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rcboosted

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I picked up 2 Tetris 16B boards, one with rom one without, both have encrypted CPU. On the complete kit, everything works. I swapped the Tetris ROM board over to the other 16B, all I get is a white screen with some pink or magenta vertical lines here and there. I awaited a bit to see if there would be sound, but I didn't hear anything, so it doesn't sound like a dead cpu battery issue. Japanese auction seller said it was working before shipping, but that was 2 months ago. Since I don't know what else to look for, I swapped the CPU with an Aliexpress 68k CPU, and I get a completely black screen instead. What should I check to see what broke during shipping? Any pointers for resources I can read through?
 

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Game code is driven by the 68000, sound code is driven by the Z80. Some S16 boards use an encrypted 68000, some use an encrypted Z80. If it’s the 68000 CPU that’s encrypted then the game won’t boot if the battery has died.

In that situation, in addition to swapping in a standard 68000 CPU, you’ll also have to program EPROMs with decrypted game code and install them in the ROM board.

If your other board also has an encrypted 68000 CPU, you can try swapping it over and see if the board boots.
 
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rcboosted

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Game code is driven by the 68000, sound code is driven by the Z80. Some S16 boards use an encrypted 68000, some use an encrypted Z80. If it’s the 68000 CPU that’s encrypted then the game won’t boot if the battery has died.

In that situation, in addition to swapping in a standard 68000 CPU, you’ll also have to program EPROMs with decrypted game code and install them in the ROM board.

If your other board also has an encrypted 68000 CPU, you can try swapping it over and see if the board boots.
Thanks for chiming in. The 2 boards look identical, encrypted CPU, unencrypted Z80. I totally forgot I need unencrypted ROM for unencrypted CPU too. So I'll try the other board's CPU. From what I've read, when the cpu battery dies, people would get sound and no video, I feel like the white screen is something else. But this is my first 16B board, so I got not experience I'll try everything. :)
 

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So I got a chance to retest. With known good ROM board and known good encrypted cpu from the good board, on the bad board. On first boot, I saw 1 short white horizontal line 1 pixel tall and some dots on the very bottom left of the screen. Then the Tetris title screen showed up. Except that it's offset to the right, and 1/4 of the right side is wrapped around to the left side. It almost looks like a very badly adjusted CRT, but I'm testing using an OSSC. Then the title screen went away and screen went dark, no sound. I turned it off then on again, the title screen would never appear again.

The short horizontal line and some dots would always show up at the bottom left. And it looks almost like a CRT with vertical collapse and all the text and graphics are squished into 1 line. If I coin up, it goes away, and displays some random blue dots briefly. Again, looks as if it's a CRT with vertical collapse, and those dots move a bit like video is condensed into that 1 line. Coin up and hitting start appears to do something, since the horizontal line goes away and turns to the blue dot. Another thing I noticed was it draws quite a bit of power. I had to adjust my power supply (RT-85A) up quite a bit to get to 5V. I've only needed to go this high on a 4 slot MVS fully populated.

There are no obvious damage to the PCB that I can tell, no cut traces or broken components. Using a thermal cam, the Z80 is around 90F, and the YAMAHA 2151 chip close to it slightly warmer at 95F. Nothing else is higher temp than those other than the amp at the corner. Anyone know what to check next?
 

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It sounds like it might have a sync issue or a problem with the video ground. Does the sync light on your OSSC stay green when it’s not displaying properly? Does your SuperGun have an adjustment for sync?

You can check the video ground with a multimeter. Set the meter to continuity test, and check for continuity between Pin 14 on the top (parts) side of the JAMMA connector on the SuperGun and the right leg of capacitor C6-that’s the video ground.
 

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rcboosted

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It sounds like it might have a sync issue or a problem with the video ground. Does the sync light on your OSSC stay green when it’s not displaying properly? Does your SuperGun have an adjustment for sync?

You can check the video ground with a multimeter. Set the meter to continuity test, and check for continuity between Pin 14 on the top (parts) side of the JAMMA connector on the SuperGun and the right leg of capacitor C6-that’s the video ground.

Thanks again for chiming in. The green LED near the power jack stays green, with the red led lighting up for less than 1 sec after power up. I also tried a HAS supergun with the same result. The HAS as far as I know doesn't have sync adjustment, but it can regenerate, which I tried. It does the same thing. I also did a push test and pushed on every chip while powered on, none made any difference.

Testing for continuity, Pin 14 on the jamma edge connects to the + of C6, while Pin 15 connects to - of C6. Further up, the + of C6 connect to pin 28 of the System 16B to JAMMA adapter. and - goes to pin 22.
 

