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Kaypro II

MikeS said:
Tell your friend that it was working fine before he knocked it over and he owes you a new one ;-)
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Sadly he's the type who would be upset and insist on replacing the machine - and the last one I saw for sale was for $2000!


MikeS said:
All the connectors solidly plugged in (especially CRT socket)? Getting power to the monitor? Filament lit?

Check those sync signals again to see if they're still there and getting to the display board.
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I will do those tests in the morning. Are those tests I did with the scope actually yeilding positive and correct results?
 
I have many monitors ranging from IBM 5151s, through stuff like Cm8833s but since coming out of storage I've not tested any yet. I have LCD monitors with composite video inputs too via phono jacks - had the Apple IIc hooked up to one of them the other day.
 
Reading the values on J1 today:

Pin 1 - 4.440v peak to peak. Frequency appears to be 15.62khz. Value appears to be between -1v and +3v approximately.

Pin 2 - Doesnt exist

Pin 3 - 4.1v peak to peak. Possibly a signal at 2mhz??

Pin 4 - 5.25 volts peak to peak. 60.24hz frequency

These figures appear to be pretty much as they were before looking at the previous videos. The readings were taken with the video, power supply and logic boards all fitted and connected in the case with the exception of J1 (the video output of the logic board) where the readings were taken.

Nothing was displayed on the front of the tube - tried playing with the brightness control to no effect. There is a dim glow at the gun end of the CRT.

Checked the voltages where power is supplied to the motherboard too, and these are exactly as before.
 
Looks roughly like the right signals, so it looks like it's the display; probably not the CRT though if it's still glowing. Try moving the brightness control (and others) a bit back and forth; sometimes they get dirty and have bad spots.

Don't suppose you've found a schematic for the display board anywhere? Which make/model is it?
 
I'll try that in a few minutes. The Video board is the Elston variety. Others could apparently be a Dotronix or a Toshiba. I can't find schematics for any of the three sadly.

The controls on the Elston board are Brightness, Vertical Size, Vertical Hold, Video Centering, Width, Focus and V Lin.

Do you want me to try all of those controls?

I guess I could try to take photos of the display board if that is any help?
 
Most monitor PCBs are single-sided affairs and because they tend to mount fairly bulky components, are subject to solder joint failures and trace cracking. I would get my iron out and go over every single joint on the board, adding solder where appropriate and being on the lookout for cracks in traces.

In my experience, this can solve monitor issues at least half the time.
 
Moving the little potentiometers back and forward doesn't seem to have changed anything. There's no sign of any brightness at all on the screen irrespective of any adjustment. My Dad, an ex-patent examiner is asking whether that suggests that perhaps the high voltage section of monitor isn't working. Is there a test we can do for this?

My multimeter (http://www.uni-trend.com/ut70d.html) appears to be able to measure upto 1000v.

Once the charge in the cards has had time to drop, I'll remove the boards, and examine the underside of the video board, which as you say appears to be a single sided board, and use the soldering iron to heat each joint. Out of interest, what temperature should I set the iron to for this task?
 
As Chuck says, the weight of the components can crack the board or break a connection; check particularly around the flyback transformer connections and any large electrolytic caps.

If you have one of those neon bulb voltage testers or screwdrivers that they usually sell at the dollar (pound?) stores, they'll usually light if you bring them close to the high-voltage lead to the CRT; if the HV is working, the electric charge will also usually attract a piece of paper to the front of the screen. Of course the usual test is to remove the anode cap shortly after shutting down and grounding it to the CRT grounding strap or frame. Not a place for your multimeter probes...
 
Ok thank you both for your help so far! It is very much appreciated.

I'll go over the board with a fine toothcomb (metaphorically!) and do the joints as suggested. I'll probably wait until the morning until I have good daylight to do this.
 
Sorry about the delays. Ive been run off my feet with work.

We've spent ages now checking the continuity of all the tracks on the video board continuity and they are fine. There are a few points where the board has obviously been scratched before, presumably many years ago, and the areas of copper that were made bare seem to have been covered in solder. There is also a date and an intial written on the board presumably detailing this repair. All the solder joints look ok visually. None of the components seem at all loose or have any undue wiggle to them.

In the morning I'll begin the resoldering process.
 
Where you asked about other monitors, I have a Sanyo DM2112 green screen composite monitor. Is there any way to connect the outputs of the video connector on the logic board to this to check that's output is still good?
 
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