This set had an arcing LOPTfmr. I replaced it and the line transistor
but still tweeting, with the LED flashing in sync. Did the same with a
bulb across the c-e and no transistor. No voltage was there.

checked all primary and LOPTfmr secondary outputs, no short found.
I replaced the STRS5707 in the psu - but still tweeting.

I suspect the EEPROM has got corrupted by the arcing. Can I just use a
'blank' one or must it be the preprogrammed one for this set /chassis?

any other ideas are welcome!
regards, B.