I wanted to add:
I get the same basic waveform at R341/V343 when selecting either A or B timebases.
Also, neon lamp B171 is _not_ lit - should it be?
Keith
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--- In TekScopes@..., "keithostertag" <keitho@...> wrote:
Hi David-
Thanks for responding, I just yesterday got a chance to look at it.
First checking power supplies, the +350 measured in excess of 470V, and the +500 measured over 580V, both with lots of ripple. I found C760 very leaky and replaced it. That took care of the ripple, but not the level. After some investigation, I replaced V754, now all rails are within spec.
No impact on the trace compression problem, however. I did find that the problem does not appear until after the unit has warmed up for 20 minutes or so.
Thinking maybe the over-voltage on those two rails may have damaged another tube in the horiz amp section, I did a one-by-one substitute of all of them- no change. That included V343, V364, V384, and V398.
Looking today with a test scope, here are a few photos:
You can see the sawtooth going into R343 at grid of V343A is misshaped slightly, but the correct level.
The sawtooth in front of that, at the cathodes of V173 has good shape but seems to be too high a level?
I couldn't find the legend in the manual for how to read the blue voltages given on the schematic- when one is printed on top of another. For instance, at the cathode of V173 the schematic has -3.7 over +60 in blue. How to interpret that?
So do I understand correctly from the above photo that the signal at V173 cathodes is about 35 volts too high?
BTW- the square wave shown on the photos is the input, but not referenced to the same ground point on the test scope as the other traces.
Suggestions on how to proceed?
Thanks,
Keith Ostertag
--- In TekScopes@..., David <davidwhess@> wrote:
I have seen this problem before in the vertical direction where a load
resistor in the CRT vertical amplifier was open.
Be sure to check power supply voltages and that the deflection plates
are actually connected. Sometimes the leads loosen and fall off.
Since the trace unrolls when the position control is used indicating
that the sweep signal is not the problem, I would look after that
point on schematic 10. There are lots of DC levels shown on the
schematic which can be checked to narrow down the possibilities.
Some of the voltages are high so be cautious.
