S+ Double Diamod Deluxe no display

[davedude95]

Who ever replaced the harness left the old one in there, I have it and it is not burnt so I was curious why it was replaced also. I plugged the old one back in and have the same results.. The previous owner said that before he moved it from his sons home to his that it would work but would only spiin a couple times before needing a key reset.. I did not get to see it in this condition only after it had been moved. all voltages seem to check out coming from power supply. Do you think it would be a waste of $$ if I just buy a couple boards and replace them as part of an elimination process? As of right now I'm about 125.00 ahead on this machine, as I only had 75.00 in the sigma that I took this machine in on a trade in for..

[CommTech]

It is never a bad idea to have spare parts.  I would recommend that you have at least a spare MPU board on hand.  After you get your machine up and running, you may also want to consider purchasing a Set and Clear chip for your S Plus as well.
The Set chip will allow you to activate your bill validator and set the machines denomination after changing the game EPROM. The Clear chip is used to clear all of the machines previous accounting records and reset the machines settings back to factory defaults.

Since the Old harness was not burnt, I would guess that perhaps the previous owner replaced it in an attempt to correct the original problem of requiring a reset after a few spins.
I would also keep the ORIGINAL harness in place, unless you can be absolutely sure that the new harness is wired correctly.  My fear would be that IF the new harness was wired wrong, it may have caused additional damage to the MPU board.
If you get a good MPU board, you would not want to have the wrong power harness in place.   

[CommTech]

One more thing to check ... I cannot make out in your picture what PROM's you have.  Your SP-xxxx PROM Should be in the GAME PROM socket and the SS-xxxx PROM should be in the REEL PROM socket.
Also both should have the notch facing down towards the motherboard edge connectors.