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@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@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@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@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@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@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@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