Sinclair ZX80 / ZX81 / Z88 Forums

Hi all,

I'm restoring/repairing an issue 2 ZX Spectrum, I went to load some software and for the life of me I am unable to do that.

I repaired another ZX spectrum in the past and I struggled then too but in the end I found a combination of SW/HW which worked. I was using my laptop sound card and OTLA. So to remove variables I checked with the "known working" ZX first... Nothing. I get the software title but shortly afterwards the loading fails. Flashing red or an error message I haven't written down.

It's the same laptop, the same ZX

I then tried a USB external interface, a Focusrite 2i2. Nothing. I then tried a WAVE file of ManicMiner - OTLA has a fast loader so I thought maybe a slower one would work. Nothing.

I am connected in mono. My oscilloscope says I'm sending 700mV p/p signals.

Any ideas? I made a repair video last time, I went back to check the settings I used with OTLA, all checks out. I'm out of ideas!

Thank you!

Edit: I found the issue! Thanks to my oscilloscope. I realised the laptop sound card via OTLA was actually sending a much stronger signal, 3V P/P. However, I could see the signal starting at 3V then lowering at around 800mV - looked like some compressor or "hearing protection".

Under Windows I checked on the output setting and disabled the "enhancements". The signal was not stable at around 3V p/p and the game loaded Yay!
(stupid windows!)

I believe this could be nice to leave here for future reference.
Thanks anyways!

Yes, Sinclair computers need a signal that is greater than 1V. Modern equipment that incorporates protection to reduce human hearing damage, or which limits by design the output level won't work well if being used to load games and programs.

Did not know that disabling the "enhancements" would help. So thanks for posting

Mark