My Issue 3 however will not load anything using the exact same setup (even the audio cable).
My LCD TV does continue to show the wobbly picture during loading and on the working machine I can see certain distinct wobbles in the pattern as information is loading, which I simply don't see on the non-working machine. Even power cycling the TV after the program should have loaded does not help. The screen stays de-synced until I hit BREAK then it returns to normal - so it's not crashing - it's as if there's no input at all going to EAR.
Where do I start with troubleshooting this? AFAIK the levels on a Tzxduino/Maxduino are appropriately loud, and besides there is no adjustment possible. What is this likely to be, a failed component, ULA trouble? Tracing back from the EAR input there's a resistor R34 and then ceramic capacitor C10, then resistor R33, then to pin 20 on the ULA. All joints seem fine but I notice that C10 seems to have some strange gloop around its base (pictured below).
Is that normal - glue perhaps, or has it failed? Is this the sort of damage that could occur by someone leaving the power jack plugged into the EAR socket for instance? If it has failed what is this cap's intended value? I can't read it without bending it over and risking snapping it.
Either scenario totally unlikely and in my experience ULAs either work or don't and as you have picture and keyboard both working would think the problem lies elsewhere.
The cap and resistors are just a filter circuit to tailor the incoming waveform as far as I'm aware and may be different values from the issue 1 so that could be worth checking. Bare in mind these circuits were meant to work with humph kicked out by the old shoe box type cassette devices,whose earphone sockets could can even power an extension speaker and modern devices tend not to have as much kick and yours may be just getting by with the issue 1 but not strong enough for the issue 3.
A better picture of the "gloop" might help too although I suspect it is some form of sticky usually found around the base of electrolytic caps' for stability as I've never known ceramic caps' to leak.
The Tzxduino/Maxduino you are using if memory serves uses an LM386 as its output which depending on the type used, on a good day with a decent voltage will kick out as little as 250ma which isn't even line level and the top 386 type just scrapes by and produces nothing like the level of the older devices.
Yes they may work as advertised but looking at the electronics involved they may be more than adequate for something a bit more sophisticated like the c64 or even the spectrum which in my experience never needed a big level to load but for something as crude as the 81 I think these devices are just scraping by.
One way I can test I suppose is to wire up the working WESPI I have to this machine since it interfaces with the EAR input. I'll see what 1024MAK's advice is before I do that.
Not sure I agree - the same tape recorders were used with ZX81s and ZX Spectrums after all. I remember setting the volume to about 7 or 8 out of 10 on the WHSmith tape recorder for our Spectrum back in the day. It certainly wasn't at the low end.Moggy wrote: ↑Sat Apr 03, 2021 4:25 pm Yes they may work as advertised but looking at the electronics involved they may be more than adequate for something a bit more sophisticated like the c64 or even the spectrum which in my experience never needed a big level to load but for something as crude as the 81 I think these devices are just scraping by.
You've admitted that your spectrum didn't have the cassette volume running flat out whereas ZX80s and 81s almost always were run at top volume (player type dependent of course) so again wonderful as they are the modern devices just don't have the same kick
If you posses a set of small powered PC speakers try feeding the signal into that then run a lead out of the mono socket some of these speakers have for the left speaker to connect to, into the zeddy, this way you can control the volume of the speakers which should have more than enough thump..
Just things to try rather than just dismiss.