(Topic ID: 298249)

Lethal Weapon 3 Ball Launcher destroying Q4 Transistor

By bushav

1 year ago


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  • 26 posts
  • 8 Pinsiders participating
  • Latest reply 1 year ago by trueno92
  • Topic is favorited by 1 Pinsider

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CN12 (resized).jpg
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#1 1 year ago

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

#2 1 year ago

Make sure you didn't wire it backwards. If there's a diode on the coil, it would create a direct short to ground.

Rob

#3 1 year ago
Quoted from Rob_G:

Make sure you didn't wire it backwards. If there's a diode on the coil, it would create a direct short to ground.
Rob

Quoted from Rob_G:

Make sure you didn't wire it backwards. If there's a diode on the coil, it would create a direct short to ground.
Rob

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.

#4 1 year ago

He means make sure the diide on the launcher coil isnt wired backwards.

Disable and remove all that extra button junk.

Check gun wiring for diode on the trigger switch.

#5 1 year ago

The coil may be partially shorted because it was locked on and overheated. It could work but draw too much current frying the transistor.

#6 1 year ago

Agreed, worth swapping a diff coil in just to test

#7 1 year ago
Quoted from Tuukka:

The coil may be partially shorted because it was locked on and overheated. It could work but draw too much current frying the transistor.

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

#8 1 year ago

The coil is definitely bad. Seems to be the only thing you haven't ruled out yet. After you remove the coil and disconnect it, perform an ohm test with a multimeter and let us know how it reads. You will want to do this with one leg of the diode disconnected from the coil.

#9 1 year ago

I've seen this before. Replace the upstream transistor even if it tests good.

#10 1 year ago

Coil maybe rubbing on bracket unseen until removed.as crazy as it sounds once ran into a diode that was labeled wrong.

#11 1 year ago

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

#12 1 year ago
Quoted from bushav:

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? If you notice in the picture below that chip has been replaced before (there is not a socket for the chip). If you think it may be the culprit do you guys know the part number off the top of your head? I'll try to find it in the online guides and manual.
What do you think?

CN12 (resized).jpg
#13 1 year ago

Replace the tip i think i ran into this before.

Make sure ur testing that single tip correctly. I think there are more than 1 way to test.

#14 1 year ago

Strange that the solenoid fuse doesnt blow. Make sure it is correct value.

#15 1 year ago
Quoted from Tuukka:

Strange that the solenoid fuse doesnt blow. Make sure it is correct value.

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.

#16 1 year ago

At least its socketed!!

Cross reference the chip, it could be different as the old chip is EOL and the new one does the same thing.

#17 1 year ago
Quoted from Tuukka:

Strange that the solenoid fuse doesnt blow. Make sure it is correct value.

Correct, f5 should be long gone now after the coil goes off and basically save the circuit from power draw... past the ppb - good cstch.

#18 1 year ago
Quoted from trueno92:

At least its socketed!!
Cross reference the chip, it could be different as the old chip is EOL and the new one does the same thing.

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?

#19 1 year ago
Quoted from trueno92:

Correct, f5 should be long gone now after the coil goes off and basically save the circuit from power draw... past the ppb - good cstch.

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.

#20 1 year ago

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.

#21 1 year ago

7408 and 74LS08 are both quad 2-input AND gates. They are made in slightly different technology however. A 7408 can supply higher current and is a bit faster. However in this circuit the LS (low power Schottky) version should be OK. The F (fast) version is more compatible with plain 7408, but are getting scarce.

#22 1 year ago

Probably more info than you need -
All variants of the 7408s are the same logic but there are variations in power consumption, current drive and speed. Suffix of part describes some variations in package such as surface mount versus Dual Inline Package (DIP). "N" and "P" are usually Plastic DIP.

7408s from all manufacturers is obsolete. Odds are that Chinese ebay parts will not be genuine 7408s and will be remarked 74LS08's or 74HCT08's.

74LS08 consumes less power but cannot drive as much current as the 7408. Texas Instruments SN74LS08N is still made.

74F08 (or 74S08) consumes more power, is faster and can drive more current than the 7408. The Texas Instruments SN74F08N is still made and fairly inexpensive. The European manufacturer of 74F08s (NXP - N74F08N) has discontinued these - I bought up a couple cases when they went onto last time buy.

74HCT08 is a very low power version of the original 7408 with very low current drive. Cheapest of the 7408 type gates.

#23 1 year ago
Quoted from G-P-E:

Probably more info than you need -
All variants of the 7408s are the same logic but there are variations in power consumption, current drive and speed. Suffix of part describes some variations in package such as surface mount versus Dual Inline Package (DIP). "N" and "P" are usually Plastic DIP.
7408s from all manufacturers is obsolete. Odds are that Chinese ebay parts will not be genuine 7408s and will be remarked 74LS08's or 74HCT08's.
74LS08 consumes less power but cannot drive as much current as the 7408. Texas Instruments SN74LS08N is still made.
74F08 (or 74S08) consumes more power, is faster and can drive more current than the 7408. The Texas Instruments SN74F08N is still made and fairly inexpensive. The European manufacturer of 74F08s (NXP - N74F08N) has discontinued these - I bought up a couple cases when they went onto last time buy.
74HCT08 is a very low power version of the original 7408 with very low current drive. Cheapest of the 7408 type gates.

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.

#24 1 year ago
Quoted from bushav:

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

You can do this if those traces cant come back - not my work, but i can confirm this worked for pretty much, many many plays.

Screenshot_20210808-205519_Gallery (resized).jpg
#25 1 year ago
Quoted from trueno92:

You can do this if those traces cant come back - not my work, but i can confirm this worked for pretty much, many many plays.[quoted image]

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.

#26 1 year ago
Quoted from bushav:

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.

The pic is the mpu side tip

Ugly, but it was bullet proof

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