Agilent E3634A Power Supply Teardown & Repair - Page 1
Forum section: electronics / repair

author: noodlebear
author_rank: Contributor
timestamp: April 06, 2013, 01:09:59 pm
content: Gerry Sweeney just released an interesting teardown and repair of a power supply:Video is here:http://youtu.be/a24Fv45FuOcHis blog also has some interesting stuff on building his own power supply:www.gerrysweeney.com

author: dimlow
author_rank: Frequent Contributor
timestamp: April 06, 2013, 02:45:27 pm
content: I found that interesting , thanks for posting.

author: free_electron
author_rank: Super Contributor
timestamp: April 06, 2013, 03:15:11 pm
content: Good video but the fault analysis is wrong...The reason for having that pulsing effect is because the current output opamp was fried. Under normal operation the output of that opamp doesnt come near 5 or -5 volts... So the 4051 will never exhibit this latchup problem.

author: noodlebear
author_rank: Contributor
timestamp: April 06, 2013, 03:51:05 pm
content: Quote from: free_electron on April 06, 2013, 03:15:11 pmRight, but that's pretty much what he said isn't it? That HP didn't need to consider that under normal conditions.

author: gerrysweeney
author_rank: Regular Contributor
timestamp: April 06, 2013, 04:10:24 pm
content: @noodlebear - yes thats what I said (thank you for making that point), if they did anticipate it, which is highly unlikely IMHO, I expect it would not have bothered them too much - but its worth knowing that the HC405x switches do this under that condition.@free_electron I did say that under normal conditions its not a problem. However, the point I was really making is that under any condition where the output of the op amp falls below -5v that the protection added (i.e. the clamp diodes) while they do protect the 4015 from damage it does does drive the chip into an unexpected condition which is clearly outside the spec of the device, the data sheet is pretty clear that the switch I/O's should not be driven above or below VCC/VEE, so the design [mod: of the HP supply in this part of the circuit] from a pure academic point is flawed. Of course clamping diodes are common practice and its really not obvious or intuitive that the chip would do what it actually does under these conditions, and for this design really does play havoc with the rest of the circuit. Anyway, the real point of the explanation was to alert others to the behaviour of a HC405x switch under those conditions - I bet that the original designers did not foresee that behaviour because if they had I have no doubt they would have designed the problem out - speculation on my part of course....Gerry

author: linrenzhi
author_rank: Newbie
timestamp: May 19, 2016, 01:37:34 am
content: Thank you very much, by watching video I repaired my E3634A, thanks again!

author: Greybeard
author_rank: Frequent Contributor
timestamp: October 12, 2023, 09:04:09 am
content: Quote from: gerrysweeney on April 06, 2013, 04:10:24 pmThe first thing I would do against such a catastrophic burn-out failure would be to add a 7A (6.3/8/10A whatever) fuse in the main current path (e.g. between secondary winding and bridge rectifier).Is there a way to change the circuit to basically prevent the problem?