8 Dec
2009
8 Dec
'09
1:36 p.m.
--- On Mon, 12/7/09, Josh Dersch <derschjo at mail.msu.edu> wrote:
Picked up an old terminal in very
nice cosmetic condition; it works fine barring a bit of
visual "jitter" on the display -- not sure how best to
describe it. The picture is clear and sharp but
occasionally a few scanlines will spike off to the right a
bit. Coinciding with this spiking are tiny crackling
noises from inside the monitor. (Or at least it seems like
they coincide, obviously I can't verify this.)
I thought it might be HV leakage based on discussions I've
seen on this list. I've run it with the cover off and
the lights off and I can see no evidence of sparking or
other visible discharge.
Are you sure it's a "crackle" and not a high pitch chirp/squeak? Your
description of some of the scanlines jumping (but not all) seems to suggest a problem in
the horizontal circuits. Probably limping electrolytic capacitors.
Also, HV leakage is pretty common to happen right under/around the anode connection
(suction cup) on dirty monitors. Dust and dirt form a conductive path. Discharge the
monitor[1], remove the suction cup, and clean the glass around the connnection. There
should be an area of clean (non-coated) glass around the suction cup, the rest of the tube
is covered with aquadag (gray coating). Careful not to clean the aquadag off - on some
tubes it seems to be water soluble... test your cleaner (Windex, etc) gently to ensure
that it won't remove it.
-Ian
[1] To discharge a monitor, connect one end of an aligator cliplead to a flatblade
screwdriver, and the other end to the metal mounting ears of the picture tube. Slide the
blade of the screwdriver under the suction cup until you feel it hit the metal contact.
Should be accompanied by a ZAP!