Search found 167 matches

by rune
Wed Jul 12, 2017 1:54 pm
Forum: Hardware
Topic: ZX81 case screws
Replies: 11
Views: 1971

Re: ZX81 case screws

They are called plastite screws. I think they are 3 x 12 mm. Got a pile of them from the scrap bin at work. I'll try them tonight and post if they work or not.
by rune
Wed Jul 12, 2017 1:34 pm
Forum: Hardware
Topic: ZX81 case screws
Replies: 11
Views: 1971

Re: ZX81 case screws

Thanks for the link. While I like Sell My Retro, 6.49 inc post for 7 tiny screws is crazy.

If I can get the size(s) its usually possible to buy them a lot cheaper...
by rune
Tue Jul 11, 2017 5:32 pm
Forum: Hardware
Topic: ZX81 case screws
Replies: 11
Views: 1971

ZX81 case screws

Every time I open a ZX81 I lose 1 or 2 screws. Can anyone tell me what type/size of screws to buy?

Thanks

Dave
by rune
Sat Jun 10, 2017 7:56 am
Forum: Hardware
Topic: Create ULA for €5?
Replies: 84
Views: 14245

Re: Create ULA for €5?

I'd like one too Paul and am happy to prepay.
by rune
Fri May 26, 2017 10:50 pm
Forum: Hardware
Topic: Resurrecting a ZX81 - Step by step help appreciated.
Replies: 26
Views: 4255

Re: Resurrecting a ZX81 - Step by step help appreciated.

Hi Mark, Im going to post a couple of pics to make sure I know what pulse/rapid pulse etc looks like: http://www.weegieboard.co.uk/Images/Pulse.jpg normal pulse eg Z80 Pin 16 .5us 5V http://www.weegieboard.co.uk/Images/Rapid.jpg rapid pulse eg Z80 Pin 19 .5us 5V http://www.weegieboard.co.uk/Images/A...
by rune
Thu May 25, 2017 10:19 pm
Forum: Hardware
Topic: Resurrecting a ZX81 - Step by step help appreciated.
Replies: 26
Views: 4255

Re: Resurrecting a ZX81 - Step by step help appreciated.

A little more work, replacing "equivalent" transistors with the correct ZTX313s and finding a short now means I have three boards all showing good signals at ULA P14, TR2 and Z80 P6. Also got decent back porch at ULA p16. On the three boards I think I have one with a good CCB Composite board, one I ...
by rune
Tue May 23, 2017 1:58 pm
Forum: Hardware
Topic: Resurrecting a ZX81 - Step by step help appreciated.
Replies: 26
Views: 4255

Re: Resurrecting a ZX81 - Step by step help appreciated.

Thanks Charlie, Heinz and Mark I've checked the connection between the C7/R6 and the transistor base which is good. Checking between both and all other pins nearby, this doesn't show a shorts. Tried without the Z80. The emitter is attached to ground. R6 is 2.20 K Ohms. The only thing that is differe...
by rune
Sun May 21, 2017 10:42 pm
Forum: Hardware
Topic: Resurrecting a ZX81 - Step by step help appreciated.
Replies: 26
Views: 4255

Re: Resurrecting a ZX81 - Step by step help appreciated.

I've selected an issue 3 board and got a bit more testing done. The oscillator left pin puts out a nice low amplitude sine wave, the right pin puts out a meandering wave. I can get a very similar meandering wave at Pin 14 on the ULA. Tracing the circuit to the ULA side of C7/R6 I get the same wave a...
by rune
Sun May 07, 2017 9:43 pm
Forum: Hardware
Topic: Resurrecting a ZX81 - Step by step help appreciated.
Replies: 26
Views: 4255

Re: Resurrecting a ZX81 - Step by step help appreciated.

Hi Mark, I did try some of the pins today and they did show signals. I never got any photos though as I didnt have a lot of time. My plan is to get all the information here printed out plus the chips pin outs and then pick a board and work on that. Thanks for your advice, its greatly appreciated. Dave
by rune
Sun May 07, 2017 10:32 am
Forum: Hardware
Topic: Resurrecting a ZX81 - Step by step help appreciated.
Replies: 26
Views: 4255

Re: Resurrecting a ZX81 - Step by step help appreciated.

Thanks Mark, there's a lot of info to digest there. I'll dig out the printer later and get all as hard copy. As you have probably guessed, Im a novice at this electronics thing, but trying to learn.

I'll stick to one board now for tests and get pics of the pins you mentioned.

Cheers

Dave