My mate Giles bought a Urei 1620 which is a fascinating 1980s-era mixer.
It's in fairly good cosmetic condition (in fact it looks very pretty) but there's something up with the output circuitry, it sounds really shrill and nasty. Since the effects loop gives out a perfect sound it must be the master output. I'll have to go over the circuit with an oscilloscope.
The phono/RCA connectors on the back are slightly corroded, and generally feel incredibly loose since they're mounted to a PCB rather than being chassis-mount. I'll likely replace them with high-quality gold plated connectors, possibly by making another PCB. The XLR connectors are similarly corroded but they can be replaced easier as they are chassis mount.
Apart from that, per-channel effects loops would also be great as the UREI does not have per-channel EQs. Giles also wants the master EQ and per-channel balance controls bypassed, and also is asking if we can have per-channel cue buttons like on the Pioneer DJM series. I'm sure all this will be possible.