Sinclair ZX80 / ZX81 / Z88 Forums

I've ordered some replacement (TI!) HC257s, and having just caught up with the thread, some HCT257s too. I'm going to replace all ICs, and will use the HCT's in 24 & 25 as recommended by Dave & Max. They're going to take a few days to arrive so you'll have a few days of rest from my witterings.

Thanks for your help folks - I really don't know what I'd do without you. I'm happy enough soldering and doing basic fault finding, but this is way beyond my level of understanding.

Trevor

I think the new chips should help. I am not saying the HCT versions will be better than HC (they didn't make a difference for me), but if flaky chips were the issue, then the new ones should get you working.

I've replace the 257's (still waiting on the HCT257's, but thought I'd try the standard ones first)

By default - no change.

I've also got one of the amplifier modules mentioned in another thread - that looks like it's going to be the difference; I still haven't got anything to load, but the loading bars on the screen look a lot thicker and more like what I remember as a youngster. I'll spend a few hours tweaking the volume to see if I get any success.

Success!.. sort of.

I've managed to load 1 file - Artic 1K Chess. That's using the amplifier between the TZXDuino and the Minstrel. output voltage looks to be around 6v at the input to the minstrel (maybe slightly under)

I couldn't get anything bigger to load - 3d monster maze looked like it was loading, until the file stopped then I got a vertical line of 0's about 5 or 6 columns in, then crashed.

I'll keep trying - and will probably swap IC24 and IC25 for HCT versions (i've bought them now - might as well).

Heading in the right direction though!

Trev

Success!

I've swapped in the HCT257s, fiddled around with volume settings on the TZXDuino, built an in-line amplifier and I now have a setup that loads successfully and consistently.

There's nothing more satisfying than seeing "Anyone there?" after watching the loading pattern for 3d Monster Maze!


Thanks for the help and suggestions; now to sort out the original 81's!

Trevor.

Mark

That's good news. Yeah I used one of these cheap mono amplifier kits off the internet TDA2030A with two mono 3.5mm jacked wires connect to it's input and output, powered by a variable power supply set I think at about 4.5V now. I don't know if it's the right way to do it but I have increased the voltage until the loading lines look good on my display (as noted in other posts, depending on the display these might not show). And I've got the Minstrel 3 to load stuff from my PC (.p files turned back to .wavs). Getting high enough signal was key. I was stumped this weekend though trygin to load something on a normal zeddy. I kept trying and trying with my goto program Dice by Psion, but it keps returning to the basic prompt at about 25seconds again and again. Almost pulled everything apart and realised that iat's a 16k programme and I didn't have a RAM pack installed!

We've all been there.

4/0

Mark