Search found 6 matches

by spodula
Fri May 18, 2018 11:49 am
Forum: Hardware
Topic: Why was Sinclair selling UK model ZX81s in the USA?
Replies: 9
Views: 5518

Re: Why was Sinclair selling UK model ZX81s in the USA?

The ULA was designed to output both 50 and 60hz signals. Swapping between 50 and 60hz was done tying pin 22 low. (Floating for 50, Low for 60) From what i gather from the schematics, USA models also required a different modulator, two resistors and a diode. Edit: It may be that is is only if you nee...
by spodula
Tue Mar 06, 2012 12:35 pm
Forum: Hardware
Topic: Ceramic Resonators (zx81)
Replies: 16
Views: 7991

Re: Ceramic Resonators (zx81)

Wierdly, it appears to be oscilating, just at the wrong frequency.

I shall try some of the links posted. Thanks!
by spodula
Mon Mar 05, 2012 12:51 pm
Forum: Hardware
Topic: Ceramic Resonators (zx81)
Replies: 16
Views: 7991

Ceramic Resonators (zx81)

Anyone know where i might get hold of a Ceramic resonator for the zx81? Cant seem to find one anywere at 6.5Mhz

I've tried using a standard Crystal, but this doesnt seem to work.

Anyone got any ideas?
by spodula
Sat Feb 06, 2010 8:49 pm
Forum: Hardware
Topic: zx81 48k memory.
Replies: 10
Views: 14744

Re: zx81 48k memory.

Ta. I shall take a look. I'm currently on a concerted effort to fix all my old computers while i have a few free days, so I will take a look at it in a bit..
by spodula
Wed Feb 03, 2010 10:45 am
Forum: Hardware
Topic: zx81 48k memory.
Replies: 10
Views: 14744

Re: zx81 48k memory.

Alas, that mod doesnt use the $8000-$bfff area, i assume because it uses the internal RamCS signal.
It looks a lot like the Rom appears at that location, so i may have to disable that.

I think i shall just try it and see.
by spodula
Tue Feb 02, 2010 3:14 pm
Forum: Hardware
Topic: zx81 48k memory.
Replies: 10
Views: 14744

zx81 48k memory.

Hi, Having recently got a zx81 (And a replacement keyboard, thanks Mr Rwap :D ) , I am interested in building a Ram pack for it. Now i have a couple of 128K sram chips around (being unable to buy only one of anything , :D ), and was wondering what the difficulties of creating 48k. Now I know by defa...