After cleaning:

many traces appear gone but it's just the corrosion under the solder mask that "bubbled" up.
I'll have to polish, tin and rebuild a bunch of these.

A few legs of the chipset aren't making contact, I'll probably have to desolder it and repair pads.

In order to have enough room to work on it I can't but remove a lot of components (caps, isa slot) and probably the keyboard chip.

Doubt:

many smd caps and res solder joints are dull, can I just put some fresh solder to make them shiny? Is it necessary? - I don't think so but...

Ram:

4 chips were present: 41256 in parity sockets. Ram chips aren't, probably they were removed and parity left behind.
4 SIPP ram sticks, 2x 44256 + 1x 41256; I guess 1MB in total.

https://theretroweb.com/motherboard/manual/30068.pdf

In order to desolder the chipset I thought using some low temp solder (I have 135 and 180 °C).

Why desolder it?
If pads are broken I need to rebuild them, and or polish traces and tin + solder mask them.

After some thinking I'll start repairing the traces on the back as I have all the room possible.

After another round of vinegar and soap,

- the chipset ic needs desoldering and resoldering to clean the legs and restore the pads on the m/b: there is a white patina I can't get rid of in any way, contact cleaner does close to nothing;
- a lot of traces I first thought were busted in fact had the solder mask lifted and thus are still making a connection; only tinning is required;
- solder of the affected area is dull, would it be best to desolder-resolder with fresh solder?

Any comment or opinion is welcome.

I was expecting U5 legs breaking off after cleaning, so thats good I guess 😉 Vias look really thick and strong. Is the PCB 4 layer?

rasz_pl wrote on 2023-09-07, 18:47:

I was expecting U5 legs breaking off after cleaning, so thats good I guess 😉

I was already planning to dremel the chip's broken pins and solder thin wires to pads.
And I was expecting pads to go bye bye to another dimension.
Yes, it looked awful but in the end it was just that. Even if some solder joints are simply dead from corrosion.

U4 wasn't that much better either... Got lucky I guess.

rasz_pl wrote on 2023-09-07, 18:47:

Vias look really thick and strong. Is the PCB 4 layer?

PCB is 2mm thick, counted 8 dotted lines between the surfaces (if you look directly). Probably 4 layers; no, I can't count layers 🙁

U5 is a LM358

I used a fiber glass pen to remove all the corroded patches and traces.
It took forever.
My dremel is dead, I absolutely need to buy a new one. I now understand why it is a must.

I tinned all the exposed traces and I'll cover them with solder mask.

---

I started to remove some through hole components but corroded solder ain't too easy though.
Plain boring.

After examining the chipset legs I discovered that a few are soldered to a loose pad on the motherboard, this makes it more difficult as I have to avoid ripping the pads .
Anchoring them isn't impossible but time is really flying by doing all this work.

---

All the smds that were affected by the leakage must be desoldered and resoldered as they come off pretty easy.
I don't have spares for all values, thus I'll clean the ones I don't have in stock. Not that I have the stock of a pro shop either 😀

more work

more yet

After all the traces I'll try reflowing all the legs.
If it doesn't work I'll then desolder it and check what's under it.

I scraped the legs and the pads and are now shining.
Hope it just works 😀

Any advice is welcome!!!

I have to find a way to make the corrosion patina on the legs and pads to be removed.

As a first idea I can only see mechanic action, or some acid. But what?

in theory flux should help remove oxidation

rasz_pl wrote on 2023-09-09, 20:39:

in theory flux should help remove oxidation

I tried 3 different brands, nothing.
I used my fiber glass pen and it did somehting but I got a full cm off.
We'll see later.

Nope, it takes forever to just do one leg.

New stuff.

Desoldered the chipset IC.

Pin 105 looks not connected, but datasheet has a function for it:
https://4donline.ihs.com/images/VipMasterIC/I … EF6B88F2AEB20B8

Does anyone know what's it for? Is it correct to be not connected?

I've had luck removing pin oxidization with Silvo (liquid silver polish) and in some odd cases Brasso (same deal but made for brass).

Might be worth a go?

ChrisXF wrote on 2023-09-13, 01:47:

I've had luck removing pin oxidization with Silvo (liquid silver polish) and in some odd cases Brasso (same deal but made for brass).

Might be worth a go?

This is an idea. Ok, pads on m/b was easy, fiberglass pen and it was fast.
The chipset actually has a sh*tload of oxide on the legs, the fiberglass works to an extent.

I'll look for something in that range and update.
Thanks!

or for the price of chemicals you could buy brand new [1pcs] VL82C331-FC Bus Controller QFP160 US $8.15 from Poland.

rasz_pl wrote on 2023-09-13, 02:15:

or for the price of chemicals you could buy brand new [1pcs] VL82C331-FC Bus Controller QFP160 US $8.15 from Poland.

Too easy. Won't fit. 🤣
My point is to learn from this.

And I already have the stuff, no expenses.

I rebuilt traces/pads.
Now I need to anchor them. Some with solder mask others probably epoxy. IDK