That's a real nice deal. The 475 is a 200 MHz scope and is quite
nice.
?
The problem sounds like a bad electrolytic capacitor in the 50/105 volt
section of the power supply. Check C-1412 and C-1414. Most likely
C-1414?has high ESR and needs to be replaced. You might take a look through
the files and photos section as well as do a search through the messages for
capacitor replacement. The capacitor that most likely is bad is on the main
interface board grouped with some other can capacitors. You will want to be very
careful removing the bad cap as there is track under the can and it pulls up
easily as well as the plated through hole.
?
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Good luck,
?
Tom
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----- Original Message -----
Sent: Saturday, July 07, 2012 7:01
PM
Subject: [TekScopes] Tektronix 475 with
no display
?
I picked up a 475 on craigslist for $10. The owner stated it worked a
couple years ago but when recently powered up, he "couldn't get a
trace".
For $10, I figured it was worth the effort to fix it. I have
experience fixing electronics and while my soldering/component testing/safety
skills are pretty decent, my troubleshooting/tracing/etc is beginner level.
Any help would be appreciated.
It came with a stand, the manual, two
10x probes (one missing the 10x pin, but otherwise intact), extra parts (probe
parts, etc), and the service manual. It also has the front cover and styrofoam
intact. So the unit appears to have been kept well over the years.
I've
opened the unit up and everything is surprisingly clean there as well. I see a
couple of spots where the solder appears slightly burnt (like a semi-poor
repair job, but not terrible). I've tested most components in those areas (but
not all yet) and they have been testing fine.
Nothing appears terribly
loose and nothing appears to be bubbled or blackened.
One major thing
I've noticed is that all of the voltage readings are low. I read that most of
them reference the +50V line and so I followed the manual's instructions to
adjust that first. The best I can get is roughly 42.3V.
To me, that
says I need to review the power section before anything else. Am I on the
correct track, or not? Also, any common failure point that would cause my 50V
line to drop?
Thanks for the help. I can post pictures of those help.
Otherwise just let me know what other info would be useful.
