Re: Help diagnosing problem.

I have a schematic for a lisa video board is there only the one version, most of the other ones I find are for apple 1's and not for mine so I want to make sure I have the right one. It would make sense for it to be U1 since (by my schematic) it powers the flyback and does not touch the filament, so it would still glow like it does.

Patrick

On May 3, 2008, at 11:45 PM, Blair Aakre wrote:

>
> Check to see if the output of U1 is around 28V. You can clip a lead to
> the bottom of R124 and measure this. (It is the large 2W resistor on
> the right hand side of the board.) This voltage should vary some as
> the width potentiometer is adjusted.
>
> This regulator went bad on one of my video boards. It also took out R1
> (120 ohm resistor) in the process. Of course, on mine the damage to R1
> was pretty obvious.
>
> Any visible sign of damage on your video board? You will probably want
> to remove it from the Lisa and give it a good look over.
>
> -Blair
>
> On May 3, 2008, at 9:53 PM, Patnukem wrote:
>
>>
>> well I did two things turned it on and did see the tube glowing in
>> the
>> back, I guess i missed it before. I also held a neon tube by the
>> flyback and I did not see it light up so I may not be getting power
>> to
>> the transformer. as far as rom I have no idea the stickers of the
>> chips that work are both faded, so I put the old ones in and unbent
>> the two pins (there would not be a reason to keep two of the rom pins
>> unconnected from the cpu board is there?) but with the pins bent back
>> in to shape it now beeps again and the roms in there now are the H
>> ones and the I/O is a B.
>>
>> Patrick
>>
>> On May 3, 2008, at 8:52 PM, Ray Arachelian wrote:
>>
>>>
>>> Ray Arachelian wrote:
>>>> controls the contrast DAC when the DEN signal is off. Try swapping
>>>> the
>>>> two VIA's on the I/O board (if they're both soldered). Or if you
>>>> can
>>>>
>>>
>>> s/soldered/socketed/g
>>>
>>> :-)
>>>
>>>>
>>
>>
>>>
>
>
> >

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