When the game is first powered up, all coils fire immediately and fuses under PF blow.

Alltek Ultimate MPU
SDB has had headers replaced and been bulletproofed. All connectors in machine have been repinned.

Sound board is presently NOT connected.

Thoughts?

Will double check everything. After I posted this I thought about the potential for a ground problem that would be common to all of the output transistors on the SDB...

Game boots fine as it is - just blows the two under PF fuses. All diagnostics work and I can start a game.

Update -

Checked all wiring to SDB. Everything meters good. Checked various continuity points around SDB itself. Can't find anything incorrect. (Of course I am assuming the schematic is correct).

So...on power up:

1) All coils lock on, but startup sequence works as planned.
2) PF fuses quickly blow
3) Once game boots into attract mode, I can enter self test or start a game. All self tests work fine.
4) When in self test for solenoids, the knocker, flip enable and coin door lockout are good - no other solenoids work (fuse blown).
5) Game plays fine - just no solenoids (and no sound - sound board is not connected yet).

I checked continuity with a couple of coils that I disconnected the Vsupply to verify no ground path to firing side. Those were good.

So...I am stumped. Never seen a Bally fire ALL the coils on power up before.

I am beginning to think I need to disconnect all controlled coils (the ground to the SDB) and then reconnect one by one to isolate the problem...but I still would not think that cause them all to fire like that...

They all run to J5 on the SDB. If I unplug that obviously there is no lock on when I boot.

Thanks dothedoo!

I think I may have found the problem last night...had a suspicion all along that maybe the issue was ground related...but I had been trying to resolve the problem through the SDB, knowing that the Q transistors complete that ground to the coil to fire it...

So i looked back at the Rectifier board I had repinned. I have continuity between ground and the 7v and one of the 6v lines. Not sure if this will relate to the 43v outputs (they seem to be fine). But what is interesting about that is no fuses (e.g. f5) are blowing on the Rectifier board, and I would have thought they would with a dead short.

So time to fix that issue and maybe that will solve the problem? Still seems strange to me that everything else works fine with two different voltage lines compromised on the Rectifier...

OK - so double checked and sure enough, I have continuity between every ground pin on the Rectifier board connectors and the 7V outputs on all three connectors. So if my thinking is correct, somewhere there is a solder splash or something bridging these two circuits.

I still am at a loss as to how this would cause all coils to fire, but that is currently beyond my brain's thought capacity.

Dothedoo - I will check U2 as well and see what I can find.

-scott

Ok here are a few pics. Let me know if we need more detail.

-scott

DSCN2551.JPG

DSCN2552.JPG

DSCN2553.JPG

Obviously I have pulled J1 header back off in the pics. Another possible culprit...

Should taps 17 and 18 have continuity at the transformer? It looks like 18 goes to ground on the schematic and 17 feeds through F5. If I take the fuse out, the continuity issue at the pins goes away. Tap 18 is black (wired to ground on the back of the board). Tap 17 is blue (wired to the header side of F5).

OK - Got the Rectifier put back together. Measured voltage on U2 and all referenced pins are reading between 3.5 and 4.1 volts DC

Retested game with J4 unplugged and coils still locked on at power up.

Ok. Here are a few pics of the SDB for grins and giggles...

DSCN2556.JPG

DSCN2555.JPG

DSCN2554.JPG

A few more of the back up close...

DSCN2560.JPG

DSCN2559.JPG

DSCN2557.JPG

DSCN2558.JPG

That's cool. Just posted the other pics as Vid had suggested.

Andrew sent you a pm regarding another board (we had talked about before Christmas).

Thanks - Scott

Replaced the 74154 with a new socket and chip - no change...any other thoughts?

-scott

Yep you are correct! I did swap in a known good SDB and everything is good. So it definitely is in this board.

Will start checking tomorrow - time to break out the scope!

-scott

Ok - finally got back to this today. I also discovered something in looking at the schematics that I had not thought through...

I have mislabeled this thread from the top - it is not "All Coils Fire" after all...it should be "Playfield Coils Fire".

The knocker and flipper enable and coin door relays all work as they should. It is only relays whose outputs come through J5 on the SDB, and coincidentally, come from U3.

So I am beginning to suspect U3 - as since the other coils work in coil test, that must indicate that U2 is fine.

I checked a few pairs of legs on U3 since the schematic shows the pairs as the terminals for each individual "transistor" inside. Both pins read "high" when tested in Coil test, but one is higher than the other. I see that pins 5 and 15 are ground.

Can someone shed some light as to what I should be looking for on the scope screen when testing the pins on U3?

Thanks and sorry for the confusion!

Hey-

Believe it or not you are on my purchase list for both parts of the tester unit! Just have not gotten around to ordering one yet. It would help tremendously.

I checked U3 and there is no movement on the pins at all. I cross checked to U1 (since those coils are working, and sure enough, the output of the knocker coil went high when the knocker fired. No activity like that on any pins on U3.

So I believe I have a bad chip. Any thoughts on a replacement since CA3081's are apparently obsolete?

Thanks again -

-scott

Ace -

Just placed my order for the tester. Looking forward to it! By the way - removed the suspect chip (U3) in preparation for a new one and to get a socket in place...decided to try the board with no U3 - everything still locked on...maybe that is norma behavior with no chip in place, but i am running out of options!

Thanks -

-scott