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WPC CPU Board - Repair

biglouieuk

biglouieuk

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5Years
Joined
Dec 22, 2019
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Kent
When Hurricane arrived it had battery damage. I gave the CPU board a nice bath in some alkaline killer. But bought a new CPU board to get up and running.

Fast forward 3 weeks and I'm digging into the damaged board.

IMG_20201116_222121.jpg

So far the board doesn't look too bad.

Having been through all the resistors, I have found a few things I don't understand. I wondered if anyone could help?

1. R14 - R21

All show as meant to be 10k.
IMG_20201116_222356__01.jpg

R14 and R15 are. R16 to R21 all show about 1.5k

Did I find some broken stuff? Odd they are all next to each other and show similar resistance.

2. R95 and R99

I don't understand the manual here. 0.1ufd ohms
Whaaat?

They both read the same on my meter anyway.

0.725 M ohms ?

3. R91

It's the weird mixing of capacitance and resistance again?

22ufd ? Micro farads?

If anyone can help advise, if you've been through one of these boards yourself, it would really help me out.
 

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Are you measuring the resistances in circuit? Because that is not a valid test.

Consider the case where you have a simple circuit with two 10K resistors in parallel. If you measure each of them - what should they read? :)
 
Fubar said:
Are you measuring the resistances in circuit? Because that is not a valid test.

Consider the case where you have a simple circuit with two 10K resistors in parallel. If you measure each of them - what should they read? :)
Click to expand...
They are on the board so presumably in the circuit?

If parallel they share the voltage supplied? 2 lamps burn as bright in parallel but kill the battery twice as quickly?

I had assumed, if I probe on each side of the resistor then I could find out if it was good or bad.

Only those few seem to not show the rating in the manual. Because their circuit is different on the board?

I'm already out of my comfort zone! Ha
 
1. all are supposed to be 10k. Not sure why you're looking to replace those as they're normally out of the way of battery corrosion.
2. error in the manual listing .01 micro Farads instead of resistance in ohms. Look at the resistor bands to determine value or remove from the PCB and measure.
3. same as 2 except saying 22 micro Farads.

Looking at your picture I'd be replacing R27 to R38, C31, L1, U18, U19 and probably U20 and probably the majority of R51 to R74 and maybe U16 and U17 - hard to tell without a close up photo.

Watch out for lifting the very thin tracks when you desolder plus it's a pig to desolder corroded parts.

More info at
https://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Repairing_Alkaline_Corrosion
 
IMG_20201117_115405.jpg
I guess I haven't seen this before so I don't know if it's bad or not! Thanks for the pinwiki link, hadn't checked there. Lots of pictures for me to compare with. Perfect.

Thank you for the advice above. I went through all the resistors because they were there and I got carried away with my highlighter pen and DMM. 🙂

Sounds like I need to be replacing loads of things.

Pic above for reference, thanks again!
 
biglouieuk said:
Sounds like I need to be replacing loads of things then!
Click to expand...

Hence why the majority of us say it's beyond economic repair...

Looking at the photo, it looks like the corrosion has caused issues in the past and that someone has tried to repair by reflowing some of the resistors that feed J208/209.

Corrosion is also under J210.

That's one hell of a lot of work and parts to replace in order to get a reliable working board. You've only shown below the batteries, if it's gone above the batteries then that could be even more work. Do you have a de-soldering unit and snips?
 
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I do have desoldering kit yup. I'm just learning all the time.

It's likely beyond economic repair but may not be beyond enthusiastic hobbyist repair! (It probably is too actually)

Thanks for putting me right on the manual having typo. That was a brain buster!

I'd like to find the parts and give this a go.

IMG_20201116_224550_971.jpg

That looks bit gnarly, but there is currently continuity on the brown bits!
 
Vingear and an old tooth brush.... see what comes off first (You need to neutralize that Alkali first, else it will keep eating away).

Then once the components are off do it again....

Then an abrasive pen to scrape off all the crap..... maybe wet&dry.....
 
i tend to cut the ic's of with side cutters then de-solder as its a bit kinder to the pcb, that doesn't look too bad to me i would agree with Paul plus and cut off u18-19 then re neutralise and replace the components.
 
Thanks Paul. Its had a bath in some alkaline eater and also some boric acid (Corrosion-Gone its called) toothbrush and then rinsed with water, dried off.

Screenshot 2020-11-17 at 13.55.08.png

I need a small wire brush I think. A robot tooth brush...

Have some wet & dry.

Going through RS Components at the moment, still not sure what to buy for R95 & R99 (manual seems to have typo I believe from above in post)

Screenshot 2020-11-17 at 13.53.26.png


and same with R91

Screenshot 2020-11-17 at 13.52.26.png

Although, to be fair, they are above the leak line so probably look ok...

I do love a good electronics close up!
 
Understood @pinballmania ... Good to know what they are, thank you!

Capacitors are next to find, C3-C26 (Bigger green ones in the pic below for the uninitiated, like me!)

