So the mpu has corrosion. Mostly on left side and up to U15 it looks like. Game works 100% no issues with switch matrix or resets.

Being a believer of if it's not broke don't fix it but ALSO understanding this WILL get worst and something will stop working, what should I do?

1. Take it out and follow terry B's damage guide and replace all affected components.

2. Neutralize damage and wait until something breaks and revert to #1.

3. Play game until something goes wrong and revert to #1
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I think I'll gather supplies and try to fix it before it gets worse. Getting a twobits board is possible too.

What do you think is easiest, assemble a twobits board from scratch or a repair alkaline damaged wpc board? Is there a market for damaged wpc bosrds?

I have not done this stuff before but am an automation engineer so it's in my realm of knowledge base and pay very good attention to detail.

Yes I corrected myself in later posts. Acid just sounds so much cooler.

Thanks for feedback. The main reason I got into pinball is for the fixing/ tinkering aspect of it. Up till now I've avoided pins with major board issues but I'm looking at this as a forced learning experience. Aka learn enough and do a good job or I'm out $180 for a new mpu.

Well. Entire bom of wpc-89 components on order from mouser, logic probe, and desoldering tools on the way. Not to mention remote mount battery holder.

We shall see how this goes.....

Good news is I have a demo man mpu to verify signals or values if I get into trouble.

Worst case I have a double E at work I could pick his brain if I have too. And all you wonderful people!

I hope I don't have to replace any upper components or stuff to right of battery holder. Just ordered all components because I'd rather have everything then pay another 7.99 for shipping of 0.1 lb of electronics from mouser.

That being said I am going to expo next week so if there are show specials on nvram, I might pick it up anyway.

It's a party zone so no midnight madness. Yes I remember reading that some games loose functionality with nvram... like TZ.

Yes I posted about new bare board here and on two bits post. Will try to fix this and weight my options if I fail.

Because of the absolute success of my two bits build I can now focus on attempting to fix this.

So I first went to neutralize the alkaline with 100% acedic acid. Seemed to help a little. Now using trusty hakko desoldering gun to remove stuff. Adding flux to the solder really helps. Small pile accumulating so far.

I’ll attempt to document this here for anyone who is interested.

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Made some more progress. I have what I think is all the affected parts/areas.

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These photos are of areas that I don’t think are affected. The stuff around the pins might be flux from old repair work perhaps?
I might take out U14 but U13 & up I can see trace and board repair so I do not want to mess with it at all. The hazy ness on component side is from the ipa flush FYI.
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Removed what I think is all the affected parts off the board. Did a second rinse/ soak with a 5% solution of hydrocloric acid. I see some darkening areas concern near the bottom left battery terminal and I will start abrasive treatment next. I only see a few traces that have darkening under the solder mask. All the pads should clean up nicely.

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Used a pointed green cratex bit chucked up in my flex shaft and under magnification brought everything down until it was all shiny.

Fixed some vias and had to add solder to remove some stubborn stuff in a few through holes. Looks like it’s accepting solder well. Last thing to do is rinse the board well with ipa and used compressed air to get any little debris out of the through holes. Then I can finally start adding components on again.

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Well this board was in fact 100% working even with the damage so I don’t think it was very severe. At least not ground plane eating kill your board in 60s flat type of corrosion. But I know it just takes time so wanted to get rid of it.

Repopulating is going well. Very angry because I thought I ordered enough 1.2k resistors but am 8 short. Plus the Q1 transistor. So now I need to wait until those items come in. I held off on the diodes and some chips because these areas have sanded traces underneath them. So the plan is to clean up the flux. Brush some conformal coating on the areas under chips/components. Then I will finish the board, test and then final clean and brush coating over the reworked section

Solder is taking well to these pads. And yes, definitely use liquid flux to assist the solder. I also used 5 core solder as well and it works great.

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So after getting a DOA processor and replacing it, board boots! All column drives strobe besides Column 8, it stays high. Pin 11 of U20 also stays high. U20 pin 8 is stuck low and so is pin 12 on U14. U14 pin 10 is grounded and pin 20 has 5volts. R74 tester good at 1kohm, good continuity to 5 volts and pin 9,j207. What to check after that?

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So tested continuity from all D7 pins back to the asic. All checked good and very low resistance.

Perhaps it’s because T2 doesn’t use column 8 and that’s the rom I have in?

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Happy to report that it was the T2 rom that was disabling the 8th switch column, its not needed for the game. swapped out with a PZ rom and it works great.

So this was a successful repair!