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Path: utzoo!linus!decvax!duke!unc!mcnc!unc-c!dya
From: dya@unc-c.UUCP
Newsgroups: net.micro
Subject: Re: DECmate II problem
Message-ID: <1121@unc-c.UUCP>
Date: Tue, 4-Oct-83 19:35:42 EDT
Article-I.D.: unc-c.1121
Posted: Tue Oct  4 19:35:42 1983
Date-Received: Fri, 7-Oct-83 02:38:44 EDT
Lines: 36

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}

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