Re: Dead 7603

Jim Ford

Thanks, everybody, for your help. Here's where I am now: Primary not
open; it measures about 3 ohms with the on/off switch on (obviously open
with it off!). Poked around P1171 and measured DC voltages. -50V,
-15V, +15V, +50V, and +130V all within spec. +5V measured 4.46 V, when
it's supposed to be 4.85V minimum. Hey, the power light is lit now!
Must have been a bad connection that I reconnected when moving the power
supply section back into place. Checking ripple and looking for shorted
tantalum capacitor(s) on the +5V rail next.


------ Original Message ------
From: "Vintage Test via Groups.Io" <>
Sent: 6/29/2018 7:31:36 AM
Subject: Re: [TekScopes] Dead 7603

Hi Jim,

On a 7603 - and I've sorted a lot of them - the main culprits of no
power-up, when you've checked all the usual suspects, is the power
supply filter capacitors. To check these, you will have to remove the
raw voltage power unit, situated at the bottom rear of the 'scope.
There are three large cross-head screws on each side of the chassis,
which allows you to carefully draw out the mains transformer and
attendant rectifier/capacitor PCB. If the capacitors are all metal
cased, it is likely that these are faulty now and need replaced.
Looking at the rear of the 'scope, there is a rectifier attached to the
bottom left corner , underneath the PCB. This is the +/- 15V rectifier
and the two caps nearest the left edge are the reservoirs. If these
don't have about 24V DC on them, then nothing else will work. Have a
look at this and get back to us.
you can never have enough oscilloscopes, DMMs, valve testers or
soldering irons . . .

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