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

----- Original Message ----- 
From: "Philip Lord" <random6000@mac.com>
To: <cbm-hackers@musoftware.de>
Sent: Thursday, May 12, 2011 9:42 PM
Subject: Re: PET 2001 fix Part 3 - RAM/ROM board etc.


>I didn't have a 5k resistor, so I used a 2k instead!!!!!
> I grounded all the pins (3,4,5,6,11,12,13,14) and found that pin 6 had the 
> lease effect. If anything it just slightly solidified the lines that were 
> already there. All other pins created new vertical lines.
>
> Phil
-----
Well, unless you can see a short or something unusual between pin 6 of B2 
and the pin it connects to on the CG, I'd try replacing B2.

Looks like there are problems elsewhere though if adding RAM in the lower 
four sockets didn't clear the screen and give you a prompt (or a reverse 
blank screen if the CG is out). Sounds like this PET is going to give you a 
hard time just like your PET64 ;-)

m

**********************************************

>
> On May 13, 2011, at 10:07 AM, Philip Lord wrote:
>
>> Hi,
>> I tried the step up transformer but that didn't seem to change anything.
>> I just tried RAM in I7, I8, J7 and J8...again, no noticeable change. I 
>> believe Ethan had checked all these ROMs as good, but I guess that didn't 
>> stop the CG ROM from going bad somewhere in transit between US and Japan.
>> I'll try the 5k resistor trick sometime today. I'll do this with the CG 
>> ROM removed so it'll be easy to see the lines.
>>
>> Phil
>>
>>
>> On May 13, 2011, at 9:08 AM, MikeS wrote:
>>
>>> 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...
>>>>>
>>>>>    Message was sent through the cbm-hackers mailing list
>>>>
>>>>
>>>>     Message was sent through the cbm-hackers mailing list
>>>
>>>
>>>     Message was sent through the cbm-hackers mailing list
>>
>>
>>       Message was sent through the cbm-hackers mailing list
>
>
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