Re: plus4 power supply

From: Hegedűs István <>
Date: Thu, 20 Sep 2012 13:39:20 +0200
Message-ID: <>
Hi Gerrit,

That is strange because I have measured an old C64 power supply and other 
plus4 power supplies which provide 5.4v. The plus4 power supply schematic 
diagram says 5.2v though.
I have checked the CPU datasheet and it says max voltage is 7v but of course 
the other components might not like it.
I know the regulator you linked here but that still needs the diode bridges 
and the 4700uF capacitor (I believe). The heat is generated by the 7805 
regulator so you are right it will be cooler (and maybe more stable).


-----Original Message----- 
From: Gerrit Heitsch
Sent: Wednesday, September 19, 2012 9:40 PM
Subject: Re: plus4 power supply

On 09/19/2012 09:25 PM, Hegedűs István wrote:
> Hi,
> I have done a major repair service on my plus4 power supply. Replaced
> the electrolyte and tantal capacitors, the diodes. Now it supplies 5.6v
> while before it supplied 5.4v. Is it dangerous for the plus4? What
> should be the voltage level of a normal power supply? (Note that I have
> only a multimeter and no scope so might be measurement difference).

It shouldn't go above 5.2V. You should do a complete rework of the power
supply remove the existing regulator, get a switching regulator, for

This one is adjustable, so adjust to 5.2V _before_ connecting the Plus/4.

As a sideeffekt, the PSU will run much cooler.

If you feel _really_ adventurous, you can put a complete switching power
supply that runs on 230V and supplies 5V 2A into the empty part of the
Plus/4 PSU. The transformer will then only be used for 9V AC.
But since one has to work on 230V AC, this is only for people who know
exactly what they're doing.


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Received on 2012-09-20 12:00:04

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