[vcf-midatlantic] Repairs to a Heath WH19 Terminal
Jason Perkins
perkins.jason at gmail.com
Sun Mar 26 12:41:21 EDT 2017
So I had some more time to look into this.
I swapped in some caps I removed from some computer power supplies as a
test... no change. I then added the original cap in parallel... it made
some improvement: down to .3v AC ripple on the monitor supply rail and a
less distorted display.
When I was trying to find the short circuit I fried 2 of the bridge diodes,
and replaced them with some modern computer PSU takeouts.I swapped all 4
out with new 1N4004's, no change.
This is such a simple circuit I'm having trouble understanding where the
ripple could be coming from. If I use a light bulb as a load on the circuit
the ripple is the same (the monitor draws about half an amp, and a 70w 120v
light bulb works as a good stand in).
Any other suggestions?
Thanks,
-J
On Thu, Mar 16, 2017 at 12:07 AM, Matt Patoray via vcf-midatlantic <
vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
> Jason,
>
> That is great news! That is also too much AC on a DC rail, I would suspect
> those caps and get replacements, 1500 uF would be hard to find but a 2200
> would be ok in this case, remember those older electrolytics may have a
> tolerance of -20% +85% and modern caps are all +- 20% or better.
>
> Sent from my iPhone
>
> > On Mar 15, 2017, at 10:17 PM, Jason Perkins via vcf-midatlantic <
> vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
> >
> > Replacing the shorted cap and blown current limiting resistors results in
> > signs of life!
> >
> > https://goo.gl/photos/nk5kvxuCT2VGztgf6
> >
> > Good: The terminal works! https://goo.gl/photos/TPoPQ1c8QajthkZM7 (yes,
> I
> > tested with a loopback adapter, then with a usb to RS232 adapter before
> > hooking it up to the Lisa :) ) The terminal draws 51 watts running.
> Nothing
> > inside seems to be getting unusually hot.
> >
> > Problems: The display has a major wave.
> > https://goo.gl/photos/wXKydMr5syKU1SWd7 Guessing there are more bad
> caps in
> > the video section. The 65V input, and 53V rail in the monitor have .5v of
> > ac ripple. Perhaps the big 1500uf electrolytic is going bad...
> >
> > The keyboard didn't work very well at first, but after typing on it for a
> > bit it now works perfectly.
> >
> > -J
> >
> > On Mon, Mar 13, 2017 at 12:10 PM, Jason Perkins <perkins.jason at gmail.com
> >
> > wrote:
> >
> >> Man what a small world... My other big not-work time investment is
> >> TDIClub, looks like the OP of that article is into TDIs a bit as well!
> >>
> >>> On Mon, Mar 13, 2017 at 11:56 AM, Neil Cherry <ncherry at linuxha.com>
> wrote:
> >>>
> >>>> On 03/12/2017 11:25 PM, Jason Perkins via vcf-midatlantic wrote:
> >>>>
> >>>> You were right, the big .22 600v cap C232 was shorted. I've placed an
> >>>> order
> >>>> from DigiKey, hopefully the impending snow doesn't delay things too
> >>>> badly.
> >>>>
> >>>> -J
> >>>>
> >>>> On Sun, Mar 12, 2017 at 6:55 PM, David Gesswein via vcf-midatlantic <
> >>>> vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
> >>>>
> >>>> On Sun, Mar 12, 2017 at 05:43:22PM -0400, Jason Perkins via
> >>>>> vcf-midatlantic wrote:
> >>>>>
> >>>>>>
> >>>>>> 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.
> >>>>>>
> >>>>>> The caps to ground look like the most obvious path to create a
> short.
> >>>>>
> >>>>
> >>> Queue eerie Twilight Zone Music:
> >>>
> >>> http://hackaday.com/2017/03/13/raspberry-pi-hitches-ride-ins
> >>> ide-vintage-terminal/
> >>>
> >>> ... but he quickly determined that a bad cap was shorting out the
> -12VDC
> >>> rail ...
> >>>
> >>> hehe
> >>>
> >>> --
> >>> Linux Home Automation Neil Cherry ncherry at linuxha.com
> >>> http://www.linuxha.com/ Main site
> >>> http://linuxha.blogspot.com/ My HA Blog
> >>> Author of: Linux Smart Homes For Dummies
> >>>
> >>
> >>
> >>
> >> --
> >> Jason Perkins
> >> 313 355 0085 <(313)%20355-0085>
> >>
> >
> >
> >
> > --
> > Jason Perkins
> > 313 355 0085
>
--
Jason Perkins
313 355 0085
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