Robotron with garbage text

[richpuch]

I'm running into a Robotron issue with graphics.
I acquired a MPU board and ROM board with non-matching numbers.
I have the boards on my test bench with a switcher power supply feeding the necessary voltage to both boards.

When I first powered it on, I got an error on the ROM board of 2-0-3...I pushed around the ROMS and that error changed to 2-0-2. I pulled both ROMS, read them in my burner and they checked out good with ROMIdent. I put them back in and now got a 2-1-0 error.

I hooked up my FPGA Catbox and it showed ROM10 as being wrong) which matches the code 2-1-0 error). So, on the board the chip reads bad but when I stuck in my GQ-4x4 it reads correct. I burned a new ROM10 and error is resolved
Progress, when I boot the system, I get the carpet screen and then garbage text, some text you can make and seems formatted correct out but for most part its garbage. I also get a bit of a screen flicker.
I replaced all power connectors because existing ones were a bit oxidized
I washed the MPU board and reinstalled all the chips
Same garbage on the screen.
Wanted to coin up and select player 1 so installed a non matching S/N widget board and system would not boot
Had continuity issues on ribbon cable, replaced with a new one and system booted with widget board.
I was able to coin up, it read coin credit on the bottom and was able to do a player 1 start
But still same garbage on the screen
washed ROM board and clean legs
replaced ROM board ribbon because everyone recommended it on KLOV
still garbage on screen
I went back to my FPGA Catbox and did signature analysis on ROM4, ROM6 and MUX circuitry and it matched (looks good), in addition all ROM and RAM tested fine.
I've been poking around the CMOS (5514) and the CS is always high with my probe, even on power on. I believe that chip is active low, but It never goes low. so I tried back tracking the trace for CS and went as far back as a LS1369 on 4G which pin 7 is always high but pins 1 -3 are pulsing. Am I barking up the wrong tree?
Is it the CMOS...or do I have bad special chips on the ROM board? Or is it something completely different? I don't have any spares ROM boards or special chips to swap.

Here is a youtube video of my issue.

Thanks
Rich

 

[ArcadeTechGW]

The good news: The program is running.
The bad news: What is in the ROM doesn't appear to be reading.

Did you clean your chip legs?
Did you (POWER OFF) check the connection from each ROM chip leg to the trace below it, looking for high resistance connections?

Remember, we're dealing with high and low signals at a low voltage. It can be a bad socket or corroded chip leg that reads fine in the GX clamp, but not in the socket.

I'll defer to @mecha as he is the Williams expert.

 

[richpuch]

The good news: The program is running.
The bad news: What is in the ROM doesn't appear to be reading.

Did you clean your chip legs?
Did you (POWER OFF) check the connection from each ROM chip leg to the trace below it, looking for high resistance connections?

Remember, we're dealing with high and low signals at a low voltage. It can be a bad socket or corroded chip leg that reads fine in the GX clamp, but not in the socket.

I'll defer to @mecha as he is the Williams expert.

With the FPGA Catbox, I'm able to read all of the chips and do a CRC32 check and they all check fine....but I was considering resocketing them all. I did pull them and do a quick fiber pen clean, they didn't look that bad, but those sockets are the original williams sockets.

 

[EVB]

Did you try known working video decoder roms?

 

[richpuch]

Did you try known working video decoder roms?

I have a pair of spare video decoder roms (not sure if they are good), but I get same problem. I did a signature analysis on both decoders and both checked out fine.

 

[HudsonArcade]

I'm not sure if they use the blitters to do simple text displays, but I'd suspect the blitters and/or sockets.

 

[HudsonArcade]

Did you (POWER OFF) check the connection from each ROM chip leg to the trace below it, looking for high resistance connections?
Remember, we're dealing with high and low signals at a low voltage. It can be a bad socket or corroded chip leg that reads fine in the GX clamp, but not in the socket.

Williams games do a ROM check at boot, clown.

 

[mecha]

I'm not sure if they use the blitters to do simple text displays, but I'd suspect the blitters and/or sockets.

I've had some in the past where the text was boxes and it was the Special Chips.

try removing Special Chips and inspect the legs to see if they're bent, potentially broken off. then switch them around when you reinstall to see if any symptoms change. it's not often they fail, but they can.

 

[richpuch]

I'm not sure if they use the blitters to do simple text displays, but I'd suspect the blitters and/or sockets.

Blitters are a new term, did some quick reseach and I'll have to look into that. Thanks. Are the Blitter chips, the special chips on the ROM board...if so swapping those chips made a difference, so I think I have a bad special chip.

 

[richpuch]

I've had some in the past where the text was boxes and it was the Special Chips.

try removing Special Chips and inspect the legs to see if they're bent, potentially broken off. then switch them around when you reinstall to see if any symptoms change. it's not often they fail, but they can.

Swapping the Special chips made a huge difference....the screen looks a ton better...now the things that were readable prior to swap are garabage but everthing else looks fine. The highscore table is clear. So it seems like I have a bad Special chips...I assume both chips are identical types. I assume those special chips are obsolete, anywhere I can source one or two?

BTW...still dealing with that flicker is that the cheapo CGA to VGA converter or can it be somehting on my board? I'm inverting the Csync with a 7404.

 

[richpuch]

UPDATE: my problem came back and to resolve it I pulled one of the special chips and although the legs looked good I cleaned them with a small brass wire wheel. All the video garbage went away. So I don't have a bad special chip they were just dirty. I may replace the sockets on both special chips. Thanks for help. You guys were spot on with issue with special chips.

Even if they look good, clean the legs.

I still have the video flicker, but I think it's either the cga to vga converter or the 7404 that i'm using to invert the sync signal. I see everyone used a ls7404 so I'll try that over the 7404.

 

[sparksterz]

Huh, that's interesting...im glad it was a no cost fix! I'll keep that in mind on my Williams machine should I ever encounter it. Thanks for sharing.