Re: Challenging 2465 PS repair


On Mon, May 3, 2021 at 3:54 AM satbeginner <> wrote:

After studying the schematic of this power supply, it is vaguely similar
to the 22xx power supplies, but with at least one major difference.

Similar is, it has a Primary switcher, and it has a secondary switcher,
but, were in the 22xx PS the secondary switcher runs at it's own frequency,
in this 246x PS the secondary switcher uses the same frequency as generated
by the primary switcher.
This makes it a bit more of a challenge to separate the Primary and the
Secondary to test them one at the time.
Switchers will run just fine on DC input, and if you have a suitable bench
supply to run it from, that gives you two big benefits:
1. Limited energy input, the current limit could be set low enough that
nothing blows up.
2. Mains isolation, so you can now peek around anywhere with your scope.

Unfortunately the DC bus on this scope runs at 2-300V (I see a 264V
annotation on the schematic), using an AC voltage doubler when on 115V
input, and not many bench supplies have that sort of voltage output. I do
find that switchers will often start way below their supposed minimum input
voltage, which may work just fine for diagnosis. You really don't want to
load them - as others have mentioned - with a low input voltage.

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