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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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On 20.02.2016 13:55, Cursitor Doom wrote:
On Sat, 20 Feb 2016 01:14:09 -0500, legg wrote: Recheck pin function before jumping to conclusions. Right; now re-checked. DC measurments proved (unsurprisingly) too close together so I re-tested using 100khz instead. These are the impedances WRT ground of the output taps of the long winding in the order they actually come out of the transformer: GND, 0.17ohms, 0.17ohms, 0.26ohms, 0.28ohms, 3.7ohms, 3.8ohms. So this doesn't seem to tally up with the schematic. Or does it? I need a pint of strong coffee to kick-start my head on this one. :-/ Anyway, later... Inductive reactance goes up with the square of the winding's nominal voltage, so you take the square roots of your impedance values. If you then take into account that the lower impedance values are strongly dominated by the DC resistance (which stays linear and does not square) and the upper one is mostly dominated by the AC reactance (which does square), the ratios seem to look just fine (well, so far as I can see, within a reasonable margin of error). But the ratios don't tell the whole story. Even if there is a winding short, all impedances will be very low (which they sort-of are, I would have expected higher values everywhere, but then 100 kHz is maybe too high, try testing at 10 kHz and see...), but the ratios between the windings would be still be mostly correct. Try to run it on higher voltage (like 15 V applied to 12.7 V secondary), and see if it pulls excessive current and warms up. That would indicate damage more clearly. Dimitrij |
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