Re: plus4 power supply

From: Gerrit Heitsch <>
Date: Sat, 22 Sep 2012 17:29:23 +0200
Message-ID: <>
On 09/21/2012 03:57 PM, wrote:
> On 2012-09-21, at 13:42, Gerrit Heitsch wrote:
>>> BTW, Gerrit - what do you think was the point in providing two +5Vs in the 64? One called +5 and the other CAN+5? Looking at 252312-right, they dropped this idea on the narrow boards. But I am wondering why they introduced it in the first place.
>> There are 3 reasons I can imagine:
>> 1) Power, 5V, 2A might have needed a different plug
> I think this DIN should handle 2A w/o problems but In fact I am not sure about the actual specs.

Hm... It would be borderline... If the contacts are just a bit worn, you 
start having a measurable voltage drop on the connection.

>> 2) Keeping the power for the VIC and clock generation seperate from the rest of the system to prevent RF noise from leaking. Remember, the first boards had the discrete PLL inside the can.
>> 3) Providing the VIC with its own power source that doesn't contain all the noise from the rest of the system which might otherwise become visible on the screen.
>> I think it's a mix between 2) and 3). With the creation of the 8701, 2) became less important.
> I see. I am mostly concerned about [3)]. Shall probably have to check it by changing the supply point for the VIC. Hopefully I won't overload the PSU with this.

As I wrote, the regulator in the PSU is a 78S05 and therefore good for 
2A. Without any expansion, the old C64 draw about 1A on +5V. VIC itself 
can draw up to 200mA and the clock generator should be less than 100mA 
(since nothing gets hot). That's below the 1.5A the PSU is supposed to 
be able to supply.

For a short (!) test, I don't see any problems.

Just remove the 7805 and run a connection between +5V and the output pad 
  of the 7805. You still need the 9VAC for the voltage doubler to supply 
the 7812 so that VIC and SID get their +12V.


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Received on 2012-09-22 16:00:09

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