Just in case anyone else is having problems with one of these, I've just fixed mine by doing a full PSU recap.
Yesterday when I went to use it, it switched on and immediately froze. Unplugging for 30s and plugging back in - the 7-seg display ran through the Klingon alphabet and then went blank.
All but 3 of the electrolytics looked cheap & nasty but read lower ESR than I was expecting - but evidently not low enough for the PSU to work correctly.
One of the electrolytics on the primary side is the error voltage smoother, its very important that this is in good condition - as its only 1uF it wasn't difficult to find a non-electrolytic replacement.
The 3 electrolytics directly on the cathodes of the 3 rectifiers were decent quality with low ESR (I couldn't find any replacements with lower) I added
10uF multilayer ceramic chip capacitors on the print side.