C64 Video Problem. [Commodore]

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From: DMackey828 on 1 Apr 2010 05:02

Hey All,
I have a C64 ASSY NO: 250425 Dated 1984. The problem is the Video
display is Grey. Other than that, the computer works just fine. I
tried Different 6567R8 VIC Chips that are Known good, Same thing.
Also replaced the MOS 8701 16 pin IC located next to the VIC chip, No
change. I have replaced EVERY IC in the board with KNOWN Good
chips. Nothing works. The Monitor is Perfect on another C64 so I know
the Monitor/Cable is good.

I'm lost...

TIA..

From: Clocky on 1 Apr 2010 08:00

DMackey828 wrote:
> Hey All,
> I have a C64 ASSY NO: 250425 Dated 1984. The problem is the Video
> display is Grey. Other than that, the computer works just fine. I
> tried Different 6567R8 VIC Chips that are Known good, Same thing.
> Also replaced the MOS 8701 16 pin IC located next to the VIC chip, No
> change. I have replaced EVERY IC in the board with KNOWN Good
> chips. Nothing works. The Monitor is Perfect on another C64 so I know
> the Monitor/Cable is good.
>

RF modulator.

From: M.O.B. i L. on 1 Apr 2010 12:58

From: Clocky on 1 Apr 2010 13:09

Clocky wrote:
> DMackey828 wrote:
>> Hey All,
>> I have a C64 ASSY NO: 250425 Dated 1984. The problem is the Video
>> display is Grey. Other than that, the computer works just fine. I
>> tried Different 6567R8 VIC Chips that are Known good, Same thing.
>> Also replaced the MOS 8701 16 pin IC located next to the VIC chip, No
>> change. I have replaced EVERY IC in the board with KNOWN Good
>> chips. Nothing works. The Monitor is Perfect on another C64 so I know
>> the Monitor/Cable is good.
>>
>
> RF modulator.

Maybe I should clarify... the composite signal is mixed in the RF modulator
and if the modulator is cactus or out of sync you can lose colour on both RF
output and on the video port.
That is why you can't just desolder the modulator and run video off the A/V
port because you lose the video signal without the mixing circuitry of the
modulator being present. I think there is an exception to that rule on a
particular C64 revision, possibly the earliest one.

Desoldering it and soldering a spare shouldn't be too difficult, there are
few connections.

From: DMackey828 on 1 Apr 2010 14:32

On Fri, 2 Apr 2010 01:09:10 +0800, "Clocky" <notgonn(a)happen.com>
wrote:

>Clocky wrote:
>> DMackey828 wrote:
>>> Hey All,
>>> I have a C64 ASSY NO: 250425 Dated 1984. The problem is the Video
>>> display is Grey. Other than that, the computer works just fine. I
>>> tried Different 6567R8 VIC Chips that are Known good, Same thing.
>>> Also replaced the MOS 8701 16 pin IC located next to the VIC chip, No
>>> change. I have replaced EVERY IC in the board with KNOWN Good
>>> chips. Nothing works. The Monitor is Perfect on another C64 so I know
>>> the Monitor/Cable is good.
>>>
>>
>> RF modulator.
>
>Maybe I should clarify... the composite signal is mixed in the RF modulator
>and if the modulator is cactus or out of sync you can lose colour on both RF
>output and on the video port.
>That is why you can't just desolder the modulator and run video off the A/V
>port because you lose the video signal without the mixing circuitry of the
>modulator being present. I think there is an exception to that rule on a
>particular C64 revision, possibly the earliest one.
>
>Desoldering it and soldering a spare shouldn't be too difficult, there are
>few connections.
>
>

Hey Clocky,
Hmm, I think I have a dead board that has no chance of recovery that I
can pull the modulator from.

I'll give that a try here in the next few days..

Thanks for the info.

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