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From: gsm@terminator.cc.umich.edu (Greg Miller)
Newsgroups: sci.electronics
Subject: Timing problems/Descrambler
Message-ID: <1991Feb1.193106.15015@terminator.cc.umich.edu>
Date: 1 Feb 91 19:31:06 GMT
Sender: usenet@terminator.cc.umich.edu (usenet news)
Organization: U of Michigan, ITD Research Systems
Lines: 37


 I too have a problem with the RE 'universal' descrambler.  Basically, the
part of the circuit that generates the colorburst clock signal (the crystal,
a variable cap, the 3126, and a few other parts) seems to generate pure garbage
on power-up.  (I don't have a scope, so I can't tell you what the waveform
looks like, alas.)  However, strangely enough, if I happen to reach into the
board, and touch the top of the variable cap with my bare (and presumably
grounded) hands, one time out of thirty the box will start functioning.

 When it isn't "functioning", the screen appears to be filled with garbage,
which I suspect is vblanking at almost random time periods.
 
 When it -does- function (after I've "touched" it), another touch to the
cap will usually set it again on an almost random output.

 I've seen exactly this problem on another one of these boxes - which I fixed
by putting a 33pF capacitor in parallel with the variable cap that seems to
be the focus for my problems.  I tried the same approach this time, and
unfortunately, it didn't help anything.
 
 I'm afraid tha tmy background is almost entirely digital, and I haven't
the damnedest what the designer is doing in either the clock generation
or the PLL locking circuitry.  Other than my previous descriptions, I
probably can't offer any more information about the problem.
 
 If anyone has seen this before on the RE box, or perhaps has seen ANYTHING
on the RE box, please get in touch with me - this has become terribly
frustrating.
 
 Thanks!
 
 - Greg
 
 gsm@terminator.cc.umich.edu
 gm@ionic.uucp
 GSMILLER@MTUS5.BITNET
 


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