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?
ZX Spectrum issue 2 12v low missing bits of copyright logo
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Re: ZX Spectrum issue 2 12v low missing bits of copyright logo
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
You can check the -5V rail on pin 1 on IC6. See the pin out here.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
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ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.