Search found 171 matches

by rune
Tue May 23, 2017 1:58 pm
Forum: Hardware
Topic: Resurrecting a ZX81 - Step by step help appreciated.
Replies: 26
Views: 7031

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: 7031

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: 7031

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: 7031

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
by rune
Fri May 05, 2017 8:55 pm
Forum: Hardware
Topic: Resurrecting a ZX81 - Step by step help appreciated.
Replies: 26
Views: 7031

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

Cheers Darren, I've tried another brand new RAM pack. No difference - Also tested across 3 ZX81s. Hi Mark, heres some results of testing. Apologies for it being so long, but I tested all three boards. There are two issue 1s and an Issue 3. I tested Pin 14 & 16 on the ULA and Pin 6 on the Z80 plus al...
by rune
Thu May 04, 2017 9:38 pm
Forum: Hardware
Topic: Resurrecting a ZX81 - Step by step help appreciated.
Replies: 26
Views: 7031

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

Hi Mark At least two of these boards did work at one point, but with the usual problems - cracked membranes, old ULA (very dark picture). I had other ZX81 that did work so I concentrated on those. Now its playtime and I'd like to try getting these working again. The PSU is good. I got the diodes cha...
by rune
Thu May 04, 2017 8:00 pm
Forum: Hardware
Topic: Resurrecting a ZX81 - Step by step help appreciated.
Replies: 26
Views: 7031

Resurrecting a ZX81 - Step by step help appreciated.

Hi guys, Im looking to try and resurrect 3 ZX 81 boards - 2xIssue 1 and an Issue3. I have an oscilloscope, a decent multimeter and a bit of time to do this now. All 3 boards have had the RAM desoldered and a 32K RAM socket added. At the moment I'm testing using a Sinclair RAM Pack. I have two boards...
by rune
Sun Sep 11, 2016 10:03 pm
Forum: Development
Topic: Vertical Scroller by mistake
Replies: 7
Views: 2972

Re: Vertical Scroller by mistake

Good luck with the search.

I agree on using real hardware, but sometimes (most times) its easier to use an emulator when the TV is rubbish but she who must be obeyed is watching it.
by rune
Sun Sep 11, 2016 9:17 pm
Forum: Development
Topic: Vertical Scroller by mistake
Replies: 7
Views: 2972

Re: Vertical Scroller by mistake

Cant you use an emulator and save the image when needed. Once you have the program working save and convert to a wav for use on the real hardware. Benschop Forth 83 is very good, but its for the Spectrum. You can save to tape, microdrive, IF1bis or any other media storage thats compatible with the 4...
by rune
Tue Sep 06, 2016 9:11 pm
Forum: Development
Topic: Vertical Scroller by mistake
Replies: 7
Views: 2972

Re: Vertical Scroller by mistake

mrtinb I can reproduce the word SHOW. This is just showing the contents of the 620 memory locations allocated to SHOW. The characters displayed arent exactly the same but that may be because were are using different hardware or emulators. Im not sure what you are trying to achieve with the second (s...