Re: TDS-420A power supply repair


Jan 18 #153753

I have a bad psu in my TDS-420A , it burned a track on the pcb bur I cannot find the cause , the switching transistor os it seems . I have had it suggested that the hybrid device is probably the fault , does anyone know what the device consists of , or better still does anyone actually have one that they would part with .

Thanks in advance for any help you can give

On Sat, Jan 19, 2019 at 08:22 AM, Bob Koller wrote:

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
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.
That is identical to the power supply I just fixed. Every single capacitor on the power supply board was bad. Either in the process of leaking or already leaked out and dried out. After replacing those and the all know SMD caps issue all seems well. You may want to check that the output connector joints are solid as well,just in case.

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