PDP 11 gear finally moved

Robert Jarratt robert.jarratt at ntlworld.com
Fri Jul 17 15:10:11 CDT 2015

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony
> Sent: 17 July 2015 20:23
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: RE: PDP 11 gear finally moved
> > When I repaired my VT100s I had to replace all the electrolytic caps
> > on the monitor control board to cure the screen wobble. Before doing
> > so I had reformed them all and I had tested them all for ESR and they
> > had all tested fine so I was unable to determine which of them was the
> > bad one. Perhaps there is other more professional test equipment I
> > could use that would have helped, I don't know. I did keep all the
original caps
> though (somewhere).
> Are you saying that if you put any of the original capacitors back
(leaving new
> ones in all other locations) you get screen wobble. If so, I am not sure I
> you. It's been some years since I repaired a VT100, but from what I
> there are plenty of capacitors that simply could not cause screen wobble
> matter what they were doing.
> Or did you recap the board and find that it then worked. In which case (a)
> perhaps only one of the capacitors was faulty or (b) it was actually a dry
> -tony
> =

I am saying that I recapped the entire board, so one or more of them must
have been bad. I agree it could have been a dry joint, but I am not going to
put them all back just to check :-) This happened on *two* of these boards,
so either I had two dry joints, or two bad caps.



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