Tech: Gauntlet 2 graphics issue

debaser138

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I have a Gauntlet 2 board that I'm working on. When I first got it, it would go into attract mode but all the graphics were just solid colors (but text was fine) and there was no sound. I fixed the sound problem by installing a good YM121 chip.

When the game starts and the attract music kicks in, it's supposed to show a title screen. Mine just shows a blank white screen. After the music is over and it goes into the mode where it tells you how to play the game, the text for Gauntlet II and the character listings, health, etc on the right hand side are all there but the left hand side is just a red screen. There are boxes with text that pop up in the red during the attract mode telling you about the enemies, etc. Basically all of the game graphics are coming up as solid colors.

I dumped the images for all the roms to make sure they were good. I found 1 ROM at R16 (labeled 1120) that was bad. I have another non-working Gauntlet 2 board so I pulled a good ROM from there. Unfortunately that didn't fix the issue graphics issue. I also tried swapping out all 12 RAM 6C-6K and 7C-7K from another board but that didn't fix it either.

If I go into self test, it first brings up a blank white screen. Then after a few moments it brings up a blank black screen. Then again after a few moments it goes into the switch test mode. From what the manual says, it there was a RAM or ROM error, the test mode would stay on the error page and not continue to the switch test so it appears that my RAMs and ROMs are ok.

I also tried swapping out the SLAGS at K1/K2 along with the AM9128 RAMs at L16/M16 but no change.

Any ideas on what the problem might be?
 
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Update: I also tried swapping the 137419-103, 137419-104, 137419-101 and 137403-001 (pokey) but no change.

One thing I noticed on this board is that there is a 2 pin jumper block labeled SROM right next to the 1119 EPROM on the lower right hand corner of the board. These two pins are connected with a jumper on them. The other Gauntlet boardset I have does not have this jumper block.

Should that 2 pin jumper block be open or closed?
 
I'm digging back into this board some more. I removde the two non-socketed color rams at 10L (intensity) and 10M (Red) and installed sockets and the replacement rams but it didn't make any difference. I'm still just getting all red where the game playfield and graphics should be.

I'm getting no errors in test mode. Also, in test mode, playfield test screens are just a black screen and the motion object test screen is a light greenish color and that's it. In the color bar test screen, it shows all the correct RGB, white and grey colors but the convergence test screen just shows that same light greenish color screen with nothing else.

Anyone have any ideas?
 
It sounds to me like you are just swaping chips and not doing much of any tech stuff :(

Have you verified any of the voltages and mad certain the power supply is good?

Get one set of working roms and use ONLY them, if you start swapping about you will eventually have a jigg saw puzzle of chips.

What test equipment do you have?

I think also you wanted to say that sound chip was a ym2151 and not a ym121.

I am sorry but I know I kind of sould like a dick here but these are things that should be done first.

Check voltages, connections, roms and probe with logic probe at the very min.
 
Here are some pictures to show what's going on.
 

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It sounds to me like you are just swaping chips and not doing much of any tech stuff :(

Have you verified any of the voltages and mad certain the power supply is good?

Get one set of working roms and use ONLY them, if you start swapping about you will eventually have a jigg saw puzzle of chips.

What test equipment do you have?

I think also you wanted to say that sound chip was a ym2151 and not a ym121.

I am sorry but I know I kind of sould like a dick here but these are things that should be done first.

Check voltages, connections, roms and probe with logic probe at the very min.

I've verified I have a set of good ROMs using the my ROM burner. I originally had 1 bad eprom but swapped it out with a good one from another Gauntlet 2 board I have, which is dead.

Yes, my power supply voltages are good. I actually had to install a new switcher as the original one was shot.

I don't have much in the way of test equipment for use in working on boards other than a DMM and logic probe.

In regards to swapping chips, I was swapping some of the custom chips and RAMs one at a time from the other board I have to see if it made a difference to help me narrow down what the problem was.

According to the manual the RAM at 10L and 10M could have been causing the problems I am having but I removed those chips and installed a socket and new RAM but no change.

Just wondering if anyone has seen this issue before and could help point me in the right direction. Thanks.
 
I've verified I have a set of good ROMs using the my ROM burner. I originally had 1 bad eprom but swapped it out with a good one from another Gauntlet 2 board I have, which is dead.

Yes, my power supply voltages are good. I actually had to install a new switcher as the original one was shot.

I don't have much in the way of test equipment for use in working on boards other than a DMM and logic probe.

In regards to swapping chips, I was swapping some of the custom chips and RAMs one at a time from the other board I have to see if it made a difference to help me narrow down what the problem was.

According to the manual the RAM at 10L and 10M could have been causing the problems I am having but I removed those chips and installed a socket and new RAM but no change.

Just wondering if anyone has seen this issue before and could help point me in the right direction. Thanks.

Ok good and no problem. I have not seen that kind of problem on these boards before and can't be much more help but I can do a bit of searching to see if this has been documented somewhere else. I have seen some filp flops do strange things but not like that. The first pic is the one that is bothering me though.
 
Here are some pictures to show what's going on.

Those are helpful. On the "playfield test", try pressing the fire button, to change from bank 0 to 1, 2 & 3. All blank screens?

Gauntlet's graphics are made up of several different "layers". Alphanumerics, playfield (PF) & motion objects (MO). The alphanumerics look OK, but I don't see any evidence of PF or MO. This appears to be a logic issue somewhere fairly deep in the video hardware. It could be an issue with the PF & MO RAM, or their pallette, or video mixing, or maybe some kind of priority/transparency thing. But it appears to be on the video output side of the hardware, as the self-test is able to write and sucessfully re-read all the video RAM (presumably, or you should get errors in self-test).

Probably not an easy issue to track down. You pretty handy with schematics and your logic probe?
 
Those are helpful. On the "playfield test", try pressing the fire button, to change from bank 0 to 1, 2 & 3. All blank screens?

Yes, all are blank.

Gauntlet's graphics are made up of several different "layers". Alphanumerics, playfield (PF) & motion objects (MO). The alphanumerics look OK, but I don't see any evidence of PF or MO. This appears to be a logic issue somewhere fairly deep in the video hardware. It could be an issue with the PF & MO RAM, or their pallette, or video mixing, or maybe some kind of priority/transparency thing. But it appears to be on the video output side of the hardware, as the self-test is able to write and sucessfully re-read all the video RAM (presumably, or you should get errors in self-test).

Probably not an easy issue to track down. You pretty handy with schematics and your logic probe?

I am decent at reading schematics but I've had very little experience in using my logic probe.
 
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