(Topic ID: 298745)

Gottlieb System 80 MPU Repair - 2nd and 4th Player Digits Flicker

By Knxwledge

5 months ago


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#1 5 months ago

Light corrosion cleaned off the board, some components replaced, NVRam added. Works on cold boot but "crashes" after a while of being on, and on subsequent boots the R/W line of the 6502 is stuck. IRQ line is pusling and reset line starts out low, then goes high on boot. Would I be safe to assume the 6502 is toast, or could something else be causing the R/W line to be stuck?

My Ni-Wumpf MPU doesn't have issues booting, and I've done lots of work to the game so it isn't a problem with the power supply, connectors not being repinned, etc.

#3 5 months ago

What about just leaving the reset board disconnected?

#4 5 months ago
Quoted from ForceFlow:

I'd suggest looking at the reset board and the pull up resistor:
https://www.pinwiki.com/wiki/index.php?title=Gottlieb_System_80#Reset_Board

Quoted from JethroP:

What about just leaving the reset board disconnected?

My game doesnt have a reset board

#5 5 months ago
Quoted from Knxwledge:

My game doesnt have a reset board

Then you might need to add the resistor.

#6 5 months ago
Quoted from ForceFlow:

Then you might need to add the resistor.

Got it, I will take a look, I vaguely remember my board having it but it's been a while since I've looked at the back side. I just read that section you linked, and it says that the chance of it being because of the resistor is slim. If the pullup resistor doesn't fix it, what else would you suggest? Is the pullup resistor a 1/4w?

#7 5 months ago

Alright I think that pullup resistor solved the boot issue! It seems like it's booting consistently. Test 20, the memory test says the 5101 is bad, I tried saving settings for default high score and it wouldn't save. I tried starting a game but after it started I heard a coil continuously firing and it wouldnt get past the part where it's supposed to kick the balls out. Switch test reports 62 (left warbase hole) and 73 (10pt switches) are stuck, I dont remember the ni-Wumpf MPU doing that but its been a while. Displays are also a bit flickery

#8 5 months ago

Fixed switch issues, both were due to stuck switches on the playfield. The Ni-Wumpf MPU switch test didnt tell me they were stuck . Game starts and works fine from the cursory test I did.

Displays are still occasionally flickery on some digits, and NVRam isnt working. I tried swapping in the original RAM that I desoldered and it didn't work either. Pics attached of the socket I added for the RAM. I checked continuity for the various input pins, some of the output pins, and also made sure there werent 2 pads under the socket itself bridged together. Im gonna keep continuity checking the output data and address lines

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#9 5 months ago

Swapped in a 5101 from a parts board that I had, and memory test shows 99 which means the 5101 is working. That NVRam module must be bad :/ Now onto the displays flickering...

#10 5 months ago
Quoted from Knxwledge:

Now onto the displays flickering...

How bad is it? I remember reading that some pulsating is normal for these displays.

#11 5 months ago
Quoted from sparky672:

How bad is it? I remember reading that some pulsating is normal for these displays.

Yeah the pulsating is there which I expect but occasionally random digits in the 2nd and 4th player will flicker. I think it's likely a problem with Z24 or Z25. I used my probe and nothing appears to be stuck but I think I would need to break out the scope to know for sure (the scope I have that I don't know how to use lol).

#12 5 months ago

Diode check on Z24 and Z25 is good, tried piggybacking a 7404 from a parts board onto Z24 and nothing changed. I noticed that Z26 also feeds digit 1 info to displays 2 and 4. Did diode test on Z26 and red lead on ground, black lead on pin 13 gave me a reading of 0.31, compared to 0.9 on the rest of the pins and all pins of Z25. I dunno if that means it's bad though considering pin 13 isn't used on Z26, so that could explain the different reading.

#13 5 months ago

2 steps forward 1 step back... MPU stopped booting again. IRQ line stuck high, R/W line stuck high, Reset pin goes low for split second then high on boot which is correct. Clock signal from pin 37 is pulsing. Sync line is stuck low.

#14 5 months ago
Quoted from Knxwledge:

Light corrosion cleaned off the board, some components replaced...

Mine was similar. The corrosion was so minor that I thought it had been all cleaned up. It wasn't.

My headaches didn't stop until I did the reset modification, which replaces something like 20 components with one plus a few jumpers. i got my MCP130-460DI/TO on Amazon for two bucks plus $3 shipping. Had to wait about a week.

amazon.com link »

When I started removing parts the problems became obvious. At least three old components were held together with nothing but friction... resistor leads fell out of resistors, and none of this damage was visually apparent while soldered onto the board. You may think all the corrosion is gone but there still might be parts that are compromised and internally corroded.

I was so happy with the MCP130-460DI/TO, I purchased a second one and put it on the driver board for a clean looking anti-thunk modification.

