GNR Magnet board issues

[robm]

I have got a guns and roses machine that i'm doing up for a mate, i got it with the fuses removed from the magnet board under the playfield.

I replaced all 3 Mosfets (IRL540s) as well as the IC (273 from memory) - i also added the capacitor between legs 10 and 11 as per this page http://www.xs4all.nl/~apronk/gnrpinball.htm.

I have 2 problems -

1. One magnet blows the fuses as soon as the machine is switched on (unless coin door is open) - all 3 magnets have a resistance of around 5.3 Ohms, so i thought they would be OK

2. During a game they still blow fuses (3A SB), so no magnets after that - is there something on the CPU board i should be looking at that controls the magnet board?

[dj10555]

Hi Rob,
5.3 ohms is good for the coil so they should be alright. Have you tried powering the game on with the J1 connector to the CPU disconnected? It may tell whether the problem is on the magnet board or CPU. Did the diodes on the magnet board also measure OK?

It looks like the magnet board is connected back to the 6821 at 11B on the CPU board. The best way to test the 6821 use Leon's DE test rom and use a logic probe to check the outputs of the suspect 6821 are pulsing. If you have to remove the 6821 from the board, you need to be very careful as there is very little clearance around the holes for the pins and tracks which run in between them.

regards Derek

[Pinballace]

Although this may not apply to you direct issue I did find this info about the magnets that may be helpful.

http://www.xs4all.nl/~apronk/gnrpinball.htm

[Homepin]

is it fixed yet? 

[robm]

is it fixed yet? 

Almost......

Mike (Homepin) dropped in last night for a yarn and a bash on some machines and we had a look at the problem - in the end it was my fault - when i replaced the Mosfets, i used some that i had grabbed for a repair to a Gottlieb Sys3 game - as it turned out these were IRL510s which are not as robust as the required IRL540 ones - hence the 510 ones spewed their guts up and blew fuses - so the 540 ones should turn up tommorrow and hopefully it will all be sweet!

Thanks Mike!

[ajlaird]

Nice work, Mike!