[vcf-midatlantic] ADM-3A display problem

[Garrett Nievin]

This project finally got popped of the stack and finished, and I wanted to 
"close the loop" on it.

The culprit turned out to be C112, a 47uF 50V in the monitor section.

Ian nailed it. Thank you!

Cheers,
Garrett


On Fri, 26 May 2017 15:22:48 -0400
Garrett Nievin via vcf-midatlantic <vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:

> Hi, Ian!
> 
> http://imgur.com/a/Z4s7V
> 
> Here is the image on imgur.  I turned the brightness way up, put a
> loopback on the serial port, and typed all these characters.  Everything
> seems to work correctly except for this negative video drive.
> 
> I'll definitely check those caps.  I replaced the 2.2 uf tantalums just
> because I had some on hand, but haven't replaced any other caps yet.
> 
> Thank you!
> 
> Cheers,
> Garrett
> 
> 
> 
> On Fri, 26 May 2017 08:36:31 -0400
> Ian Primus via vcf-midatlantic <vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
> 
> > I've been really busy lately - sorry I didn't see this earlier. The
> > picture did not come through - the list doesn't support attachments,
> > could you upload it to imgur or something?
> > 
> > IIRC, there isn't a way to invert the video on the ADM3A with a
> > switch, it sounds like you have a failure in the monitor section. It
> > is very possible for a component failure to drive the video negative
> > like that. Check C119 and C112.
> > 
> > -Ian
> > 
> > On Sun, May 21, 2017 at 4:07 PM, Garrett Nievin via vcf-midatlantic
> > <vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:  
> > > I'm restoring a Lear Siegler ADM-3A, and I'm not the most CRT-savvy guy
> > > around (but I did really enjoy Ian's excellent class at the most recent
> > > VCF-E).
> > >
> > > Attached is a photo of the issue.  If I crank the brightness to clearly
> > > see the raster, I can see that the text is actually displaying as dark
> > > instead of bright.
> > >
> > > Pointers?
> > >
> > > Cheers,
> > > Garrett
> > >
> > >
> > >    
> >   
> 
> 
>