David

[Diabolical Artificer]

Big electrolytic's like Sprague's tend to be ok and don't need replacing, big electrolytics are very expensive too especially at the moment with the state of the supply chain. Not sure about HP manual's but Tektronix manual's give a list of AC ripple specs for power supply's which is a good general indication of whether a cap's ok, get the service manual and look. As a general rule of thumb if you measure under 100mV then a cap is ok, over 1v further investigation is needed.

As you have the cap out you could be nice to it and reform it slowly, just connect to a bench supply with a resistor in series, something like a 100k - 330k. Use an ammeter to monitor current, once it drops to below 100uA it's good to put back in the power supply (10uA ish better).

Andy.