Re: C64 to C64C mobo conversion

From: tokafondo_at_tokafondo.name Date: Wed, 29 Jun 2022 20:28:07 +0000 Message-ID: <157bbf1a09cb5f8dfb2b4715592f96c5_at_tokafondo.name>

24 de junio de 2022 5:46, "Gerrit Heitsch" <gerrit_at_laosinh.s.bawue.de> escribió:

> On 6/24/22 03:26, tokafondo_at_tokafondo.name wrote:
> 
>> I have a pre-8701 C64 motherboard and a C64C motherboard.
>> If I wanted to test 8580 and 8563 chips in the C64 motherboard, would it > be just enough with
>> replace the 7812 with a 7809?
> 
> No, the VIC from a C64C expects 5V on Pin 13. You can get that from Pin 40, but it's a good idea to
> run it through a ferrite bead and put a 100nF capacitor between Pin 13 and GND.
> 
> Also, you might have to rework the modulator since the 856x VIC expects a 1kOhm pullup while the
> 656x VIC wants a 500 Ohm pullup on the luma signal. This pullup is found inside the modulator. Just
> replacing the VIC might result in a dark video signal.

FYI: I don't know if this is the right thing to do, but by only getting the pin 13 fed with +5V and putting a 100nF capacitor as you said, it's working with no ferrite bead, and no 1kOhm pullup replacement. The video signal is clear and bright.

> 
> Gerrit