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Well, it doesn't look like it'll be an easy problem to sort out. I get the impression that the game code is running since it flashed the screen when you coined up, but the graphics aren't drawing. Is there any sound?

Anyway here's a few suggestions on things to try:

1) Remove the ROM board and double-check that there aren't any bent or damaged pins on the four connectors.

2) If you gently flex or twist the board, does the display change substantially? If so, you may have an SMD chip or two that needs reflowing.

3) If you have access to a CRT, try connecting the board through that instead. CRTs are more flexible than upscalers on what they'll display with an out-of-the-ordinary vertical sync signal, so if you do have a Vsync issue with the board then you might be able to see more of the playfield than you are able to with the OSSC.

4) If you have access to an oscilloscope, probe Pin 14 on the JAMMA edge and make sure you're getting Vsync signals.

5) If you have access to a logic probe, probe the Address, Data and Control lines on the graphics ROMs and make sure that they're being accessed by the graphics custom. I made a tutorial video on probing a graphics ROM with a logic probe that you might find useful if you're not familiar with the procedure.
View: https://www.youtube.com/watch?v=2PAtTIAijeA&t=517s


With Tetris, the ROMs at B9, B10, and B11 are background tiles, and the OBJ ROMs are sprites. If the lines for those ROMs don't show activity then you may have a problem with the graphics custom or some of the other hardware in between.

Schematics are available for that board if you want to check continuity on any of the lines:
https://www.jammarcade.net/files/Schematics/Arcade/system16b_schematics.pdf
 

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Well, it doesn't look like it'll be an easy problem to sort out. I get the impression that the game code is running since it flashed the screen when you coined up, but the graphics aren't drawing. Is there any sound?

Anyway here's a few suggestions on things to try:

1) Remove the ROM board and double-check that there aren't any bent or damaged pins on the four connectors.

2) If you gently flex or twist the board, does the display change substantially? If so, you may have an SMD chip or two that needs reflowing.

3) If you have access to a CRT, try connecting the board through that instead. CRTs are more flexible than upscalers on what they'll display with an out-of-the-ordinary vertical sync signal, so if you do have a Vsync issue with the board then you might be able to see more of the playfield than you are able to with the OSSC.

4) If you have access to an oscilloscope, probe Pin 14 on the JAMMA edge and make sure you're getting Vsync signals.

5) If you have access to a logic probe, probe the Address, Data and Control lines on the graphics ROMs and make sure that they're being accessed by the graphics custom. I made a tutorial video on probing a graphics ROM with a logic probe that you might find useful if you're not familiar with the procedure.
View: https://www.youtube.com/watch?v=2PAtTIAijeA&t=517s


With Tetris, the ROMs at B9, B10, and B11 are background tiles, and the OBJ ROMs are sprites. If the lines for those ROMs don't show activity then you may have a problem with the graphics custom or some of the other hardware in between.

Schematics are available for that board if you want to check continuity on any of the lines:
https://www.jammarcade.net/files/Schematics/Arcade/system16b_schematics.pdf

Thank you for all these steps to check. I will check each one of them. I do have a scope and probe, so I can check each of those as directed. As for CRT, I do have one, but I have to go through a RGB -> composite board since it doesn't have RGB input (yet). Hopefully that doesn't add/subtract anything to the signal, it's a straight converter, not buffered, so I think it's ok.

I get the impression the code is running as well. There's no sound other than the buzz. It does get interrupted etc when I coin up etc, so something's running.
 

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Ok I ran a bunch of tests:

1) Checked the pins, they look ok, straight, nothing is bent

2) Flexing didn't seem to do anything that I can tell.

3) CRT produced the same result, as my previous video shows. Just those lines and dots.

4) So pin 14 on JAMMA is the video ground, I think I need to check is if Video Sync is coming out? I tested that between pin P (Video sync) and Pin 14. I got a good signal with scope I think, I attached the pic. I also traced Pin P back to the System 16B PCB and tested from a test point there, same signal. Attached is where I tested from.

5) My Tetris ROM board seems to be different than what you're describing. Maybe because this is Japanese version? I'll attach it here as well and here are my results: The ROMs in A5 and A7 have activity on address and output pins. The ones in B1 and B5, which are OBJ ROMs, they show activity on address line, but nothing, no beeps high or low on the output lines. From your data sheet in the video, output O1, O2 etc all the way to O7. CE is low. For the ones in A14, 15, 16, address lines have activity, and output are constant LOW. I didn't look up the pin out for the ROM at A10, so I didn't test throughly, but I hear activity on various pins.

