Re: C64 to C64C mobo conversion

On 6/24/22 12:49, tokafondo_at_tokafondo.name wrote:
> 24 de junio de 2022 9:46, tokafondo_at_tokafondo.name escribió:
> 
>> 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.
>>>
>>> Gerrit
> 
> I want to thank you again for your advice. I created a small adapter by using a 40 pin female socket and put the 8565 in the C64 board and now it works, so the culprit here was the 6569R3 ceramic chip.
> 
> Now I want to test the 6581 in the C64C board, as the 8580 makes no sound at all, and I found the 6581 to actually work.

The 6581 uses different filter caps than the 8580, so you not only have 
to change the diode on CR7 from a 9.6V to a 12.6V zener diode, but also 
C70, C71, C80 and C81 on a 250469 board.

  Gerrit