On 18 Mar 2006 12:40:11 -0500, Sam Goldwasser
wrote:
Jim Yanik writes:
Sam Goldwasser wrote in
:
Jim Yanik writes:
"Ancient_Hacker" wrote in
oups.com:
Oh, there's also a big voltage divider resistor (the white ceramic
thing) Any moisture, dust, or leakage there and you tend to get
unstable HV.
The HV thick-film resistor network(TEK-made) has the HV feedback for
regulation on one side,and the CRT focus divider on the other. Either
one can go out-of-tolerance,and the metal pins can crack and be
intermittent.I've never been successful in resoldering them,either.
I do not think this part would be the cause of his intensity
modulation.
Followup: The frequency of the chopped line does NOT correlate with
line frequency.
Perhaps HV oscillator freq?
I don't think so. It's order of a few hundred Hz and not constant.
And I should note that at low intensity, it is worst going full off.
With the intensity turned up, it's not visible. There is minimal
if any geometric distortion of the trace (outside of the focus
problem, which doesn't always appear) so I doubt any LV power supplies
are involved that also feed the amps.
Then you're down to decoupling caps.
It's almost as if the Z input has some oscillation on it. When I
first noticed, I thought maybe the chopped blanking was misbehaving,
but this occurs on all vertical modes.
A thought occurs to me;there's a 1uf/150V(IIRC) electrolytic on the wiper
of the CRT grid bias pot,to ground;that could be going bad.
I'll check that.
It's also related to warmup. At power-on, there is no problem. It
takes a of couple minutes to show up. The fan is running.
And even then, the severity varies randomly.
So, what could affect the Z modulation AND sometimes focus, but not
geometry?
If it was the HV divider I guess a parts unit is the only source for a
replacement?
Yes,it was a TEK-made part,from their defunct hybrid/ICO in-house plant.
Removing a good one from a motherboard without damaging it is not an easy
task
Now it really doesn't like even normal intensity.
But the geometry (beam stiffness, etc.) is not affected. So, I'm
leaning toward a problem in the grid circuit, not the HV itself.
Does anyone know of a free source for decent quality schematics? I have
several complete manuals downloaded from various places but the resolution
of the schematics tends to be terrible and only marginally useful.
I think we have the 465b manual at work, I'll have to check on Mon.
If we do, I'll only be able to copy a couple of pages so I'll just be
able to get the power supply and maybe a few others, but I'll give it
a shot.
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