Wires solder masked, anchored and let(s hope it'll work.

While I was putting solder mask I came across a few more issues, the LM358 and some caps + res came off.

At a glance they look soldered and poking doesn't make them come off.
Handling the board I hit some and then they came off clean ripping the contacts, and on those tiny 1206 it's simply replacement time.

The LM358 was sturdy but it was just rotten solder. It looked more like greyish goo and it was actually just sticking thanks to a couple of legs being less corroded.
It wasn't difficult to remove (it came clean off almost springing but the trace that was still soldered to came off as well) , clean and prepare for resoldering but as I have many replacements I'll just put a new one, also because the marking has come off and it costs me nothing to do it.

It was a chore doing all the curing because my UV lamp works well only when batteries are at full capacity.
I need to buy a new one, with way more LEDs - has 12 (51 is enough?).

After resoldering the chipset IC I'll try a power on with what is on it and if it fails I'll wait until replacements arrive.
Worst case it won't POST or some tantalums will explode - I'll wear protection as I love my eyes.

After job pics.

Old solder was rotten to the core and wasn't easy to remove. I even saw a few small 0.45 like solder balls float around, like if the initial solder job at the factory wasn't that successful.

Next is to desolder the diodes and maybe replace those as well. Ferrite beads are ok.

Quick question: why PSU Ground is connected to a Ferrite Bead and then to all the rest of the motherboard?

Nexxen wrote on 2023-09-13, 02:28:

Too easy. Won't fit. LOL My point is to learn from this. […]
Show full quote

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.

Are you sure it still works the VLSI?

Robin4 wrote on 2023-09-16, 19:44:

Nexxen wrote on 2023-09-13, 02:28:

Too easy. Won't fit. LOL My point is to learn from this. […]
Show full quote

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.

Are you sure it still works the VLSI?

Internally I hope so, I couldn't test it as the board was visibly damaged beyond power on.
At least I didn't want to power on a board that had 0% chance of POSTing.

I did test gnd + Vss with other leads, it showed no shorts.
Address and others aren't between them. I didn't check all of it, worst case I simply desolder. This is a test project, like medicine students stitching pork...

As far as this is my "hope" it'll work. Otherwise I have a link for a replacement.

Of 4, 3 are 1N4148.
Need id of this diode, the white one:

Edit: from another source I found the same diode with markings on. It appears to be a germanium diode, 1N34A.
It looks okay (see pic).

I tested all the tantalums that I desoldered.

A few have above 10 ohms ESR, I guess that's not good. The others have 0.x, I believe this to be the correct value.
One actually broke as soon as I removed it, it had cracks and it just fell apart. This is new 😀
Another had a lead come out, as it had no contact to the cap itself. I assume, for a test, I can replace it with a ceramic of same value.

Required components came in today.
I'll probably start soldering the chipset and the smds this w/e.

Soldered the IC.
I took a good 45 minutes to get it done and checked (all pins are solid, not better than factory). I watched Drive-in massacre in the while; it was not so bad a movie.
Pics of all the sides.

I just noticed that a few leads may need some adjustment after testing.
If it works I'll make it cosmetically perfect. I don't own a microscope and it is hard just with a magnifying glass and the occasional cell phone pic.
Cell phone is good to check but can't be used as a microscope 🙁

One lead was so rotten it came off and I had to dig a bit in the plastic to solder a wire to it and then to the pad.

Repopulated the board with new components.
Just waiting for the last sot-23 couple and then it'll be done.

I had to touch up a couple of leads but it's now perfectly stable.

I checked for continuity with ISA and other components and ran across this issue:

pin 121 : -IOCHK wasn't connected to anything. ISA has a pin A1: I/O CH CK.
There was a trace going from pin121 to ISA A1, I could see it ending there, but maybe it's by design... IDK, my guess was yes, the trace was corroded.

https://upload.wikimedia.org/wikipedia/common … SA_Bus_pins.svg
https://4donline.ihs.com/images/VipMasterIC/I … EF6B88F2AEB20B8

To me they are the same thing, I went on and soldered a wire to the trace and now it's perfectly working.
Before I kill anyhting, could anyone confirm it's correct?

Board has now a dead short (0 ohm) between GND and +12V.
Go figure what it is.

I surrender. My next move is to desolder the keyboard chip and test it elsewhere.

Repair attempt: FAILED.
I can't even change it to PASSED à la David Lightman...

keyboard controller doesnt touch 12V, rip off tentalums again

rasz_pl wrote on 2023-10-07, 01:49:

keyboard controller doesnt touch 12V, rip off tentalums again

I'll try that.
I was tired and so done with it, it made me wanna quit. Frustration...
Today I gave check on the VLSI and found 2 desoldered leads. One has to do with ODD comunication, normal it wasn't detecting the bios.

Tantalum it was, showing now as an inductor 0.1mH.
A few leads of the VLSI came off and had to resolder.

I was thinking about the 2 transistors, 3904 and 3906 (I ordered replacements).

IRDY is not showing, with or without them, but mine (04+06) could be dead as was the LM358.
Are these always just involved in recharging the battery or they have other purposes?

Edit: I mean in this setting, I know they are push-pull in conjunction. My concern is if they could be powering something I'm unaware of.

Soldered the last two missing components but the board still doesn't POST.

IRDY on my post card still doesn't light up. I see this behaviour when it cannot access the BIOS.

New quest: find the BIOS link to CPU, or Chipset on 286.

I checked all the connections from ISA to VLSI C331 - ISA BUS Controller: all is good and connected.
Same for C320 - System Controller / data buffer: all is good and connected.

Last thing I have to check is the CPU. I'll desolder it and check it in another boad. Even if it a 20MHz model it'll work great underclocked @16MHz

I would like to hit my head on a wall, a very hard one.
Soldering back a jump wire that came off I soldered it to the wrong hole..........................................................

In fact it now works.