Also swapped the bad CPU to the good PCB, it showed all white screen just like when it was on the bad PCB, so probably a bad CPU.
 

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ShootTheCore

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First off, everything looks good with your vertical sync signal from your scope - 15khz is the correct frequency.

It turns out that there are three different Tetris B Boards, so my earlier directions on which ROMs to probe were incorrect - sorry about that. Thank you for the picture of your B board.

Let's dig into probing your ROMs a bit further. First off, the pinout diagram in my video was for the 27C301 EPROMs that Fire Shark uses. I don't have a Tetris board, but it'll use either 27C256 or 27C512 for the object and sprite data EPROMs. Check the fine print on the EPROMs for the chip model and then Google the appropriate data sheet. Since the ROMs don't use the entire socket in your photo, I'm guessing that they're 27C256.

Anyway, if the output lines still look dead after re-probing the OBJ ROMs, check the CE (Chip Enable) and OE (Output Enable) lines. Both CE and OE have to be pulled low simultaneously to trigger an output. From the schematics, Output Enable (Pin 22) should be tied to ground for all the ROMs and thus should read low all the time. Chip Enable (Pin 20) comes in from the bottom board through the edge connectors, so if it doesn't show any pulses then check for breaks in the lines. Page 9 of the schematics has the pinout for the edge connectors of the ROM board while Page 10 shows the lines for each EPROM.

The Chip Enable lines for the OBJ ROMs are generated on the bottom board by the 315-5197 custom chip, so if the CE lines are dead and the lines test for continuity then that custom chip may have failed.
 
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First off, everything looks good with your vertical sync signal from your scope - 15khz is the correct frequency.

It turns out that there are three different Tetris B Boards, so my earlier directions on which ROMs to probe were incorrect - sorry about that. Thank you for the picture of your B board.

Let's dig into probing your ROMs a bit further. First off, the pinout diagram in my video was for the 27C301 EPROMs that Fire Shark uses. I don't have a Tetris board, but it'll use either 27C256 or 27C512 for the object and sprite data EPROMs. Check the fine print on the EPROMs for the chip model and then Google the appropriate data sheet. Since the ROMs don't use the entire socket in your photo, I'm guessing that they're 27C256.

Anyway, if the output lines still look dead after re-probing the OBJ ROMs, check the CE (Chip Enable) and OE (Output Enable) lines. Both CE and OE have to be pulled low simultaneously to trigger an output. From the schematics, Output Enable (Pin 22) should be tied to ground for all the ROMs and thus should read low all the time. Chip Enable (Pin 20) comes in from the bottom board through the edge connectors, so if it doesn't show any pulses then check for breaks in the lines. Page 9 of the schematics has the pinout for the edge connectors of the ROM board while Page 10 shows the lines for each EPROM.

The Chip Enable lines for the ROMs are generated on the bottom board by the 315-5197 custom chip, so if the CE lines are dead and the lines test for continuity then that custom chip may have failed.
Thank you for going over my results! I looked at the EPROMs I have at A5 and A6, they are 27c1000, and the pinout matches your example, at least on the CE and output pins, so my results for that should be good. The other masked ROMs have stickers on them, I didn't want to remove them, so I couldn't see what they are. But I tested them as if they were 1000s. Can you tell what they are from this pic? Probably not, they could be anything. But I'll check out the pinouts for 256 and test it that way at least. Then I'll trace the lines using the schematic.
 

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ShootTheCore

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The two 27C1000 chips are main CPU code. If they’re getting signals on the output lines then the main CPU should be running.

I’m pretty confident that your OBJ ROMs are 27C256-the board is designed to use either 27C256 or 27C512 for them and there’s not enough pins on your chips for 27C512.
 

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The two 27C1000 chips are main CPU code. If they’re getting signals on the output lines then the main CPU should be running.

I’m pretty confident that your OBJ ROMs are 27C256-the board is designed to use either 27C256 or 27C512 for them and there’s not enough pins on your chips for 27C512.

Alright, I will use the 256 pinout to test them.
 

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The two 27C1000 chips are main CPU code. If they’re getting signals on the output lines then the main CPU should be running.

I’m pretty confident that your OBJ ROMs are 27C256-the board is designed to use either 27C256 or 27C512 for them and there’s not enough pins on your chips for 27C512.
Got some time to test the board again. So for the OBJ ROMs at B1 and B5, when I probe OE on pin 22, which is supposed to be tied to ground, I do get a low on the probe. But I could not get a continuity from it to ground on the edge connector or CN2's A21-A23 which are supposed to be ground. I do get a continuity to CN2's A9, which is supposed to be tied to pin 20 for CE!
Probing Pin 20 on the OBJ ROM, which is supposed to go to CN2 connector's A9, but I get nothing. Nothing to ground at either CN2's A21-A23 or ground at edge connector.

