Re: Kaypro II Video Problem
- From: "Fred J. Scipione" <fjscipio@xxxxxxxxxxxxxxxx>
- Date: Sat, 13 Aug 2005 06:14:00 GMT
"Tarkin" <nuke48386@xxxxxxxxx> wrote in message
news:1123895370.870151.60580@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Hello all,
> I recently had a Kaypro II donated to me, very compleat
> with even the *dealers* manual. Recently ran it for four hours
> trying to get it to talk to my PC (more on that in another post).
> Screen flickered and and has now "dropped"; My prompt
> "Kaypro CPM 2.2 <c/r><lf> A>", which is normally at the top of
> the CRT is now approximately shifted 50% down. Sifting through my
> copious documentation, the Chilton's Manual proclaims the video
> board as Toshiba. Tried fiddling all the adjustments relating to
> vertical: linearity,hold,&size....only made it unreadable, so
> tweaked it back to normal. The internal case brace on the video
> side is nylon, so I used it to variously probe, tap, and bend
> the video board & tube looking for bad solder joints...to no
> avail. In desperation (and casual disregard for safety), I broke
> the hot-melt glue on the deflection yokes, the display rotates in
> stange ways (you could say they gyre and gimbal in the wabe), but
> will not deflect above the imaginary half-height line.
> Does anyone have any insight into this problem?
>
> Thanks,
> Tarkin
Well, what you have described is a problem in the vertical
deflection circuitry on the driver board. Most likely either
one of two transistors in a 'push-pull' amplifier's power drive
stage has quit, or one of the two voltage supplies to the power
drive stage has gone. If it is in a voltage supply, it may be
a bad rectifier or bad capacitor. Bad capacitors have been
mentioned before in this group as a frequent cause in failures
when old equipment is re-powered after a long idle period.
Be warned that there are lethal voltages present in the video
circuitry. You should only attempt a repair if you are qualified,
experienced, and take proper precautions (such as having someone
with CPR training available while you work!). If your manuals
provide a schematic for the Toshiba board, use it to understand
the vertical deflection circuitry and to find key voltages you
can measure in a 'divide and conquer' search for a bad component.
If a schematic is not available, you may have to remove the
Toshiba board and create your own (partial) schematic of the
vertical section by manually tracing the connections from the
yoke connector back across the printed circuit board and its
attached components.
The good news is that your horizontal deflection circuit must
be working, and still producing (most) of the derived voltage
supplies on the board.
Video monitor repairs are like T.V. repairs (without the tuner).
Of course, T.V. repairmen are a dying breed, since the cost of
a new T.V. now equals that of most part+labor repair costs.
Still, you might find someone knowledgeable who might advise you,
or who finds a restoration project an interesting challenge.
Some books from the library on T.V. repair might be helpful too.
.
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