Sinclair ZX80 / ZX81 Forums

well i have ordered more chips so thats one less task...

Andy

Hi papalapa,

not really sure, lots of personal things going off right now, so little time left to devote to the hobby.

hopefully but no promise sometime in the next few weeks

regards Andy

Just one more thing.. the transistor composite mod inside the modulator housing... remove or bypasss it. thie signal from the ULA should go direct to the output socket on the modulator. it doesn't need buffering. @Mark yes got a 26Mhz osc module on board... the really 2011 ULA i did had a sort of co...

Hi Again, yesterday i soak tested a ULA for over 3 hours and all is well it is been packed up now ready to wing its way over to you. the commodore monitors work fine but do need the link on the ula shorting as they have a high impedance input on that composite input. from the scope trace it does loo...

unless you really need the capacitor i'd ditch it... most modern tv's don't have any DC bias on the composite inputs.

regards Andy

Don't let Moggy know but try a heatsink on the ULA...

BTW which composite mod did you do?

Andy

Welcome, hope you find some useful information.

Regards Andy

Hi

is this keyboard available yet ?

regards Andy

Andy (a member here) has seriously overclocked a ZX81. However he was using his older ULA replacement module. With a standard Sinclair ULA, overclocking is difficult as you can’t change the frequency without messing up the screen display. Mark Slight correction, the older ULA could do 2X speed... m...

Paul wrote: ↑

Mon Apr 01, 2019 6:23 am

Hi Andy, I guess it would be possible internally as well?
Which bytes have to be changed?
Do you know how the channel 2/3 selection works? Maybe this could be (ab)used for ROM switching?
Kind regards Paul

Nice idea, worth looking into for sure.