Bally 2518-35 MPU board repaired

[63wizz]

I have just completed my first Bally mpu corrosion repair, and the board is working fine (so far).

When i got my Dolly Parton project machine a couple of years ago it had a complete set of boards but the mpu was not working and had none of the socketed chips in it.

so when i needed the board to get Dolly going i purchased a working one from Boxerdog (Tony) with the correct roms for Dolly Parton. since then the old board has been sitting waiting until i learned enough to attempt a board repair.
over the last week i have been working on this board, and enjoying it very much,
I got a corrosion repair kit from Ed at GPE, i didnt realise the kit did not come with the two inductors at L1 and L2 so i had to use some from the board that i got from Tony.( i have ordered some from Ed today).

I also jumpered the board for the 3 2716 roms U1,U2 and U6.

I installed new sockets at U8,U9,U10,U11 and installed the corrosion kit, had an old computer power supply and made a bench test fixture and hooked up the repaired board. As you would expect the LED was locked On, i followed clays guides but could not work the problem out, i changed a few chips at U15,U16,U14,U18 and U19 still no glory.

I swaped the resistors at R113 and R16 from 2K to 2.2K as this is what is in my other board, this did not do anything.

reading through the Bally pinball repair guide it seemed to be telling me it was a jumper problem or a shorted trace or socket. I double checked the jumpers all ok tested the sockets for shorts all ok. I ended up testing heaps of traced and through holes for continuity, and i found a plated through hole at E6 was not making contact so i soldered a piece of wire through the hole and on to the traces each side of the board, put the board back on the test rig and got a flicker and 6 flashes out of the LED i was very exited.

next step try the board in the machine.

Back soon just got to put the kids to bed .

[Strangeways]

Ian - Well done mate  These are just about the hardest boards to repair. If you can fix these boards - you can fix almost anything electronic !

.. and it is VERY satisfying once you are done.

[ddstoys]

Great Work Ian
                I have a few boards im waiting to attempt myself once i get my bench all setup after seeing this im really looking forward to it now 

[63wizz]

When i put the board in the machine it flashed 5 times and then about 30 odd seconds later flash number 6 and 7.the playfield mpu controled lights were very dim and seemed eratic, and the score displays were pulsing bright and dim ( only very slight ).
I switched the game off and back on 5 flashes and waited for a while there were no more flashes.
I turned it off again then back on, 5 flashes a long pause then flashes 6 and 7 again, so i put a credit on and played a game ok.

when i turned the game off again it would not boot past 5 flashes, i read clays guide again and replaced the 555 timer at u12 and replaced the two resistors at R113 and R16 with the 2K ohm instead of the 2.2k, i got 6 flashes on the test fixture, i reinstalled the board into the game and powered it on, I got all 7 flashes in normal time the game started normal, the PF lights were normal brightness and the score displays were steady.

so with a bit of luck it will stay good.

cheers Ian

[ajlaird]

Well done, that is some serious fault-finding there!