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(Topic ID: 247751)

Bally '78 Lost World MPU - Locked - I screwed up

By midcoastsurf

4 years ago



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  • Latest reply 4 years ago by BigAl56
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#1 4 years ago
OP
 
LIT

midcoastsurf

Lit Frames

US Naperville, IL

11y 100K 2,035 2

Hello,

I have a new project I'm working on. The LED on the MPU is locked on (no flicker). The board is getting +5.0 vDC at TP1. I tried jumping R1/R3 to ground per suggestion of repair guides, but I must have grounded the wrong side of the resistors (left side) as the green LED instantly went off and no longer comes on (a component must now be open is my guess?). Also, pin 40 of U9 is only 0.78 vDC, but should be 5vDC (reading before I screwed up).

Here is a pic of the board. Looks like there could be some acid damage.

Thoughts on where to start?

Thanks

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#3 4 years ago
OP
 
LIT

midcoastsurf

Lit Frames

US Naperville, IL

11y 100K 2,035 2

Quoted from slochar:

You probably blew transistor Q1, which makes sense since you no longer have a working reset circuit to put the 5volts up on pin 40 of the cpu chip.
Since you have to remove all the components in the bottom there anyway to clean up the corrosion, you'll be rebuilding that section as you do that.
Get the leaky nicad off the board now.....

Thanks for the help. Nicad is cut off the board. I’ll buy an MPU repair kit. Will probably build a test fixture as well to test out of game as I go.

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