A long strange (repair) voyage with a Game King

[Badbaud]

I must admit I am no expert on Game Kings. Change a lock, change a battery, repair a monitor is about it.

We, Larry and I, were called to a customer to put a lock in his GK upright, video multi game.

This was an older game with a I/O board tray above the MPU board. The customer had just purchased it and wanted to secure the contents.

The machine had no coin assembly or Hopper but took bills.
After installing the lock I noticed it kept throwing up random "coin in" errors so I inspected the coin in jumper plug and one of the pins was broken off inside the connector.
Closing the door and the broken pin would move in and out of the plug breaking the connection and causing the coin in error. I fixed that with a new pin.

Then I noticed the fan was not running and addressed that concern with the customer but told him he would have to bring the machine to the shop to get the fan replaced.

The machine showed up at the shop two days later. After un-plugging everything and removing the top board frame I could get to the fan. I noticed the fan wires had been cut
and were not connected. Spinning the fan manually told me it was froze up.

I removed the fan and handed it to Larry and told him to get another one of the same out of our good fan box. I installed a 2 pin connector and plugged it into the machine side fan connector.
I left the board tray out and turned on machine power, the fan ran for about a minute and started smoking.
I pulled the fan out and it was hot. I couldn't understand what was going on. The new fan was the same 12V model that I had removed. The voltage to the fan had read 16VDC so I assumed it would be down at 12VDC if everything was plugged in.

Just to be sure I pulled some GK schematics and checked the machine wiring schematic. Damn, the fan in the schematic was listed as a 24VDC fan not a 12VDC fan.

So, someone in the past had put in a 12VDC fan, burned it up, and simply cut the fan wires, removed the 2 pin fan plug, and sold the machine with no fan flow instead of putting in the correct fan.

I put in a 24VDC fan and turned on power, without the board tray installed yet, and the fan blew just fine with no escaping smoke.

I then re-installed the board tray and reconnected all of the plugs, put in the monitor, and turned on power thinking I was done.

Nope, the power supply starting pulsing on and off. I tried another power supply out of our  test GK in the shop and got the same pulsing from our power supply.
Tried each power supply back in our test machine and our game came up.

That told me it must be something in the machine causing the overload. So I started doing a process of elimination by removing first the MPU board and power up, same pulsing.
Removed the I/O board, still pulsing, unplugged the bill validator -- the pulsing stopped.

Re-installed everything and took the BV to my bench and lubed it and cleaned it and calibrated it using our DT104 to power it. Also lubed the gears in the cash can.
After all of that the BV was running much smoother, on the bench.

But in the machine the power supply would still pulse. So I removed the BV and this time the power supply would continue pulsing with it out.
Well the center of the problem appeared to be with the power supply, but trying it in our test machine again and our game came up.

The only difference between our test game and the customer game was our game had NO BILL VALIDATOR.

The bill validator runs off of 12VDC. No 12VDC load in our machine and the PS worked, BV load in the customers machine caused the power supply to pulse.
This means the 12VDC in our test machine was also weak so someone had removed the BV and related wires before we got the machine because the BV would not work.

Next step, I re-capped the power supply (BTW this is day 2 of my journey) and installed it in the machine. I pulled the MPU board and I/O board to make sure the BV would cycle because it was now getting a good 12VDC. It cycled just fine, a good, strong, sounding cycle.

Next I re-installed the I/O board and MPU board, turned on the machine, and the power supply started pulsing again. DAMN!

Using the same process of disconnecting one plug at a time until the pulsing stopped I discovered that the plug that comes directly from the power supply to the bottom left of the back plane, when disconnected, would allow the power supply to run with no pulsing.
Still a power issue somewhere.
So I plugged the plug back in and removed the MPU board, powered up, and the power supply did not pulse, the BV even cycled.

Now something on the MPU board was dragging down the power supply.
I got out my Ohm meter and  started checking Tranzorbs to see if one of them had shorted. No luck. I checked the 5V power supply for shorts, it was fine. I checked the audio amplifier IC and found a dead short from pin 3 to pin 5. Yes, power and ground to the Amplifier were at less than 1 Ohm, that's the 24VDC power from the power supply. But removing the MPU board and powering up and the fan and fluorescent modules ran fine.

I removed the Amplifier from the MPU board and still had the short. I started to Ohm the 24VDC bypass capacitors and every cap read dead short. So somewhere on the MPU board was a dead short to 24VDC.

Time to go home, day three will continue on Thursday.
If anyone can give me a clue as to where this short is before I start clipping bypass caps all over the board please let me know.

[Amechanic]

OMG.. What a job. Now that I've read this part, I can't wait for chapter 2.....

[Badbaud]

Thursday.... Found the short on the MPU board. It was U71, a 74HC240 octal buffer.  I removed it and put in a socket with a new 240 IC and my Ohm Meter no longer read a dead short.

Yay! I plugged in the MPU board and Monitor - turned the machine on - and within a minute the power supply started pulsing again.

I pulled out the MPU board and the new 240 IC had a burned pin 18 and 5. Both outputs for this chip. If I could find a schematic for this system it would be easier to trace the short (I assume it is a short to 24VDC).

So I removed the 240 IC and left it's socket empty, then powered up the game and everything came up, a picture on the screen and no power supply pulsing.

BUT... now it does not recognize some door being closed.  The game tells me on the screen if I open the main door, or the cash can door, or remove the cash can and clears those tilts when the related door is closed but it still reports a door C being open and I swear to heck there is no door C anywhere on this machine.