Screenshot 2020-11-17 at 14.16.54.png

Marco shows them as looking different to the ones in the above image. Little orange jobs as in below image

Screenshot 2020-11-17 at 14.21.27.png

Pinwiki has some repairs that use the ones that look like Marco. (on the left here in C11,12,13,14)

Screenshot 2020-11-17 at 14.24.22.png

I assume the ones on the board I am working on, no longer exist in that form and CAPACITOR 470PF 50V +/-20 AXIAL like the pic at Marcos, are how they now look? Perhaps.

Either way, can't find them on RS yet :)
 

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biglouieuk said:
When Hurricane arrived it had battery damage. I gave the CPU board a nice bath in some alkaline killer. But bought a new CPU board to get up and running.

Fast forward 3 weeks and I'm digging into the damaged board.

View attachment 125433

So far the board doesn't look too bad.

Having been through all the resistors, I have found a few things I don't understand. I wondered if anyone could help?

1. R14 - R21

All show as meant to be 10k.
View attachment 125434

R14 and R15 are. R16 to R21 all show about 1.5k

Did I find some broken stuff? Odd they are all next to each other and show similar resistance.

2. R95 and R99

I don't understand the manual here. 0.1ufd ohms
Whaaat?

They both read the same on my meter anyway.

0.725 M ohms ?

3. R91

It's the weird mixing of capacitance and resistance again?

22ufd ? Micro farads?

If anyone can help advise, if you've been through one of these boards yourself, it would really help me out.
Click to expand...
 

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They are all surface mount one by the looks of it. Not what you need. You want DIP not SOIC, but it doesn't look like they stock them any longer.
 
Thanks @G-501 looks to be the case. I wonder if I should be socketing them too? I'll try another source, had hoped to get everything from the same spot.

Does the type of LM339 matter, so long as it DIP?

Anyway, some progress this evening,.some good and some bad.

IMG_20201117_231302.jpg

Pulled a couple of LM339 and a 2803 and a couple of capacitors. All corroded.

The bad news is, I did lose one fine trace. It's still there, but it did pull a little, I was too heavy handed at the start.

IMG_20201117_231313.jpg

You can just about make out the lifted trace at the back left. Idiot.

I've rubbed it with a little very fine Scotchbrite to shift some crud. Surprising amounts underneath!

I'll give it a bit of acid tomorrow with toothbrush again.

It's bad that I enjoyed it isn't it!? Ha

Need sharper snips, but once one side is snipped and then both are solder suckered, a gentle back and forth brings the other side out with the legs if you are careful.
IMG_20201117_231317.jpg
 
biglouieuk said:
Need sharper snips, but once one side is snipped and then both are solder suckered, a gentle back and forth brings the other side out with the legs if you are careful.
Click to expand...
I find it easier to snip both sides then you can desolder the legs one at a time.

I think you might need some rework on U18, especially at pins 2, 13 and 14, as it looks like there is nothing there to solder back onto. Given their location next to the battery, it's always going to be very tricky to remove without some issues. :thumbs:
 
G-501 said:
I find it easier to snip both sides then you can desolder the legs one at a time.

I think you might need some rework on U18, especially at pins 2, 13 and 14, as it looks like there is nothing there to solder back onto. Given their location next to the battery, it's always going to be very tricky to remove without some issues. :thumbs:
Click to expand...
Oh no, define rework! Haha

Looks to have eaten the hole away, so what to do? Eyelet repair videos, here we come!
 
If some of the traces are too damaged, easiest to just replace them with a wire. It can be made to look quite neat if you take the time.

PCB-Rework2.png
 
Fubar said:
If some of the traces are too damaged, easiest to just replace them with a wire. It can be made to look quite neat if you take the time.

PCB-Rework2.png
Click to expand...
Copy that. Lost one so far, but suspect it won't be the last.. plus if I am lightly cleaning stuff maybe will loose some then.

I'm trying to find the Inductor at L1 from Farnell next.. (I think it's an inductor)

Then I think my order can come from one place.

EDIT : Only in Germany https://www.pinball.center/en/shop/...ponents/8338/inductor-4.7-uh-3a-5551-09822-00
 
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Thanks Ped. I think I'd like to give that a go!

I've been watching the total legend that is "Michigan Bob" too..

Edit: @Ped do you have a link to that article you screenshot?
 
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IMG_20201118_222531.jpg

Went through maybe 30 connections, about 30% don't have continuity on the board. Mostly connections to the LM339 ICs where the pads took a real beating.

I think this one is a losing battle, bit learnt a tonne so far.
 
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With a lot of patience and hard work you could spend the rest of lockdown 2.0 getting it to the point where you throw it into the bin and buy another one . Time to take it on the walk behind the shed with the axe perhaps :)
 
Ped said:
With a lot of patience and hard work you could spend the rest of lockdown 2.0 getting it to the point where you throw it into the bin and buy another one . Time to take it on the walk behind the shed with the axe perhaps :)
Click to expand...
I think you're right brother...I think you're right. 🙂
 
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