Re: No Video on Lisa 2/5

Hi Jason, Tom,

Thanks very much for the schematics and the advice. I’m almost done pulling the video card out and will likely wrap that up in the morning. I’ll take a look at Q5 and see if i see similar behavior. I’ll also check out the pots.

Will keep you all posted. Thanks again.

James

On Tue, Feb 13, 2018 at 6:38 PM Tom Stepleton <stepleton_at_email.domain.hidden> wrote:

> 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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