A lot of microwavers use the FT290 Mk1 as a tuneable IF and thus
might find this experience useful.
A recent fault manifested itself on my pretty aged 290. Pressing the
PTT made the usual audible "click" but produced no red Tx LED and no
Investigations showed that the relay contacts on the relay, at the
rear of the unit, on the top PCB were dirty. One can carefully
prise off the clear plastic cover and remove it. Then a squirt of
contact cleaner into the relay seems to clear the problem. The relay
cover can then be replaced to keep the contacts clean.