Galaxian - Right side of Screen Doubled?

KI4SWY

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Anybody ever see this? i thought maybe an issue in the vert/horiz counters, but all looked fine, and logic compareds just about chip there in about...

game boots fine, and goes thru self test ok, just the screen is doubled.

(the star field is NOT doubled) see attached image.
 

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So, for posterity - how did you fix this?
 
oh, i will give you some credit there darren, but thats only after i starting looking farther down the line!

Galaxian Repair #2 was even more fun!

symptoms: DEAD

dumped roms, checked with rom ident, recorded the Fluke Sigs.

pulled out the fluke, z80 pod, connected it up, RAM, OBJ_RAM, VID_RAM tested fine, but no go on roms, replaced those pesky sockets, retest, good to go.

still no video... ok, check the V/H Counters, there working OK.... then just worked down the line, looked like everything was working OK, but just no video.

Turns out the /6mhz clock was being shunted to ground, so swapped out the 7404 (schematics show 74386?) still shunted.. so pulled out the leak seaker... found it to be the input pin on 1U, installed socket, new chip, wala! video, but no star field... hunting around the star field logic, found a broken trace, so fixed it, and all is good!

the romsets on these were wierd, the had the 1 h/k/j/l roms from Galaxian, and u/v/w/y/z from Galaxian Hack 4 ? but not the hjkl roms from Glaxian hack 4.

other board had war of bugs :p

http://www.youtube.com/watch?v=KDQSuqm4Si0
 
So, for posterity - how did you fix this?

I read the schematics.... Just followed the data path down from the start of the Vert counters, until something didn't seem right (the horizontal looked fine, just the vert was messed up )
 
Turns out the /6mhz clock was being shunted to ground, so swapped out the 7404 (schematics show 74386?) still shunted.. so pulled out the leak seaker... found it to be the input pin on 1U, installed socket, new chip, wala! video

I'm confused. I don't see the /6MHZ line as an input to 1U. You mean CLK? Or do I have different schematics maybe? (or maybe you mean 1E?)

Wasn't familiar with a "LeakSeeker". Googled, and it looks pretty neat... just what I need to find a GI short somewhere in my HH pin...
 

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yep, the /6mhz is the same as "CLK" on 1U ... i searched the whole schematic and highlighted the /6mhz and checked every one... then used the leak seeker and was able to trace it up the 1U... looks like a typo, who wants to notify the manufacture to fix it :)

and the leek seeker is pretty sweet. first time i actually used it
 
yep, the /6mhz is the same as "CLK" on 1U ... i searched the whole schematic and highlighted the /6mhz and checked every one... then used the leak seeker and was able to trace it up the 1U...

OK, it the CLK line was pulled to ground, then CLK, 6MHZ and /6MHZ must have all be stuck (low, or high in the case of 6MHZ perhaps... but the point it not pulsing).

Now the part that confuses me is how the game was running (playing blind). The CPU is clocked by 1H. The 1H signal comes from the 7474 flipflop at 6C... which is clocked by the 6MHZ line (which it CLK inverted). So... in summary I don't really understand how the CPU was running with CLK not running.
 
the cpu is clocked from 1H, 1H is derived from the 6mhz signal, only the /6mhz was shunted.

the CLK on 1U is not CLK but /6mhz it is mislabeled. the clk @ 1e was fine.

cpu, vert/horiz were all being clocked from the 6mhz line so everything was working, however, the /6mhz was not, so there was nothing on the screen.
 
Theoretically, the CLK = an Inverted 6Mhz, but not delayed by two not gates.

i am thinking when it came to board layout, they switched the input of 1U from CLK to /6MHZ but never updated the schematic, this was a REV C board, the Schematics only covered REV B.
 
Ahh, I got it now. I thought the typo you were referring to was the 7404 vs. "74386", but there's another typo, where CLK should be /6MHZ.

Thanks for clearing it up. I'll make some annotations in my schematics on the 1:1e6 chance I ever run across a Galaxian board with an issue in those areas...
 
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