Thanks for prompt reply - must say this forum is a dream come true.
My console is a 48 ch, previously owned by SVT (Swedish state TV) i Malmö. Serviced well, in use until the day before I bought it.
Symptoms: First started shutting down the +/- 20 feed (indicator lamps turns off, desk goes into "safemode"), then escalating into totally shutting down all power with loud "smack" - all indicator lights off, restart possible, but then after a while - same again. Did try this only once...
The chassi of the PSU feels a bit extra hot probably just after the shutdown. Otherwise properly ventilated et al. In use here for about three years, powered on 24/7, 365 days/year.
Extremely grateful for all suggestions and help - I am not a "under the hood" kinda guy... Currently rescheduling work due to the situation...