Re: PET 2001 fix Part 3 - RAM/ROM board etc.

Hi Philip,

If you get that vertical line with the CG completely removed it is almost 
certainly a bit stuck low in B2, the 74LS165 shift register, or a short 
somewhere on the PCB around it. If you have a 5K or so resistor you could 
try shorting each of the pins (3,4,5,6,11,12,13,14) to ground through that; 
each one should add a line and the one that doesn't is presumably already 
grounded internally or externally somewhere. You may well also have another 
issue, but I'd start by checking for a short and/or replacing that chip.

BTW, if you have four good spare RAM chips why not install them in I and J 7
& 8; if your ROMs are good that's all you need.

Good luck!

mike

----- Original Message ----- 
From: "Philip Lord" <random6000@mac.com>
To: <cbm-hackers@musoftware.de>
Sent: Thursday, May 12, 2011 4:30 PM
Subject: Re: PET 2001 fix Part 3 - RAM/ROM board etc.


> Hi guys,
> It's early here (5:06am), so please excuse the brevity of my message as
> I'll be going back to bed for a couple more hours after.
>
> I did change out the video SRAM as there were a few left over from the
> main RAM that were still good. Unfortunately this did not change the
> problem. Pulling the SRAM completely created a checkerboard effect, but
> there were diagonal lines strafing through the pattern. I'll test this
> again because at the time I didn't realize this was a valid testing
> technique.
>
> Pulling the CG ROM takes the image back to its original state, blocks and
> lines.
>
> One thing, late last night as I was briefly poking around with the logic
> probe, there seemed to be many places where I probed that slightly
> effected the pixel flicker. I didn't do much testing as it seemed a little
> random and inconsistent. So maybe as Mike mentioned, it could be a power
> issue. I have the  board out on my desk hooked up to an original spare US
> PET 2001 transformer. Maybe there is some issue with it being a US version
> on 100v Japanese power. I think I have a JPN to US power step up converter
> somewhere, maybe I'll try to find that.
>
> Thanks again
>
> ZZZzzz...
>
>
> On May 13, 2011, at 4:31 AM, MikeS wrote:
>
>>
>> ----- Original Message ----- From: "MikeS" <dm561@torfree.net>
>> To: <cbm-hackers@musoftware.de>
>> Sent: Thursday, May 12, 2011 3:28 PM
>> Subject: Re: PET 2001 fix Part 3 - RAM/ROM board etc.
>>
>>
>>> Looks like the problem is mostly in the fifth character column; wonder
>>> if
>>> that's where the horizontal line was originally?
>>
>> D'oh! VERTICAL line of course...
>>
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>
>
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