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ak_47_boy 1st July 2008 04:34 AM

Power Supply Problem/Repair
I have an oscilloscope with a bad switching power supply. I have it out of the scope and set up with the correct dummy loads for testing. I see no visible burnt components or capacitor leakage. The switching transistor gets very hot, i would say about 80C (180F). It should output:
+12, +12, -12, -5.2, +3.5, +5.2
I measure:
+12, +12, -2.6, -2.6, +3.5, +5.2

Old electrolytic caps? Bad regulator? It is a double sided board and quite compact so i am having a lot of trouble following traces. I think i am going to start desoldering and testing all the components individually.

Eva 1st July 2008 05:08 AM

Find the diode that feds the negative rails, it may be the same for both, being the -5.2V one derived through a linear regulator. Check that it's not shorted.

ak_47_boy 1st July 2008 11:20 PM

Tested all diodes and rectifiers. They are all good. Could they only be failing to work at high frequency?

star882 7th July 2008 10:36 PM

Looks like an overload. Check components on negative rails for partial shorts.

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