I think there's a lot of knowledge in pinball, and I think it's great that so many people are willing to openly share it. There are techs who don't participate in forums like this, and don't share knowledge. Without share of knowledge, it dies with us.

I have a lot of practical knowledge from doing, but I have no formal education in this area.

I've learned at least something from everyone who has posted an opinion in this thread in the past. I don't look at anyone posting here as 'right' or 'wrong'.

So, I don't know that I agree with the 'start your own thread' thing - it's easier to have an open discussion with multiple opinions in one thread. It helps if everyone checks their ego at the door and the thread can go in a civil direction. I'm not pointing any fingers here. Anyone reading this thread can form their own

I think there's more than 1 way to skin any cat. I have repaired a significant number of PCBs for a number of people over the last few years, and I turn away boards with large amounts of corrosion. I do this for multiple reasons... including but not limited to...

1) Cost of repair. I'm not doing this as a volunteer effort. It helps me with my master plan to get out of debt, helps me support my family, and from time to time, supports my hobby. I have a very limited number of hours in any given week to fix pinball boards. A WPC CPU like you're using in this repair guide would be returned un reparied by me. That's not saying it's not repairable - any board is repairable, given enough time - it's not economically repairable. Considering the readily available replacements from Rottendog, Two Bits, or anyone else, you can't spend hours on a CPU board repairing it if you are charging a labor rate. I can't charge a guy $125 to repair an original WPC CPU when they can buy a repro that has never been exposed to the alkaline for $50 more. There are very few exceptions to this rule - a few boards that are not reproduced, or are not available used in reasonable quantities. Those might be worth putting a little more into.

2) I can't be certain on a repair like that that I'll catch everything. I don't do a repair where I don't give the customer some sort of a warranty. I try hard to get it all, and I hope I got it all, but as alkaline travels through the air, you may never see a bit of it that somehow got under a chip.

I too have opinions, and have operated as sort of a 'Switzerland' of pinball for years. I try to respect everyone, and I value everyone's opinions. As stated, I've learned from everyone with an opinion here in some format.

I bought a bead blaster in 2014. Part of this was based upon Clay's advice, but I had also wanted a bead blaster for cleaning up metal parts for vehicles and metal brackets etc for pins for years. So, I figured even if it wasn't useful for PCBs, I would get my moneys worth out of it.

I've fixed a number of rotten boards where people did the whole 'douche the PCB' with vinegar and water, and there was corrosion under ICs and resistors that may not have been there before. It also may have been there before - obviously I haven't been watching the board since the beginning of time to know for sure. So, I've not been a fan of that method *solely*. IMO, that method solely may buy people some time - but we don't know how much time that is.

The bead blasting has worked better some times than others for me. I haven't had much luck with WPCs, probably due to lack of finesse. I think I use mine differently than Clay uses his, however. I will blast an area so I can desolder any affected components. I cut the ICs and resistors out, leaving the lead intact, and then blast the board so solder will flow, desolder the components, and then get the traces clean before sealing them. I don't want to send someone a board where the stripes are gone off the resistors, for example. I think if you've blasted a resistor that much, odds are, you've shortened its life. Resistors are cheap.

My favorite tool for cleaning corrosion is my fiberglass pen. I feel it gives me the most control. You can use a light touch, or a firm touch, and it cleans depending on how firm of a touch you give it. It's aggressive enough to remove the alkaline, but not so abrasive that it instantly burns through traces. Even on a Sys11 where the battery traces are fine under the battery holder.

I'm playing with Cratex, a rubberized abrasive in stick format, similar to the socket cleaning sticks that PBR and Marco sells. It's a machinists tool that one of my local collector friends/customers brought by for me to check it. It has potential too.

I know several guys who just use regular ole sandpaper and do a good job. I think that may be a more likely tool for a hobbyist to have in their toolbox, as those are the people who are going to repair a CPU like the one in the pics. Someone who has time to invest in something like that board as a fun side project.

It's also worth pointing out that pinball boards are not expensive boards. Yes, $200 for a aftermarket CPU seems expensive, but when I say expensive, I mean boards that may cost multiple thousands or even tens of thousands of dollars in a MRI machine or something. I expect the people working on those to have a much higher degree of training, better equipment, etc. If every pinball tech had that level of equipment and experience, none of us would be able to afford the pins!

So, please keep the open discussion going IMO. But let's keep it civil - and fun!

