I washed the upper PCB of the ART DR-X effects unit today. This process consisted of the following tools:
One used toothbrush (largely defunkified through prior use with isopropyl alcohol), one 8x10 photo developing tray, one gallon of distilled water (of which approximately one pint was used here), an air compressor and a heat gun.
I pulled the following shot from the previous write-up:
Since chemistry isn't my strong point, I can only guess that the white chemical growth at the legs of the pins is caustic potash. Therefore, I reason that a mild detergent is probably not required, since the caustic nature of the build up is going to provide more "cleaning" power than I probably need to begin with.
I poured enough distilled water to just cover the top of the ICs, and before agitation a considerable amount of the white build up dissolved. After 30-40 seconds with the brush, I hit the PCB with compressed air to disperse most of the water, then followed up with the heat gun. In order to avoid overheating the PCB, I held it by hand while distributing heat (which was a huge motivator to keep that gun moving). The idea behind the heat gun is to encourage evaporation of moisture remaining after the compressed air.
Something had been bothering me about the source of the saponification; in the past when I've seen this build up it has been localized (or at least centered around) a decomposing battery or electrolytic capacitor. This was distributed more or less evenly across the entire PCB, moreover the back-up battery and capacitors did not exhibit any of the build up.
An aspect of metallurgy is that dissimilar materials will often facilitate corrosion at contact points. In comparing before and after wash pictures, I can't help but notice that a good portion of the build up is centered on joints that were not completely filled in the soldering process.
A closer inspection of the lower, largely digital board reinforces the theory that the poor infill is, if not the root source of the failure, at least largely contributing to the problem. By the mid to late 1990s I recall that ART effects from the earlier part of the decade had gained a reputation of unreliability, which leads me to wonder if the chemical build-up around the legs, which certainly may have been allowing functionally disruptive crosstalk, wasn't isolated to this unit alone.
Perhaps I'll trip over some similar era non-functional ART units upon which to test this theory.
I'll need to grab a larger tray to wash that board though, so this process remains in a state of limbo.