Struggle with Bally MPU LED Solid

Hi everyone.. Hope all are doing great. I am new here working on a Bally Playboy pinball machine 1978 vintage.

This is my neighbors unit and had worked in the past while he owned it. He has regained interest in setting it up for his daughter to play and the game is not coming up. The lights come on but no displays work and the MPU LED stays solid with no start up flashing at all. Not even the quick flash.

I have run through to the point where I attempted to run just only the U9, U11 and U6 and no change.

I have also done the short on U9 pins 39 & 40 with no reset. Pin 40 shows 5.25v DC and when shorted drops to ~.5v DC and no boot sequence.

The board is very clean with no signs of battery leakage front or back or corrosion so I don't suspect the reset circuit is affected. Attaching pics so you can see what we are working with.

I have seen a test for shorting the junction where resistors R1 and R3 connect together. I located the resistors at the lower left bottom but not clear where the junction is to do this to check if the V drops on U9 pin 40.

I see a lot of steps from here with various paths to troubleshoot but wanted to see if the experience here could help make sure I'm going down the right road from here. From what I'm reading the board should boot with U9, U11 and U6 if the reset circuit is good. I assume the 12v is fine since the LED lights and I get 5V on pin 40 on U9. I have also removed all connectors except J4 to the board just to see if any change and no dice.

Given what I'm seeing the indicators seem to point to either one of the IC's causing this but my little experience is hesitant to just replace parts at this stage but that may very well be in order.

Any thoughts or guidance would be greatly appreciated so this younger generation can enjoy such a classic machine even though it is a PlayBoy .

Thanks in advance!

Stan

IMG_9062 (resized).jpg
IMG_9068 (resized).jpg

#2 3 years ago

DBS

Skidave

Pinside member

6y 63,550 1,288 9

Do you have a logic probe? Next thing will be to look for clock signals feeding U9. Dont have a schematic in front of me, but others will chime in with the pin numbers.

#3 3 years ago

???

JethroP

Pinside+ Frequent

6y 101K 3,133 9 14 1

Have you tried pulling J4 and reseating it? Maybe a poor connection. Have you checked the 12V signal on the Solenoid driver board?

Try checking the clock circuit with a logic probe. The clock signal is pin 3 on the CPU chip (U9), and the shifted clock signal goes to pins 36 and 37. If the clock signal is missing, pull U9 first to make sure the CPU chip isn't damaged, and test it again.

Also, save that board....remove that old battery before it starts leaking!

#4 3 years ago

???

T-Tommy

Pinside+ Frequent

Prescott Valley, AZ

7y 36,300 158 5

The board looks great so let's assume that the problem isn't related to any board damage. I would start out by getting rid of the 6800 at U9 which is made by AMI. It's well known that these are problematic. You can get a 68B00, and other awesome parts at Great Plains Electronics. If this solves the issue then great. If not, the socket at U9 (and all of the rest) should be changed to the twin leaf style. If the LED is still locked on after a new 6800 and sockets, make sure pin 40 of the 6800 is 'high' with a logic probe (5volts with your meter). If it's low (0v) then components in the 'reset' section need to be replaced. If pin 40 is high (5v) and the LED is still locked on then the PIA at U11 should be changed (might as well replace U10 also, part Number W65C21N6TPG-14 at Great Plains Electronics). If the LED is still locked on at this point, break out the logic probe again. As Skidave suggested, the 6800 must be receiving a clock signal. U9 pins 3, 37 must be pulsing. Also the VMA at pin 5 should be pulsing. If the pulses are present it would sound like board damage such as a broken trace (or sloppy soldering on the sockets). If any of these pulses are missing then you will need to dig deeper. (Remove the battery and replace with a 2032 and battery holder or Nvram)

#5 3 years ago

???

sdynak

Inactive member

Thanks guys!!

Skidave - I do not have a logic probe but have very good Fluke 88 DVOM from my auto days. As you mention I see some other suggestions so will check those.

JethroP

Quoted from JethroP:
Have you tried pulling J4 and reseating it? Maybe a poor connection. Have you checked the 12V signal on the Solenoid driver board?
Try checking the clock circuit with a logic probe. The clock signal is pin 3 on the CPU chip (U9), and the shifted clock signal goes to pins 36 and 37. If the clock signal is missing, pull U9 first to make sure the CPU chip isn't damaged, and test it again.
Also, save that board....remove that old battery before it starts leaking!

Sorry.. yes.. I pulled the entire board and cleaned all the pins and really focused on the J4.. really everything physically looks great. Will go through these checks. I did pull all chips and cleaned the pins gently with fine sandpaper. The chips all look good physically. It is hard to pull that battery with the way things look but agree after seeing some of the damage it can cause. Will do.