I keep junk boards to practice on.... I know what I'm trying next!

So, a bit of an update on the cratex product I've been trying in stick form...

It works. But it's slow, and tedious. So it's not good for me, as time = money. And I can have a 3-4 week backlog of work at any given time. And what I charge for a given job has to be proportionate to what a board costs to replace. Any board is repairable, but many are not economically repairable.

One of my Facebook friends shared that he was using abrasive 'bullets' in a dremel. He even sent me a sample. It looked like it might be promising after working on a board a bit, so I bit the bullet and bought a starter pack for about $75 shipped, with 4 different grits and mandrels.

I figured this would allow me to try all 4 grits in various sizes and shapes, and I could reorder what I found to be most useful.

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So, I started with a complete POS sys6 CPU. This is a board that might come out ok with a bead blasting job - but is probably not viable if I'm doing a rebuild for a customer under normal circumstances. Exactly the kind of board to experiment with.

I did have to remove everything in the corrosion zone. IC and resistor leads will cut through the abrasive bullets like butter.

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Under 10 minutes later, it's looking pretty decent.

A few initial thoughts

1) this is messy! Eye protection and maybe even a face mask are necessary. I'm not sure what is getting released into the air while you grind. Don't do it at the dinner table or in your 'clean' area.

2) this is a slow speed thing on the dremel. It'll throw the bullet right off the mandrel if it spins too fast. Start at the slowed speed and increase slowly.

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So, the board is rebuilt and ready to go back in the game, once I throw a NVRAM on it, and the correct game ROMs instead of the test fixture ROM.

I'd say this is a great alternative to a hobbyist who wants to repair their board instead of replace it or hire a pro. It gives great results at a price that isn't outrageous - assuming you already have the dremel or equivalent rotary device. And if you don't, there are a hundred and one uses for one around the house, it might be worth the investment.

It does make a mess, you need to be prepared.

Pros:
-Easy to use. Nothing to misunderstand.
-Different grits of abrasive allow you to use a coarse grit when you've got a lot to cut through, and an ultra fine when you are trying to just remove a tiny bit, or polish something up.

Cons
-Makes a mess.
-Doesn't clean the board with components in place. So, you'll need to desolder everything first.

I also use a bead blaster. The driver board that went with this CPU had drip damage down the back of it. The leads of components and ICs would quickly destroy the 'bullet', as they are sharp and would cut into it. The bead blaster is an excellent alternative here, because it can blast through the hazed solder. Then, you can go back and reflow solder. At that point, you can often cleanly desolder components and then you'd have a smooth surface to polish. In a few situations, I had solder pads that had surface corrosion on them, but the component side of the board was fine. In that case, I reflowed the solder joint, desoldered it, and then resoldered it. Once the repairs are done, I'll seal the board with conformal coating, which keeps oxygen away, which should help prevent the board from tarnishing again.

I put a light mist coat of the conformal coating on the component side of the PCB before populating it, to protect the traces below other parts.

As things are right now, I don't think this setup saves enough time that I'm going to pursue more and more battery damage repairs.

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On a board with this much damage, I started with the coarse and finished with medium.

I see a few spots where I zoomed I where I may take another very minimal pass.

I'm going to try the ultra fine on a junk wpc mpu and a junk sys11 CPU next I think

On to the next Cratex test case...

A WPC-89 CPU with medium alkaline damage.

The board took probably 3 hours from start to finish.

I calculate supplies on the repair at ~$15 including parts.

No damaged traces thankfully, so no jumpering required. That can often add significant time to a repair, and makes it unappealing. Also, it hadn't been previously reworked - these fine traces likely won't withstand multiple repairs.

I used Cratex's 'ultra fine' bullet on this. I think it was #14. Might have been #15 - they are similar.

Cost on these is about a buck, but you have to buy 100 of them to get that price. Ran at the #3 speed setting on my Dremel - will try to find out what RPM that is. Used about 1/2 to 2/3rds of the bullet.

After the traces were cleaned up, I did a light coating with MG Chemicals 419C. Stuffed the board, soldered the parts in, cleaned flux, tested, and sealed again after complete with a slightly heavier coat.

I think the Cratex will work very nicely on these.

Probably will 'batch' the next job, have resistors and such on order from jameco as I ran out of 1.2k ohm 1/4 watt resistors and had to use 1/2 watt on this board. I think if I do multiples, I could cut 1/2 to 1 hour per board from the job.

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