Re: TDS-420A power supply repair


Bob Koller <testtech@...>
 

Where is the burn? Can you post a picture?

I just finished two of these PSU's, I think you need to replace ALL of the small electrolytic caps, don't bother testing, etc, just replace, they are all past it.
One of the problem areas in this unit is the black potted mains switching circuit in the primary. It controls the input doubler configuration by automatically sensing 120 vs 240 mains input. It can be removed and jumped across.
The other issue is the regulator board mounted vertically near the output connector. These can get dirty from the fan, causing leakage paths, and subsequent erroneous shutdown signals.

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