Here we go again... (another HP instrument PSU failure)

[nfmax]

...this time in my 8591E spectrum analyser. So far the score is four bulging but still leak-free 'Samyoung' 470uF 200V electrolytics. Two still about the right value, one reading ~20uF and one 50nF. This time the fuse didn't blow and the rectifiers are OK, but no sign of life. Closer inspection shows that one of what looks like the snubber networks has got so hot the capacitor case is cracked, as is the actual PCB! There is another overheated resistor, I think this one is part of the network that balances the voltage across the two series capacitors in 230V mode (this is a switched input voltage design). I expect the main switching transistors have failed as well. I'm still tracing out the circuit. This is a complex design spread over three PWA's so it may take a while.

Again, if anyone has a schematic for this PSU I'd be very glad to see a copy. The part number is 5062-8229 serial number KR33601085. Nothing in the service manual, though it does warn against operating the PSU without a load.

Quite a pleasant way of recovering after the Christmas celebrations, though!

Max

Max

[tggzzz]

http://artekmanuals.com/manuals/hp-manuals/
Hewlett Packard   8590E, 8591E, 8592E, 8593E,8594E, 8595E   CLIP   YES   5963-2951   $25.00   FULL SCHEMATICS SCANNED AT 1200 DPI

I recently purchased the manuals for my Tek 492AP, and am a satisfied customer

[nfmax]

Thanks tggzzz! CLIP ordered, just waiting for the download link to arrive.

[EDIT]
Arrived OK! 
Assembly A8 PSU not included! 

Back to circuit-tracing...

Max

[TheSteve]

Any chance it is the same or similar to the 8593 power supply?
Here some info on it that someone clearly spent some serious time on:
http://www.ko4bb.com/manuals/download.php?file=HP_Agilent/HP_8593A_Power_Supply.pdf

[tggzzz]

Thanks tggzzz! CLIP ordered, just waiting for the download link to arrive.

[EDIT]
Arrived OK! 
Assembly A8 PSU not included! 

Back to circuit-tracing...

Max

I would mention that to Artek.

[nfmax]

Any chance it is the same or similar to the 8593 power supply?
Here some info on it that someone clearly spent some serious time on:
http://www.ko4bb.com/manuals/download.php?file=HP_Agilent/HP_8593A_Power_Supply.pdf

Unfortunately no more than a family resemblance. I suspect the secondary rectifiers and post regulators are the same, but the primary side appears to be a current-fed push-pull forward converter. It uses the same FETs more or less, but has an inductor and a freewheeling diode as well as the main transformer. The 'always on' supply is derived using the balancing network across the main electrolytics.

I didn't get much further forward today - spent the morning cycling in the New Forest and the afternoon chopping firewood, instead 

Max

[nfmax]

Circuit mostly traced out, no apparent damage in the high-voltage section apart from the electrolytics and a cracked capacitor in the snubber network. The power FET's are all OK (tested up to an amp or so DC drain current at about 1V VDS) as is the flyback diode. I found a 215 ohm 1/3W resistor in the input suppression circuit, which was apparently undamaged but reading open circuit. I wonder if it was ever correct? It's possible there is another problem in the control circuit, FET drivers or the isolated side, but the symptoms point to a primary side problem. I've ordered replacement electrolytic (Kemet 470uF/200V) and a replacement WIMA FKP-1 for the snubber, even though the original was still reading 913pF - this is outside the tolerance band, so it may have suffered a partial internal failure. However it's odd that bad electrolytics could give a total failure to start, unless the bootstrap supply was not coming up properly. I hope not, as that seems to use a mysterious unmarked VDR(?) which reads about 1kohm at low voltage, switched straight across the rectified mains by a power FET.

[KJDS]

I've probably got a good 8594E PSU, yours for £100 including VAT and shipping. Let me know if you're interested and I'll dig one out and test it.

[nfmax]

I've probably got a good 8594E PSU, yours for £100 including VAT and shipping. Let me know if you're interested and I'll dig one out and test it.

Do you have a test jig or do you plan just swapping them about? They seem most complicated and pernickety beasts! I'll see how I get on when the parts arrive, but I may well be interested.

[nfmax]

It has been a very long time, but my spectrum analyser is now working again! Even after replacing the dead PSU capacitors there was still no sign of life. After that, with one thing and another (and another, and another...) I had too little free time to work on it.  A couple of weeks back, I spotted a reasonably-priced replacement PSU on eBay and the seller accepted my offer! Swapped it in and it all worked - sort of. The display was unstable, as though it couldn't synch properly, and had massive vertical linearity issues. This had appeared before, but I thought it might have been due to the PSU as well. However I had bagged a NOS replacement monitor just in case (for £25) when it first started to happen. Today I swapped this in and everything is now fine. I fitted a GPIB card as well. One happy bunny!