The metal cover is a shield for electromagnetic interference (EMI). It may
be needed in order to meet a specification somewhere, but the scope should
work fine without it.
We're not necessarily looking for a bad tube, we're just disabling
different parts of the circuit by removing tubes because they are socketed
and thus easy to remove and reinstall. The actual cause of the problem may
be a resistor or a piece of loose metal that cause a short somwhere, etc.
Finding the tubes that prevent this fault from overloading the -100V bus
will help us determine where the fault is.
Just like V374 and V384 in the horizontal amplifier, there are V474 and
V484 in the vertical amplifier. You can try pulling those. You can also try
pulling V45, V135, V145, and V160 one at a time to see if any of them are
the smoking gun. If none of those point to the issue, then you'll have to
start un-soldering various connections or measuring a lot of different
voltages to suss out the issue.
Another thing to try with all the tubes installed and your meter hooked up
to monitor the -100V bus is to adjust all of the various controls and see
if any one control has a significant impact on the supply voltage. Again,
that doesn't mean that particular control is bad, but it might tell you
which part of the circuit is burning all that power.
It is also still possible that the problem is with the -100V supply itself.
A leaky filter capacitor such as C682 or C684 could be the problem. You
might see if either of these are particularly warm after the scope has been
on for a minute (but turn the scope off before you feel them up - not sure
if the whole can sees -100V or not).
On Sat, May 6, 2017 at 7:29 PM, enchanter464@... [TekScopes] <
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