--- In TekScopes@..., "tinkerer138" <siggi@...> wrote:
--- In TekScopes@..., Bob Koller <testtech@> wrote:
If the power supply seems OK, just turn up the CRT Bias pot and see if it lights up. A common failure is the Z-Axis hybrid, which, if bad, will cause no display. If a display appears, you may be able to see which self test is failing, and take it from there.
Sadly no joy on cranking the bias pot up. Thanks for the hint, though.
I take that back - turns out I was messing with the MCP bias which isn't too helpful. When I cranked up the CRT bias I got an error message display - very exciting - thanks!
"TEST 05 FAIL 42".
Apparently this is a line trigger self test.
Given that I'm getting a picture, the CRT and the high-voltage supply are presumably OK. Can I also assume the horizontal/vertical/Z machinery is OK?
Looking at pictures of original PSUs, I'm now thinking this PSU is pristine - e.g. hasn't been re-capped.
Perhaps I'll take another hard look at the rails, it'd be great if it were that simple.
I seem to recall a ~10mV spiky "beat" on one of the 5V rails presumably the analog - I'll have to look closer tonight.
The other 5V rail was pretty fuzzy, but only around 5-10mV. I did see it take a little bit of a wiggle when I mess with the front panel controls, though I'm hard put to quantify the amount.
Also, between the front panel LED flicker and the 50 Ohm input setting reverting, I'm thinking this might be (or at least manifest as) a control issue. While the LED shift registers are non-latched, I don't think I ought to be seeing noticable flicker on every LED each time they update?
The 50Ohm termination resistors are monitored for overheating, and presumably the toggle-back means the CPU's "seeing" them warm. So if the rails are really checking out, I may start looking back from the thermistors toward the CPU.
Any other ideas?
