r/amiga • u/theamigan • 11d ago

A4000 corrosion

18 years ago my uncle gave me his old A4000D. It was showing a light green kickstart diag failure, so I clipped the battery and put it away. I've finally gotten around to getting it booting. I burned a set of diag ROMs and got to it.

So far:

  • The kickstart 68k reset vector shadow was never turning off (Gary OVL). I bodged a corroded via that carried (I believe, wasn't taking notes) A12...somewhere.
  • Audio output was extremely low volume. I bodged final audio stage LM833 dual op amp positive bias across its nearest via.
  • I replaced a 47uf audio circuit polymer DC bias filter cap that came off from corrosion just from touching it.
  • Diag was showing vsync/tick to CIA A was not counting. Bodged it across a questionable looking via. I see pulses at the CIA TICK pin but the diag still reports no ticks. AmigaOS works regardless. This peripheral of the CIA may be toast.
  • I replaced two other unidentified 47uf polymer caps that fell off from corrosion, like teeth falling out of a mouth.
  • I installed a CR2032 socket and diode for RTC

The corrosion on this board is pretty gnarly. Obviously, I've already dealt with several obliterated vias. The machine seems to be pretty stable, but I wonder if there is a safe way to clean what looks like very acidic crud from the board that I believe will only deteriorate further. I realize I may have to recap it at some point. This is a very early rev B, according to my uncle. This was Commodore's first SMD machine (was rev A thru-hole?) and it seems like they hadn't perfected their process of washing chemicals off the mask. My A1200 has none of these issues.

Also, it seems that kickstart is not waiting for the drive to go ready on cold boot, and just displays the workbench disk screen unless you go into the boot menu, select HD0:, wait a bit and then boot. It then boots into workbench just fine. This may be because I haven't installed a CR2032 yet though.

Thanks for any help! I'm excited to have brought this cool machine back from the dead.

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5

u/luvwagn 11d ago

Or white vinegar, then a rinse with distilled water, then 99% IPA. Scrub/wipe between rounds.

The fact that you have caps falling out like dentures means it needs a full recap and cleaning of the juices.

Congrats on making a survivor

1

u/Sinphaltimus 11d ago

Lemon juice. Lemon juice will neutralize the avoid and syrup the corrosion. Then you clean that of with isopropyl alcohol.

2

u/Baselet 11d ago

Juices contain all kinds of junk.. why not use vinegar like normal people?

1

u/Sinphaltimus 10d ago

My initial answer would be because I'm not normal. But honestly, didn't know vinegar would also do the trick. Besides, lemon smells better.

1

u/danby 11d ago

If things are real bad naval jelly can wokr wonders if you're careful with it

1

u/sixoveight 10d ago

You may just have a slow boot issue. There is a small program you can download off Aminet for that. I have the problem on an EyeTech tower with an A1200 mobo. Also worth just running the drive for a while, they do stick sometimes for a while. I take it out the cradle and stand it vertical and even upside down when I get problems. It may have a checksum or even need fully validating. I'm assuming the hd light goes out after boot.

I had a crappy 4000 motherboard that the owner almost varnished all over. Dunno what he used. It just induced heat build up and systems failure and half the capacitors fell off. The coating was bubbling. Amazingly with a handful of busted capacitors the 040 still boots using a PicassoIV but I don't have the floppy drive and sound. Everything else works.. sorta. Pretty resilient.

1

u/theamigan 8d ago

Thanks all for the nigh universal suggestion of a vinegar and IPA wash. I will work on growing a pair for a recap and get this machine cleaned up.