(Topic ID: 162539)

WPC89 Desoldering Advice


By Cheddar

3 years ago



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  • 22 posts
  • 9 Pinsiders participating
  • Latest reply 3 years ago by
  • Topic is favorited by 2 Pinsiders

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#1 3 years ago

I am debating whether I want to attempt this job for a friend. The target is a BoP WPC89 MPU with battery damage. The damage appears to be limited to the 2 chips and some resistors below the batteries.

I have the Hakko FR300 and I have done work on Sys11, Bally-18 and Williams system 6 boards without lifting traces. All that aside I am concerned about the tiny traces on this board.

Here's some pics of the damage:

WPC89 FrontWPC89 Back

The board is having switch problems as expected.

If I do attempt this any advice from you guys? Lower/higher heat. Cut components off first? Add solder?

Thanks

#2 3 years ago

Well, the battery holder is easy : cut it off, then heat and remove the legs that remain.

The chips, you'll just have to attempt to desolder and see how clean it comes apart.

I often find adding a little solder to re-tin the point, then desoldering, works wonders.

Basically, you heat 'til the solder flows, hit the button, and the vacuum sucks the solder right out of the hole.

If you have the technique down pat, you won't overheat anything.

Once you have all the chip holes clean, use a pair of needle-nosed pliers and gently twist the chip in one direction, and then the other, to break all the legs loose, and it should lift right out of the holes.

Any resistance, stop immediately, so you don't pull up any traces.

#3 3 years ago

You caught it pretty early thankfully. It puked HARD though.

Instead of desoldering the battery holder, snip that thing out. Hold it upside down over a trash can and just let it drop in. Neutralize with vinegar. Clean with Alcohol or Naphtha. Some wire brushing. And then see where you are.

Don't forget to inspect the connectors below too.

Use remote battery holder, or better yet a FRAM chip.

#4 3 years ago

interesting your comment about twisting the chip. I have taken to pushing on the legs with a pick to "break" the remaining solder connection.

So would you say I am more likely to lift traces pulling on a component than lifting the pad with heat alone?

#5 3 years ago
Quoted from barakandl:

Use remote battery holder, or better yet a FRAM chip.

I don't use batteries anymore if I can avoid it. Set and forget is how I like to handle pinball memory.

#6 3 years ago
Quoted from Cheddar:

interesting your comment about twisting the chip. I have taken to pushing on the legs with a pick to "break" the remaining solder connection.
So would you say I am more likely to lift traces pulling on a component than lifting the pad with heat alone?

The pads lift from mechanical stress. Heat just makes it weaker.

Pads flake off when you rub the tip against the pcb. Through holes and other pads get ripped out when you pull a lead through they hasn't been desoldered all the way and you try and pull the through hole out.

If something doesn't desolder well. Add more fresh solder and try again. The hole / pad must be filled in with solder to desolder it. A halfway cleared out hole with not desolder properly until you fill it back in. Surface tension and heat transfer.

#7 3 years ago

any heat advice? I run the fr300 at about 1 1/2

#8 3 years ago

Cut the parts off. Heat from the back. Most should come out with gentle persuasion.
--
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact/
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info

#10 3 years ago

If you do it right, this is how clean it can get (this was with a Pace Solder-X-Tractor) :

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#11 3 years ago

Thanks for the advice guys. I'll give it a try. Based upon what I am seeing here I am looking at less than $5 in parts + labor. The batteries that leaked on this board may have cost more than the parts/

#12 3 years ago

snipped the battery holder off and it's clean underneath it. I don't have any bubbling under the mask as far as I can see. I'll neutralize and clean and see where to go from there.

Something I've never seen before is a bright blue growth on the legs of some of the affected components

#13 3 years ago

FWIW, from your picture it appears "gunk flow" may have reached (and possibly flowed underneath) the J206 header so you may wish to replace that too.

#14 3 years ago

I've found that flush cutters are very helpful when cutting parts off a circuit board...

https://www.hakkousa.com/products/chp-hand-tools/cutters/chp-170.html

#16 3 years ago

If you see some of the pads are a very dull grey from leaking batteries, try scraping them clean first before adding new solder, otherwise the solder may not flow. I will always apply fresh solder before desoldering because it cleans the contact allowing better heat transfer and thus less time to desolder the pin.

I think the pads lift when desoldering in part due to the adhesive holding the trace/pad to the board loosening from the heat, and in part due to physical pressure and motion.

It's best to suck the solder out first, applying as little physical pressure and motion as possible, then let the board cool so that the adhesive is strong again.

To break any remaining solder that might he holding a component pin, I like to use a needle nose pliers to hold the end of the pin (from the backside) and wiggle in a circular motion (don't pull on the pin as you may yank out a feed through that makes contact from the front to the back of the board). You can usually tell when the pin is moving freely in the hole. If it doesn't move freely that means there is still too much solder holding the pin (often happens on pins connected to a ground plane). If that happens, apply fresh solder and try again. If you still can't remove enough of the solder, then cut the pin and remove it individually.

The component usually just falls off the board when all pins are free.

#17 3 years ago
Quoted from jadziedzic:

FWIW, from your picture it appears "gunk flow" may have reached (and possibly flowed underneath) the J206 header so you may wish to replace that too.

"Gunk Flow" love it! I have header pins so those will be replaced

Quoted from Jvspin:

If you see some of the pads are a very dull grey from leaking batteries, try scraping them clean first before adding new solder, otherwise the solder may not flow.

I'll use a fiberglass pen to polish them up then add flux and solder to get a good base to melt/remove

Thanks for all the advice guys. I think I have flush cutters in my future

#18 3 years ago
Quoted from Cheddar:

I'll use a fiberglass pen to polish them up then add flux and solder to get a good base to melt/remove

A brass brush works well for this too.
Here's one I did recently. The bare copper is sealed with an encapsulant.
--
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info

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#19 3 years ago

Looks nice Chris!

#20 3 years ago

If you have a pad that lifts whats the best
Type of glue to use to stick it back

#21 3 years ago

Fixed the board. Neutralized with white vinegar, carefully removed the components, cleaned the board and then put in New components.

The connector has some gunk under it so I removed the one beneath it and it was clean.

There were a couple lifted pads but since there was obvious rework before I got it I'm going to blame the other guy. None of the traces lifted so that was good. I was able to tone out all the traces. I think I got lucky the damage wasn't worse.

Here's some pics.

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#22 3 years ago

Well executed!

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