Poorly HP 8593A SA with PSU problem

[Clive G3GJA]

I'm hoping that this post about a poorly HP 8593A will attract the attention of David ('Radio Wrangler') who posted in 2014 that he had a copy of the 859x series analyser's power supply. If you read this David please get in touch!

This analyser has been sitting in a garage for five years and the display lit up for 20 seconds or so when turned on and then tripped the earth leakage on the ring main.

I've replaced the X2 filter caps so it now doesn't take the trip out but now it doesn't fire up. I could do with the diagram so that I can power it up into some loads while not stuffed into the SA chassis. It looks like a fairly standard UC8342 switcher for the always on supply and a UC8344 for the main PSU. Any other help would be appreciated.

I've also got an HP 8569A SA that's got an issue for another post.

Thanks

Clive G3GJA

[Radio Wrangler]

I'm pretty certain I have one, somewhere, but I've just checked the file where I think it ought to be. I remember the trouble getting it. The PSU lumps were bought in (Astec?) and only ever replaced as units, never fixed. So diagrams of it weren't generally kicking around. There are a few other possible places I can check next week.

Usually, with switchers that don't show any signs of life, the start-up circuit is the most common culprit with a high value resistor that goes higher.

David

[Clive G3GJA]

Thanks for looking David and hopefully you'll come across it next week.

The start-up resistor (100k 2w) was the first thing I looked at but I can't do any hot checks until I can simulate the loading and power switch.

It's just not possible to find out whether the always on 18v supply is working whilst the PSU is in the chassis and there's no status LED for it.

It's likely that another fault has developed since the earth leakage was fixed; it looks as though there's a power good feedback so anything in the SA could upset that.

Even when I get it powered up I know there's a RF fault on it, allegedly making it BER, so probably some clot stuffed several watts into the front-end. At least I know the tube is good as the display looked quite sharp for the short time it appeared.

Clive

[Radio Wrangler]

The display is a little TV monitor, and there is a video output in the bottom corner of the rear panel. Hidden in the soft key menus is a facility to switch between 525line/60Hz and 625 lines/50Hz formats. So if you ever have a display fault on an 859x analyser, there is an easy way out. THe HP 856x analysers use analogue X-Y electrostatic CRTs to do vector writing. Tubes are rare and very sought after.

David