All that being said, I only had one boot problem with many weird symptoms. Whenever it booted successfully, I had zero issues no matter how long I played. However, it did not always boot. Sometimes it sat there with garbage on the displays, sometimes the displays stayed dark, sometimes coils locked on. Whenever I worked on the board, I thought I was making progress. However in reality I was just physically disturbing broken components elsewhere and the symptoms morphed or it would start working again for a little while. I mistakenly thought "I found it" at least three dozen times before I actually replaced the reset circuit with something reliable. All that wasted time and money chasing ghosts instead of just literally getting rid of anything that was touched by the alkaline.

#15 5 months ago
Quoted from sparky672:

Mine was similar. The corrosion was so minor that I thought it had been all cleaned up. It wasn't.
My headaches didn't stop until I did the reset modification, which replaces something like 20 components with one plus a few jumpers. i got my MCP130-460DI/TO on Amazon for two bucks plus $3 shipping. Had to wait about a week.
amazon.com link »
When I started removing parts the problems became obvious. At least three old components were held together with nothing but friction... resistor leads fell out of resistors, and none of this damage was visually apparent while soldered onto the board. You may think all the corrosion is gone but there still might be parts that are compromised and internally corroded.
I was so happy with the MCP130-460DI/TO, I purchased a second one and put it on the driver board for a clean looking anti-thunk modification.
All that being said, I only had one boot problem with many weird symptoms. Whenever it booted successfully, I had zero issues no matter how long I played. However, it did not always boot. Sometimes it sat there with garbage on the displays, sometimes the displays stayed dark, sometimes coils locked on. Whenever I worked on the board, I thought I was making progress. However in reality I was just physically disturbing broken components elsewhere and the symptoms morphed or it would start working again for a little while. I mistakenly thought "I found it" at least three dozen times before I actually replaced the reset circuit with something reliable. All that wasted time and money chasing ghosts instead of just literally getting rid of anything that was touched by the alkaline.

Here's my board as it currently sits with corrosion cleaned up. Nothing damaged on the backside. I might consider that reset modification but this is just a backup for my Ni-Wumpf MPU so depending on how hard it is I might just forget it. When your board stopped booting did the clock signal get disruped too, or only the CPU output?

20210817_193711.jpg

#16 5 months ago
Quoted from Knxwledge:

Here's my board as it currently sits with corrosion cleaned up. Nothing damaged on the backside. I might consider that reset modification but this is just a backup for my Ni-Wumpf MPU so depending on how hard it is I might just forget it. When your board stopped booting did the clock signal get disruped too, or only the CPU output?

I never lost the clock, but I thought I was having clock issues (some misleading info in an online guide) and I replaced the crystal and two chips... my symptoms morphed greatly but the booting issues persisted. I am still glad I changed those components because they were not expensive and now they're brand new.

The reset modification was so super ridiculously easy. There's a color coded guide and it's just a matter of removing those parts. Use existing holes to solder in solid wire jumpers and the new reset chip. Super easy and so glad I did it.

As far as your board... it doesn't matter how good it looks because we cannot see inside components. A couple of my 4 transistors were disintegrating up where the lead attached to the body and I could not see it. Leads fell out when I removed them. Resistors falling apart when I removed them... everything looked good at first glance, just like your board. Speaking of your board, it appears like a couple of your resistors are physically damaged... is the coating chipping off? Are those cracks where the leads enter the body? Get those replaced for sure, but at that point, might as well do the reset mod.

BTW, why is there a battery on your board when you said you installed NVRAM?

damaged resistors?

reset mod

#17 5 months ago
Quoted from sparky672:

I never lost the clock, but I thought I was having clock issues (some misleading info in an online guide) and I replaced the crystal and two chips... my symptoms morphed greatly but the booting issues persisted. I am still glad I changed those components because they were not expensive and now they're brand new.
The reset modification was so super ridiculously easy. There's a color coded guide and it's just a matter of removing those parts. Use existing holes to solder in solid wire jumpers and the new reset chip. Super easy and so glad I did it.
As far as your board... it doesn't matter how good it looks because we cannot see inside components. A couple of my 4 transistors were disintegrating up where the lead attached to the body and I could not see it. Leads fell out when I removed them. Resistors falling apart when I removed them... everything looked good at first glance, just like your board. Speaking of your board, it appears like a couple of your resistors are physically damaged... is the coating chipping off? Are those cracks where the leads enter the body? Get those replaced for sure, but at that point, might as well do the reset mod.
BTW, why is there a battery on your board when you said you installed NVRAM?
[quoted image]
[quoted image]

I went with the coin cell battery because I think the NVRam legs messed up the socket I installed. It was way too easy to pull chips out of the socket so I replaced the socket and went with regular 5101 ram. That was why my game kept saying the 5101 was bad, the legs weren't making good contact in the socket.

