Re: 2246A Power supply failure turning on / off


Milan Trcka
 

A lot of potential problems seem to have been eliminated. Next I would
start looking for a potential overload on the power supply which may (or
may not) cause the PS to go into a shutdown to protect itself (electronic
fuse?). Another scope is likely needed to poke about the various sections,
starting with the first reference (5V?) and going up the voltage ladder.
This for checking time-related changes (caps charging etc.). Maybe
disconnecting the loads from the power supply might give you a clue whether
the problem is load related and which section is the offender on either
side. Unloaded supply may be easier to check for faulty components.
Unfortunately this level of troubleshooting needs to be done under power so
be careful as to not letting the smoke as well as not getting hurt. (FWIW)

Milan

On Wed, Aug 19, 2020 at 7:50 AM JorgeTop <jdavidtop@ieee.org> wrote:

Hi!

Some time ago I got a used 2246 oscilloscope which was working quite well
until recently. First it began to show a single point on the screen and
then it would return, or you just had to turn it off and turn it on again.

Soon after, it started to cycle on and off and sometimes I needed to turn
it off for a moment and turn it on again to get it working again.

Now it kept turning on and off cyclically without stabilizing. So far, I
have changed things like some electrolytic capacitors (I read right here
that it is a common fault), however I have not found all. I have also
changed zener diodes and some transistors without success.

With the service manual I have tried to measure some points however since
it turns on and off the voltage is erratic. I have not yet found a similar
power supply for sale so at the moment it is not an option and I would like
to be able to repair it.

Any suggestion?




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