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Question about a power supply cap..

R

redk9258

AK Subscriber
Subscriber
I'm working on VCR that I bought as-is, will not power on. I pulled the power supply out and started checking things out. No fuses are blown. Right away, I found a 47 μF / 63V cap that showed as a dead short on my meter. There is a 10 Ohm fusible resistor upstream that is open. I pulled them both from the PCB and the short from the PCB is gone. Out of the circuit, the cap now checks fine.

Did the heat of the soldering iron "fix" the cap?
 
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BTW, I'm not implying that by the cap being "fixed" that I would entertain putting it back in. I've ordered new caps and a new resistor.
 
Parts came in. I replaced that cap and resistor, plus one other cap that had 15 Ohms ESR on the power supply PCB. I checked for shorts across the newly installed 47 μF cap and it was in the MegaOhms. So, I plugged it in and powered it up. It plays tapes pretty well. I wasn't really thinking it would without at least cleaning or replacing the belts. There are a few problems with the VFD. Certain parts are not lighting up. I will look at that later on.
 
Checking components in circuit will read parts from other components connected to it.caps need to be removed for testing.
Resistors and diodes need 1 leg lifted most of the time or often.
 
Jimbo40 said:
Checking components in circuit will read parts from other components connected to it.caps need to be removed for testing.
Resistors and diodes need 1 leg lifted most of the time or often.
Click to expand...

Yes, I understand that but was looking for a short circuit first. With the cap in the circuit my meter read 0 Ohms across it. I removed the cap. The cap was no longer showing 0 Ohms. I don't remember the value, but the cap did not measure as a short circuit. With the cap off the circuit board, the same 2 pads measure in the mega Ohms if I remember correctly. With the new cap in the circuit, it read in the thousands of Ohms. After replacing that cap, plus another high ESR cap and the 10 Ohm resistor. the power supply is working great.

I'm tempted to open the cap up to see if anything looks weird inside.

C25 was showing the short but not C24.
R17 was open.

ps.png
 
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