I've been working on this issue for a while now and have come up short. The DMD on my NBA fastbreak does not display anything when the game is booted up. Everything else works correctly and the game is able to be played with the exception of nothing is displayed on the DMD. Here is what I have already done:

1) Rebuild the HV section of the board - this had no effect on my game, but when installed in a friends NBA fastbreak, it worked correctly.
2) installed new ribbon cables - again, had no effect on the functionality of the display
3) tested the DMD from my NBA Fastbreak in my Johnny Mnemonic - The DMD worked in Johnny
4) tested the DMD from my Johnny in my NBA Fastbreak - still nothing
5) tested voltages going to the DMD reading as follows
Pin 1: -118.3
Pin 2: -106.7 (-95.9 with DMD disconnected)
Pin 6: 5.1
Pin 7: 11.3
Pin 8: 67.3

If anyone has suggestions to what I should be trying next, please let me know. This problem has me pretty stumped. Also, if any additional photos would be helpful, I can provide them.

Thanks!
LRN

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I can try to convince him to let me borrow the board. I did try my board after rebuilding the HV and it worked fine in his game so I believe that board is not the issue. Is there anything else I would learn by swapping his board into my game?

I will bring my CPU when I go to grab his board and try swapping those around as well.

Thanks!

I have tried the DMD in another game and it works fine. Trying a different DMD in fastbreak did not work tho.

As for the CPU, are there any specific components I should be inspecting that may be causing the issue of the DMD turning on when the game is booted? Based on what I’ve tested and done already, I’m guessing there is an issue in my CPU (will confirm with a donor) but I am not sure which components would be related to the DMD not booting.

Not sure how much this helps but I did notice that some of the pixels in a line across the display flash when the switch is turned off (normal to other DMD games of the era). I’m guessing this means that it’s getting sufficient power and maybe just not getting any display signals from the CPU?

Ok. Thanks for the info. I will check the GI to see if it is functioning. Its bright in my shop so I may have not noticed if it was out. As for outgassing, I have tried other DMDs in this game and it did not make a difference. I can get a picture later when I am near the game.

Was at my friends place today and installed my CPU board into his game and the problem appeared. So I think I got it narrowed down to the CPU being the problem now... here is a picture of the battery damage. Getting this thing cleaned up and repaired is definitely the next step.

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Forgot to mention this: The GI was working in my game when I checked. The GI was also working in my friends game when my (pictured above) CPU was installed. Is there a possible scenario where failure in this area of the board would only cause problems to the blanking signal to the DMD and not the GI?

I removed all the components from the affected area and cleaned up the damage. I then installed new components and put the board back into the game. Now when I turn the game on it boots but I have no display and also have no GI (except for the slinghshot GI). Also noticed that when I start a game, the flippers are not functioning and there are no coils working. All the voltage LEDs on the power driver board are on. And the LEDs on the CPU seem right. Bottom solid and middle blinking quickly.

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The above image was a jumper for pin 13 of U5 to R94. That part I believe is ok. Thanks for advice regarding sockets. Will definitely do that next time!

Tracing continuity this morning I think I may have found part of my problem. The connection from pin 1 of U5 to R120 outlined in red is not made. I’m guessing I have a blow out trace (runs under U5 where the majority of the damage from the battery was).

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Update on the status of this repair:

I removed U5 again and the surrounding components. Sanded a bit more to expose the broken trace between U5 pin 1 and R120. It was indeed broken between the IC pins where it ran between pins 13 and 14 of U5 (this was also the area where the corrosion from battery damage was most apparent). Fixed this with a small jumper and reinstalled all new components (socketing U5 this time ).

This did fix the issue with the display and the DMD is now working as it should. However, I still have the new issue of no GI or Solenoids. The only other component that I removed and replaced while doing the work on the CPU was U27. Looking at the schematic, I cannot make sense of this as it doesn't seem to match the board traces. Best I can tell from the schematic, pins 6, 9 and 13 should be connected. However, on the board, pins 4,5 and 7 are clearly connected by one of the main large traces going through this area (see picture below)

I'm going to move forward with replacing it either way since when I look closer, I think i see some bridges. I will socket it this time and while I have the chip removed, I will snap a couple pictures to clearly show the traces since I can't seem to make sense of the schematic. Hoping this will solve the issue but if anyone has any ideas here, please let me know. Thanks!

