OT - HH Multi Echo - Tape echo debug

[the3secondrule]

Hey y'all,

I have received one of these behemoths in trade - not working.

Passes clean signal, tape spins. no Echo.

I've audio probed, and I'm getting signal right up to the output of IC9 - right before the record head.

Opamps are all receiving +/- 16v

I'm getting a hiss when each play head is switched on, which gets louder when the echo volume is turned out - so can I assume the play heads are working?

what else should I be looking for here?