Galaga character video pcb prob

[whatchitfoool]

...
i have a video problem with some of the characters being split and showing up twice...

(here is a video. way better then a text description)
http://www.youtube.com/watch?v=AH5eEVuNxOY

the ram has been changed to 2148's (well 49s ). no sign of unrepaired broken traces...
problem def on the video board.

its a orig midway pcb, it a full galaga upright.
power supply is original, but its working good with the onboard voltage a intcy bit over 5.1v

anyone have some ideas?

 

[ajcrm125]

My guess is either the sprite RAM or the horizontal/vertical counter addressing circuitry leading up to the RAMs.

 

[whatchitfoool]

could you give me some location addresses?

 

[HudsonArcade]

My guess is either the sprite RAM or the horizontal/vertical counter addressing circuitry leading up to the RAMs.

addressing itself should be fine... it's only affecting odd or even columns... more likely to be traces, since the 2147s have been stripped and replaced with 2149s.

 

[whatchitfoool]

if you split the screen horizontally into 1/4ths, counting from the bottom, the 3rd 1/4th up is fine. if its out of that area, its messed up.

there is a pin on chip 5D of the video board (pin#12 i think, one of the 4 of the chips outputs) thathas a trace leading to somewhere under (vid ram) chip
6D ,that is broken and i do not know where its to connect. anyone know?

 

[whatchitfoool]

any manuals i could find were too blurry to make out where pin 12 goes to (a trace) under 6D.
if no one can look at their board, how about a hi res galaga manual?

 

[channelmanic]

if you split the screen horizontally into 1/4ths, counting from the bottom, the 3rd 1/4th up is fine. if its out of that area, its messed up.

there is a pin on chip 5D of the video board (pin#12 i think, one of the 4 of the chips outputs) thathas a trace leading to somewhere under (vid ram) chip
6D ,that is broken and i do not know where its to connect. anyone know?

The file you want is "galaga_schem.pdf" and has a pretty clean scan of the schematics.

Pin 12 of 5D is signal D46C and goes to Address line 6 (pin 17) of each of the 2147 RAMs at 6C, 6D, 6E, and 6F then to pin 1 of the 2148 RAM at 6B.

 

[whatchitfoool]

damn it. its pin 11, not 12.
i just got to the board, im going to try to find that file. if anyone posts where pin 11 goes anyway, i'd be appreciated.

 

[channelmanic]

damn it. its pin 11, not 12.
i just got to the board, im going to try to find that file. if anyone posts where pin 11 goes anyway, i'd be appreciated.

Pin 11 of 5D is signal D47C and goes to Address line 7 (pin 16? Hard to read schematic. Go find the data sheet for the 2147) of each of the 2147 RAMs at 6C, 6D, 6E, and 6F then to pin 17 of the 2148 RAM at 6B.

Google the file name for the schematic. It's easy to find.

As for the data sheet for the 2147? Try http://www.datasheetarchive.com

RJ

 

[whatchitfoool]

well, after repairing the trace and replacing the 74ls161A (5d) , the character doubling problem is no longer there. but the evens or the odd lines are gone in them all together. while investigating, i swapt the 2478s and saw no change. i kept the one at 6b out, and saw no difference in the characters. i checked the traces to this ram chip (thought it wasnt powered) and found them to be ok.
i was thinking the problem was in 5a, maybe 5b, but i had ran out of time to look into it.
ill post a vid to show what i mean...

anyone else ever see anything like this?

 

[whatchitfoool]

its like the 6b ram isnt working at all