These photos were taken from a new-in-box 16kB memory expander for a Timex Sinclair 1000 computer. As far as I'm aware, it was never used.

The box was made of thin cardboard with a two part styrofoam insert. There are plenty of large air gaps for atmosphere to penetrate behind the plastic housing to the PCB.

It doesn't seem to be centered in any one area and instead clings to any of the open solder connections. At first it looked like battery corrosion but there is no battery inside. Inspecting it with my microscope makes it look less like something you might see from a battery and more like a viscous white substance. Maybe something from a flux residue?

I have several other ram packs and none of them display this type of substance on the surface.

I'll probably just wash the PCB in the sink with some soap and an anti-static brush, and that has done well for me when cleaning flux residue in the past.

Has anyone ever seen anything like this or know what caused it?

Sorry for the poor microscope pictures. I have to hold my camera up to he lens and it's almost impossible to get a clear shot.

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  • 1
    \$\begingroup\$ Probably the used flux was acid. The industry did a lot improvements since then, specially the flux was a big problem those days. \$\endgroup\$ Feb 11, 2020 at 11:32
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    \$\begingroup\$ Looks like the joint itself is damaged too, they don't look healthy at all. I'd probably remove em and solder them anew. \$\endgroup\$
    – Lundin
    Feb 11, 2020 at 11:47
  • \$\begingroup\$ How do the component legs look? \$\endgroup\$
    – rdtsc
    Feb 11, 2020 at 13:38
  • \$\begingroup\$ I do not think acid core solder was ever use for electronics. Plumbing, maybe, but not electronics and not on PCBs. At least I've never come across that. \$\endgroup\$
    – SteveSh
    Feb 11, 2020 at 14:00

2 Answers 2


Looks like it got wet with power applied. Inspect for traces corroded through after you clean it. A toothbrush and isopropyl alcohol or just plain water (deionized is preferable) work well. Allow to dry thoroughly.

  • \$\begingroup\$ He wouldn't need to spend much time if he undo/redo all the soldering. \$\endgroup\$ Feb 11, 2020 at 11:34
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    \$\begingroup\$ The question states this was a new-in-box unit, never used before. As such I find this explanation unlikely to be true; at least the wet with power applied part. \$\endgroup\$ Feb 11, 2020 at 12:29

Looks like corrosion to me. Lead turns dark over time, tin turns white. Looks like a mix of both; perhaps the solder's just breaking down. Probably from random stuff in the air over these decades (nitrous oxides, water as humidity, etc.) Notice that the tracks are solder-coated (wave soldering), but they all appear fine as the green solder resist has prevented air from reaching them.

All of the exposed solder joints look horrible and should be redone.

  1. Use rubber gloves. The following presents a risk of lead poisoning due to metal salts.
  2. Submerge the whole board into a disposable* bowl of >=93% isopropyl alcohol.
  3. Scrub everything very thoroughly with a disposable* toothbrush.
  4. Remove board, set upright to dry.
  5. Using a desoldering tool (pump, braid) of suitable temperature, remove the solder from one of the joints. Careful, as excess solder on the tracks can be removed; leave those alone.
  6. Resolder the joint using "old" 60/40 solder if available.
  7. Repeat steps 4-5 until every joint has been desoldered and resoldered.
  8. Scrub the board in the (dirty) bowl again to remove all flux. Rinse both sides with fresh alcohol.
  9. Throw everything used (toothbrush gloves, etc) into the bowl. Let the bowl evaporate outdoors away from ignition sources. When dry, treat bowl as (dangerous) lead waste.

*Recycle if possible. An electronics repair company will likely be able to recycle it.


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