Re: plus4 power supply

From: Hegedűs István <>
Date: Thu, 20 Sep 2012 14:42:29 +0200
Message-ID: <>
Hi Julian,

Ok, thanks. This might explain why my plus4 died earlier... from these it is 
obvious that the regulator is broken.
I decided that I will go for the regulator that Gerrit advised. I assume 
however that as it is a DC-DC step down regulator I still need the graetz 
bridge and the 4700uF Elko Capacitor which is before the original 7805. Can 
someone confirm it?


-----Original Message----- 
From: Julian Perry
Sent: Thursday, September 20, 2012 2:31 PM
To: Hegedűs István
Subject: Re: plus4 power supply

Hello Hegedűs,

Thursday, September 20, 2012, 9:39:20 PM, you wrote:

When replacing my C64 power supply innards with a regulated switchmode
version, I noted a voltage drop of 0.2V across the power lead into the
C64 under load - so the PSU needed to output 5.2V, to have 5V
available at the C64. (I adjusted it by measuring the voltage of the
5V rail on the PCB, with the C64 operating).

I presume it is similar on the plus4.
Fortunately, the output voltage on the switchmode PSU I purchases was
adjustable. It DOES raise the question - what effect high drawing
devices such as the Z80 cartridge, and REU would have on the "on-pin"
voltage on the 5V rail.

(as to Gerrit's question - I'd be alarmed at 5.6V - that's %10 over)


> 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).

> Istvan

> -----Original Message----- 
> From: Gerrit Heitsch
> Sent: Wednesday, September 19, 2012 9:40 PM
> To:
> 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
> example


> 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.

>   Gerrit

>        Message was sent through the cbm-hackers mailing list

>        Message was sent through the cbm-hackers mailing list

Best regards,

       Message was sent through the cbm-hackers mailing list 

       Message was sent through the cbm-hackers mailing list
Received on 2012-09-20 13:01:07

Archive generated by hypermail 2.2.0.