Bally MPU

[Retromanic2]

I am trying to fix a Bally MPU Board with a locked on LED using the late great Leon Borre’s test Eprom at position U6 and the 6800 CPU chip in position U9.

Following his instructions it says connect the test Led, negative to pin 15 of U9 and the resistor lead to TP5.

However reading this Old Pinball Guide, it says connect the resistor lead of the test Led to pin 15 of U9 and the negative to TP4

So can anyone explain the difference between these write ups as I am getting a little confused at the moment.

Thanks All

 

[SUPERSPRINT]

So swapping the polarity will give you a positive or negative voltage depending on how you look at it.

Tp4 and tp5 are different voltage test points as far as I can see, tp4 is or should be ground and tp5 is 5v.

To confirm this, I would check continuity between known ground and 5v lines before testing via the ic.
Once confirmed you'll then know what readings you are getting and how they refer to the expected results.SUPERSPRINT2020-01-12 13:35:05

 

[Retromanic2]

But the test Led will only work one way..is that correct.

 

[SUPERSPRINT]

Not necessarily, but after testing you’ll have a better idea of how the testing lead works and should be able to test what you need. With that info you can check your kit and get familiar with it.SUPERSPRINT2020-01-12 13:35:55