Looks like I'm going to have to look into a logic probe. Will do further checks and come back.

@T-Tommoy

Quoted from T-Tommy:
The board looks great so let's assume that the problem isn't related to any board damage. I would start out by getting rid of the 6800 at U9 which is made by AMI. It's well known that these are problematic. You can get a 68B00, and other awesome parts at Great Plains Electronics. If this solves the issue then great. If not, the socket at U9 (and all of the rest) should be changed to the twin leaf style. If the LED is still locked on after a new 6800 and sockets, make sure pin 40 of the 6800 is 'high' with a logic probe (5volts with your meter). If it's low (0v) then components in the 'reset' section need to be replaced. If pin 40 is high (5v) and the LED is still locked on then the PIA at U11 should be changed (might as well replace U10 also, part Number W65C21N6TPG-14 at Great Plains Electronics). If the LED is still locked on at this point, break out the logic probe again. As Skidave suggested, the 6800 must be receiving a clock signal. U9 pins 3, 37 must be pulsing. Also the VMA at pin 5 should be pulsing. If the pulses are present it would sound like board damage such as a broken trace (or sloppy soldering on the sockets). If any of these pulses are missing then you will need to dig deeper. (Remove the battery and replace with a 2032 and battery holder or Nvram)

Yes.. this board is like new. Since my buddy had it nothing was changed but all was working. Just went to pull it out after sitting for some years and would not go into play. Guess he got lucky here with this board and battery. Will go through the suggestions and report back. Do not have a logic probe but looks like one is in order possibly from all the suggestions so far to keep moving through.

Thanks so much guys.. I really enjoy this kind of stuff. It takes my mind off my stressful job and gets my mind in a different direction. Never knew there was so much to these. I'm intrigued and the knowledge here is amazing.

#6 3 years ago

???

sdynak

Inactive member

https://www.greatplainselectronics.com/proddetail.asp?prod=W65C21N6TPG-14

Quick question.. The U10 & U11 are the same chip correct? At Great Plains - W65C21N6TPG-14

Figure if going to make an order for the 68B00 to get 2 of these also.

Thanks!
Stan

#7 3 years ago

TPR

frunch

Pinside member

OP
Quoted from sdynak:
Quick question.. The U10 & U11 are the same chip correct? At Great Plains - W65C21N6TPG-14

Correct!

Good luck! I'll be following the thread

#8 3 years ago

TPR

frunch

Pinside member

Also, not sure what you want to do about replacing the battery, and there's many choices nowadays (with many different opinions as to which is best). I usually just install a memory cap in place of the battery and it works fine. CERS-1.5F-5V at Great Plains Electronics. NVRAM is another option, or a remote battery pack. Whatever the case, it's very fortunate the battery didn't leak on that mpu!

#9 3 years ago

???

sdynak

Inactive member

Quoted from frunch:
Also, not sure what you want to do about replacing the battery, and there's many choices nowadays (with many different opinions as to which is best). I usually just install a memory cap in place of the battery and it works fine. CERS-1.5F-5V at Great Plains Electronics. NVRAM is another option, or a remote battery pack. Whatever the case, it's very fortunate the battery didn't leak on that mpu!

frunch - Thanks for confirming the U11/U10! You are local to me. Right in Bayville! Used to live in Howell before we moved down here on the lagoon. Will look into battery options also.

#10 3 years ago

AXE

YeOldPinPlayer

Inactive member

Unknown

8y 111K 6,454 4 12

OP
Quoted from sdynak:
Will look into battery options also.

This NVRAM is by barakandl You can’t go wrong with his stuff: https://nvram.weebly.com/

#11 3 years ago

TPR

frunch

Pinside member

OP
Quoted from sdynak:
frunch - Thanks for confirming the U11/U10! You are local to me. Right in Bayville! Used to live in Howell before we moved down here on the lagoon. Will look into battery options also.

Small world, lol! I have plenty of electronics parts on hand if you need anything. Chips, transistors, caps, fuses, etc...not to mention pinball parts. I'm also pretty handy fixing these games, so if i can be of assistance in any way, drop me a line!

#12 3 years ago

???

sdynak

Inactive member

Quoted from frunch:
Small world, lol! I have plenty of electronics parts on hand if you need anything. Chips, transistors, caps, fuses, etc...not to mention pinball parts. I'm also pretty handy fixing these games, so if i can be of assistance in any way, drop me a line!

Thank you! Might be in touch depending on how far my skills let me get in trouble here

#13 3 years ago

???

sdynak

Inactive member

Quoted from YeOldPinPlayer:
This NVRAM is by barakandl You can’t go wrong with his stuff: https://nvram.weebly.com/

Good stuff..

