Sinclair ZX80 / ZX81 / Z88 Forums

PokeMon wrote:So I meant to measure the pin 27 of EPROM (/WR).
What voltage do you have here ?

That pin is high on my board - ROM position 6.

I have J100 positioned over the rightmost 2 pins, with one unconnected pin immediately to the left.
Okay, just to check - my IC2 is a 28C256 chip, and the pinouts I see on the internet say that A14 is pin 1 not pin 27. That would be 27C256. I maybe gave you some bad information earlier.

This is all encouraging, thanks guys! By the way, you have to reset after turning the ROM switch or turn it while power-off - I hope this is clear. ;) Yep, I got that. :) Okay, pin 1 - A14 - is 0 as expected. So that's something. In fact, A14 to A9 are all zero. /WE is 1 again as expected, /CE is 1 ...

That's great to know. But if there were connection problems between the ROM selector and the EEPROM, couldn't that have done something nasty to that chip?

Oh sorry, the voltage (logic level) - I was rapidly falling asleep. I'll measure it tonight. I've got a horrible feeling, with the demise of the Aszmic image, that my investigations have destroyed a chip. It was good to see that flashing cursor though, and every keypress worked. Sigh.

Thank you so much for your help! Yes I soldered R100 - a 10K resistor? Unfortunately, after trying positions 4 and 6 again (and getting a lot of random garbage on the screen), going back to position E there is no longer the Aszmic image running correctly. :o It just gives a black screen and red LEDs...

Thanks for that info guys. This evening I managed to solder some new legs onto the damaged X1 component - so it's back in action! :lol: Doesn't look that great, but it'll do until the new one arrives. I checked all the IC legs - no bent pins. I checked for shorts, and found three - all underneath ju...

Didn't check bent pins. I'll check all again - and will pick up an oscilloscope 8-) Meanwhile I'll have a relaxed weekend and not worry about the broken pins! EDIT - Just had a look, and apart from the HPS140i there's no way I can afford any of the oscilloscopes right now. Is that one capable of sho...

Well, in a structured pseudo-code it would be: do k$=inkey$ loop while k$<>"1" and k$<>"2" case k$ "1": blah blah blah for case 1 "2": blah blah blah for case 2 end case So my first attempt might be: 100 LET K$=INKEY$ 110 IF K$<>"1" AND K$<>"2" THEN GOTO 100 120 IF K$="1" THEN GOTO 1000 130 IF K$="2...

Those 6.5MHz filters seem hard to come by, so I've just ordered another directly from you PokeMon. Project will be on hiatus until next week! I hope that was what caused the problem - half-expecting you to say "no, doesn't matter which way round you put X1..."