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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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EDC 521 DC calibrator blowing fuses
Here's one I haven't seen before. Bought an EDC (now Krohn-hite) 521 DC
calibrator on the surplus market that was blowing fuses. There were two power supplies that seemed to be causing the problem +-150V. Turns out that there were two 22K 2W carbon comp resistors that are used as bleeders across the two 470uF filter caps. Both had changed resistance - one was about 2K, the other was 150 ohms! I've seen carbon comps drift, but never saw ones that drifted *that* far. Also, in circuits like this where they are dissipating over a watt, they usually drift high; at least in my experience... Well, after replacement it seems to be working well. May need a calibration though. |
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