Both cards have significant corrosion and were very dirty.
The process was as follows:
- Wash in soapy water. Scrub with toothbrush. Blow off and allow to dry.
- Inspect and gently remove socketed ICs (one had corroded on to a socket).
- Apply soapy vinegar, rinse.
- Apply soapy vinegar, rinse. Blow off and allow to dry.
- Apply de-oxit to corroded legs and leave for 24 hours.
- Clean legs with wire brush on Dremel.
- Clean with soapy water. Blow off and allow to dry.
Most ICs have oxidised legs. The legs on socketed ICs can be easily checked for integrity – in some cases, a small nudge was sufficient to make them fall off. It’s harder to check those that are directly soldered. It appears that in many cases the plating has been penetrated and is prone to flaking. I attempted to re-tin some ic legs, but the solder would not take even with lots of flux – I suspect the material required electroplating and that’s not happening. De-oxit is probably the only practical way to protect them. Of course, they could all be replaced, but that will be time-consuming and will risk damage to the PCB.
The MC3446 line drivers (for the IEEE-488 bus) are located near one of the case openings. One had legs corroded through. The others were in poor shape. They have been replaced with new ICs and sockets.
The PCBs are in generally good condition. The edge connectors had lost some plating, but the oxide has been removed with deoxit and the copper re-tinned.
On the second board, a damaged socket was replaced. I favour machined sockets, but this board never used them and the sockets that have been added in the past are either zero insertion force or dual wipe (the originals are probably single wipe).
The wire to the piezo was missing, so it has been replaced.
The configuration links in the middle of the board were untidy and used the wrong gauge wire. They have been replaced.
Other links have been made with wire wrap. The wires were unnecessarily long, making them vulnerable to breaking. The posts were too high, so they were prone to bending. The posts were cut down and the wire wrap redone.