(Topic ID: 259683)

*solved*South park not booting, weird coil activity


By CanadianGamer

11 days ago



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  • Latest reply 5 days ago by Comox-Rocks
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#1 11 days ago

*solved. It was a burnt trace near the battery after all.

Where to start?! I'm working on South Park for a friend, and he got it from someone that obviously robbed parts from it to fix another. I'll try to list everything I've done to it, and have videos to show what's happening currently when I try to fire it up.

I've replaced missing coils, switches etc with new matching parts, new ribbon cables, new DMD power supply, clipped and checked every diode on every coil under playfield, New Bridge rectifier on BRDG21 for 5volt, all connectors reset several times, connectors and pins in great shape (no burning), I re-flowed the solder on all the connectors, socketed chips removed and replaced (all in great shape), I buzzed out the legs of the chips around the batteries and all are connecting, Remote battery pack installed although no alkaline damage at all on board, New fuses throughout and clips in good shape.

The 5 volt seems to be unstable for some reason, or else both of my crappy dmm's are lying to me. It will stay at 5.1volts sometimes, then seems to drop below 4.5 and back up, over and over, then stable again. This was why I replaced BRDG21 in hopes that the 5 volt would stabilize. I tried measuring it on the MPU board as well and it was doing the same thing of course. I tried removing J16 and the 5 volt was still unstable on the driver board. I haven't tried testing my DMM's on the 5 volt circuit in another game yet but should probably do that.

The L200 light goes on and off on the MPU, sometimes stays on, sometimes stays off. I guess it suggests an issue with the MPU, but it could be the 5 volt issue, or ROM, RAM, CPU chips. The MPU is pretty much immaculate looking with no battery damage and no previous work done to it. The DMD does flash the initial screen from time to time but that's it, and I get a little blurb of the startup music every once in a while.

The driver board has had a few transistors replaced, and the bridge, but nothing else that I can see and the work looks well done. I got the old bridge off with ease by cutting the legs on the old one and heating them to pull them through, and it went very well. It didn't change the 5 volt stability at all though.

I have looked through every forum topic to try to figure this out, but I'm getting to a point where I really could use a little help. It would be much appreciated.

I didn't do anything different between the 4 videos below, just turned the machine off and restarted it. It does something different every time I start it lol.


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#2 11 days ago

Further testing...

I tested my DMM's on a different machine and they read 5 volts with no problem... just wanted to check that off the list.

I fired south park up again when my friend who owns it was just over, and showed him the 5 volts that was going up and down, only it wasn't. I guess it depends on what stage the CPU gets to as to whether or not the 5 volt will jump around. I have to try to get that to happen again, and see if the L200 light was on or not. I restarted the game and the 5 volts was jumping around again, but I didn't notice what was happening with the lights on the board when these things were happening.

#3 10 days ago

Did you check the back of those boards?Burnt traces ect.
Also go over the ribbon cables again and make sure the connectors are placed in the correct order and connected properly and not missing any row of pins

#4 10 days ago
Quoted from pinmike:

Did you check the back of those boards?Burnt traces ect.
Also go over the ribbon cables again and make sure the connectors are placed in the correct order and connected properly and not missing any row of pins

Thanks pinmike. Yes I did check the boards and nothing is burnt anywhere, they look great. I haven't gone as far as checking every trace with a meter, but I did meter around the battery area where there is no sign of alkaline damage at all. As I mentioned, I re-did the solder on all the connectors of both boards, and none of them look at all burnt.

The ribbon cables are all new and the red lines go to pin 1 on all of them. They are definitely connected properly and not missing any rows of pins.

I will go over everything you've mentioned again anyhow, and thanks for the input.

#5 10 days ago

Try removing the short ribbon cable between the CPU and driver board and seeing if the CPU board boots up.

Check ALL the fuses and verify they are all the correct values.

You need to see if something is drawing down the power supply when it energizes (ribbon cable) or is over fused.

If that checks out, check the 5V regulator circuit. Start with measuring the input to the 5v regulator section (across C203) which should stay over 10V

#6 10 days ago
Quoted from Schwaggs:

Try removing the short ribbon cable between the CPU and driver board and seeing if the CPU board boots up.

I did that and it didn't change how the CPU booted up. Sometimes L200 would stay on, and sometimes not.

Quoted from Schwaggs:

Check ALL the fuses and verify they are all the correct values.

I replaced all the fuses before doing anything to it. Some of them were the wrong value but they're all good now.

