Z88 power supply

[Chris_68]

Hi,

To be sure not to draw power from the batteries I have set the voltage to 7v.
If anyone planning to upgrade RAM/Flash then I recommend to follow the instruction where you don't have to cut any tracks.

/Chris

[Sparrowhawk]

First things first: I got the Z88 out of storage and it does still work (a slight high pitched sound when I inserted the batteries though - anyone know why this should be? I could not tell from what end of the beast as my hearing is not great at higher frequencies.

So now to that power supply. I've not found anything that matches the exact spec, so wondered whether something like this would be suitable?
https://www.amazon.co.uk/Zolt-Universal ... 09DNX42CQ/ It does not have 6.5V but does have 6 and 7.5.
Would 7.5V be OK or is that too high? I was looking at this one as I don't know the actual diameter of the socket.

Also, does anyone know if a serial to USB adapter based on the Prolific PL2303 chip has the handshaking required by the Z88 to talk to the outside world? I have one of these somewhere (more rummaging needed). If not, what chipset is recommended?

[Pr0f]

The Z88 does have it's own rather clever little power supply that can produce a bit of high pitch wine when operating - usually caused by the small ferrite transformer / inductor on the board being a tiny bit loose. Sometimes a small blob of silicon sealant on it can anchor it to the PCB sufficiently to stop the squeal - some Z88's seem to be more prone to it than others.

[Pr0f]

I've used 7V without a problem, not sure about 7.5V - It is dropped by one diode forward voltage (about 0.6-0.7 vols), and feeds the circuit that would normally see the 6V from the batteries. Very fresh batteries could provide close to 1.6V each - giving a voltage of 6.4 against the 6.9 you would see from the 7.5V supply.

[Sparrowhawk]

THanks Pr0f. I'll keep looking - I'd rather be closer to the values you've all provided than go off piste too far..

[ones' complement]

Measured my Z88 PSU. Off load was 6.34V, with 27ohm resistor load 6.25V at 210mA. Z88 load (+128K rampack) was never more than 100mA.