Broken via on Model F sensing PCB

arcticfox

27 Dec 2020, 03:50

Hello DT,

I'm in the process of restoring my first F122. I desoldered the original flat cable so that I can put on an xwhatsit controller. However I noticed that 2 of the vias has detached from the PCB.
IMG_20201225_234545.jpg
IMG_20201225_234545.jpg (1.56 MiB) Viewed 382 times
I'm pretty new to soldering, does this mean I left my soldering iron on the PCB for too long, or is it just 35 year old PCB falling apart?
Can this be repaired or should I look into getting a new PCB?

pandrew

27 Dec 2020, 22:51

You took a picture of a couple column pins. Those are only connected on the bottom side, and we can't see on this picture if and how destroyed the pads are on the other side.
Assuming pad pad looks good on the other side, you may still be able to solder to it SMD style.

Pads can be lost for various reasons: (probably incomplete list)
* Too high temperature on the iron
* Corrosion (there's usually obvious visible signs of it)
* Mechanical forces on it after soldering. (e.g. if the solder didn't wick through to the other side, and then you pushed vertically on the pin)
* Low quality PCB. (I think unlikely with IBM, but who knows, could be some older technology)

Always use flux when soldering/desoldering, and always make sure your soldering iron tip is shiny. It's easy to make the mistake of trying to desolder an old oxidized solderjoint with no flux, and a dull-looking soldering iron, and then thinking you need more temperature, because it didn't melt, and dialing up the temperature too much, so that now it will destroy the pad.

Rayndalf

27 Dec 2020, 23:22

What temp are you running your iron at? I killed a couple PCBs that way pretty recently. My iron tip was a mess and I wasn't using proper flux, so I just upped the iron temp to compensate. Needless to say I'm still not sure what part of those boards I cooked, but 500 degrees was too high. 250-300°C is generally reccomended.

arcticfox

28 Dec 2020, 05:19

Been using a cheap iron without temperature control, guess I learned that the hard way.
The actual trace on the other side isn't damaged as far as I can tell, though I need to desolder the current wire first to be sure; I'll do that once my soldering station arrives.

arcticfox

28 Dec 2020, 05:23

Also been reading about via repairs using eyelets/rivets, think it's worth a shot?
https://youtu.be/hdl_shaDTfs
https://www.ebay.com/itm/273600722151

arcticfox

04 Jan 2021, 17:37

Bump
Anyone has experience with PCB eyelets/rivets?

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DMA

07 Jan 2021, 01:30

Lifted pads aren't usually a problem if your wires are not pulling them off PCB. I usually just cut the lifted part with x-acto knife, scrape off small bit of the solder mask on the part of the trace that isn't delaminated, and solder to it using a thin wire.

But eyelets should be a bit more permanent solution.

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