Love the ZX81, my first computer. Had a home made decent keyboard and composite out into a tiny b/w monitor. Showing my age. It's AC! Blue and Brown are both positive and negative
Yes it did, it turns out 14.5v is about right for an unloaded original PSU. I will do a follow up then the new keyboard arrives just to go over the errors and mistakes I made or said in this video :-P
Does it use anything other than 5V, can't remember. That voltage regulator is 5V output though. I'd be tempted to remove that, do away with the power brick and run it directly from a usb cable!
Interesting idea.... however I have a feeling maybe the RF modulator or the cassette tape interface requires more then 5v? maybe? there must be a reason for 9v DC input?
@@WiFiSheep Pretty sure ZX81 was entirely 5V. Although the dodgy RAM packs might generate 12v -5v? for the DRam? Those voltage regulators always require a greater input than the output and will take a wide range of inputs but usually most efficient (although not efficient at all compared to modern equivalent) at certain sweet spot around 8. The Acorn Atom, of a similar vintage, has instructions and jumpers on the board to bypass the case melting 7805 with your own 5V supply, so a common mod even back in the day.
Brown = LIVE, Blue = NEUTRAL, Green/Yellow = EARTH (when fitted)
Yep...... I knew that.... (he says lying)
@@WiFiSheep yeah, and positive is the one that's fused 😀
And for non-technical:
bRown goes Right
bLue goes Left!
Love the ZX81, my first computer. Had a home made decent keyboard and composite out into a tiny b/w monitor. Showing my age.
It's AC! Blue and Brown are both positive and negative
Great video. Did the power supply output drop back to 9V when loaded ?
Yes it did, it turns out 14.5v is about right for an unloaded original PSU.
I will do a follow up then the new keyboard arrives just to go over the errors and mistakes I made or said in this video :-P
Does it use anything other than 5V, can't remember. That voltage regulator is 5V output though. I'd be tempted to remove that, do away with the power brick and run it directly from a usb cable!
Interesting idea.... however I have a feeling maybe the RF modulator or the cassette tape interface requires more then 5v? maybe? there must be a reason for 9v DC input?
@@WiFiSheep Pretty sure ZX81 was entirely 5V. Although the dodgy RAM packs might generate 12v -5v? for the DRam?
Those voltage regulators always require a greater input than the output and will take a wide range of inputs but usually most efficient (although not efficient at all compared to modern equivalent) at certain sweet spot around 8.
The Acorn Atom, of a similar vintage, has instructions and jumpers on the board to bypass the case melting 7805 with your own 5V supply, so a common mod even back in the day.
Great video but your maths is a bit off. 1981 is 40 years ago. 😂
Im missing about 10 years somewhere in my life so it works out fine in my world :-P
@@WiFiSheep 😂 Me too. I only picked up on it because it's my birthday tomorrow. I prefer your calculations if I'm honest.
First!