From: William Levak (wlevak_at_sdf.lonestar.org)
Date: 2006-06-22 07:28:22
On Wed, 21 Jun 2006 r.lagendijk@hccnet.nl wrote:
> Hi,
>
> I've tried to find a short on the PCB but have not found it yet.
What I meant was that one of the IC's is shorted internally so that when
both bits 8 an 9 are high, the chip malfunctions. This could be one of
the IC's controlling addressing logic, or one of the RAM chips, or one of
the ROM chips.
> I got 6540 ROM's and 6550 RAM's on the board.
>
> ROM part numbers (I hope this is the number below the MPS6540):
>
> H1 = O19 5078 A
> H2 = 013 4478 A
> H3 = 015 2878 A
> H4 = 016 4478 A
> H5 = 012 2978 A
> H6 = 014 4178 A
> H7 = 018 4378 A
>
> A2 = 010 2678 A
This is Basic 1 with the revised $C000-CFFF ROM. This version has a
built-in diagnostic. You put a diagnostic connector on the user port and
on the keyboard connector and disconnect anything on the cassette ports.
You then turn on the computer and it runs the diagnostic and displays the
result on the screen. It usually displays at the top of the screen, so
you should be able to run it. When it finishes successfully, it turns on
the red LED on the system board.
User port diagnostic connector:
(Looking from the back of the computer and numbering from left to right)
Connect top 2 to bottom 2
top 3 to bottom 3
top 4 to bottom 4
top 5 to bottom 5 to top 11
top 6 to top 7 to top 8
top 9 to bottom 9
top 10 to bottom 10
Keyboard diagnostic connector:
(Numbering from one end to the other with the key at 19)
connect 1 to 9 to 17
2 to 10 to 18
3 to 11
4 to 12
5 to 13
6 to 14
7 to 15
8 to 16
wlevak@sdf.lonestar.org
SDF Public Access UNIX System - http://sdf.lonestar.org
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