I did replace a couple of the components you circled and it didn't help. I ordered one of those MCP-130s from GPE, I'm gonna do the reset modification as you suggested.

1 week later
#18 4 months ago
Quoted from sparky672:

I never lost the clock, but I thought I was having clock issues (some misleading info in an online guide) and I replaced the crystal and two chips... my symptoms morphed greatly but the booting issues persisted. I am still glad I changed those components because they were not expensive and now they're brand new.
The reset modification was so super ridiculously easy. There's a color coded guide and it's just a matter of removing those parts. Use existing holes to solder in solid wire jumpers and the new reset chip. Super easy and so glad I did it.
As far as your board... it doesn't matter how good it looks because we cannot see inside components. A couple of my 4 transistors were disintegrating up where the lead attached to the body and I could not see it. Leads fell out when I removed them. Resistors falling apart when I removed them... everything looked good at first glance, just like your board. Speaking of your board, it appears like a couple of your resistors are physically damaged... is the coating chipping off? Are those cracks where the leads enter the body? Get those replaced for sure, but at that point, might as well do the reset mod.
BTW, why is there a battery on your board when you said you installed NVRAM?
[quoted image]
[quoted image]

The reset modification appears to have fixed my board not booting, thanks! Still having issues with the digits on player 2 and 4 flickering. Looks like every digit besides the far left digit is doing it. I suspect Z24 because it is a 7404 associated with digit strobing that feeds all but one digit of players 2 and 4.

#19 4 months ago

Finished the reset mod and it helped the game boot once, but then it froze up and now wont boot again. Reset line is pulsing, r/w and irq lines are stuck on the 6502. I noticed after leaving it on for a while the 6502 was getting quite warm, probably as warm as the RIOT chips (which I know normally run warm). Is this normal or not? Also when it was running the 2nd and 4th player digits were flickering again so I suspect Z24 but I'll have to get to that later.

#20 4 months ago

Changed the crystal and it appears to boot consistently now. Changed Z24 to fix the digits and it didn't help...

#21 4 months ago
Quoted from Knxwledge:

Changed Z24 to fix the digits and it didn't help...

What are the chances that 5 out of the 6 connector pins are loose on A1-J3 ? That seems to be the only other thing common to digits on player 2 and 4 since they share these wires. Is Z24 getting a solid ground and 5 volts to its corresponding legs?

#22 4 months ago
Quoted from sparky672:

What are the chances that 5 out of the 6 connector pins are loose on A1-J3 ? That seems to be the only other thing common to digits on player 2 and 4 since they share these wires. Is Z24 getting a solid ground and 5 volts to its corresponding legs?

The digits only flicker on this MPU, I have a Ni-Wumpf MPU and it doesn't do it. I will have to check out power and ground on Z24 but I don't see why it wouldnt be

#23 4 months ago

I see there's a cap (C31) connected to pin 14 of Z24 I could try changing or looking at. I have a parts board I can use to get Z25 and the cap, but it was robbed of the RIOT chips. Highly doubt it's a RIOT chip issue though as if a RIOT chip was failing I think I would have other way more drastic and visible issues.

#24 4 months ago

Ok wiggling J3 caused other segements and digits to bug out so it is actually J3. Musta happened from me plugging and unplugging the original MPU for testing. Thought I was done repinning this game!!

Edit: repinning J3 didnt fix it AAAAAAAAh

#25 4 months ago
Quoted from Knxwledge:

wiggling J3 caused other segements and digits to bug out so it is actually J3. Edit: repinning J3 didnt fix it.

On mine, I had a cracked copper trace coming from an edge finger. Could only see under magnification and it was causing intermittent problems until it failed outright. So just because you have new clean shiny pins inside the edge connectors, doesn't mean the connections on any particular board edge are clean, solid, continuous, or good.

#26 4 months ago
Quoted from sparky672:

On mine, I had a cracked copper trace coming from an edge finger. Could only see under magnification and it was causing intermittent problems until it failed outright. So just because you have new clean shiny pins inside the edge connectors, doesn't mean the connections on any particular board edge are clean, solid, continuous, or good.

Some of the fingers had copper exposed so I retinned all J3 fingers with a tiny bit of solder, then continuity checked every trace going into and coming out of Z25, and all traces leading to J3 fingers. No change. Last thing I can think of before I shelve it is to repin J2 as well.

#27 4 months ago

Repinning J2 seemed to fix the displays then after I had it on for about 5 minutes the board froze up and stopped booting consistently again

Edit: displays arent fixed, game still boots inconsisently. Tried replacing Z2 Z3, no change.
When it did boot I still saw the displays bug out. I gave it my best effort but board repair is my weakest area and System 80 boards arent exactly noob friendly. Im shelving this for now. Hopefully in 6 months or a year I can bump this thread if I make headway.

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