Osborne monitor service information ?

From: Dave Dunfield <dave04a_at_dunfield.com>
Date: Sat Nov 6 18:39:06 2004

Hi Tony,

>I would start by tracing the horizontal drive signal. My guess (without
>seeing it) is that the 555 is part of the vertical circuit and can be
>ignored for the moment. You may find the horizontal drive signal goes to
>the base of the drive transsitor, transformer coupled to the base of the
>horizontal output transistor, thence to the flyback.

Thats pretty much exactly the circuit --- This monitor is not designed to
be very easy to work on - there's a metal plate right under the circuit
board, and the other side of the board is right up against the neck of
the CRT - makes it pretty hard to take measurements in circuit.

This afternoon, I pulled it all apart, checked continuity through the
flyback, and pulled the horizontal drive transistor and checked it - it
appeared to still be a transistor (correct "diode" junctions from both
B-C and B-E).

So - I put it back together, planning to leave it for another day - on
a whim I tried it, and it worked! - And I used it for a couple of hours
as I checked out the rest of the machine with no further problems.

I still have no idea what the problem was - perhaps a bad contact in one
of the connectors, although I wiggled and jiggled everthing and was unable
to deter the monitor for working perfectly after I put it back together.

dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Vintage computing equipment collector.
Received on Sat Nov 06 2004 - 18:39:06 GMT

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