Re: No Video on Lisa 2/5

Sorry---correction, my friend told me to investigate Q5, not Q9. (Which was fine, although you couldn't tell for sure without desoldering it---depending on the kind of fault, a broken Q5 and a broken CR9 could both have produced the reading we were seeing when we were testing CR9 in circuit.)

And just in case it wasn't clear---we investigated the diodes and transistors in circuit but not the *board* in circuit---we had to pull the board out of the Lisa to get access to anything :-)

--Tom

On Tuesday, February 13, 2018 at 11:20:46 PM UTC, Tom Stepleton wrote:
>
> 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> 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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