Soekris R-2R: Damaged isolator fix

A friend of mine had a little accident with his DAM1021 which resulted in him frying the on-board isolators.

We are talking about these three ICs, with part number “SI8620BB-B-ISR”.


It turns out that the specific ICs are at their End Of Sale, so both Mouser and RS did not have them in stock. Luckily, it turns out that the TI ISO7420FEDR is a good alternative. Unfortunately, it is also about 2.5 times the price of the Si part, but what can you do.. The order was placed, in time the ICs were delivered, and it was time to do the work.

This is what my workbench looked like:


You see the DAM board, a collection of different width Capton tapes, the ISO7420FEDR ICs and my favorite set of tweezers. In the far right you see part of my magnifying glasses. They are necessary for repairs of SMD stuff.

What you don’t see is my hot air rework station which is also necessary.

First I had to use Capton tape to cover the “innocent” components close to the isolator chips. The hot air could damage them if I was not careful.


Using the hot air rework station, I desoldered the offending ICs:


And using my normal soldering iron I managed to solder in the replacement ICs:


It may not look as good as the original solder work, but the board is now as good as new. 🙂