16 Apr
2012
16 Apr
'12
6:55 a.m.
On Mon, Apr 16, 2012 at 9:02 AM, Win Heagy <wheagy at gmail.com> wrote:
The tolerance is more like 10%, so your Vcc appears fine.
Try powering up with the video RAMs removed (they are in the back and
look like they have dots on them). With no RAM, the PET should power
up to a blank screen whether the CPU can write the video RAM or not.
If you see an all-white screen or screen with the same character all
over, you have a problem with one or more chips in the video circuit.
It is repairable but will take some measuring and sleuthing.
If the screen is blank when no video RAM is installed, you might just
have a dead RAM or two.
-ethan
On Sat, Apr 14, 2012 at 2:12 PM, Dave Caroline
<dave.thearchivist at gmail.com> wrote:
Yep. You have a 1st generation board with 6550 SRAMs.
On Sat, Apr 14, 2012 at 7:52 PM, Win Heagy
<wheagy at gmail.com> wrote:
> I recently picked up a PET 2001-8. ?It has a video issue...see
> http://imgur.com/PKc97
2 The processor cannot write to the video ram
(and therefore clear it)
>>That's also a distinct possibility.
>>Which version of Static PET do you have?
?They came with different
>>types of ROM and RAM...
Is it possible to tell the version by looking at the board? I posted a pic
at
http://imgur.com/3aeiL >>Before
worrying about RAMs, check your Vcc... there are 4 regulators
>>and 4 legs of +5VDC.
I checked the 4 regulators and they are all outputting +5VDC. ?The most
deviation I saw was +4.94VDC.