(Topic ID: 179133)

Fried Transistor in Road Kings

By BroMike

4 years ago


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  • 16 posts
  • 6 Pinsiders participating
  • Latest reply 2 years ago by JT-Pinball
  • Topic is favorited by 1 Pinsider

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#1 4 years ago

I bought a Road Kings a couple weeks ago (first pinball machine) and had to do a couple easy fixes (resolder right flipper wires and left kickout wires) but it's been playing fine. Last night about an hour into playing, I noticed a burning smell so shut the machine off. After inspecting everything, it looks like the Q79 transistor fried/burnt up. Any ideas on what would cause this? I'm going to buy a new one (or a couple just in case) and replace it but don't want another one doing the same thing if I can prevent it.

Thanks,
Mike

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#2 4 years ago

Q -79 controls the lower pop bumper. You need to check the switch for that coil to make sure it is not stuck closed. You will need to check the coil sleeve to see if its melted. If the coil sleeve is melted then you need to replace the coil. If the coil is not melted then you need to remove the diode on the coil and check the coil for the correct ohms. If the ohms measures good then install a new diode correctly on the coil. Then you need to replace Q-79 and Q-78 on the MPU board. Lastly you need to remove connector 1J18 from the MPU board and measure ohms between the ground braid and pin 9 of 1J-18 on the MPU board. If it reads low ohms then you will need to replace ZR-7 on the MPU board. Then replace 1J-18 connector and remove the fuse for the solenoids on the power supply and power up the machine. Touch the fuse to the holder and watch for a spark, if there is no spark then install the fuse and test the pop bumper.

#3 4 years ago

That's an excellent response GRUMPY.

#4 4 years ago

Awesome, thanks for the detailed response! The switch was stuck closed which seems to be the culprit. The coil didn't look melted and measured 3.6 ohms so I think it's still good. I also measured pin 9 of 1J18 and the ground braid and came out with 4.86k ohms so I think that's still good also? I'm going to buy a new Q79, Q78 and diode for the coil and replace them. Thanks again for the step by step run down!

#5 4 years ago
Quoted from BroMike:

The coil didn't look melted and measured 3.6 ohms so I think it's still good

You should look this up on a coil chart to know for sure. Page 2 in the manual has a 23/ 800 coil for the pops.

http://r.search.yahoo.com/_ylt=A0LEVkB68YRYJTUAYo8nnIlQ;_ylu=X3oDMTEyNzEzOWJ0BGNvbG8DYmYxBHBvcwM0BHZ0aWQDQjI2MThfMQRzZWMDc3I-/RV=2/RE=1485136379/RO=10/RU=https%3a%2f%2fwww.flippers.com%2fcoil-resistance.html/RK=0/RS=0Wpwm8BSB_40adnm8VjQJDb3GVA-

This states your coil should be 4.2 ohms. So it maybe time for a new one.

#6 4 years ago

Ok cool, thanks for the info. I'll go ahead and replace the coil while I'm at it. The other coils (same type) are measuring 3.8-3.9 ohms so they might be on their way out too.

#7 4 years ago

Your DMM may also be reading a bit low. Do you have a different DMM to double check this as I wouldn't want you to spend money for nothing. There are 11 coils of this size in your pin, check some more to get an average for your meter.

#8 4 years ago

I don't have another DMM, but I think mine might be reading low. The 9v battery in it is only measuring 7.5v but I'm not sure if that would cause the low readings. I measured all 11 and they're all about the same: 3.9, 3.8, 3.9, 3.8, 3.9, 3.8, 4, 4.1, 3.7, 3.9, 3.9. The one that previously measured 3.6 is now showing 3.7. I might just replace the diode on it along with Q78 and Q79 and see where that gets me.

#9 4 years ago
Quoted from BroMike:

The 9v battery in it is only measuring 7.5v

Put a new battery and retest.

Quoted from BroMike:I might just replace the diode on it along with Q78 and Q79 and see where that gets me.

