Sinclair ZX80 / ZX81 / Z88 Forums

Hi

I have dug my zx spectrum out of the loft after 25 yrs and thought id give it a go

ok so power on and RF output is very wonky

so i did the RF mod and then tried again

now boots up and I get the Sinclair logo and its stuck there

looking at the logo its seems to be missing various bits of it

so i dug my multimeter out and tested the rails on the lower ram chips

and it seems the +5v and +9v are there

but the 12v rail is low at 10v

any ideas?

The most important supply rail as far as the ‘lower’ RAM (made up of 4116 or equivalent DRAM chips) is concerned is the -5V rail. If this is out of specification (-5.5V to -4V) or missing then there is a problem with TR4 (and maybe a problem with TR5).

You can check the -5V rail on pin 1 on IC6. See the pin out here.

Mark