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My Mac doesn't recognize my TV's resolution on (so far) 3 VGA cables I've tried but it works just fine using other seemingly old VGA cables. My roommate had the same experience on Mint Linux.
What's the difference between VGA cables? What should I look for in a VGA cable that I buy? Are those still being made?
Leo Jweda
Posted 2015-07-21T01:42:54.887
Reputation: 153
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As @Wyzard says, computers talk to monitors via DDC and this uses 4 pins on the vga. See the pinout on wikipedia.
A working vga cable needs all the pins wired independently from each, and also from the cable shielding to the chassis, i.e the metal cover of the plugs and sockets. Only pins 4 and 11 can be missing or not cabled.
Inside a monitor there is a small eprom holding information on the monitor's resolutions (the EDID). This eprom is accessible even when the monitor is powered off, as it is independently powered from the computer by 5 volts on pin 9, with ground on pins 10 and 5. The eprom is read using i2c clock and data signals on pins 12 and 15. These days with DDC, the i2c bus can do other things too.
The analogue video signals on pins 1, 2, 3 have independent analogue ground on 6, 7, and 8.
Some bad vga cables will not have these analogue grounds, nor the i2c ground, and assume the cable shielding will do. This often does not work. The only way to check vga cables is with a continuity tester (multimeter) ensuring that all pins are wired through, and none are in common, including the shield.
meuh
Posted 2015-07-21T01:42:54.887
Reputation: 4 273
Update: I got a C2G cable that works. Thanks. – Leo Jweda – 2015-07-24T03:41:29.803
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Detecting a monitor's resolution depends on information provided by the monitor itself via DDC. In a VGA cable, this uses several pins and wires that are separate from the ones used for the actual video signal.
A cheap VGA cable might be missing some of these wires (to save on costs), or the wire might be present but broken (due to wear & tear).
Wyzard
Posted 2015-07-21T01:42:54.887
Reputation: 5 832
1How do I find a cable that has all the wires? I tried cheap ones from Amazon and a $20+ one from a brick and mortar store and none of them worked. The only ones that have worked are old ones for some reason. – Leo Jweda – 2015-07-21T02:54:30.643
Don't know, sorry. I've never encountered a cable with that problem, but I haven't used VGA cables in a long time. – Wyzard – 2015-07-21T03:18:13.650
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Simple Answer, stop using VGA cables, use HDMI or DisplayPort
Long answer: well quality and length of vga cables has alot to say about resolution
nwgat
Posted 2015-07-21T01:42:54.887
Reputation: 961
1I'm aware of the drawbacks of using VGA cables but my current setup requires me to use one.
I highly doubt it's length because I've tried different lengths and that did not seem to have an effect on the quality. After all, my setup only requires about 2 feet. – Leo Jweda – 2015-07-21T02:11:40.473
However, note that a quality VGA (and most other kinds of) cable need not cost a fortune nor have gold plated pens. The important factors are being wired-properly with the right gauge wire, and being shielded. – martineau – 2015-07-21T09:29:29.453
length also plays a big role, longer cables will lose signals – nwgat – 2015-07-21T10:00:28.927
TVs don't commonly have VGA, and I've generally had to set it manually. What sort of Mac? Macs haven't had VGA out in years so what sort of adaptors are you using? – Journeyman Geek – 2015-07-21T02:51:57.987
@JourneymanGeek It's a 3-year-old Samsung TV, relatively low-end. It has an HDMI port which I use for my RPi and a VGA port that I use for my 2013 MacBook Air. I have an Apple adapter to convert I believe display port to VGA. – Leo Jweda – 2015-07-21T02:53:28.243
I half suspect the adaptor may come into play. I'd also add, as of 2015, no major computer manufacturer is supporting VGA and DVI, so chances are those cables will stop being made in a few years. You can still find some systems with support, but in general dp's the preferred standard for Monitors, and HDMI for TVs. PCs will output both, of course. – Journeyman Geek – 2015-07-21T03:14:58.003
@JourneymanGeek Like I said, in the exact same setup, with the exact same adapters, some cables work and other don't. It most definitely NOT the adapter.
Cute dog BTW. – Leo Jweda – 2015-07-21T03:17:49.643