OK, not exactly a repaired log, more a notepad of what I am doing to try and fix a System II board that is giving me grief.
1st board problems:
Paperboy character is broken, parts of him work, other parts are solid red blocks. Problem obviously is in the RED path or what generates the data that travels along the red path. The RED colour path is the D12 to D15 components of the 16-bit Data stream on the video board.
I followed that using my basic Video Probe - a jumper wire that connects to the RED output cap C14 after I lifted an end of L2 to isolate the RED signal, the other end has a pointy wire end of a 100R (R means ohms) series resistor for probing. I want to trace RED backwards from the RED colour drives (12L & 13K - see Sheet 17A). So I put the probe (try using something between a 50R to 330R resistor) to 12L pin 11 (R3) and checked that the image looked much like one level of RED brightness seemed OK, and so on with R2, R1, and R0. This was done during the scene of the Paperboy doing his route.
I should mention that the Motion Object test seems OK. Not well documented is that, or any of the so-called 'tests' - Atari didn't bother telling you what to look for when the test didn't work right. A book on System 2 servicing would have been nice - like THE BOOK for TTL repairs they made in the 70s.
Moving backwards I can trace the source of the RED brightness levels through Sheet 16B where they change to CRD15 (C RED Data 15 - not sure what C means, probably Control), then back to sheet 16A and the Colour RAM 11H-11 (convention will be chip number-pin number) then going back to Sheet 13A as VPD15 (Video Playfield Data 15), which being the Playfield background is not the issue here, and Sheet 15A (HS9 Horizontal Scroll 9 - not issue here), Sheet 11B (2R-2) - this is where the moving boxes (motion characters) merge - the problem should be around this Sheet, and Sheet 10B where VPD15 goes the CPU board via 1L-18 (Video) then J18-17 (interconnect) to DAL15 (Data Address Line 15) straight to the T11 CPU.
Pulling ROMs out showed me that the following ROMs are for these jobs:
6F/H and 6M - running kid
6H/J and 6N - Yellow car, exploding things, Black car (paperboy hits this in attract mode)
6K and 6P/R - Housebreaker, dog, "SMACK" (paperboy hits car in attract mode)
6L and 6R/S - Paperboy, tricycle & kid, papers on sidewalk
There are more, that is what I found though.
So, Paperboy has issues, but none of the other images appear to be bad. ROM is OK, traded with another board. Something that is only active during the selecting of 6L & 6R/S which is controlled by MOROMOE0 (from Sheet 12A IC 2M-4).
Phew!
More later as I explore how the Alphanumeric/Motion Object RAM
are built and synchronized with my trusty Video probe. I am suspecting
one of the 74LS153s at the moment of failing to select correctly.
It
was helpful to write this out as it helped me follow the path backwards
from where the video gose happily off to the monitor to where the images
are generated.
I will make a short video once I have this figured out and post it. There is not much info out there on fixing these boards!
John :-#)#
PS, stay tuned!
jrr2016-04-09 20:48:20
1st board problems:
Paperboy character is broken, parts of him work, other parts are solid red blocks. Problem obviously is in the RED path or what generates the data that travels along the red path. The RED colour path is the D12 to D15 components of the 16-bit Data stream on the video board.
I followed that using my basic Video Probe - a jumper wire that connects to the RED output cap C14 after I lifted an end of L2 to isolate the RED signal, the other end has a pointy wire end of a 100R (R means ohms) series resistor for probing. I want to trace RED backwards from the RED colour drives (12L & 13K - see Sheet 17A). So I put the probe (try using something between a 50R to 330R resistor) to 12L pin 11 (R3) and checked that the image looked much like one level of RED brightness seemed OK, and so on with R2, R1, and R0. This was done during the scene of the Paperboy doing his route.
I should mention that the Motion Object test seems OK. Not well documented is that, or any of the so-called 'tests' - Atari didn't bother telling you what to look for when the test didn't work right. A book on System 2 servicing would have been nice - like THE BOOK for TTL repairs they made in the 70s.
Moving backwards I can trace the source of the RED brightness levels through Sheet 16B where they change to CRD15 (C RED Data 15 - not sure what C means, probably Control), then back to sheet 16A and the Colour RAM 11H-11 (convention will be chip number-pin number) then going back to Sheet 13A as VPD15 (Video Playfield Data 15), which being the Playfield background is not the issue here, and Sheet 15A (HS9 Horizontal Scroll 9 - not issue here), Sheet 11B (2R-2) - this is where the moving boxes (motion characters) merge - the problem should be around this Sheet, and Sheet 10B where VPD15 goes the CPU board via 1L-18 (Video) then J18-17 (interconnect) to DAL15 (Data Address Line 15) straight to the T11 CPU.
Pulling ROMs out showed me that the following ROMs are for these jobs:
6F/H and 6M - running kid
6H/J and 6N - Yellow car, exploding things, Black car (paperboy hits this in attract mode)
6K and 6P/R - Housebreaker, dog, "SMACK" (paperboy hits car in attract mode)
6L and 6R/S - Paperboy, tricycle & kid, papers on sidewalk
There are more, that is what I found though.
So, Paperboy has issues, but none of the other images appear to be bad. ROM is OK, traded with another board. Something that is only active during the selecting of 6L & 6R/S which is controlled by MOROMOE0 (from Sheet 12A IC 2M-4).
Phew!
More later as I explore how the Alphanumeric/Motion Object RAM
are built and synchronized with my trusty Video probe. I am suspecting
one of the 74LS153s at the moment of failing to select correctly.
It
was helpful to write this out as it helped me follow the path backwards
from where the video gose happily off to the monitor to where the images
are generated.
I will make a short video once I have this figured out and post it. There is not much info out there on fixing these boards!
John :-#)#
PS, stay tuned!
jrr2016-04-09 20:48:20