Hey Tom,
Thought you might be interested to know that CR9 looked OK, but Q5 may be
problematic. The B<->E readings are near zero in both directions. The B<->C
readings look OK, however. There is at least one trimpot that needs to be
replaced (Vertical Hold). I don't have an easy way to test U1, as I don't
have a bench top power supply.
Will keep you updated as this thing progresses.
James
On Tue, Feb 13, 2018 at 10:55 PM, James Denton <busterswt_at_email.domain.hidden> wrote:
> 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
>>>>>
>>>>> --
>>>>> --
>>>>> -----
>>>>> You received this message because you are a member of the LisaList
>>>>> group.
>>>>> The group FAQ is at http://lowendmac.com/lists/lisa.html
>>>>> To post to this group, send email to lisa..._at_email.domain.hidden
>>>>> To leave this group, send email to lisalist+u..._at_email.domain.hidden
>>>>> For more options, visit this group at http://groups.google.com/
>>>>> group/lisalist
>>>>> ---
>>>>> You received this message because you are subscribed to the Google
>>>>> Groups "LisaList" group.
>>>>> To unsubscribe from this group and stop receiving emails from it, send
>>>>> an email to lisalist+u..._at_googlegroups.com.
>>>>> For more options, visit https://groups.google.com/d/optout.
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Jason Perkins
>>>> 313 355 0085 <(313)%20355-0085>
>>>>
>>> --
>> --
>> -----
>> You received this message because you are a member of the LisaList group.
>> The group FAQ is at http://lowendmac.com/lists/lisa.html
>> To post to this group, send email to lisalist_at_email.domain.hidden
>> To leave this group, send email to lisalist+unsubscribe_at_email.domain.hidden
>> For more options, visit this group at http://groups.google.com/
>> group/lisalist
>> ---
>> You received this message because you are subscribed to a topic in the
>> Google Groups "LisaList" group.
>> To unsubscribe from this topic, visit https://groups.google.com/d/
>> topic/lisalist/w0-jorfCE_c/unsubscribe.
>> To unsubscribe from this group and all its topics, send an email to
>> lisalist+unsubscribe_at_googlegroups.com.
>> For more options, visit https://groups.google.com/d/optout.
>>
>
--
--
-----
You received this message because you are a member of the LisaList group.
The group FAQ is at http://lowendmac.com/lists/lisa.html
To post to this group, send email to lisalist_at_email.domain.hidden
To leave this group, send email to lisalist+unsubscribe_at_email.domain.hidden
For more options, visit this group at http://groups.google.com/group/lisalist
---
You received this message because you are subscribed to the Google Groups "LisaList" group.
To unsubscribe from this group and stop receiving emails from it, send an email to lisalist+unsubscribe_at_googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
This archive was generated by hypermail 2.4.0 : 2020-01-13 12:15:17 EST