Restoration of EMT 250s

The model 250 digital reverberator from EMT is quite special. First of all, it looks like the oil radiator from Uhura’s boudoir. In germany the EMT 250 is usually called <Weltraumheizung> (space radiator) because of that.

As the developers of the digital circuit, Dynatron, feared that their design could be copied they removed all markings from the ICs – and there are many – of the logic board. Only the RAMs and some static shift registers used for pre-delay are usually untouched.

The main logic board is completely wire-wrapped, something not seen that often outside of vintage industrial control, aircraft and military equipment.

(Images an some info on the first 250 I worked on will follow…)

The second 250 was hit much harder. Some kind of heavy corrosion destroyed about two dozens of ICs. Their pins look rusty and broke off partially while trying to pull the ICs from their sockets. All of them seem to be from one manufacturer, other ICs with a different looking body do not show any traces of corrosion.

Further investigation with a microscope immediately after removing an IC revealed that some pins were already broken some time before the attempt to pull the IC:

The next task is now to remove the remainings of the pins, clean the sockets and re-populate the board with ICs.