I know there is a lot of info on Data East coils, diodes and transistors. I have read everything I can get my hands on and would like suggestions. On a good note I did get my VUK coil working properly using these forums and guides.

My ball launch coil had a push button wired into it by the previous owner. Obviously a wrong repair technique. I replaced Q4 which tested bad and replaced the diode on the coil. The upstream transistors on the MPU tested good. The switch on the gun is still hooked up and seems to work as I can use it in the game to shoot the bad guys during video mode.

Long story short I am still frying Q4. I wired the push button back in for the time being. I have tested Q27, Q19 and R70 on the MPU and they seem to test just like the transistors/resistors next to them on the board. around .45 on the transistor test (both legs). I have two more TIP 36C transistors here so I can replace Q4 again but until I find the culprit it is useless.

Any suggestions? I posted this under my restoration thread but no one responded today so I figure it is buried too deep for anyone to see.

Thanks,
Lane

I double checked. The coil diode/power wire is correct. Large Violet/Yellow wire on banded side of diode. I wonder if the push button that was installed to bypass the gun trigger is causing Q4 to destroy itself. There is not a diode on the homemade fire button. I kept checking Q4 all along today and it and Q2 were checking fine even after power up. As I worked on the VUK I quit checking Q4. Then when the VUK was repaired I played a couple of games using the homemade fire button. It was then I started on the task of troubleshooting the ball launch coil and realized that Q4 had blown again. So it probably happened while I was playing.

The mystery remains as to why is the launch coil energized whenever the game is powered up. It seems it should only be energized when the MPU is ready to fire a ball and the trigger is pulled.

Your right. I have not tried changing the coil out. Good idea.

I made progress with troubleshooting this morning. I installed the boards and tested some more after installing a new Q4 on the PPB. If I power up with CN12 disconnected from the MPU then I don't have voltage at the ball launch coil leads (they are disconnected from coil to protect Q4). If I power up the game with CN12 connected to the MPU then I have 70 Volts on the leads for the ball launch coil.

So, the MPU is telling the PPB to fire the ball launch coil. I figure Q4 is sitting there getting hotter and hotter until it burns up (even with the coil disconnected). That leads me to suspect Q27 (TIP 122) or Q19 (2N4401) on the MPU. However, on the board they test identical to the other dozen components just like them in the same area of the board. Do you think the IC chip could be bad (SN74LSO8N)? If you notice in the picture below that chip has been replaced before (there is not a socket for the chip).

EDIT!!! This chip is a different part number than the other three chips. The hard soldered chips are DM7408N and the manual shows that all four should be the same part number (7408). Obviously someone replaced the second chip, added a socket (whew) and substituted a different part number. Maybe they are interchangeable and maybe this is my problem.

What do you think?
CN12 (resized).jpg

trueno92 and Tuukka Notice my edit to the above post. The chip controlling those solenoids was replaced with a different part number rather than the prescribed 7408 chip. I have new fuses and they are all the proper rating for the application.

From what I can see in my manual the chip and the three next to it should be 7408 chips. The one in the bad circuit is a 74LS08N which from what I can tell is not interchangeable. It seems that the hard to find 7408N is interchangeable with 74F08. I have ordered several new 7408N's from China via Ebay and one vintage 74F08 from Michigan via Ebay.

If this chip is removed from the board and everything else hooked up would this be a good test to see if the transistors Q27 and Q19 are shorted. I am thinking if the chip is removed and the transistors are not shorted I should not have 74 volts on the coil leads. But if the chip is removed and I still have the 74 volts then one or both of the MPU transistors is shorted. Does this sound reasonable?

Since I have the coil disconnected F5 isn't getting a draw on it. It is the + side of the equation. My issue is on the negative side of the circuit. The transistors on the PPB and MPU complete the ground circuit so F5 isn't being taxed with my coil unhooked.

7408N is a gate ic and the one that was used 74LS08N is a quad, two input ic. If I am reading the type data sheets correctly these two ic's are not the same animal.

Great info -- for every hobby repairman like me.

While mowing the grass just now I decided I'm going to replace this chip, the pre pre driver transistor (Q19) and the pre driver transistor (Q27). Then when the board goes back on there should be no reason it will not work properly. Q27 is going to be tough to get to as it is buried in a line of transistors. I ordered some solder wick and a suction gun to aid in desoldering from the back side without access to cut the legs off. It will take a week to receive all the parts and tools so I'm working on Fan-Tas-Tic and Eight Ball this week. They are both playing great. I need to install rubbers on Fan-Tas-Tic and get the coin apparatus working on Eight Ball. Our first three pins came in a package deal with none of them working. $2600. I'm very pleased with pin ownership.

Ughh. I hope I don't have to resort to that. My PPB is getting pretty sketchy at Q4. The back half of the trace pad is gone on all three terminals. Still bridging to main part of trace but I hope Q4 doesn't need replacing again. If I do have to replace it again I might leave the old legs attached and solder to them.