TLD%mit-mc@sri-unix.UUCP (10/01/83)
From: Thomas L. Davenport <TLD@mit-mc> I am blessed (?) with several DECmate II's that seem to have continuing problems with vertical hold. DEC service helps, but only for a while. Can anyone tell me how to attack this problem myself? Should I just give up? -Tom-
dya@unc-c.UUCP (10/05/83)
References: sri-arpa.12216
Organisation: The University of North Carolina at Charlotte
Ah, yes! the typical Motorola monitor rolls afflict another DEC
user. Actually, the problem is also prevalent in their consumer TV's
which share the common circuitry and componentry with the DECmate 11
monitor.
What happens is that (usually) the emitter AC decoupling capacitor
in one or more vertical sync amplifiers opens, leaving the affected stage
(voltage amplifier) with a gain of approximately nil. Then, the vertical
oscillator can't synchronise worth a tinker's damn.
If you have Motorola (DEC Part number 63065.65A08) check C2 (collector
degeneration,first video amp); R24 (a 33 megohm resistor which is
CRITICAL...oops, 3.3 megohm); C34 and 35 (integrator); and C37-38 (the
infamous electrolytic caps). Also, these sets will roll when the
vertical output transistor partially fails (forcing one to jack up the
gain through the linearity and height controls).
if you have GTE/Sylvania, C310, C307,C309 are all likely candidates.
......But, it sounds like a Motorola monitor to me. They ALWAYS seem to
roll. Your oscillosp
cope is your best friend through this mess.
Happy troubleshooting,
--David { .....duke!mcnc!unc-c!dya}
DECmate and DEC are trademarks of Digital Equipment Corporation