I may have not been clear on this but you always replace the diode when a coil has locked on, even when the coil is not melted. The diode has been stressed and may short at any time after. If it shorts after you replace Q-78 and Q-79 then all of your time and work is for nothing as it will wreck Q-78, Q-79 and maybe the coil again. This is not worth it for a .07cent diode.

#10 4 years ago
Quoted from GRUMPY:

Put a new battery and retest.

I may have not been clear on this but you always replace the diode when a coil has locked on, even when the coil is not melted. The diode has been stressed and may short at any time after. If it shorts after you replace Q-78 and Q-79 then all of your time and work is for nothing as it will wreck Q-78, Q-79 and maybe the coil again. This is not worth it for a .07cent diode.

Congrats to you sir for the very specific info to a brand new game owner! You are an example of the best Pinside has to offer!

Quoted from BroMike:

I don't have another DMM, but I think mine might be reading low. The 9v battery in it is only measuring 7.5v but I'm not sure if that would cause the low readings. I measured all 11 and they're all about the same: 3.9, 3.8, 3.9, 3.8, 3.9, 3.8, 4, 4.1, 3.7, 3.9, 3.9. The one that previously measured 3.6 is now showing 3.7. I might just replace the diode on it along with Q78 and Q79 and see where that gets me.

...and to you BroMike. With your "I'll try anything" attitude, you're going to be a pro in no tjme.
Congrats on the new pin ... one of many to come I hope

#11 4 years ago

Thanks again for your help GRUMPY! I replaced the coil diode, Q78 and Q79 (also adjusted the pop bumper switch) and I'm back in action. Quick question, is there anything that references which transistors correspond to which switches? I've looked at manual and schematics and can't figure it out. The schematic looks like it goes to STS6T, although I'm probably looking at it completely wrong.

#12 4 years ago

Good job on the repair!!

Quoted from BroMike:is there anything that references which transistors correspond to which switches?

On a system 11 game there are three types of switches. One group of switches goes thru a matrix and the to the cpu. These switches are not tied to any transistor order. The second group of switches bypasses the matrix and goes straight to the cpu, these are the interlock and 2 of 3 switches on the coin door. If the switch matrix craps out you can still get to testing mode with the door switches. The last group of switches are for the 6 special solenoids, these switches don't go thru the cpu but go directly to the the transistor to make it fire. Williams thought it would make for faster action on the playfield not having the cpu slow down the signals. These six special solenoid switches are labeled in the schematics as to which transistor they control. On page 52 look at the six pair of transistors on the right side of the page, for example take Q78, Q79 the ones you just changed, the emitters of all the transistors are tied to ground. The collector of Q79 goes to the right and is labeled 1J19-9 STS6T with a line over it. The 1 stands for CPU board, J stands for jack 19 and -9 is for pin 9 of the connector. Right above this is the switch input and it is labeled 1J18-9 SS6T with line over it. The line over the label means it low activated. So when you push on the skirt of the pop bumper and it closes the switch SS6T the signal on this wire will go low. The output of Q79 will then go low activating the coil STS6T. There is more info on page 2 about this also. The coils are numbered on the left, then labeled and the coil control wire color. So #22, Lower jet bumper, Special #6, Blue wire with a black stripe, goes to the cpu board at P19-9, goes thru a molex connector 8P3 pin 22, Q79 transistor turns it on and lastly the correct coil type is an AE-23-800-03

#13 4 years ago

Nice to see it's up and running again. You could check the fuses to see if the values are the right ones: normally a fuse should blow when a pop-bumper is stuck for too long.

#14 4 years ago

Thanks GRUMPY, the info on page 2 is what I was looking for, I just skipped right past it because I thought it would be toward the back of the manual with the diagrams and schematics.

Sven, thanks for the info. I checked and sure enough, the fuse was wrong. It calls for a 2.5a but a 7a was installed. I probably should have checked all the fuses when I first got the machine so I'll chalk it up to a learning experience. I picked up a 2.5a and replaced it so hopefully won't run into any more trouble!

#15 4 years ago

There's no order in the manuals what so ever. But lots of good info so you should read the whole manual front to back.

2 years later
#16 2 years ago

Just what I needed

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