Universal coin-in assembly and error 21

[uniman]

Below is a picture of a typical Universal coin-in assembly used in the older machines having the 8116 or 8800 mpu board.
Most have a cc-16d coin comparitor wired for 24 volts. The one pictured here has a dollar token in it. Universal supplied three wires to the comparitor, but with the cc-16d only two are used. The Universal manual has an added section on the cc-16d. There they show the third wire, blue, connected to the cc-16d lockout coil. This is not needed and I have not seen a machine wired this way. This was in the early 80's and I believe the coin comparitors were upgraded after the manual publication. Also, Universal suggested adding a resistor to the purple wire to drop down the voltage as this wire actually has 32 volts. Can't remember the size of resistor, thought it was 300ohm, but one member here said 150ohm. If I did the math I would know but since I don't use the resistor at all, don't really care. I've seen machines with and without the resistor. My home machines do not have the resistor and my cc-16d's are holding up just fine.

How the comparitor works;
A sample coin matching the size, weight, and metal makeup is inserted in the comparitor. When powered off the comparitor's coil is de-energized and the rake connected to the coil deflects all inserted coins to the tray. When you power up the machine the 32volts is sent to the comparitor, but the ground is interupted by the mpu until the machine is ready for play. Once the door is closed, locked and ready for play, (no tilts) the ground circuit is completed and the comparitor is powered up. A coin is inserted and the comparitor, using an electrical field, compares the inserted coin to the sample coin. If they match the coil is energized, the rake moves out of the way and the coin is allowed to drop to the hopper. If the coin does not match the sample coin the coil is not energized and the coin is rejected to the tray.
The comparitor works on it's own and the mpu does not communicate with it. The mpu does control the ground circuit to powerup/powerdown the comparitor. When the acceptable limit of coins is inserted, the mpu powers down the comparitor to prevent further coins from entering the machine. The machine will accept one coin over the max limit and will then count it to the next game. Two or more coins over the max limit will cause a tilt and error 22.

The optics;
After passing through the comparitor the coin will then pass through two optics. The coin must pass through the two optics between 0-2000 milliseconds. They are then counted by the mpu. If they do not pass through the optics within this time limit an error 21 will occur. This 0-2000 millisecond limit is factory set and can be adjusted. I say DON'T MESS WITH IT!
When the coin passes through the optic there is a red indicator LED that lights/flashes on the optic.
There is a third optic below the diverter solenoid, more on that later.

ERROR 21;
Now that we are at the optics let's talk about error 21. Several things can cause error 21. Lack of a sub-board at location A1 of the mpu will cause intermittant error 21's. A bad optic can cause error 21. A misaligned optic and unwired/disconnected optic will cause error 21. Bad components on the mpu can cause error 21. The two optics connected backwards will cause error 21.



Hope this helps,
Uniman

[uniman]

Had to break up my post into two messages as I exceeded the 5000 character limit.      First time for me.

Troubleshooting the optics;
Turn on the machine and with the door open look at the two optics just below the comparitor. The little red LED on each optic should NOT be on. If they are there is either something blocking the optic, the optic is not seated in it's proper location, or the optic is bad. If both optics look ok (no red LED) then remove the comparitor and drop a coin through the optics. You should see the LED's on each optic flash while the coin passes through. Below in the second picture I connected a spare optic and put a screwdriver in it to show the red LED.
Here is my troubleshooting method;
One optic flashes and one does not.
If one optic does not flash then swap it with the other optic and see if the problem is the optic or wiring. If the problem moves with the optic then I replace the bad optic. If the problem stays at the location then the wiring is checked. The big black plug connecting the door wiring to the machine is my first suspect. Check to make sure no pins and sockets are pushed down.
Both optics flash;
Check the connectors to the optics. The top optic should have pink/blue wbs(With Black Stripe)/black wires, the bottom optic should have pink/green wbs/black. Make sure they are not swapped. Also check that black plug connecting the door wiring to the machine. Even though the optics are working they send a HI/LO signal through the blue wbs and green wbs wires back to the mpu. If this circuit is broken you get an instant error 21.
Both optics do not flash;
Never had this one. Would check for 5volts dc on the pink wires. If I had 5 volts, then would check the ground (black wire). Check wiring and then mpu if no power/ground. (Note: even in TILT the machine will still power the optics) If power/ground ok, then replace both optics.

Diverter Solenoid;
After passing through the optics the coin has two possible paths to follow. There is a diverter solenoid that when energized sends the coin to the hopper. When not energized it drops the coin to the drop box hole in the bottom of the machine. The diverter is de-energized when the mpu detects that the hopper is full. To prevent an overflow of coins from the hopper the de-energized diverter allows the coins to drop into the dropbox that would be located in the slot stand. These diverters can be troublesome. And Universal used two different types. If you have an early 8116-A2 board with a late model diverter solenoid it will fail to stay energized. Even if you don't they still can fail to stay energized. So what I do is plastic tie the diverter solenoid shut. This way there is no question all coins are going to the hopper. Just make sure your not overflowing your hopper. Usually not a problem for home use.

Coin Box optic;
Below the diverter solenoid is coin box optic. This optic counts "coins to the cashbox" as seen on the meters. Of no use to me. I use it as a spare and it can be swapped with a bad coin count optic. This optic generates no errors if it fails or is misaligned or unplugged. It has pink/white wbs/black.


Hope this helps,
Uniman