Quoted from Schwaggs:

If that checks out, check the 5V regulator circuit. Start with measuring the input to the 5v regulator section (across C203) which should stay over 10V

I measured across C203 and it was 11 volts. The 5v has actually been steady when checking it today, but like I said it does something different every time I start it up. Thanks for the input, much appreciated.

#7 9 days ago

Today it had all the lights on the boards lit steady, including the blanking which was a first, usually it flashes non stop. Nothing was happening though, the game didn’t start. Then it went to the mode where L200 goes out and all the play field lamps flash along with the relay clicking and blanking light flashing. I’ve heard a lot of people get to that stage but for me it’s always something different every time I fire it up. Cpu board must be wonky somewhere, or both boards.

#8 9 days ago

If you are sure the 5V is stable, it sounds like the CPU is not running reliably. If it locks up, the blanking will engage.

Do you have a logic probe? If so, when it isn't running correctly, try probing the pins of the CPU to see if it is running. Start with pin 35 (clock) then the address lines (8-23) and confirm they are oscillating. Also confirm 5V is reliably, locked on at 5V all the time.

Is the CPU board original to Southpark or did you get it from another game?

From the schematics:
A watchdog is used to monitor the CPU and the 5v supply. If the 5v supply is below 4.75 the watchdog will hold the CPU/Sound Board & I/O Board in reset. The watchdog must be fed at a rate of 250ms or faster. The signal used to feed the watchdog comes from the EPROM Bank select signal used to load U211. The CPU has a timer interrupt used as a heartbeat for the system this signal comes from counter U2. The clock for this counter is the CPU Q CLOCK. Clearing the timer interrupt is done by reading the DIP Switch. The timer interrupt can be observed at TEST POINT FIRQ. In normal operation "FIRQ" should be toggling at a rate of 976Hz.

#9 9 days ago
Quoted from CanadianGamer:

The MPU is pretty much immaculate looking with no battery damage and no previous work done to it.

What does the area where the batteries were look like? Got a clean picture of just the area around there?

#10 9 days ago

Meh. Sell it to me instead. If no, please post a picture of the cpu board including the battery box and surrounding areas in as high rez as you can.

A bad cpu socket or ram socket or their IC's will cause this. Battery acid damage is by far the most common though.
I am looking for a south park at any rate. Broken is fine
Cheers

#11 8 days ago

Thanks very much for all the great input! Had you guys not asked for Hi-res photos I wouldn't have seen this. There was a broken trace after all. Just one small trace that doesn't connect to the chips, and before I only buzzed the chip legs to the underside of the board to check the sockets. The traces all looked good for the most part, but there were a couple that looked a bit darker than the rest when I looked close with the camera. I buzzed them all and this one little trace was dead, so I jumpered it on the back of the board with a small wire and it works!

I didn't have time to do any testing but it fires up and is begging for coins!

I'm sorry if I wasted your guys' time, and I know now to look much closer around the batteries! Thanks very much, can't wait to get a game going! Cheers!

And Hawk, I'll let my friend know you're interested, but I know he wants to keep it in the family for now. Still living on that wee island? You guys have (or had) my Last Action Hero. Cheers.

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#12 8 days ago
Quoted from CanadianGamer:

Thanks very much for all the great input! Had you guys not asked for Hi-res photos I wouldn't have seen this. There was a broken trace after all. Just one small trace that doesn't connect to the chips, and before I only buzzed the chip legs to the underside of the board to check the sockets. The traces all looked good for the most part, but there were a couple that looked a bit darker than the rest when I looked close with the camera. I buzzed them all and this one little trace was dead, so I jumpered it on the back of the board with a small wire and it works!

Battery damage is always suspect #1 in cases like this. But if the board wasn't cleaned properly/well enough, the residue will eat other traces and you'll have ongoing problems.

#13 8 days ago

Thanks, I’ll clean it with vinegar and water mixture, sand off any alkalinity etc and see if I can make it last. At least we’ll know what to look for if this problem occurs again.

#14 7 days ago

Hey my friend. That is not fixed. It needs the socket removed the area sanded and vinegar treatment then water then iso. Then replace the components. There are several traces I can see that are bad. More under socket I bet. It hides in the worst places.
Not hard to fix with the right tools, just time consuming.

#15 7 days ago

And yes I know you. lol We are still on the tiny island. Love the last action hero. A friend talked it out of us for a while but it will come back again.
Looks too good next to T2.
If you ever need help shoot me a pm anytime. Always happy to help.
Cheers

#16 5 days ago

I’m looking forward to getting it into the mancave once ian finishes it up. I’ve sent board over to my microelectronics wizard to get it properly repaired as it’s a Grad gift for my daughter.
Thanks for your help hawk!
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