Re: No Video on Lisa 2/5

Worth noting that Bitsavers has an original Apple schematic online as well:

http://bitsavers.informatik.uni-stuttgart.de/pdf/apple/lisa/hardware/050-4012-E_Video.pdf

The one Jason linked to could be just as good, although I seem to remember some revision differences or errors on the one for the Lisa PSU.

Now... just last Saturday I watched a friend---who is very well-versed in Apple video systems of that era---diagnose a broken Lisa video board.

For this one too there was no video at all---and curiously, when we went to extract the video board to investigate, there was no 'pop!' from discharging the anode. Based on these symptoms, my friend told me to put a diode tester over all of the diodes on the board (in circuit---not extracting anything) as well as on the transistor Q9. Sure enough, CR9 had failed closed. Friend concluded that the IN4936 was maybe a bit underrated for the job.

As it turned out, we had an analog board from a dead Mac that we could cannibalise (the diode it uses in the same role is larger in rating and in size), and sure enough, it worked. Maybe someday I'll have the electronics skills my friend has, but it'll probably be a while before I do!

My friend supposed that CR9 might be a common failure point for these video boards---it would be interesting if you found the problem on your board as well.

--Tom

On Tuesday, February 13, 2018 at 12:49:20 PM UTC, compu_85 wrote:
>
> I'd start with the video card (after swapping the power supplies around).
> If you look at the schematic you'll see the width adjustment pot at the top
> of the board has the 28v output from the regulator on it. Begin there... no
> B+, no picture.
>
> http://www.freeinfosociety.com/electronics/schemview.php?id=1424
>
> -J
>
> On Mon, Feb 12, 2018 at 11:34 PM, James Denton <bust..._at_email.domain.hidden
> <javascript:>> wrote:
>
>> Hello all,
>>
>> I recently picked up a Lisa 2/5 with known memory issues that I managed
>> to resolve relatively quickly with known-working cards. When I power up the
>> machine, I hear the beeps that indicate all tests passed and it's waiting
>> for a boot disk, but there's no video at all on the screen. I moved the
>> entire card cage to my other chassis and confirmed working video output
>> there. While I do see some slight mirroring on the left side of the screen,
>> and the picture seems a little narrower, I believe it may be due to the 3A
>> ROMs installed on this board.
>>
>> Where is a good place to begin troubleshooting the lack of video output
>> on this Lisa? Should I simply look to recap/rebuild the analog board or is
>> there something that can be looked at before taking that on?
>>
>> Thanks in advance,
>> James
>>
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>
>
> --
> Jason Perkins
> 313 355 0085
>

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