If I power the probe up first, and I probe pin20 for CE, I get a low. Then I power the board up, I'll get that low for about 15 seconds, then it'll stop. These are some pretty confusing results. If I do the same for pin 22, I get low the whole time. The testing was done via the CN connector's soldering pins next to the ROM sockets. I have to assume the B board is good, as I was able to play this game on the other 16B board. Tried tracing OE to the 315-5197 custom chip, I found the pin, but that pin doesn't have continuity to ground. But then I couldn't get continuity to ground for CN2's A21-A23 either, which are supposed to be GND according to the schematic. Maybe I'm reading all these wrong?

The other 256 ROMs at A14, A15, A16 are showing low on pin 20 and 22.
 
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Hmm ... I agree that your B board should be good since it works with another A board. I just don't believe this A board is communicating with the B board properly.

Are the OBJ ROMs showing activity on the address and data lines?
 

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only the address lines have activity, outputs are dead. Here's a video of the ROM at B1, the Rom at B3 does the same. I marked with masking tape and red sharpie where the CE and OE pins are. I think I need to figure out why OE pin isn't getting anything reading right? But when I traced the line last week, I couldn't even find a ground on the CN2 connector that the schematic showed. I think I'm doing something way off.

View: https://www.youtube.com/watch?v=x6fHvrimLnc
 

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Thanks for the video - that's very helpful. Here's my observations as I watch the video:

The Chip Enable line at Pin 20 and the Output Enable line at Pin 22 are both floating (showing no activity) so the chip won't output anything until those pins are made active.

Also, it looks like Pin 28 in the upper-right corner isn't reading High - that's the 5V Power Supply for the chip, so outputs won't enable until power gets to it as well.

The Ground at Pin 14 is reading Low properly so the chip is grounded properly at least.


So we know that the B Board is good from cross-testing it with another A Board, and we know that the CPU is running and is trying to read from the chips (since the address lines are showing activity). The problem is with the lines that provide Power, CE and OE functionality.

According to the schematic, the CE signal for that ROM (Pin 20) is labeled as CGB0 and feeds in to the B Board from Pin 9A on Connector 2. It originates from Pin 31 on the 315-5196 custom on the A Board. Test for continuity on that line and make sure its good.

The OE signal for that ROM (Pin 22) should be tied to ground. I'm not sure why you're not getting a ground signal there, but presumably the ground should come from Pin 21A, 21B, 22A, 22B or 23A on Connector 2. Test each of those pins on the A Board connector and make sure they read continuity to ground. For testing, you could try running a small jumper wire temporarily from Pin 14 to Pin 22 in the socket to force the ground signal.

The Power for Pin 28 should come from Pin 23B, 24A, 24B, 25A or 25B on Connector 2. Measure those pins on the A board side and see if they're providing any power. For testing, you could try running a small jumper wire temporarily to Pin 28 in the socket from a 5V source.


I'll be honest - I suspect that the 315-5196 custom chip on your A Board has failed or is malfunctioning. Inspect the pins on it carefully under magnification - if you're lucky, a few pins may have lifted off of pads and it may just need to be resoldered. Otherwise, I think this A Board will be more trouble to fix than it's worth - a replacement isn't expensive or hard to find.
 

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Thanks for the video - that's very helpful. Here's my observations as I watch the video:

The Chip Enable line at Pin 20 and the Output Enable line at Pin 22 are both floating (showing no activity) so the chip won't output anything until those pins are made active.

Also, it looks like Pin 28 in the upper-right corner isn't reading High - that's the 5V Power Supply for the chip, so outputs won't enable until power gets to it as well.

The Ground at Pin 14 is reading Low properly so the chip is grounded properly at least.


So we know that the B Board is good from cross-testing it with another A Board, and we know that the CPU is running and is trying to read from the chips (since the address lines are showing activity). The problem is with the lines that provide Power, CE and OE functionality.

According to the schematic, the CE signal for that ROM (Pin 20) is labeled as CGB0 and feeds in to the B Board from Pin 9A on Connector 2. It originates from Pin 31 on the 315-5196 custom on the A Board. Test for continuity on that line and make sure its good.

The OE signal for that ROM (Pin 22) should be tied to ground. I'm not sure why you're not getting a ground signal there, but presumably the ground should come from Pin 21A, 21B, 22A, 22B or 23A on Connector 2. Test each of those pins on the A Board connector and make sure they read continuity to ground. For testing, you could try running a small jumper wire temporarily from Pin 14 to Pin 22 in the socket to force the ground signal.

