Hey Harold,
I'm no expert on U800 failures, but the two videos I found show different
symptoms: . While the trace is
affected, the on-screen-display is not in both of those cases. Of course we
don't know whether you've turned the OSD off on your scope, and there is
likely more than one failure mode for U800, so YMMV.
Does the scope successfully complete power up? If it's failing
power-on-self-tests, it'll stop at some point with a single front-panel LED
lit, and when you press A/B TRIG, it'll continue to operating mode, which
will click some relays.
After that, the first thing to look at is the power supplies at J119.
There's a table in the service manual that specifies limits on voltage and
ripple. The next thing to look at IMHO are the -1.25V and +1.36V references
on the A5 board. If any of those are out, there's no point in looking at
anything else.
From there it's a process of elimination, I'd say, and if you haven't read
this document: , maybe
that's a good start. It's a fun read, if nothing else.
Some things to try:
- Does the beamfinder do anything?
- Does the OSD show?
- Does X/Y mode work?
- Does the B-sweep work?
- Does the 10X horizontal magnify do anything?
Since the symptom is so severe, you should be able to quickly figure out
what is bad in the horizontal or the HV.
Good luck,
Siggi
On Wed, Apr 2, 2025 at 9:18?AM Harold Foster via groups.io <halfoster=
[email protected]> wrote:
That was the kind of thing that I was worried about. I do have a parts
unit so maybe that could be used if needed. I'm not sure when I will get
the chance to dig into it but I very much appreciate the ideas. I've not
worked on these before so at least knowing where to start reading up is
extremely helpful.
Thanks!
