I have perhaps foolishly tackled the repair of my freeview box -
Tvonics MDR-250 - for which no service information appears to be
available. I'm an amateur, btw. (Fault is it's powering on and
immediately shutting down repeatedly.)

I have a suspect component, marked Q700 on the PCB, suggesting that
it's a transistor of some sort, and marked 654Z. I've tried googling
for this part number but can't find any information.

Its a 6 legged device, and I don't know of any 6 legged types of
transistor. The only alternative device I've come up with is an opto-
isolator - though I don't know what the standard PCB identifier would
be for one of these.

2 pairs of pins are connected together, so there are effectively 4
legs. It's in a very cramped part of the board (next to the power
socket and what I think is a fuse on it's own little sub-board) so I
can't really work anything out from what it's connected to.

Anyways, I need some info because it's either completely short
circuit, or it's connected to something which is completely short
circuit, and I can't do much unless I find out what the thing is.

Any suggestions welcome
TIA
Alexis