Re: C-64 PSU

On 2012-04-24, at 12:57, William Levak wrote:

>> Since I have now quite a bunch of stuff sticking long way out of my EXPANSION port and also some from the tape port - I am thinking to eventually replacing my 30 years old and still reliable PSU. I have the one with two fuses and a power switch, which is quite rare and I wouldn't like to make it fail as it seems to get running quite hot with everything attached. Now - what's the problem you may ask. The problem and question is always the 9VAC. ALthough all the PSUs are rated at 9VAC, I recall that they supply somewhere between 11V and 12V. Moreover I recall that back in the days, when I supplied a "true" 9V of AC some things didn't work properly on the 64. I don't remember today what was failing but I remember that delivering a proper 9V didn't work out. Does anyone know why:
>> 
>> a) why PSUs rated as 9V (have to) deliver 11+
> 
> Power supplies rated 9V appear to be at 11 or 12V, but actually are not. The 9V rating means 9V effective voltage delivered to the equipment at full power load.  To measure this, you would have to put a resistor across the power supply of sufficient wattage to match the maximum rated output of the power supply, and then measure the voltage drop across the resistor.  Of course, you would also need a calibrated voltmeter in order to get an accurate reading.

I recall measuring under (C64) load. Of course it might not have been enough to utilise full output rating of the PSU but it was still noticeably more than 9V. I also recall that problems when I was supplying 9V (also under the same load).

-- 
SD!
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