STE issue: works in B/W hi res but not TV or colour monitor output

[Chandler]

I have an STE which works fine in high res, however if i connect it to either a TV via the RF port or colour monitor via a 13 pin scart cable (tested 2 of them) then the screen is black and dark

What happens is as soon as i switch on the STE i can see briefly the white screen appearing as it boots. Then as soon as the orange floppy LED illuminates, the screen goes dark, also there is no sound either in these modes but there is sound and picture in high res mode

Does anyone have any idea what this could be?

[1024MAK]

Not sure if this exactly matches your symptoms, but the monitor DIN socket uses an input on one of the pins to detect which type of monitor (if any) is in use. If there is a fault on this input circuit, the computer will only work in the high resolution mode.

Mark

[kolli]

If there is a fault on this input circuit, the computer will only work in the high resolution mode.

Pin 4 has to be grounded to switch the machine to monochrome hi-res. The 'circuit' for this is in the monitor plug: pin 4 and pin 13 shorted. So, I can't imagine a Situation where pin 4 would internally get shorted out of a sudden.

[Chandler]

I have seen this problem before but the other way around. ie: no high res but colour ok and that was the U405 IC

Just wondering if this could be the cause again again this time? or even the MC 1377P?

[Chandler]

REPAIRED! it was U405 IC