Bally mpu 35 stopped working......ITS NOW WORKING AGAIN

[63wizz]

Hi i had the local under 8s soccer breakup at home on Saturday, the kids and parents gave my pin collection a bit of a bashing.
poor old Xenon couldn't handle the pressure and decided to die,
the LED is locked on as soon as the power is switched on, no flicker at all.
so far i have tried,
tested resistors in the corrosion area
replaced U15, no change.
checked transistors Q1,Q2 and Q5 they seem ok.
shorting pin 39 and 40 on U9 to trigger a reset, it did not reset.
reseated all socketed chips, with no change.
swapped U9, U10, U11 chips from another bally board, no change, the chips from Xenon work ok in Dolly Parton.
swapped U7 6810 with another, no change.
swapped SDB with another and checked voltages on all boards, volts ok, no change to problem of locked LED.
Mpu has been re pinned and acid damage repaired, the acid damage was not to bad on this board, and the game played fine for a month or so after doing these repairs.

what would you try next, i dont have any replacement chips for U16,U20,U17,U18,U19 and U14, could it be one of these chips?

Ian

Ps: the kids just love pins, its funny when they look at them and there eyes pop out of their heads, and they have no idea how to play, you have to tell them about the flipper buttons on the side, but it dosent take them long to get the hang of it.

[dj10555]

Hi Ian,

I would try the board with just U6, U9, U11 installed and all other socketed chips removed first. The board can start the first test with just these 3 chips + the other soldered in chips working. The other socketed chips are faulty they can stop the test from running.

It depends if the Dolly Parton has the same type/number of Roms installed as the Xenon, but if they do you could also try U6 in the Xenon to verfiy this is working.

If the U6,U9,U11 check out (and you have already tested U9, U11) you are looking at one the soldered chips which has failed or possibly a damaged track in the corrosion area. Sometimes the tracks look fine but actually don't connect when measured with a meter.

I have replaced a few U16 chips on these boards which provide the clock but this would only be a guess and would really need a logic probe to confirm the fault.

regards Derek

[63wizz]

I cant swap the U6 chip with dolly it has 2716 replacement chips in U6,U1 and U2.

i will try with just U6,U9 and U11.

thanks for your reply to my problem

Ian

[AskJacob]

Silly question but have you checked your 5v supply? with the 5v missing but 12v OK, the LED will still light up - but nothing else will happen...

Cheers
Jacob

EDIT: yes, silly question - you mention you checked the voltages. Carry on

[63wizz]

Hi Ian,

I would try the board with just U6, U9, U11 installed and all other socketed chips removed first. The board can start the first test with just these 3 chips + the other soldered in chips working. The other socketed chips are faulty they can stop the test from running.

It depends if the Dolly Parton has the same type/number of Roms installed as the Xenon, but if they do you could also try U6 in the Xenon to verfiy this is working.

If the U6,U9,U11 check out (and you have already tested U9, U11) you are looking at one the soldered chips which has failed or possibly a damaged track in the corrosion area. Sometimes the tracks look fine but actually don't connect when measured with a meter.

I have replaced a few U16 chips on these boards which provide the clock but this would only be a guess and would really need a logic probe to confirm the fault.

regards Derek

I pulled all socketed chips except U6,U9,U11, nothing happened.

I have replaced Q1,Q2,Q5,CR5,VR1. no change to locked on LED.

checked and buzzed tracks and chip legs.

5 Volts is measuring 5.4 is this ok.

Ian

[dj10555]

Hi Ian,

5.4V for the 5 volt rail is too high and strange faults may occur. The voltage should only be a high as 5.1V max. May need to look at rebuilding the 5 regulator. Can you try your faulty MPU again in the Dolly Paton machine just to make sure if doesn't flash?

Was the socket on U8 change during the corrosion repair. I would also check for and damage to this socket.

regards Derek

[63wizz]

Hi Ian,

5.4V for the 5 volt rail is too high and strange faults may occur. The voltage should only be a high as 5.1V max. May need to look at rebuilding the 5 regulator. Can you try your faulty MPU again in the Dolly Paton machine just to make sure if doesn't flash?

Was the socket on U8 change during the corrosion repair. I would also check for and damage to this socket.

regards Derek

I just thought, i replaced the SDB with a spare that i have and it still didnt work.that should have fixed the 5.4v

the U8 socket was replaced, i have buzzed out all the legs and adjoining solder connections.

i didnt put the whole board in Dolly just the 6800 chips were swapped.

Ian.

[dj10555]

If you have access to a logic probe, I would check that you have a clock signal coming from U16 up to the CPU.

It would be a pain to do but if you re-jumperd the Xenon MPU temporarily to match the Dolly Paton, you could then swap the Roms and confirm that U6 is not at fault.

[63wizz]

probably not as big a pain as you think, because U1 and U2 are jumpered for 2716's already.

Ian

[Retropin]

Where are you checking your 5V rail? At TP1 or at the chips themselves?

Make sure you have 5V at pin 8 U9 etc.

Reason i say this is that after TP1 there are a whole array of ceramic caps - one of these goes down and you will not get the logic voltage to the chips or TP5, but it will read at TP1

[63wizz]

I changed the jumpers on the Xenon board to take the 2716  from the Dolly board at U6, i put it back in the Xenon machine, but did not boot.

i put the Dolly board in the Xenon game and it booted up fine.

I put the Xenon board in the Dolly machine and it did not boot.

I will try Retropins suggestion next.

Ian

[63wizz]

Where are you checking your 5V rail? At TP1 or at the chips themselves?

Make sure you have 5V at pin 8 U9 etc.

Reason i say this is that after TP1 there are a whole array of ceramic caps - one of these goes down and you will not get the logic voltage to the chips or TP5, but it will read at TP1

I measure 5 volts at TP1 and TP5 and pin 8 on U9.

I have just swapped C14 and C15 (470pf capacitor) with some i de soldered off another board this did not work either, LED still stuck on.

must be U16 (9602) or U15(MC3459L or 74S37) anyone got both of these chips for sale PLEASE.

Ian

[63wizz]

Xenon is up and running again, turned out to be a bad 9602 at U16.

A big thanks to Skybeaux Ken for supplying a 9602 chip which he posted out very quickly 

also thanks to everyone for there suggestions and input to my problem.

Ian

[Skybeaux]

That's quite alright Ian , i'm happy to have been able to help you out

[Strangeways]

9602 - Hard to find these days.

Good Stuff Ken