Re: Apple Lisa Display

[mjmahon@aol.com (Michael J. Mahon)]

In article <qh4r6s2di5.fsf@ruckus.brouhaha.com>, Eric Smith
<eric-no-spam-for-me@brouhaha.com> writes:

>fsbilly@yahoo.com (Billy) writes:
>> i have a Lisa 2/5 that was working great a couple of weeks ago.  now
>> when i start it, the screen shows a bright horizontal line and a bunch
>> of dimmer diagonal lines.  i'm thinking the display card has taken a
>> dive, but i dunno.
>
>Normally a single bright horizontal line, typically across the middle of
>the tube, would indicate that vertical deflection has failed.  But in
>this case, the dimmer diagonal lines indicate that this is not the
>problem.

It probably is still a fault in the vertical sweep circuit.

The normal sawtooth current waveform to the vertical deflection coils is
now just a pulse (which produces the bright horizontal line with the few
diagonal lines--during the pulse).  A little diagnostic work in the vertical
sweep circuit will turn up the problem pretty quickly.  (Unlike the horizontal
sweep circuit, the vertical sweep is quite straightforward.)

First check for bad/loose/oxidized connectors and dirty pots.  Then check
for almost-zero capacitance electrolytics (my favorite way is by bridging them
with a know-good, suitably rated electrolytic while watching for the symptom
to be fixed).

Good hunting--and be careful if you haven't worked around high voltage
before.  (Come to think of if, be careful even if you have.  ;-)

-michael

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