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Tom Miller
Are you sure all the caps are installed the correct way? My experience has been that the aluminum electrolytic fail open or low capacitance and tantalums fail shorted.
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You could put a 100 watt light bulb in series with the line to limit the current then trace around to find what part of the supply is not coming up. Can you tell us a bit more about the board? What kind of power supply is it using, linear or switching/ Did you mean radial lead capacitors, both leads come out of the same end? Do you have soldering rework equipment available and someone that knows how to do the work? If it is an irreplaceable assembly, why not get someone skilled in that type of repair? But most important is to stop trying to run it with a higher current fuse. It was designed to use a 1/2 amp fuse and using a 2 amp fuse is asking for trouble. Do you have a DMM with the diode test feature? Can you get an ESR meter? Maybe it's not a bad capacitor. Regards, Tom ----- Original Message -----
From: David Speck To: hp_agilent_equipment@... Sent: Tuesday, August 30, 2011 7:55 PM Subject: [hp_agilent_equipment] Favorite bad capacitor debugging techniques? Looking over the list, I have noted that the majority of problems with old equipment is failure of the electrolytic capacitors in the power supplies over time. I wonder if the veterans can offer any suggestions on their favorite techniques for finding bad caps in circuit, especially those that have not been so considerate to have blown their end caps off or otherwise developed obvious physical failures. I have a critical undocumented circuit board of relatively recent construction with about 25 vertically mounted axial lead caps. It's begun eating fuses at an increasing rate, and now, even a 2 amp fuse blows instantly in a slot intended for a half amp fuse. No way to lift one lead of the cap without pulling it out of the PCB, with the attendant risk of ruining the irreplaceable board. (well, I could replace it for another $6-7,000, but that's not in the budget this week!) I figured I could put in another 2 amp fuse, and run it on a Variac at reduced voltage while watching the current consumption, and see what component heats up, but I really don't want to trash the microcomputer on the board. Any one have suggestions for any specific low voltage instruments for in-circuit cap checking, or home-brew gimmicks that one can work up, to give better information than the typical DVM and scope? Thanks in advance, Dave [Non-text portions of this message have been removed] |