The Power for Pin 28 should come from Pin 23B, 24A, 24B, 25A or 25B on Connector 2. Measure those pins on the A board side and see if they're providing any power. For testing, you could try running a small jumper wire temporarily to Pin 28 in the socket from a 5V source.


I'll be honest - I suspect that the 315-5196 custom chip on your A Board has failed or is malfunctioning. Inspect the pins on it carefully under magnification - if you're lucky, a few pins may have lifted off of pads and it may just need to be resoldered. Otherwise, I think this A Board will be more trouble to fix than it's worth - a replacement isn't expensive or hard to find.
These are lots of good points to test! I will do these more systematically this weekend. Hopefully I can find something. I want to believe that the seller was honest that it was a good board when stored. But I'll have to accept defeat if I can't find anything. The custom chip looks ok on the underside, but I'll take a jeweler's loupe and check extra carefully. Thank you for your continued support on this! I really appreciate it.
 

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Thanks for the video - that's very helpful. Here's my observations as I watch the video:

The Chip Enable line at Pin 20 and the Output Enable line at Pin 22 are both floating (showing no activity) so the chip won't output anything until those pins are made active.

Also, it looks like Pin 28 in the upper-right corner isn't reading High - that's the 5V Power Supply for the chip, so outputs won't enable until power gets to it as well.
The ever confusing results. Pin 28 indeed had no reading from the probe. However, I had the probe powered by the 12V rail. If I power it with the 5V rail, it shows high. With a MM, I do see 5V going there. So I reran the probe test on the EPROM, I got high on VCC and high on OE and CE.

View: https://www.youtube.com/watch?v=aXrsZC-9AHs


The Ground at Pin 14 is reading Low properly so the chip is grounded properly at least.


So we know that the B Board is good from cross-testing it with another A Board, and we know that the CPU is running and is trying to read from the chips (since the address lines are showing activity). The problem is with the lines that provide Power, CE and OE functionality.

According to the schematic, the CE signal for that ROM (Pin 20) is labeled as CGB0 and feeds in to the B Board from Pin 9A on Connector 2. It originates from Pin 31 on the 315-5196 custom on the A Board. Test for continuity on that line and make sure its good.
CE pin has no continuity to CN2 pin9. I traced pin9 from top of B board all the way to the CPU, I found continuity on one of the pin. I can't find a pinout for the cpu to confirm that is pin 31. But I attached a picture here. It has a not so obvious red sharpie dot under it. So I think the 5196 to B board CN2 pin9 connectivity is there. I can't find the trace that goes from CN2 pin9 to the EPROM. The trace goes under a LS138 chip on the B board, but it's obscured by the chip itself. I do get continuity to some legs of the LS138, as well as the row of jumpers enroute to it. Do I need to set any of these jumpers labeled S3, S4, S17, S18 etc etc? I also tried tying CE to pin9 with a jumper, while OE is grounded, no video.
IMG_20210827_200550173.jpg

The OE signal for that ROM (Pin 22) should be tied to ground. I'm not sure why you're not getting a ground signal there, but presumably the ground should come from Pin 21A, 21B, 22A, 22B or 23A on Connector 2. Test each of those pins on the A Board connector and make sure they read continuity to ground. For testing, you could try running a small jumper wire temporarily from Pin 14 to Pin 22 in the socket to force the ground signal.
The OE pin 22 has no continuity to GND, and as seen in the video, it showed high on the probe. If I tied it to GND (pin14) I still get no picture. The CN2 pins 21A to 23A themselves are tied to GND though. Funny enough, OE pin 22 has continuity to CN2 Pin 9!!!
The Power for Pin 28 should come from Pin 23B, 24A, 24B, 25A or 25B on Connector 2. Measure those pins on the A board side and see if they're providing any power. For testing, you could try running a small jumper wire temporarily to Pin 28 in the socket from a 5V source.

I was able to confirm power is going to EPROM pin 28 now. I also observed that on power up, I get a high and activity on the output pins on the EPROM, but 14 seconds later they go away.
I'll be honest - I suspect that the 315-5196 custom chip on your A Board has failed or is malfunctioning. Inspect the pins on it carefully under magnification - if you're lucky, a few pins may have lifted off of pads and it may just need to be resoldered. Otherwise, I think this A Board will be more trouble to fix than it's worth - a replacement isn't expensive or hard to find.
The custom chip seems to be through hole, so probably no pad to lift? But I will try reflowing all the pins. *edit* I reflowed the 5196 chip, no change.
 
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