HP/Agilent 6653a Power Supply Troubleshooting - Page 1
Forum section: electronics / testgear

author: rx8pilot
author_rank: Super Contributor
timestamp: January 13, 2015, 11:42:32 pm
content: I picked up another one of these supplies super cheap but as-is. So far, it powers up with no errors and the front panel works as expected - but no output. I set it on max voltage (35v) and it sent out a varying voltage of about 12-15 volts. But at lower voltages it is zero.I have done a general inspection for burns or other physical damage - it looks clean. Cable, wires, are good to the eye. I does not look like anyone has ever touched it other than the calibration header.I have the service manual and have started down that path by looking at test point voltages - nothing abnormal yet although I have not probed all possible points yet.There have been a number of discussions on the forum about this family of supplies and I am wondering if this sounds familiar to anyone. No errors, buttons and display work, over-voltage is clear, etc - but no output. Obvious internal test points are good and I will move on to the harder to get to ones asap.Hoping this is a reasonably easy fix.EDIT: The components are ancient, so if this is one of the silicon parts - this may be a dead supply.

author: rx8pilot
author_rank: Super Contributor
timestamp: January 14, 2015, 03:53:22 am
content: I took the supply apart to clean and inspect.I found two problems - the easiest problems ever. Problem one was jumper cable was swapped by someone. That brought the supply alive and I was very thankful for the service manual to ID that little problem. The second problem was operator error on the DMM. I had clipped the DMM to the screws on the output of the supply - Nothing!I eventually figured out that the previous user had put lock-tite on the screws which was insulating them from the bus. Removed screws, clean off lock-tite and I now have a fully functional unit. For a second, it was looking intimidating. A cable swap and some acetone was all I needed to get this 500 watt beast working. $200, not bad.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 14, 2015, 05:55:39 am
content: Good job on the repair and thanks for sharing the diagnosis and fix.

author: VK5RC
author_rank: Unknown
timestamp: January 14, 2015, 06:15:16 am
content: A good bargain and repair, I just spent a week trying to fix a 6644, some sod took out a filter cap, refilled the holes with solder and cleaned the flux residue.

author: rx8pilot
author_rank: Super Contributor
timestamp: January 14, 2015, 06:53:24 am
content: I got lucky on this one for sure. Not sure how long these things last, but for the moment, the performance is amazing. Nearly every component is far past obsolete so if anything does go bad other than passives, it becomes a boat anchor.Now I need a lower current model that can do 1mv steps.

author: VK5RC
author_rank: Unknown
timestamp: January 14, 2015, 07:15:45 am
content: I wouldn't be so pessimistic, in the process of trying to find the fault in my 6644 (has the same manual as 665x series and similar layouts - mostly) an IC clip slipped around shorting two IC pins out and I fried the gated -15V supply of one of the op amps and one of the transistor arrays, with some careful eBaying I was able to get them all and all is happy now. It only has a few specific ICs, most ICs are relatively straight forward op amps and transistor arrays.The most difficult part for me was working through the schematics which are for multiple models and include parts which often aren't there, refer to the parts list!!! ARRRRGGGHHHHRecently I was also able to repair a 1980s HP 5342 having found its problem (eventually- I am slow) and its fried 1980s logic gate (I didn't do that ) wasn't too hard to find.PS I just looked, your model is still available and supported so most if not all parts will still be available through Keysight (but they are slowish and not cheap)http://www.keysight.com/en/pd-839362-pn-6653A/500-watt-system-power-supply-35v-15a?cc=AU&lc=eng