So my Firepower ( Williams system 6 ) has been working and used regularly for years. The other day it powered on in audit mode. The batteries were completely dead. Changed them but now the game plays with defualt settings ( coin only and 3 balls ). I cannot enter the settings menu or enter diagnostics. Game boots up in game over attact mode and plays fine. I checked door switches ( at the switches and the MCU board connector ) AND grounded the advance button on the MCU board connector ( top left ) but has no effect. If I press diagnostics button the 2 leds blink twice ( passes test ) and the displays blank. door switches do not have any effect and I cannot do lamp test , etc. Any help where I can start troubleshooting would be greatly appreciated. Weird thing is the game is playing perfectly. The door switces did work previously ( a few years ago ). Nothing changed except for my batteries going dead

Ya, I actually removed the MCU and Diver boards. re-soldered the 40 pin connecetors as a few were showing signs of cracking. No effect. I beleive it only has to do with the MCU board and not the dirver board and 40 pin connectors as the game plays properly. Thx thhough.

Not so much near the battery holder, however the board does show signs of age and previous repairs. The green coating on the circuit board is "wavy" in some locations. I went through and inspected for any signs of a bad connection. I even checked the TP1 to TP9 values and they all seem correct ( except TP-1 is 9.?? volts DC rather than 12V DC, but I think this is ok from another post i saw ).

I get around 4.3 VDC which is what I was told to expect.

I don't think so. Coin slot works to add credit. Game stores and updates high score. Game plays great and strong ( i reflowed the 40 pin connector). Door switch to reset high score works. The adjust and auto up do give proper states at jumper ij2 ( 2nd top left connector ) but game won't enter audit or do a diagnostic. Im at a loss as to what more to check.

With door open, i can still add credits with coins and start game. Not sure if that is normal or significant.

Thx guys. I have tried to mimic the switches directly on the board no effect. Ill test IC5 as you recommended and report back.

Sorry Jethro what is a PIA ?

OK, so I think there is a problem with inputs to IC5. Here are results from testing:
Pin8 is 4.8V no press (adjust) 0.12V with press ( adjust)
Pin9 is 4.8V No press 4.8V with press
Pin10 is 0.19V no press 0.23V with press

for pins 11,12 and 13 I might have my adj/man switch upside down ( reversed)
Pin11 is 4.8V switch up 4.8V switch down
Pin12 is 4.8V switch up 0.12V switch down
Pin 13 is 0.29V switch up 0.13V switch down

For an inverted nor gate I require both inputs to be 0V to get 5V at output I believe.
Pins 8 and 12 are changing states but pins 9 and 11 are staying HIGH.
Pins 9 and 11 are tied together and seem to be the IRQ line. I am only using a multimeter to measure voltage on the pins. perhaps I can't detect IRQ going low ? This is TP5. is there a way to further test this ?

Here is the schematic for CPU board I'm referencing.

s6sch1.pdf

JethroP, I think you hit it. I just noticed IC11 output is the input fed to Pins 9 and 11, which I believe are not behaving after analyzing IC5

So TP5 seems to be this IRQ line which is the output from IC11. Can I tie that to 0V to test or is that a really bad idea ??

Ok so unfortunately the PIA in the CPU board is soldered in. There are 3 - 6821 pia's in sockets in the driver board as it was probably previously repaired by someone.

I guess I'll order a 6821 chip ( I read somewhere I should replace with 6821 rather than 6820 ) and a 40 pin socket and hope...

I must say everything on the cpu board looks in excellent shape and orriginal except IC19 seems to have been replaced. solder work looks so so.
Could this chip have any affect on my issue ( cmos ram address ?? ). I also noticed that the spec sheet calls for a 5101 CMOS Ram chip, but the chip installed is a Toshiba TC5501P chip. ( I'll attach a pic).

TC5501P (resized).jpg

Ok, so if I understand correctly, you are thinking it's a problem with IC11 on the driver board.
Yes I can swap IC11 with one of the other PIA's on that board. I'll try that tomorrow night after work.

Thanks again for your help.

Ok so I have more info. I swapped IC11 PIA with the lamp PIA beside it. Turned the machine on adjust button still has no effect. Everything seemed the same. I did a close scan of all components and touched all chips for heat. I then noticed the 8A 18V lamp fuse was blown and play board lamps were out. I changed the fuse with a 7.5A ( didn't have an 8A ) and lights came on. fuse did not blow again ( prob old and weak ), BUT I decided to try and play a game and although it played normal the playboard lamps were all ( or mostly ) on where they should not have been. So I guess that chip is bad, but why did it not allow me into diagnostics after the swap ???

The one chip for the solenoids which I did not touch is a motorola 6821P
The other 2 that I swapped I don't recognize the logo. here is a pic. Possible SGS Thompson ?
So are you thinking there could be an issue with the IC socket as well as with the actual chips ?

20221128_190219_resized (resized).jpg

Well I received 3 new PIA chips and sockets yesterday. After the changeout the the 2 leds for the memory tests stay on solid now. only lights come on no score displays etc. This just got a whole lot worse

OK here they are. let me know if you need more. I assumed you wanted pics of driver board only. One more piece of info is when I disconnected the driver board and powered the machine, the 2 diag LEDs blinked once then stayed on. With the driver board installed, they just stay on no blink. Before I switched the PIA chips around and replaced them I got 2 blinks then off. so everything went south since I've started playing with these PIA's

driver_back.jpg

driver_front1.jpg

driver_front2.jpg

Yes I tesed it right to the MPU, this is not the issue unfortunately.

Well I checked all the darlington transistors and they are fine. Checked all solders on the new chip sockets. All good.
no changes.Still have 2 solid LEDs for mem test at boot up. I'm at a loss for what else to check.