Search found 3470 matches

by 1024MAK
Sun Mar 07, 2021 3:36 pm
Forum: Hardware
Topic: No video output, could use some advice
Replies: 13
Views: 598

Re: No video output, could use some advice

The keyboard being removed makes no difference. A ZX80, ZX81 or ZX Spectrum will start up quite happily without a keyboard being connected. So from those results, if you are getting different different frequencies on the various address lines (A0 to A15) then I would say that the Z80 is okay. It doe...
by 1024MAK
Fri Mar 05, 2021 6:57 pm
Forum: Sinclair Misc
Topic: 40 years ago...
Replies: 6
Views: 357

Re: 40 years ago...

A lovely day to celebrate the ZX81’s 40th birthday :D

Well done to all the ZX81 machines that are still working :D 8-)

Mark
by 1024MAK
Fri Mar 05, 2021 6:55 pm
Forum: GAMES
Topic: The comp.sys.sinclair Crap Games Competition 2021: 25th edition extravaganza!
Replies: 14
Views: 1383

Re: The comp.sys.sinclair Crap Games Competition 2021: 25th edition extravaganza!

Hopefully, in the next two hours, I will be sending an entry to celebrate the ZX81’s 40th birthday :D

Mark
by 1024MAK
Fri Mar 05, 2021 12:03 am
Forum: Hardware
Topic: Wait mod + ZXPand+ issues
Replies: 2
Views: 227

Re: Wait mod + ZXPand+ issues

As far as I am aware, the ZXpand and ZXpand+ require the ZX80/ZX81/TS1000 to run at their stock speed.

Although the SRAM and EEPROM chips may be okay with a faster computer, I’m not sure if the microcontroller that is the brains of the ZXpand and ZXpand+ can cope with a faster Z80.

Mark
by 1024MAK
Thu Mar 04, 2021 11:17 pm
Forum: Hardware
Topic: 3.3V logic with the ULA
Replies: 1
Views: 121

Re: 3.3V logic with the ULA

I’m not totally sure about the ULA, but it is configured for its digital input pins to be TTL compatible. As a TTL logic high at an input is 2V or greater, both the ULA and the Z80 should be okay if the Teensy can manage to pull up to above 2V. Note that the clock input pin on a Z80 is different and...
by 1024MAK
Wed Mar 03, 2021 1:59 pm
Forum: Hardware
Topic: Changing the ZX81 ULA, newbie question
Replies: 8
Views: 372

Re: Changing the ZX81 ULA, newbie question

Do extract the existing ULA carefully, using a flat blade screwdriver or blunt knife. Lever up each end a bit at a time, and keep a finger on top of the chip, but lever between the plastic of the socket and the chip, not against the PCB (you don’t want to cause any track damage). If you are too ener...
by 1024MAK
Wed Mar 03, 2021 8:44 am
Forum: Hardware
Topic: Changing the ZX81 ULA, newbie question
Replies: 8
Views: 372

Re: Changing the ZX81 ULA, newbie question

Hi guys, I have a ZX81 that have an old ULA (ULA2C184E) and I have problems connecting it to all TV sets I have, I get a very dark, blurry and noisey image, you can barely see something turning the bright all the way up. I learned that there's an issue with this ULA that hasn't this "back porch" th...
by 1024MAK
Sun Feb 28, 2021 9:34 pm
Forum: Hardware
Topic: ZX81 Unbuilt Kit - What changes to add while building
Replies: 2
Views: 143

Re: ZX81 Unbuilt Kit - What changes to add while building

Hello Harry, welcome to our forum :-) About 40 years ago I ordered a ZX81 Kit but it came in assembled. Wow! Did you have to pay the assembled price or the kit price? I'm considering making the following changes: Replacing the original Z80 with a newer Z80 CMOS CPU Replacing the original 7805 Voltag...
by 1024MAK
Sun Feb 28, 2021 9:27 am
Forum: Hardware
Topic: 48k Issue 4B low sound
Replies: 3
Views: 201

Re: 48k Issue 4B low sound

Sounds like TR7 (ZTX450) is the culprit, specially if the 5v line has gone high at some stage, this can happen if a lower ram chip has badly failed and spiked the 5v line, Ive not seen D9 fail before, but might be worth replacing if TR7 doesn't remedy it. And the standard speaker should read 40 Ohm...
by 1024MAK
Sat Feb 27, 2021 2:26 am
Forum: Hardware
Topic: Blue tint video issue
Replies: 8
Views: 367

Re: Blue tint video issue

Now the unit is producing video which is yellow-ish and keeps switching on and off, cutting in and out. Perhaps I need to perform the RGB SCART blanking signal mod? It appears I am using the proper RGB-to-SCART cable as I have the +2A or +2B model. The most strange portion of this mystery is everyt...