LOTR - Auto Launcher Coil burning out as soon as the machine is switched on

[cmrl9]

Hi,

I've been restoring my LOTR and have the following problem:

I fitted the auto launcher coil wires the wrong way round, when I turned the machine on it blew the F6 Fuse.

I fitted a new fuse and new coil from pinball heaven.

I turned the machine on all flippers fired.

Started a game, noticed some light smoke coming from the bottom by the auto launcher (thank god i noticed it). Turned the machine off, coil was red hot and the bracket red hot. Sleeve has fused to the coil.

Thought maybe its a faulty coil, put the original coil on the machine. Did the same started getting hot.

No fuses blown.

Checked all other coils all cool to touch.

Now its a serious fire risk, any one have any clue what would cause this, its only on the auto launcher?

Because it a fairly serious problem:

Any onee know any one in Northern Ireland who an expert who could take a look? (paid or a favour )

Any one in England that could check it all, if I bought it over (paid or a favour), I'm thinking possibly pinball heaven but any other trusted people on here?

very sad, but could have been worse. Everything is working and turned off straight away.

Appologies for the second posting on a new thread but I figured most of the people who might know how to troubleshoot this problem arn't following the worlds most boring shop log!

 

[Fubar]

Most likely blown transistor is in short-circuit. Surprised the fuse doesn't blow each time... First step is change the FET for that coil.

But you say all flippers fired - do you mean that every single coil is locked on ?!

 

[cmrl9]

Most likely blown transistor is in short-circuit. Surprised the fuse doesn't blow each time... First step is change the FET for that coil.

But you say all flippers fired - do you mean that every single coil is locked on ?!

Hi,

Thanks so much Fubar for your response:

To clarify:

1) turn machine on

2) Machine goes through its checks correctly, everything is fine

3) start game, everything fine, press flipper button, works. everything works as expected. COuld have played it

However noticed smoke coming from coil, fortuantely the selotape glue behind the paper was smoking a little. Turned off.

I fitted a 7amp fuse, I prety sure this is the corect one.

I'm totally unfmilar with circuit boards, but taking a quick look I can see its something on the power driver board based on this:

Understanding Pinball SS Transistors, Diodes & Rectifiers -

Learn how to read and understand electronic circuits in pinball machines. Test transistors, diodes, rectifiers, FETs, and understand Triacs.

homepinballrepair.com

I fried this when I got the diode direction mixed up.

Would you know someone on here who could fix, check the powerdriver board?

It's not something I'm comfortable doing and will leave to the experts.

 

[Fubar]

If you can use a soldering iron (which I assume you can if you can change coils), then changing a FET isn't too hard. It'll be one of the Qxx parts sticking out on 3 legs - look in the coil table in the manual.

Cut the legs with some snips, then pull them out one by one (heat leg, pull with pliers). Resist the temptation to pull before the solder is flowing! Otherwise you risk lifting a trace. Generally if you have a choice try to pull towards the PCB side which doesn't have the trace.
Once that's done, clean up with solder wick on both sides until the board is clean and the hole is clear.
Pop new part in the holes, solder each leg (from the back) - job done.

There are many people on here who can do this - it's pretty routine for these FETs to blow, and being through-hole parts they aren't too hard to change.

 

[cmrl9]

Hi Fubar,

thanks so much for the detailed response, have been feeling a little sorry for my self.

Its not something I'm comfortable doing for the first time on a board, I will look at getting some junk boards I can practice on first. Pinball heaven have kindly agreed to fix it for me, going to send it to them after christmas.

I'm 99% sure your diagnostics is correct.

Thanks again