(Topic ID: 295426)

WPC89 No diagnostic switches

By HighVoltage

3 years ago


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#1 3 years ago

MPC in my BSD started malfunctioning. Well, it still boots into "Factory Settings Reset", but the coindoor diagnostic switches are not registering so I can't get beyond that. I remembered the flick the power off/on trick and I can get to attract mode, but still can't coin up anyway.

I've followed all the direct switches debugging info in PinWiki, but it didn't lead me to a proper conclusion.

I've assessed that the problem is on the MPU, and it looks like it has had some corrosion from the past that doesn't look too bad. It was mainly the U16 quad comparator that seemed to get it. I put a new LM339N in U16. I can see with my logic probe the inputs do go low when I ground the direct switch pins at J205. PinWiki then says to check the outputs at U15. They're not changing. So I though I'd check the outputs directly on U16 and they aren't even changing there. I've tried two different new LM339Ns so seems unlikely they're faulty.

Any thoughts what is going on, or what else I can test? Also was wondering if I don't have the J205 connector from the coindoor connected to the MPU, do I need to bypass the lock/enable signal somehow? I'm assuming not, or PinWiki would have mentioned it somewhere.

#2 3 years ago

I know first, I would like to see a picture of the board. Do you have power and ground on the U16? Make sure you are testing on the legs of the part, especially if you have it in an IC socket.

The battery corrosion may eat into the trace and sever it right at the pin pad and may not even notice it, especially if you already lightly sanded the trace to expose the copper.

#3 3 years ago

If the board had battery acid leak in the past and it wasn’t neutralized, I’d grab your ohmmeter and beep out the traces surrounding the corrosion you describe. I’d also remove the battery holder (if it still exists) and inspect the traces under it. I’ve repaired a few of them that failed years after the batteries were removed as the acid will continue to do damage if not properly treated. Good luck!

#4 3 years ago

I did buzz-out the whole lower half according to @zaza's excellent diagram. I did remove the battery holder. I've tested all continuity, all resistors, all diodes on the lower half everything passes. I did add a socket and tested directly on the IC legs. I wish I would have tested the old comparator before removing it, just for reference. It's the only thing that looked somewhat bad, and made sense since it handles the direct switches. I'll check with my multimeter tomorrow, I'm done for tonight. Thanks for the input.

I see Zaza peeked in here. Question for you, on your diagram you mention keep an eye out for a follow up better version, but I never did see any follow up. Is there one?

#5 3 years ago
Quoted from HighVoltage:

Question for you, on your diagram you mention keep an eye out for a follow up better version

The diagram was a 'work in progress' and the first few versions in post #1 were unfinished/incomplete. In Januari 2017 I made the final corrections and all previous versions were deleted from post #1.

Quoted from PinballManiac40:

Do you have power and ground on the U16?

That is important to know.
The LM339 needs besides an INPUT, also a reference input (+5V) and power supply, (+12V and GND), check all those pins on U16

#6 3 years ago

U16 and U17 do not have voltage. U18, U19, U20 do. I'm not sure where to trace it, is there a picture of the bare PCB somewhere?

#7 3 years ago

Hope these help. Remember LM339's have different connections for + and ground.

On an LM339, pin 3 is B+ and pin 12 is ground.

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#8 3 years ago
Quoted from pins4u:

Hope these help. Remember LM339's have different connections for + and ground.
On an LM339, pin 3 is B+ and pin 12 is ground.
[quoted image][quoted image]

Yes, U18 and U19 are also LM339s, so I could compare. Looks like the power to U16 must be coming from U20. Seems that trace is bad. Thanks!

#9 3 years ago

Need to be sure you remove all the black areas of the battery corrosion from the board, or it will still continue to spread like cancer and continue to eat up traces and parts. An example of one I had repaired.20170408_115512 (resized).jpg20170408_115512 (resized).jpg20170421_185553 (resized).jpg20170421_185553 (resized).jpg

#10 3 years ago

Fortunately, this one's not nearly as bad. What do you think? I'm guessing this board must have been treated in the past.

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#11 3 years ago

You definitely have some more work to do. Pretty much can follow the corrosion from the bottom left and right battery pack holder holes and see the damage from there that spread up the traces and also and fumes that got to the resistor leads that are marked off. Picture does not have good light on it, so there could be some another area that I can't see affected. Could even use other pictures from other angles. Hard to really tell if L1 and C32 were affected. Some of the resistors I marked off on the right may not be damaged, just might be the way the light hit the area.

Basically, if the solder joint and solder leads are not shiny, need to suspect it for having battery corrosion. Magnifying glass is your friend for closer examination.
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#12 3 years ago

Would you replace any parts, or just treat it? ZEP? What do you use?

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#13 3 years ago
Quoted from HighVoltage:

Would you replace any parts

I always replace the parts there were hit. I remove the damage parts, sand the affected areas down to the copper, treat the areas with vinegar, clean the board with alcohol, fix any damaged traces, reclean with alcohol, and repopulate with new parts and coat the bare copper areas.

My opinion, I can not see how the Zep is supposed to clean inside the parts that were affected. Sure it may look like it from the outside of the part, but you can't exactly scrub inside a part, much less under a part if the part is mounted tightly to the board.

https://pinside.com/pinball/forum/topic/terrybs-guide-to-repairing-alkaline-battery-damage

#14 3 years ago

If you use the Zep instead, still make sure you are replacing the damaged parts. I definately would remove that IC16 socket just so I can get underneath and clean the board under it.

#15 3 years ago

I repaired a very badly damaged CPU for someone only 2 months ago...It was so bad I had to remake at least 12 Tracks on the Board with wire links.
When I first tested it just one of the Coin Door switchs wasn't working, Can't remember which one it was, after 1.5 hours fault finding the Track under U 15 was open circuit on Pin 3. U 15 didn't even look like it had any corrosion. I'd be paying attention to U 15. Measure for Continuity between U 16 & U 17 and the relevant Pins on IC 15. Also measure continuity between pins 19 & 1 of U15 and back to U9 Pin 50.

If you have done full Continuity Checks on 16 & 17 I'll bet Money that one or more Tracks is stuffed on U 15

#16 3 years ago

Good call! Those traces under U16 seem very susceptible. After I fixed power to it, all the switches except "Down" worked. Continuity to U15 was lost for that one. Maybe it was already hurt and when I soldered the socket in, probably the trace got disconnected right at the pad.

Probably a good idea to re-buzz after any fixes. This one's all working now, thanks for the tips.

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