Corrosive foam on the 4 slots...

[channelmaniac]

Hey folks, when the fish paper and foam on the under side of the top board hardens, it will start corroding traces under it.



The 4-slot sent to me had a complaint of graphic corruption on slot 4. Here's the corroded via that was the cause of the complaint:



BUT... the customer's board had a bad cap kit job so they would be rubbing up against the pins of the chips above them. This meant I had to un-eff the board as part of the repair.



Now with the caps installed properly...



The top board fits without any interference from below!



And if you were wondering about the repair for slot four... It was a simple Kynar patch to the via on the top side of the PCB.

 

[maki]

the PCB will corrode by itself, something in the solder mask that will attack copper

the foam is underneath the battery, and sometimes in other places, its not needed at all and can attract moisture/soak up nasty stuff like the battery acid.
IPA and petrol/label remover will help removing it, getting rid of it is a good thing

FWIW those long legs for the caps is a bad idea, its just asking to be bent and shorted

 

[Neo Alec]

I didn't know the foam could cause problems. I've never heard of it before. Thanks for the call out on this.

 

[egg_sanwich]

the PCB will corrode by itself, something in the solder mask that will attack copper

the foam is underneath the battery, and sometimes in other places, its not needed at all and can attract moisture/soak up nasty stuff like the battery acid.
IPA and petrol/label remover will help removing it, getting rid of it is a good thing

FWIW those long legs for the caps is a bad idea, its just asking to be bent and shorted

I think he was fixing those poorly installed caps.

But yeah that foam stuff is nasty, always a treat to remove.

 

[ratson]

the PCB will corrode by itself, something in the solder mask that will attack copper

the foam is underneath the battery, and sometimes in other places, its not needed at all and can attract moisture/soak up nasty stuff like the battery acid.
IPA and petrol/label remover will help removing it, getting rid of it is a good thing

FWIW those long legs for the caps is a bad idea, its just asking to be bent and shorted

That's why he re-installed the caps properly. It says right there in the first post including pics .

 

[max 330 mega]

That original recap job… wow.

 

[skate323k137]

That original recap job… wow.

I wager the original "work" was probably done by someone who has only recapped single sided PCBs, but tried their hand at dual layer and couldn't get the caps in. Probably heated alternating pads while shoving the legs through, likely after failing to clear the thru holes to begin with

 

[max 330 mega]

I wager the original "work" was probably done by someone who has only recapped single sided PCBs, but tried their hand at dual layer and couldn't get the caps in. Probably heated alternating pads while shoving the legs through, likely after failing to clear the thru holes to begin with

I mean in that case, sometimes in old AM radios, snipping leads from old caps- leaving those standing legs long and twisting new caps with presnipped legs into them and soldering those together in a very specific pattern is a technique, but this doesnt even look like that. I have no clue what this person was thinking.

 

[maki]

I think he was fixing those poorly installed caps.

That's why he re-installed the caps properly. It says right there in the first post including pics .

Thanks, yeah my bad, didn't read it properly.

 

[dragonpt]

That original recap job… wow.

Yeah. That was done professionally...

Thanks for the foam advise, i always remove the foam of my boards. Just takes time and lots of patience and lots of IPA

 

[maki]

I mean in that case, sometimes in old AM radios, snipping leads from old caps- leaving those standing legs long and twisting new caps with presnipped legs into them and soldering those together in a very specific pattern is a technique, but this doesnt even look like that. I have no clue what this person was thinking.

yeah they looked a like that:


technicians didn't have a PCB back then to work on, parts would be wired directly to each other

 

[max 330 mega]

yeah they looked a like that:
View attachment 64308

technicians didn't have a PCB back then to work on, parts would be wired directly to each other

Thats what I was describing; that’s not what you got. Fucking learn some electronics repair basics,

 

[maki]

Fucking learn some electronics repair basics,

you'll get there if you keep trying

 

[ratson]

you'll get there if you keep trying

Coming from someone with reading issues is a bit controversial don't you think?

 

[maki]

Coming from someone with reading issues is a bit controversial don't you think?

controversial like ad hominem from someone who identifies with multiple mental health issues?

there is no value in normalising dysfunctional behaviour

 

[ratson]

controversial like ad hominem from someone who identifies with multiple mental health issues?

there is no value in normalising dysfunctional behaviour

Ok, you know nothing, that much is clear.

 

[channelmaniac]

the PCB will corrode by itself, something in the solder mask that will attack copper

the foam is underneath the battery, and sometimes in other places, its not needed at all and can attract moisture/soak up nasty stuff like the battery acid.
IPA and petrol/label remover will help removing it, getting rid of it is a good thing

FWIW those long legs for the caps is a bad idea, its just asking to be bent and shorted

No, it will not. SNK had a lot of problems with cleaning during manufacturing and you'll see a lot of crap inside of vias on many of their Neo Geo boards and that crap will eat away at the vias, but the amount of damage from that over the years that I have seen can be counted on 2 hands. The foam itself is corroding these when it turns hard. The pins on the ICs were green and crusty where the foam was touching them.

 

[channelmaniac]

I wager the original "work" was probably done by someone who has only recapped single sided PCBs, but tried their hand at dual layer and couldn't get the caps in. Probably heated alternating pads while shoving the legs through, likely after failing to clear the thru holes to begin with

They had used lead free solder too. It was a bitch to remove, even from the solder joints that weren't attached to the heavy ground plane. I had to add leaded solder to it to get it to flow better and come out.

 

[channelmaniac]

controversial like ad hominem from someone who identifies with multiple mental health issues?

there is no value in normalising dysfunctional behaviour

Hey @Takumaji - someone needs to be locked in the War Room for a while please.

 

[GohanX]

You're doing God's work channelmaniac. That original cap job is yikes.

 

[MCF 76]

Damn what a disaster waiting to happen with those caps that's crazy.

 

[Gremlin]

Lmao @ that original cap job



Thanks for the heads up - should pop by my brother's place and scrape it off his four slot as a preventative measure

 

[channelmaniac]

Thanks for the heads up - should pop by my brother's place and scrape it off his four slot as a preventative measure

Just make sure the caps won't touch the pins on the bottom side of that upper board!

 

[Neo Alec]

Be nice to @maki . He's by far the best member to join in 2022.

 

[ratson]

Be nice to @maki . He's by far the best member to join in 2022.

We didn't start it, so fuck him