I purchased a LW3 out of a dude's backyard shed. It is in pretty poor condition. I am really looking forward to saving this machine. After some troubleshooting I pulled the trigger on some parts. Today I installed a new power supply board. Previously I had tapped 5 volts into the MPU and got it to boot up after reseating the EPROMs. Today with the new power supply the machine came to life! Of course fuse F5 kept blowing. I traced the problem to a shorted coil on the VUK. O well, another parts order headed out to Pinball Life!

The game is playing good with the exception of the VUK and one other issue. The previous owner rigged a push button to bypass the gun trigger. It is just two wires hanging out of the cabinet with a push button that launches the ball. I checked the switch on the gun and it is working just fine. So I am not sure why he would have "hot wired" the launch coil. I am going to post a few pictures and see if you guys can help me with how the standard wiring is suppose to be.

Near the coil there is a Purple wire with Yellow stripes. This is of course the 50volt wire. It has been cut and a Red wire with Yellow stripes spliced in going to the coil terminal. A Brown wire with Yellow stripes has been lengthened and heads out of the cabinet to a dangling push button which returns to the other coil terminal.

If the coil is wired like the other 50V coils then the Purple/Yellow is carrying voltage and the Brown/Yellow is the switch circuit? If so then the Brown/Yellow must be shorted and staying on all the time. I figure that is why a push button was wired in. Can you guys confirm that I am reasoning correctly and give me some hints as to how to fix this issue correctly and put the gun back into action. I would appreciate any advice.

It was this forum that helped me troubleshoot the power supply and shorted coil. I used some threads that were up to 6 years old.

Lane

Edit: I just saw some pics on another thread that confirm the Violet/Yellow wire and the Brown/Yellow wire do go to the coil that launches the ball. That means I need to figure out why the coil is staying energized and the previous owner installed a "push to launch" button in the Brown/Yellow wire. Is this most likely a CPU issue? I'm guessing I should run a switch test tomorrow and see what the CPU reports. If it shows a switch stuck on hmmmm.

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Don't laugh. It is rough. But....if you love pinball you will be happy I saved it from ruin. It's working!!! And, I received a decal wrap today, new flippers, new rubbers and other goodies. I just ordered a VUK rebuild kit and coil. It will look great when I am done. Seller threw in an Eight Ball and Fan-Tas-Tic and came down $400 so I paid $2600 for the three. Eight Ball and FanTasTic are now playing great after some repair and rebuild. The LW3 is what I really wanted and it was in the worse condition (just needs a fuse)!
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When I say it's working I mean except for the VUK coil which I have ordered and the mystery I must solve with the launch coil. Any help appreciated.

Q2 and Q4 test bad with the multi meter. All transistors on mpu test good. I’ve ordered some replacement parts from pinball life.

I changed the flippers (spider cracks) and rubbers today. I also cleaned and polished the playfield.

Then the wife and played a few games. Can’t trigger tri ball with the VUK out of service but still fun to see it working.

The launcher coil was replaced before I purchased the pin. The previous owner did not know how to troubleshoot so he just installed an external pushbutton which you press to launch the ball. When I arrived and we turned it on the VUK locked on and the owner gave me a lame story about how that was "normal". As I have said he was the proverbial "just a fuse" guy.

I have ordered a new coil and VUK rebuild kit. I think the launcher coil will be fine. I will test after replacing Q2 and Q4 and before soldering the leads to the coils. I'll test the diodes. Hopefully they are OK since I didn't include them in my order

I appreciate the Pinside forum for the help you guys provide in keeping these machines functioning. It is fun to research, test, repair, play.

Help please!

As a recap the previous owner of my LW3 was a hot wire and ignore guy. I had to replace power supply board and that got game playing except:

1) Originally when I powered up the VUK locked on. Coil was melted. I found Q2 bad and replaced with TIP36C. I called myself checking upstream but I guess there is something wrong upstream.
A) Replaced coil with new coil and diode. Before soldering wires to coil I hooked voltmeter up to leads and ran a coil test. No voltage showing.
B) I hooked coil up and as suspected it did not work.
C) I ran a switch test and there are no closed switches. I manually tripped VUK switch and it doesn't show as closed in diagnostics. I tripped other switches just to be sure I was doing this test right. I shorted across switch terminals in case VUK switch was bad. Still not showing in switch test.
D) I tested diodes and resistors on MPU at switch drive 4 and switch return 7. Seems to test good with DMM in diode mode. I am not sure where to go from here. I seems that the VUK switch circuit is not working.

2) Original owner had wired push button switch in line with ball launch coil. You can press this button and coil fires anytime. Gun trigger still is talking to MPU and gun trigger works for shooting the bad guys within the game play. So I surmise this coil is locked on rather than a gun trigger issue.
A) Tested Q4 and it was bad. I tested upstream and found no issues. Replaced Q4
B) On power up Q4 immediately blew again.

Any help you guys can offer is greatly appreciated. I have studied the schematics and presently I am not making progress.

I just tested the MPU switch matrix by a jumper with a diode from CN8 pin 4 to CN10 pin 2 and I can trigger the VUK switch logic on the MPU. So MPU is not the issue.

OK OK OK. I got the VUK working properly. Replaced Q2, coil and diode. I tested MPU signal matrix at Drive 4 and Switch 7 and it tested good. I noticed micro switch on VUK was adjusted improperly and staying depressed so I adjusted wire switch lever. I found a cold solder on one of the large ceramic resistors on the PPB and repaired. I then found a wire for the VUK damaged at the crimp on MPU CN 12 at position 8. I repaired and voila VUK is working like it should. YES!

Now for the plunger. It fried Q4 again. I had replaced Q4 and coil diode. I guess there is something else wrong. The small "ground" wire on the coil is staying "grounded". You always have 74 volts on the coil when you test the two connected wires. I disconnected them from coil and they still test at 74 volts. I think both of these wires should only test 74 volts if the negative of the DMM is connected to a ground in the cabinet. As I understand it the MPU sends a signal to the PPB to take the small wire to ground and this fires the coil. So, something is shorted somewhere keeping this small wire grounded and the coil ready to fire when I push the hillbilly switch that the previous owner installed. Evidently while the small wire is sitting there with a ground circuit the board is heating Q4 up and frying it. Any suggestions? I'll keep testing.