s plus mother boards (repair ????? )

[Kenokarz]

got in 2 machines both  had no power to the reels , and no display . lights work /b/v cycles , check the power cords to the mother board on my test machine  its all good
so did a swap of the mother board with known good mother board , and everything is  good on both machines , so mother boards look clean  no burnt traces, and when you look at it there really nothing to them , so has anyone ever repaired these , if so where do i start to check for problems , i got more of these to pick up but if all have bad mother boards i might just have to pass on the deal , unless i can find out how to repair them 

[shortrackskater]

so did a swap of the mother board with known good mother board , and everything is  good on both machines , so mother boards look clean  no burnt traces, and when you look at it there really nothing to them...

If you've done a swap with a known good mother board, then I'd say your problem ins't the mother board.
I'd focus on checking the MPU boards. I'd start with checking wiring, connectors, and making sure the MPU is seated in it's connector as well.
Another knowledgable member will chime in soon. 

[Kenokarz]

traced it down to a bad motherboards , put known good cpu in and same problem , replaced the motherboard and all is good , so one of the members here  told me to check for cold solder joints on  the 6 pin connector on the motherboard and than test the ohms  on the diodes,  also the power harness from main power supply to the motherboard  has been tested with know good power harness i will post my findings

[Stayouttadabunker]

There's a small 8-pin chip that goes bad too.

On the motherboard on the floor when it's along the back wall, it would be located on the left hand side.

I've had to unsolder that chip, install a socket and throw in a new chip.

I'm not exactly sure what it does but I think it has something to do with machine settings.

I could be wrong on this.

The guys are pointing you in the right direction though.

Those six power header pins on the MB tend to get oxidized and cause really bad connections for power.

An older member named Buzz once actually soldered those to the wiring harness and never had a connection problem with them again....