Re: 475A Problem


The "Low Line" light does come on, but goes out when the
problem seems to go away.

I saw a +50vdc line in the Power Supply, which measures
+46.2vdc, which rises to +48.4vdc when the problem seems
to go away.

Dick, W1KSZ
From: <> on behalf of Dave Peterson via <>
Sent: Sunday, June 20, 2021 9:32 AM
To: <>
Subject: Re: [TekScopes] 475A Problem

Looks like your "Low Line" light is on, meaning your +55v supply is low. The +55v drives all the low voltage regulators, so that needs to be fixed first. See the power supply calibration procedure in the service manual.

I would guess you have a problem with a rectifier or power supply cap (or both).

I'm more of a 465 guy, so I may very well be off in the 475A details. Is it +55v in 475A as well guys?


On Sunday, June 20, 2021, 9:26:46 AM PDT, Dick <> wrote:

I have a 475A, ex-IBM with DMM Option. It recently developed a problem.
You can see a picture of what it looks like in the Photo's section, under
475A problem.

If you let it run for 10 minutes or so, the problem seems to get better, but not
completely gone.

Probing the DC Voltages while the problem is there shows the -8vdc line has
dropped to -2.1vdc, and the +5vdc line has dropped to +1.0vdc. When the
problem seems to go away, those voltages come back up to normal.

Anyone have any ideas what to look at ?

Thanks for any help,

Dick, W1KSZ

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