GNR Magnet Problems

[Slash]

I suspected for a while that not all the magnets had been working and today when playing it non of them were working.  So I finally decided to test it out.  I noticed all 3 fuses on the magnet board under the playfield had gone.  I replaced them and turned the game on.  There was an audible hum for about a second when I turned the game on (a noise I usually associate with the magnets), then it stopped.

Turns out fuse F9 on the PPB is blowing as soon as the game is turned on.  I suspect it's related to the magnet issue as I disconnected the magnet board then replaced fuse F9 and it's fine (doesn't blow when turned on).

So could this be an issue with the mosfets on the magnet board?  How do I test if they are working or not?

Any other ideas?

[Homepin]

I guarantee the MOSFETs on the driver board will be shorted - a VERY, VERY VERY common problem with this machine.

Replace them ALL with logic level driven FETs, nothing else will work correctly.

There are a few mods you can make to help the circuit to be a little more reliable but unless you are prepared to relocate the driver board to within 6 inches of the MPU in the backbox and extend the heavy wires to the coils from the relocated driver board you are likely to always have issues with this part of the circuit.

The general thinking is that ramdom spikes get into the control wires of the driver board and cause it to lock up - relocating it so it is close to the source of the control lines minimises this interference issue.

Basically it is a design fault, built in from the factory.

[Slash]

Damn thought I might have to do that, I wasn't looking forward to the prospect though as I don't trust my soldering skills on a board, I'll probably fry the damn thing.

When I purchase replacement FET's how do I know if they are logic level driven? (Please excuse my ignorance). Edit - Im Guessing something like IRL540N is logic driven because of the "L" in the name?

I have read the suggestion before of relocating the board, but it sounds like a lot of messing around.

[Homepin]

When I purchase replacement FET's how do I know if they are logic level driven? (Please excuse my ignorance). Edit - Im Guessing something like IRL540N is logic driven because of the "L" in the name?

Exactly right - the L signifies Logic Level drive.

You may not like the idea of moving the board but there really is no other way of curing the problem 95%

[Pintoxicated]

Is there any more info on this mod?  I would like to do it to my GnR machine at some stage.  Some pics of where to put the board would be appreciated or a link to any info would be just as good.  Thanks.

[Homepin]

Is there any more info on this mod?  I would like to do it to my GnR machine at some stage.  Some pics of where to put the board would be appreciated or a link to any info would be just as good.  Thanks.

I don't know of any link or pics but I would mount the driver board as close as possible to connector 3 (I think it is - near the top right of the MPU) and make the wires carrying the data as  short as possible.

Then extend the magnet wires using heavy cable to run up to the relocated driver board.

[Pintoxicated]

Thanks Mike.  I have got some time off over Easter so I might give it a crack and see how it goes.

[Slash]

Thought I would ask a question since I know very little about electronics/circuit boards etc.

Got my new MOSFET's during the week so I pulled the magnet board off today.  One of the MOSFETS has this extra wire on it.  I'm guessing because one of the traces is broken?  So after I finish desoldering the old  MOSFET's and putting new ones on, I assume I should be adding the extra jumper wire back on on (or whatever the correct terminology is)?

Here is a pic.  There are 3 MOSFET's, you can see them on the right hand side of the board with one of them having a thick green wire on one of the legs of the MOSFET's:


On a separate note I have often wondered what these spare plugs/outlets are on the game and whether I could possibly use one of them (maybe the first black and white one) to be able to plug any of my mods in, such as under cabinet lighting or LED flipper buttons, shaker motor etc?
The first one is just sitting on the side near the left flipper button and the other two on the right hand side near the service outlet.

[Homepin]

Yes, that jumper wire is to connect the gate of the MOSFET to the resistor that connects to it by the track on the board that is WAY too thin and probably broken where it joins the pad. I beef all of these tracks up on my replacement boards - there is NO cost difference and it escapes me why they make the tracks so fine - there is no logical reason???

[Retropin]

Yes, that jumper wire is to connect the gate of the MOSFET to the resistor that connects to it by the track on the board that is WAY too thin and probably broken where it joins the pad. I beef all of these tracks up on my replacement boards - there is NO cost difference and it escapes me why they make the tracks so fine - there is no logical reason???

Considering the board originally started out as one whole sheet covered in copper that gets eaten away to make tracks.. having thin tracks makes absolutely no sense whatsoever.. in fact - quite the opposite

[Slash]

Thought I would post a follow up to say I got some new heat sinks today to go with the MOSFET's so was finally able to solder them onto the board.

Bingo magnets are working (despite having a muppet soldering them - me)!

I did wonder tho since there are 3 magnets, is it an all or nothing thing, In other words if one magnet doesn't work then neither will the other 2? Because it's hard to determine just by holding a ball over the top of the playfield if they are all working. I'm still wondering whether my dodgy soldering was good on all of them or maybe just one or two.

[Homepin]

There is no real need for heatsinks on this board as the FET won't get hot or even warm under normal conditions.

They certainly help give them physical support however.

[Slash]

Fair enough, they were already on the board so I thought it was best to be safe and just replicate it.

When I first reconnected the board it didn't work, so I went back and tidied up some of the solders and then it worked. That's why I wondered whether one or two of them might still not be working and I just managed to get maybe one going.

[MrMaloo]

Try pulling the magnet fuses out from under the playfield . Have the game in magnet test and with just one fuse in test each magnet individually . You'll have to change the fuse to the next magnet's fuse holder each time but will give you an indication on whethereach individual magnet is working correctly .

[Slash]

Great idea, I will give that a try thank you.