12 March 2016
n WITH TIM BROWN
In this column, Tim answers questions about
all aspects of electronics, including computer hardware, software, circuits, electronic
theory, troubleshooting, and anything else of
interest to the hobbyist. Feel free to participate with your questions, comments, or suggestions. Send all questions and comments
• Commodore 64 Problem
• Reliability Tutorial
Commodore 64 Video Problems
QThe recent interest in the electronics community in reviving old computers caused me to pull out my beloved Commodore 64 and the associated ADC and voice synthesis boards I built for it.
I was looking forward to seeing the C64 Basic screen on
a decent monitor, and used the NTSC composite out in
the 64 into a composite input on the HD TV I use for my
Raspberry Pi monitor. Much to my surprise, I received the
message “Invalid Signal.” I changed output channels on
both the 64 and the TV, but the message remained. I then
took the 64 to my living room HD TV and tried that input
with the same result.
Has the NTSC composite signal changed since the
1980s and, if so, how can I build something to allow me to
use the HD TV monitor with my 64?
AThe Nuts & Volts operations manager is actually kind of a Commodore nut, so I’m going to let him answer this question for me. Tim
As I read your problem description, it made me
wonder about how you are setting up your Commodore
64. The C64 does indeed have an NTSC output, but that
signal does not appear on a “standard” jack on the back
of the C64 itself. The Video Out jack is a circular eight-pin
version and requires a special eight-pin to three RCA style
connectors and should look something like the ones shown
in Figure 1.
This cable is typically used to connect to an “S-Video”
Chroma/Luma connection such as that on the back of a
Commodore 1702 monitor shown in Figure 2.
On the other hand, the RCA jack on the back of the
Commodore 64 puts out radio frequency (RF) signals on
channel 3 or 4, and is connected like the one shown in
As 300 ohm connectors are rarely found on the back
of today’s TV sets, a better way to connect your old C64
to new TV sets is to use a special cable to connect to the
SHVS (or S-Video) connector on your TV. Instructions for
building the cable are available at ilesj’s blog (see Q&A
SIDELINES). Or, you can buy one off of eBay as they seem
to be a readily available item (See SIDELINES).
Of course, this is assuming that you connected the
RCA jack on the back of the C64 to the NTSC composite
(yellow) Video In connector on your HDTV. If that isn’t
the case and you were using the eight-pin DIN connector
and proper video cable, then it might be that the signal
from your C64 is slightly out of range due to the age
of the internal video generation system. Discussion of
this problem can be found on the Lemon64 forum (see
Q & A
Image credit - www.softwareoldies.com Image credit - www.lemon64.com
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