Heavy Metal Meltdown
Bally, 1987
Special Force
Bally, 1986Years after my last attempts to start that Special Force game, I had the occasion to purchase a Bally Heavy Metal Meltdown.
So I've been able to test my boards on a functional machine, and I've realised that the sound board is preventing the game to boot correctly.
When the sound board is disconnected, the game starts.
Has this kind of problem already been reported?
Thanks for your help !
It is quite possible.
The sound board is connected to J5 on the mpu board.
J5 connects to the Peripheral Bus, which leads directly to the 6803 processor.
Any fault on those lines can have this effect I think.
Check the PIA (6821) on the sound board.
Also remove capacitor C12.
Here is a topic about this cap.
https://www.pinwiki.com/wiki/index.php?title=Bally_6803#Sounds_Deluxe_Board
I'll attach the best schematic I could find from the Sounds Deluxe board.
Peter
http://www.inkochnito.nl
Bally_Sounds_Deluxe_schematic.pdf
Not risky at all. Press on.
--
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/Contact ... for board repairs
http://www.PinWiki.com - The Place to go for Pinball Repair Info
Well... That's odd...
So.
I did cut the cap, and tried the 6821 on my non working sound board : no change.
I tried the "non working" 6821 on the functional sound board : it worked.
So i guess both 6821 are ok.
Back with the non working sound board connected, I noticed that on TP1 I had 0 volts on my DMM, while the functional one shows a 5.12V...
I guess it tells something about this issue.
Quoted from wylcot:Well... That's odd...
So.
I did cut the cap, and tried the 6821 on my non working sound board : no change.
I tried the "non working" 6821 on the functional sound board : it worked.
So i guess both 6821 are ok.
Back with the non working sound board connected, I noticed that on TP1 I had 0 volts on my DMM, while the functional one shows a 5.12V...
I guess it tells something about this issue.
It is probably those f*&king tantalum capacitors. Hard to tell from the pic but C33 looks like it exploded and there is just some bits of leads left. Use a 10uF MLCC or electrolytic.
paint (resized).pngQuoted from barakandl:It is probably those f*&king tantalum capacitors. Hard to tell from the pic but C33 looks like it exploded and there is just some bits of leads left. Use a 10uF MLCC or electrolytic.[quoted image]
Good find!
Indeed the cap look blown away.
It is part of the 5V power supply on the board.
Most likely the 7805 (U17) is broken (defective) and needs to be replaced.
That is why you do not have the 5V at TP1.
Be sure the new cap is rated at 25V or higher.
It is receiving 14V (maybe up to 16V) from the power supply.
And another tip, replace the print headers.
If they are not encased in a plastic socket, replace them.
https://www.pinwiki.com/wiki/index.php?title=Bally_6803#Replacing_header_pins
The headers on this era of midway boards do suck but be careful trying to install new ones. The originals seem to be press fit wedged into the board. I find these to be the hardest ones to replace without mangling the board. The plated hole wants to come out with the header pin and then the new replacement needs to be pressed in.
The 7805 has short circuit protection. Hopefully it was able to save itself. The bits left on the board might still be creating a dead short.
Quoted from wylcot:So I've changed that cap for a 10uF 50v, but still nothing.
Is that 7805 the next in line ??
Doubtful. Those rarely fail. And, it is easy to test the device.
Meter on DC.
Power on.
Black on game or board ground.
Red on each of the legs of the 7805 one at a time.
One leg is ground.
One leg is incoming voltage and should be something above 5V
Last leg is 5V out.
Measure.
I think you will find the device working fine.
—
Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
http://www.PinWiki.com/ - The new place for pinball repair info
Quoted from wylcot:So I've changed that cap for a 10uF 50v, but still nothing.
Is that 7805 the next in line ??
measure resistance from 5v / 12v to ground. Is it still shorted? I think there are at least a couple 4.7uF tantalums. If one is bad, i wouldn't trust any of the others and would be cutting them out one by one looking for the short to clear. Careful where you are probing at out of the game as I am pretty sure this board has some isolated ground returns for the regulator vs analogue stuff.
