[vcf-midatlantic] Repairs to a Heath WH19 Terminal

[Ian Primus]

Check the actual voltage of the B+ rail. It may be a bit too high. If
so, then suspect your voltage regulator transistor/transistors. It's
possible to have a bad voltage regulator, but still have things almost
working, but there will be too much ripple and you won't be able to
get rid of it with capacitors.

-Ian

On Sun, Mar 26, 2017 at 12:41 PM, Jason Perkins via vcf-midatlantic
<vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
> 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