For now if I cut out the battery the only impact is keeping high score? I'd like to get this working first and then do some updates like this but would feel better knowing the battery is out sooner than later. This board is too clean to ruin at this point.

#14 3 years ago

TPR

frunch

Pinside member

The board will still boot fine without a battery installed. I always cut the battery off first thing when i get a game that has an original one.

#15 3 years ago

GTX

gdonovan

Pinside member

7y 185K 13,220 70

Quoted from T-Tommy:
The board looks great so let's assume that the problem isn't related to any board damage. I would start out by getting rid of the 6800 at U9 which is made by AMI.

I had an oddball problem with my Trek that can be laid at the feet of an AMI 6800.

Looked like a write issue with the ram but turned out to be the CPU instead.

#16 3 years ago

???

T-Tommy

Pinside+ Frequent

Prescott Valley, AZ

7y 36,300 158 5

Quoted from T-Tommy:
Also the VMA at pin 5 should be pulsing.

6800 pin 5 goes through U17 and U18. If either of these support chips are bad the 6800 can't 'find' the game code. Had this happen on a board I was working on. This can also cause a locked on LED. I'm not a software genius, but I think this is how it works.

#17 3 years ago

???

sdynak

Inactive member

Quoted from frunch:
The board will still boot fine without a battery installed. I always cut the battery off first thing when i get a game that has an original one.

Good to know and thanks for your support so I could continue to reply to my own thread ..

Best,
Stan

#18 3 years ago

???

sdynak

Inactive member

Quoted from gdonovan:
I had an oddball problem with my Trek that can be laid at the feet of an AMI 6800.
Looked like a write issue with the ram but turned out to be the CPU instead.

For the cost of the 6800 it seems like a good reason to get one and even have handy.. thanks for the feedback. Probably going in this direction first.

Best,
Stan

#19 3 years ago

GTX

gdonovan

Pinside member

7y 185K 13,220 70

OP
Quoted from sdynak:
For the cost of the 6800 it seems like a good reason to get one and even have handy.. thanks for the feedback. Probably going in this direction first.
Best,
Stan

Come to think of it, I think I had the same problem you do.

Do you have another board you can swap out the CPU for testing?

Mind you there are a number of sound boards that have a 6800 on them as well!

#20 3 years ago

???

sdynak

Inactive member

Quoted from gdonovan:
Come to think of it, I think I had the same problem you do.
Do you have another board you can swap out the CPU for testing?
Mind you there are a number of sound boards that have a 6800 on them as well!

Interesting thoughts.. double checked and the sound board on this units does not have a 6800. Here are all pics just so everyone can see what I'm working on. Front glass is not in at the moment.

Thank you!
IMG_9073 (resized).jpgIMG_9074 (resized).jpgIMG_9075 (resized).jpgIMG_9076 (resized).jpgIMG_9077 (resized).jpgIMG_9078 (resized).jpgIMG_9079 (resized).jpgIMG_9080 (resized).jpgIMG_9081 (resized).jpg

#21 3 years ago

GTX

gdonovan

Pinside member

7y 185K 13,220 70

OP
Quoted from sdynak:
Interesting thoughts.. double checked and the sound board on this units does not have a 6800. Here are all pics just so everyone can see what I'm working on. Front glass is not in at the moment.
Thank you!
[quoted image][quoted image][quoted image][quoted image][quoted image][quoted image][quoted image][quoted image][quoted image]

I was thinking of another title like Flash Gordon which has a Bally Squawk and Talk board, it has a 6800. Some Gottlieb sound boards do as well like Black Hole and Haunted House if my memory is correct.

#22 3 years ago

???

sdynak

Inactive member

Quoted from gdonovan:
I was thinking of another title like Flash Gordon which has a Bally Squawk and Talk board, it has a 6800. Some Gottlieb sound boards do as well like Black Hole and Haunted House if my memory is correct.

Cool.. got it. All we have is this girl at the moment to work with. No spare parts even and starting from the ground up. It worked at one time while my buddy owned it. Just broke it out and now she is playing games with us .

Thank you for the suggestions.. all good and learning.

Best,
Stan

#23 3 years ago

???

sdynak

Inactive member

So I am marking this post resolved!!

It was the 6800 CPU!

The awesome thing was frunch helped us out locally with lots of parts to get through this and then some. What an incredible genuine person he is. Thank you so much for your help and everyone that chimed in to bring this girl back to life.

We feel like a kid again .. Hopeful I can return the favor to someone in the future.

Thank you again.. Some final pics attached showing working displays and playfield.
IMG_9083 (resized).jpgIMG_9087 (resized).jpg

Have some tests to go through and bulb changes but the progress made in just a few days is short of amazing when a community comes together to help one another.

#24 3 years ago

TPR

frunch

Pinside member