The potential energy in the tantalum capacitors is a bit scary. Once they go runaway and the power supply does not shut down you can get a fireball shooting across the room. I think most repair people hate those tantalums even more than electrolytic. Be careful powering up this board if it is still shorted, wear eye protection.
Is there any evidence of that capacitor pinging off the backglass? They can fly off with some good force when they explode.
Hey guys !
I'm digging this thread out as I'm back onto fixing this game.
So, I was reading all this again to remember where I was at, and I'm about to go and test the 7805 like ChrisHibler suggested.
But I just looked at the 4.7uF caps. They seem to be c33 (the one that exploded) and c34.
Looks like it had been changed before i bought the game.
I don't know... It looks odd to me. Wasn't it soldered the wrong way ?
IMG_20220811_113504 (resized).jpg
Quoted from ChrisHibler:Doubtful. Those rarely fail. And, it is easy to test the device.
Meter on DC.
Power on.
Black on game or board ground.
Red on each of the legs of the 7805 one at a time.
One leg is ground.
One leg is incoming voltage and should be something above 5V
Last leg is 5V out.
Measure.
I think you will find the device working fine.
So yeah, definitely something weird with it :
I measured it, and I got 0.8v on #1, 0v on #2 and 0v on #3.
I tried on the working soundboard, and I got approx 12v, 0.1v and 5v.
Do you guys think it could be faulty, or something before it..?
Quoted from wylcot:I measured it, and I got 0.8v on #1
This is a problem. There is no incoming 12VDC.
The tantalum cap you pictured is installed correctly.
See image below.
Measure between each point and ground.
The banded side of D2 should have about 14VDC.
The banded side of D3 should have about 14VDC - 1*(.7VDC) = 13.3VDC
The banded side of D4 should have about 14VDC - 2*(.7VDC) = 12.6VDC
The banded side of D9 should have about 14VDC - 3*(.7VDC) = 11.9VDC
The banded side of D10 should have about 14VDC - 4*(.7VDC) = 11.2VDC
...assuming the general rule of thumb of .7VDC voltage drop across each of the 1N4004 silicon diodes.
Keep measuring until you find the voltage irregularity. Once you find that, the diode upstream has failed.
Bally used this "cheat" to drop the incoming 14VDC somewhat before piping it into the 7805 regulator.
Let us know what you find.
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
https://www.youtube.com/c/ChrisHiblerPinball
http://www.PinWiki.com - The Place to go for Pinball Repair Info
pasted_image (resized).png
Quoted from ChrisHibler:This is a problem. There is no incoming 12VDC.
The tantalum cap you pictured is installed correctly.
See image below.
Measure between each point and ground.
The banded side of D2 should have about 14VDC.
The banded side of D3 should have about 14VDC - 1*(.7VDC) = 13.3VDC
The banded side of D4 should have about 14VDC - 2*(.7VDC) = 12.6VDC
The banded side of D9 should have about 14VDC - 3*(.7VDC) = 11.9VDC
The banded side of D10 should have about 14VDC - 4*(.7VDC) = 11.2VDC
...assuming the general rule of thumb of .7VDC voltage drop across each of the 1N4004 silicon diodes.
Keep measuring until you find the voltage irregularity. Once you find that, the diode upstream has failed.
Bally used this "cheat" to drop the incoming 14VDC somewhat before piping it into the 7805 regulator.
Let us know what you find.
AWESOME !!! It was exactly that !
D4 was faulty.
Well, the values are a bit higher. It starts around 15VDC, but after I changed D4, the led flickered at last, and sound comes out of the speakers.
Thanks so much ChrisHibler
Inkochnito and
barakandl !
You rock !
Now it seems that one of the two CPUs boots correctly but can't have the sound going.
The adventure is still on 
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Piershil
Chesterfield, MO