Bally MPU Corrossion – Woes and Repair

U8 image

U8 image

I’ve cleaned up the corrosion on my Dolly Parton MPU (Bally) – BUT Some of the traces were really damaged and a few I can’t determine where they should connect, and others might not have continuity any longer.The only component apparently affected that I have had to replace and am concerned about is the U8 chip.Unfortunately I can’t read a schematic well enough to figure out where on the board I should be checking.

I’ve been looking online for a quick guide of what to check and where each pin should connect on all the normally damaged components as this is a REALLY common problem with Bally’s, BUT I haven’t found anything that will really help. Basically a trace diagram for the MPU would be awesome but alas I’ve not turned one up.  And I’ve not found high enough resolution images of the front and back to work from reliably.So, does anyone know off the top of their head where all 22 pins on the U8 should have continuity to?  🙂  If I need to add jumper wires it would be awesome to know where they should land.

I’ve been trying to map this out and here is what I have so far.  I know some of the legs should have continuity with other legs on the same chip – but not 100% sure which those might be, and if the pair also should have continuity to some other component.My notation is IC identifier.pin / or resistor/capacitor #.  e.g. U7.1 = Chip U7 Pin 1

1 – U7.20
2 – U7.21
3 – U6.6
4 – U7.23
5 – U7.18
6 – U7.17
7 –
8 – GND
9 –
10 – U11.29 (??Paired with 9?)
11 – U11.28 (pair12)
12 – U11.28 (pair11)
13 –
14 – U11.68 (??Paired with 13?)
15 – U11.26 (pair 16)
16 – U11.26 (pair 15)
17 – U18.6
18 – U17.8
19 – U17.6/ U10.23
20 – U18.7
21 – U6.4
22 – R12 left leg (also Big pad which I believe leads to Batter + terminal)

Do Pins 11 and 12 only link to the other? Should there be a connection anywhere else? As you can see I’m missing a couple which I’ve not been able to identify.

———-Update———-

One of the GAPAS members (Ken) sent me the following based on his review of the schematic:

1 – (A3) U7.20 / U6.5
2 – (A2) U7.21 / U6.6
3 – (A1) U7.22 / U6.7
4 – (A0) U7.23 / U6.8
5 – (A5) U7.18 / U6.3
6 – (A6) U7.17 / U6.2
7 – (A7) U6.1
8 – GND
9 – (DI 0) U11.29 / U7.6 (pair 10)
10 – (DO 0) U11.29 /U7.6 (pair 9)
11 – (DI 1) U11.28 /U7.7 (pair 12)
12 – (DO 1) U11.28 /U7.7 (pair 11)
13 – (DI 2) U11.27/ U7.8 (pair 14)
14 – (DO 2) U11.27/ U7.8 (pair 13)
15 – (DI 3) U11.26 /U7.9 (pair 16)
16 – (DO 3)U11.26 / U7.9 (pair 15)
17 – (CE 2) U10.34 / U11.34
18 – (OD) U18.6
19 – (CE 1) U17.8
20 – (R/W) U18.7 / U10.21 / U11.21
21 – (A4) U7.19 / U6.4
22 – (VCC) R12 left leg (also Big pad which I believe leads to Batter + terminal)
The (A)ddress lines and (D)ata lines will go to multiple chips.

8/22/13
QUESTION: should I be getting continuity between 8 (gnd) and 22 (VCC) ? If not then I’m wondering if I need to replace C13

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3 Responses to Bally MPU Corrossion – Woes and Repair

  1. Pop says:

    Know the chip function, have a part # ID? that could help determine the pin destinations. If it isn’t an “off the shelf” chip then no help here…

    • David says:

      QUESTION: should I be getting continuity between 8 (gnd) and 22 (VCC) ? If not then I’m wondering if I need to replace C13 possibly –

      On the IC stand I’m getting pins 8 & 22 having continuity – not sure if that should be the case.

  2. David says:

    Hi Pop,

    I have the schematic (sending you a copy directly).

    But also one of the other pin guys (Ken) sent me an email with what he sees on the schematic. I’m going to post his summary in the post above.

    The IC in question is a 5101

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