[GreenKeys] Info-Tech M-200

[Tom Hunter]

I am still in  need of a service manual for an Info-Tech M-200
NOT an M-200E
NOT an M-200F

This is an M-200 with NO suffix.

I have no video. I just tried the trick of re-seating all the IC's
on the video board. I re-seated the connector to the lower
board - still nothing.I have a perfect 5.0 VDC on the video
board. The -12vdc is only -11.25V, but that is not unusual.

When I feed tones into it, the mark and space LED's flash alternately.
Someone has added an NSD131 transistor right across the loop jack.
I looked it up, since it is an NPN, I took a chance and connected my
80V loop supply and meter to it. The meter indicates it is keying the
loop. It is not convenient to connect a Teletype to it on the dining room
table.

Further testing - A 'scope showed V & H sync pulses. The fifth monitor I
tried shows faint video. I have solid lines of ATATAT...SHSHSH...WIWIWI...
COCOCO...THTHTH...TOTOTOTO...Black Rectangles.

At least it is trying to work.

I pulled and re-seated the chip that looks like a character generator -
no change.

I have gone over and over it with a magnifying glass. I see no pins out of
a socket or folded up.

I just moved the M-200, loop supply and meter into the den, and my 28
skintight is typing from it.

Anyway the lower board seems to work. Still I would like to have the video.
There is not much more I can do without the service manual.


Tom   N3CRK
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