Fixing the "coininJ" error - wms 400

[cfh]

I had a machine that was giving an "coininJ" error on the red
LED displays below the reels. this happens when one of the
coin in optos is bad.

There are three transistors on the coin-in optic board.
They all test the same using a DMM set to diode function,
and the red DMM lead on the center transistor leg.
The two like resistores (2n6427) should show 1.2 and .6 volts DC
with this test. The lone 2n3904 should show .6 volts on either leg.

But the transistors weren't my problem. So first I turned
the game on with the opto boards removed (the two
boards are tied together with a stiff ribbon cable.)
Using a digital camera, I looked at the transmitter board,
and saw one of the four optos was not glowing purple.
The digital camera allows you to see infrared on the
camera's LCD screen. Neat trick for testing opto transmitters.

Since I had a williams slant top opto board for parts,
I transplanted an opto transmitter to the wms 400
opto board. Now all four coin opto transmitters were
glowing purple. But still got the "coininJ" error.  By the way
I was booting the game with the opto boards removed
from the metal coin receiver, and just had the two
opto boards right up to each other.

So the next trick is with the game on and the questionable
opto board installed (but not bolted in place), to put a DMM
set to DC volts on the legs of any of the opto transmitters.
with your finger over the transmitter (blocking any light),
it should show 1 volt. If you put the opto transmitter in front
of the opto receiver so it sees the infrared light, the voltage
on the transmitter opto leads should drop to 0 volts.

I had two optos that did not act as described above. I replaced
them with transplants from the slant top opto board and
the game now worked!

[Neonkiss]

Clay,
Great post. 
I have a optic board that is not working.
I just replaced it with a spare.
Once thins settle down a little,  I need to dig into it so thank for the heads up.