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I do not have a logic probe but could definitely pick one up if it would help. Testing using voltage I could do tonight but don’t know what I’m looking for.

I removed and cleaned up and replace U27 (again with a socket) and tested continuity. All seemed good and continuity followed the traces based on the photos I took (still not sure if I’m just reading the schematic wrong or if something isn’t right on the schematic).

I still have the same problem after I reinstalled the board. DMD works now (that was the original problem) and so does sound and switches. However, all of the controlled lighting including the GI (minus the two always on strings) are not working and the none of the selenoids are working (neither in game or in test mode). Fuses all check good and I reseated all ribbon cables. It’s possible I have something hooked up wrong since I had both the cpu, DMD driver, and DMD out at once but I’ve looked everything over a few times now and don’t see anything.

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I just tried with the original short ribbon cable and this one (new). I originally replaced all of them except for the thin cable going to the DMD (they didnt have that cable in stock) in attempt to get the DMD working.

OK will do. Should I just probe U5 or U27 as well? Both were replaced

I did try that as well with no affect :/

OK... So I was measuring voltages on all the pins on the two ICs that were replaced. Finished U5 and figured i may as well record U27 as well. While doing this I accidentally shorted (with my multimeter probe) pins 3 and 4 of U27 causing all the GI to flash on. Did it again and realized that the GI and inserts were all working while i had these pins shorted. Held the probe in place and started a game and found solenoids were as well.. Think i accidentally stumbled upon the problem.

My only issue now according to the schematic, I don't think these two pins should be connected. I still feel like I'm either missing something when trying to interpret the schematic or something is incorrect. The attached picture (with this area of the board held to a bring light) is the photo I took to check continuity against. The traces on the schematic don't seem to match. I'm not super familiar with the operation of these chips so I could definitely be missing something though :S

My question now is: Am I safe to jump pins 3 and 4 of U27? Does your game have continuity there? or would this just be a bandaid to another issue?

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Awesome. Thanks Zaza. That’s exactly the info I was looking for (didn’t want to just jump some pins because it seemed to work when that jumper didn’t match my schematic and also didn’t seem to match the board traces) as I was scratching my head trying to figure out the difference between my game and schematic. Looking at the old chip I threw out that had battery damage, it does look like it was a 74LS08. Comparing the drawings, it does look like the TOTAN board since it does not have R130. Here is a picture of the markings.

I have the 74LS08 on order and will post an update once it arrives

Any idea where I could find the schematic for this CPU? It would be helpful to have if future repairs are needed

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Here is the comparison between the drawings in the NBA fastbreak manual and the TOTAN manual and what my board actually looks like.

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Awesome. Thank you!

Just wanted to make one last post to update on the status.

I went back in and examined everything for continuity after the 74LS08 chips arrived using the correct schematic above and everything checked out. Installed the new chip and everything is working as it should now.

Thanks for all the help diagnosing this issue. Much appreciated!

I have recently moved this game to a new location and am now having issues again but not with the DMD. Here is what I am seeing.

When the game is started up, I get the error message saying “OPTO TROUGH BAD CHECK CONNECTORS, WIRES, AND 12V SUPPLY". If the game is tilted or the coin door is opened and closed, it will start kicking balls into the shooter lane and firing them into the playfield. It does this with about 10 balls and then seems to be functioning fine. However if the coin door is opened again it starts firing balls again until 10 have been launched and returns to a normal state.

Then, once the normal state is reached, if a game is started it works fine until both flippers are pressed at the same time. When this happens the game immediately resets and displays the error message again.

I have since replaced the cap and 4 diodes for the 12V unreg and it has had no effect.

Wondering what I should look into next...

Thanks!