Thanks everyone:
I'll try to respond to everyone who has responded to me so far:
Yes, I've been searching the archives but getting a lot of generic results. I may just be using too many generic words in my searches (like "475 no display" or "475 power supply" etc). Since I wasn't completely sure of the issue, I wasn't completely sure of the search terms.
I've tested the voltages and these are the results:
+110 = 85.4 (77.6%)
+50 = 42.4 (84.8%)
+15 = 10.9 (72.667%)
+5 = 4.1 (82.0%)
-8 = -6.1 (76.3%)
(These readings are with the 50V adjustment cranked all the way up.)
I assume that is pointing to a larger issue with the 15V line, but if I'm off on that, let me know.
I'll check the specific caps mentioned, but otherwise it looks like the searching I have done is all pointing to the same things (mostly the tantalum caps or the main electrolytic ones).
Upon further review, I noticed that the "burnt" areas I initially saw were really just flux that wasn't cleaned up. I'm less worried about that now, but still paying attention to joints in those areas.
Also, I'm pretty sure my meter is accurate (based on readings from other items that match what I expected). I do not have an ESR or another scope at this time, so my testing is limited. I will be investigating my options for borrowing another scope to aid in my testing.
As I move along, I'll update this thread with my (hopeful) progress.
Thanks again everyone.
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--- In TekScopes@..., Merchison Burke <merchison@...> wrote:
Are you sure that your meter is reading correctly? If your meter is
correct then you should check the ripple level on the 50V supply. If
that is OK, then check the components in the 50V regulator.
On 2012-07-07 7:01 PM, i814u2.geo wrote:
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.
