Skee-Ball Model S - help needed (SOLVED!)

[Lescell]

I picked up a 10' Model S with the SBC-1-A board. It currently does not work. The fan turns on and so does 1 LED on the board, but the displays don't work and can't start a game. I have no manual for this specific board, and I see no buttons on the board to enter a diagnostic mode. Can anyone offer some troubleshooting?

 

[gutz]

If the controller successfully boots, you should hear a chirp/squawk from the speaker and the display should be strobing zeroes. You drop a coin to start a game. There is a fuse to check near the transformer on the inside. The outside fuse should be fine since the fan is running, and the third fuse in the vertical holder is for the ball release and wouldn't cause a no boot.

 

[Lescell]

I feel like an amateur, posting for help before performing simple checks like voltages. I checked for 12V at a few points and was getting nothing, then switched to AC and found AC voltage at the DC points. Looks like the bridge rectifier went bad. Not sure what else may have gotten fried, but that's where I need to start.

I'll keep this thread updated.

 

[Lescell]

So, it's not the rectifier. Looks like the fault lies in the transfomer. She should step down from 120VAC to about 18VAC, but she's outputting about 60VAC. Unless someone chimes in, looks like I'll try and hunt down a transformer.

 

[Talljust1n]

Are transformers readily available?

 

[JakesArcade]

Full disclaimer I have not worked on a Skee ball before, however looking at the schematic, it looks like it just regulates the 18v to 12v and 5v. It should be trivial to attach a standard arcade power supply to these points and see if you have any life on the PCB. If the transformer is really outputting 60v those voltage regulators (7812 and 7805) are definitely cooked.

 

[Jetkidish]

Full disclaimer I have not worked on a Skee ball before, however looking at the schematic, it looks like it just regulates the 18v to 12v and 5v. It should be trivial to attach a standard arcade power supply to these points and see if you have any life on the PCB. If the transformer is really outputting 60v those voltage regulators (7812 and 7805) are definitely cooked.

This is the way to go in my opinion, I have a game that also runs on the model S hardware (Circus Hi Rise) and the transformer went bad. I just bypassed and put in a switching power supply. The game will be way more reliable.

 

[big420atx]

This is the way to go in my opinion, I have a game that also runs on the model S hardware (Circus Hi Rise) and the transformer went bad. I just bypassed and put in a switching power supply. The game will be way more reliable.

that's pretty interesting for sure.

 

[gutz]

Transformers are pretty tough and hard to kill (unless someone overfuses them). When they are bad, they either smoke, blow fuses, or do nothing. I'd say 93.467% of all arcade threads that start down the path of "my transformers bad, where's a new one?" ultimately come back to incorrect techniques of measuring the transformers windings or multimeter issues. Unplug the transformer connector from the pcb and apply power, you should have 120vac between pins 1 & 3, and you should have 18vac on 4 & 5. Remember AC doesnt have a GND reference, you are measuring AC volts between the wires. Thats all you need to test and verify the transformer is good. The 18vac might read a bit high since its not under load.

 

[Lescell]

Thanks gutz, looks like I was measuring the transformer incorrectly. If I measure it as you suggested, I get about 14VAC out of the transformer with no load. Even though it's lower than expected, why am I getting 60VAC out of the bridge rectifier when I should be getting 12VDC? I'm still learning how to read schematics and understand logic, but I must be missing something. Any other tests you recommend?

 

[MrGorf]

Set your meter to DC and measure across the 15,000 uF. cap (C13). What is the reading?

 

[Lescell]

Set your meter to DC and measure across the 15,000 uF. cap (C13). What is the reading?

15.5VDC

Other notes..

R32 and CU17 are getting extremely hot
R32 is a 5 ohm resistor while the schematic calls for a 10 ohm. It looks factory though.
D30 and D31 (12VDC LEDs) are not lit
Only getting about 2.5VDC at the 5V pin on the processor

I tested all 4 voltage regulators (U16, U17, SRC2 and SRC3) and all check out ok. I even replaced U17 since it was getting real hot and no change.

I don't understand the logic enough to understand what's not working correctly. My next step would be to replace R32 and try again.

 

[MrGorf]

Sounds like something is loading down the 5V line. Can you run the power supply without anything else connected? If so, do D26 (12V LED) and D29 (5V LED) light up?

 

[Lescell]

This is being tested on the bench with no accessories plugged in. D28 (5V LED) lights up, just not the 12v LEDs (D30 and D31).

 

[MrGorf]

Looking at the schematic, D30 and D31 look to be part of the circuit for the opto-isolators that control the ball release solenoid and the flasher circuit for the beacon on top.
They should only light when the opto's get a signal to trip either the beacon or ball release.
There should be a LED (D26) near the LM7812 (12V Reg). Does that one light up?

 

[Lescell]

Oh, ok, I was misunderstanding what those LEDs were for, but that makes sense.

D26 does light up, yes.

 

[MrGorf]

So it sounds like you have both 5V and 12V at the power supply.
Where are you measuring for 5V on the CPU?

 

[Lescell]

For 5V at the CPU, I'm measuring across pins 35 and 39 (using pin 35 for +5V and pin 39 for ground).

Don't forget, R32 and U17 are getting smoking hot, still don't know why that is either.

 

[MrGorf]

It looks like the CPU is an 8085. Pin 40 is +5 and pin 20 is GND, although where you are measuring should be OK as those pins are tied to +5 and GND.
If you measure pin 2 of each regulator what is the reading? Sounds like the 12V is fine but is the 5V good or is that low.
If the regulator is getting hot then something must be loading it down. Do any of the chips feel hot? Are they all orientated correctly in their sockets?
If they are socketed, try removing them one at a time and see if the 5V recovers.

 

[Lescell]

Here's some of the readings..

R32

Voltage IN = 15.3
Voltage OUT = 5.1

U17

Voltage IN = 5.1
Voltage OUT = 2.9

U16

Voltage IN = 14.7
Voltage OUT = 12.6

I removed all socketed chips one at a time and nothing brought the 5V back up. To me it seems that R32 is dropping the voltage too much and the input at U17 should be about 2V higher, but I also have very little idea of what I'm talking about