"DaveM" wrote in
:
"bz" wrote in message
98.139...
The saga continues....
Removing the plug in module DID clear the 100 ohm 'short' to ground on
the 100 volt line.
Swapping tubes did NOT fix the -150 volt supply however.
It only measures -131 volts (after several minutes of 'post hv turn on'
warm up). It drifts much more during the warm up than the -150 volt
adjustment pot will swing to voltage. In fact I see very little change
as I adjust the pot.
The 100 volt supply is putting out about 130 volts and the rest of the
supplies look about normal (have not checked the HT supply to the CRT.
I wonder if it being too high could cause all my symptoms).
Measured the current out of the -150 and 100 volt supplies (across the
5 and 10 ohm series resistors). ~.95 volts /5 ohms = 190 ma for the
-150 supply
~1.4 volts/10 ohm = 140 ma for the 100 volt supply. I am assuming that
those values are not unusual. I have not looked at ripple, etc., yet.
Looks like I am going to have to measure voltages at several points and
try to make sense of any patterns that emerge.
--
bz 73 de N5BZ k
I don't remember whether you posted that your scope is the older 545
model, or the later 545A or 545B model.
It is a 545. No A or B.
I still have a copy of the 545B scope handy. As I remember, the low
voltage power supplies are pretty close from the basic 545 thru to the
545B models. According to my manual, the resistances to ground (power
off and all supplies totally discharged, no plug-in installed) a
That 'no plug-in installed' is more important than I knew!
-150V 2K
+100V 2K
+225V 2K
+350V 1K
+500V 15K
Will double check these, but I think that seems like about what I was
seeing.
Ripple specs are pretty tight, and must be to specs for a good trace and
waveform display.
-150V 5mv
+100V 10mv
+225V 5mv
+350V 20mv
+500V 20mv
Will check.
Going back to your earlier posts, you started with a good -150V source,
but all others were way out of tolerance ????!!!!!
-150 was ok as were MOST of the others:
"Checking voltages, the 220 volt test point on the upper right side is only
about 135. Other voltages (500, 350, 100, -150) are all good."
Kinda hard to do
with this instrument, since all the other LV sources are referenced to
the -150V source. Are you sure that your test instrument is good??
Moderately sure but I have several meters that I can check it with.
If
you have another source of known voltage, check it and eliminate or
identify that as a source of error.
Will do.
Next, remove and reseat all the tubes in the power supply section. Old
tubes and sockets get a bit of fungus or mold in the works, and can
create all sorts of havoc.
Oxidation, etc., can cause problems, for sure!
Work the tubes in and out of the sockets
several times; you might even clean the tube pins with a bit of fine
emery cloth.
I may do that and run a small rat tail file in and out of each pin in the
tub sockets.
I did pull the power supply tubes and check them in my tube checker.
Straightened the pins while doing that (always do in order to protect the
tub sockets in the checker). It was after I checked the tubes that the -150
volts went to hexxxx went crazy.
Cheers!!!!!
Thanks for the suggestions. Once I fix the scope, then I have another piece
of equipment that I wanted to use the scope on.
--
bz 73 de N5BZ k
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
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