[vcf-midatlantic] Repairs to a Heath WH19 Terminal

[Jason Perkins]

Ok, I removed the HOT, and the short / overload is still present. If the
flyback is unplugged the extra load goes away. I found that with flyback
pin 3, the red wire, unhooked the extra load goes away too. Unplugging the
yolk makes no change.

There aren't many things on that ground return from the flyback, I'll take
them out one at a time till I find the shorted part.

-J

On Sun, Mar 12, 2017 at 1:15 PM, Matt Patoray via vcf-midatlantic <
vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:

> Jason,
>
> Pull the HOT and try to power it on, and see what the current draw is then.
>
> Sent from my iPhone
>
> > On Mar 12, 2017, at 12:37 PM, Jason Perkins via vcf-midatlantic <
> vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
> >
> > Looking for some advice on getting a Heath WH19 terminal going again.
> >
> > First, some schematics:
> >
> > http://www.rsp-italy.it/Electronics/Kits/_contents/
> Heathkit/Kits/Heathkit%20H-19%20video%20terminal.pdf
> >
> > My annotations on the x-ray view: https://goo.gl/photos/
> PF8N7wRDPLc1czUU7
> >
> > What I observed:
> > When first powering the terminal it did nothing. The fast blow 1A fuse
> was
> > open, the wire was broken. As it was handled it broke more, suggesting it
> > could have simply failed from vibration? The manual said that a 2A slow
> > blow fuse is appropriate for 120v operation.
> >
> > I replaced the fuse with the smallest one I had on hand, a 4A slow blow,
> > connected the terminal to a current meter, and powered it up. It beeped
> :)
> > But was drawing 5A :( and then there was a little smoke :( :( I quickly
> > powered it off.
> >
> > R263, a 1.2 ohm 2W resistor had cracked. R263 supplies the +53v rail to
> the
> > horizontal section.
> >
> > C228 seems to be good (open resistance, correct mfd), D208 and D211 seem
> to
> > be good (.5v one way, open the other), C229 isn't shorted but my meter
> > can't measure its capacitance.
> >
> > I replaced R263 with a 4w 1.2 ohm resistor I had on hand, and powered up
> > again. Still too much current draw, and more smoke in the area of Q217.
> >
> > Does this suggest Q217, the HOT, is bad? I pulled it out and did the
> diode
> > test on it, it seemed to test OK? It's a BU500, and I see some NOS ones
> on
> > ebay.
> >
> > I'm unsure what my next step should be.
> >
> > Thanks for your input!
> >
> > --
> > Jason Perkins
> > 313 355 0085
>



-- 
Jason Perkins
313 355 0085