Search found 1538 matches

by Andy Rea
Mon May 06, 2019 8:57 pm
Forum: Hardware
Topic: TS 1000 artifacts after warming up
Replies: 14
Views: 326

Re: TS 1000 artifacts after warming up

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...
by Andy Rea
Mon May 06, 2019 8:50 pm
Forum: Hardware
Topic: TS 1000 artifacts after warming up
Replies: 14
Views: 326

Re: TS 1000 artifacts after warming up

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...
by Andy Rea
Mon Apr 22, 2019 12:13 am
Forum: Hardware
Topic: Composite mod done Zx81 great picture but somethkng is wrong
Replies: 14
Views: 447

Re: Composite mod done Zx81 great picture but somethkng is wrong

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
by Andy Rea
Sun Apr 21, 2019 1:36 pm
Forum: Hardware
Topic: Composite mod done Zx81 great picture but somethkng is wrong
Replies: 14
Views: 447

Re: Composite mod done Zx81 great picture but somethkng is wrong

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

BTW which composite mod did you do?

Andy
by Andy Rea
Sun Apr 21, 2019 1:38 am
Forum: Welcome Area
Topic: Hello all from Wellington, New Zealand
Replies: 3
Views: 177

Re: Hello all from Wellington, New Zealand

Welcome, hope you find some useful information.

Regards Andy
by Andy Rea
Sat Apr 13, 2019 3:04 pm
Forum: Hardware
Topic: ZX81 External Keyboard
Replies: 37
Views: 4284

Re: ZX81 External Keyboard

Hi

is this keyboard available yet ?

regards Andy
by Andy Rea
Fri Apr 12, 2019 10:37 pm
Forum: Hardware
Topic: Overclocking the machine
Replies: 3
Views: 194

Re: Overclocking the machine

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...
by Andy Rea
Mon Apr 01, 2019 7:07 pm
Forum: Hardware
Topic: TS1500 50Hz which resistor
Replies: 6
Views: 324

Re: TS1500 50Hz which resistor

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.
by Andy Rea
Sun Mar 31, 2019 10:18 pm
Forum: ZX BASIC
Topic: what is the largest number that can be stored on a zx81
Replies: 10
Views: 548

Re: what is the largest number that can be stored on a zx81

lets assume we are going to use the whole 16K to store a single whole number dont want ony of the rounding loss business with floating piont numbers and exponents ( although the number you could store would be huge ) so we have 16384 * 8 bits to store our large integer (2^0 + 2^1 + 2^2 .... + 2^1310...
by Andy Rea
Sun Mar 31, 2019 10:04 pm
Forum: Hardware
Topic: TS1500 50Hz which resistor
Replies: 6
Views: 324

Re: TS1500 50Hz which resistor

Not certain it can be done that way, least i never was able on my ts1500, however you can use and external rom and hardcode it for 50hz

regards Andy