You might remember the dead 2440 I'd resurrected last year. It mostly
works now, except for annoying ripple (and grat illum, which I'll get to
later). I have a little time to work on it now.
===
Looking for some advice on this problem.
shows annoying
ripple on a trace that should be flat (gnd cplg). (FWIW, on pretty much
all of the online photos of this family of scopes running, there is +/-
1 pixel noise in otherwise flat traces, so not getting perfectly flat is
endemic. Averaging would fix that anyway, and does mitigate the present
problem somewhat, but my good 2440 doesn't have this problem.)
shows my good
2440 measuring +5V on the bad 2440's side board, with a 1X probe. The
other low voltages look similar (+/- 5 & 8V). The remaining supplies
are much cleaner. All I can see in common is that the +/- 5/8 all pass
through these back-to-back zeners, CR845, CR846, CR551, and the others
don't. Either those are bad (unlikely--all the DC readings are good),
or I need to replace more filter caps (which ones?).
===
When I pull the graticule illuminator leads and measure across them, I
get between 14 and 15VDC, and that varies only 200mV between 0% and 100%
graticule illumination. Can that be right? I keep forgetting that I
can test the good scope, but I don't much want to open it and risk
turning it into a bad scope.... I ask because I've seen the replacement
part on that auction site and would rather not speculate.
--
Jeff Woolsey {{woolsey,jlw}@jlw,first.last@{gmail,jlw}}.com
Nature abhors straight antennas, clean lenses, and empty storage.
"Delete! Delete! OK!" -Dr. Bronner on disk space management
Card-sorting, Joel. -Crow on solitaire
