Why does my TV turn from color to b&w?

January 1, 2007 6:00 PM

Why does my new LCD TV go from color to black and white?

I replaced my prior TV with a new LCD HDTV. The old TV worked fine, but this new one sometimes changes from color to b&w. When I turn the TV off and then back on, it usually fixes the problem for a while. The signal is NTSC from my cablebox to the TV, via a coax cable. This didn't happen before, and isn't related to the cablebox as I have played a dvd via coax with the same result. Any ideas about why, and what to do?

posted by torpark to technology (10 comments total)

It's new, so take it back and get another one.
posted by kindall at 6:02 PM on January 1, 2007

Ordered it on... the internet! I could probably take it back, but if it isn't really an issue with the TV, but the cable I'm using, I really don't want to resort to that.
posted by torpark at 6:09 PM on January 1, 2007

I don't know of any way it could possibly be the cable, because on a coax cable the color signal is not carried separately in such a way that it could be interrupted without also interrupting the luma (black and white) signal.

I bought a plasma online that turned out to have a problem and it was a real pain dealing with it, not least because it was a refurb. So, no more buying big TVs online for me.
posted by kindall at 6:46 PM on January 1, 2007

RMA time. Hope you bought from a reputable dealer.
posted by SirStan at 7:11 PM on January 1, 2007

Which model is it?
posted by k8t at 7:13 PM on January 1, 2007

It is one of those Emprex 32" HD-3201 from Frys.
posted by torpark at 7:19 PM on January 1, 2007

I googled Emprex "black and white" HD and found this

problem with 720p only:

http://www.avsforum.com/avs-vb/showthread.php?t=617249

Looks like that forum has lots of discussion of this issue.
posted by k8t at 7:37 PM on January 1, 2007

In those forums they make a good suggestion - try another HD source (XBox?) to see if it is your cable company.
posted by k8t at 7:38 PM on January 1, 2007

It's not a problem with the display. By which I mean the actual pixels. It's either a problem with the tuner or the connection hardware. Try a different source and try jiggling the cable at the connection point. I'd just send it back.
posted by jeffamaphone at 12:59 AM on January 2, 2007

Coax from the cable box to the TV? So you are tuning to channel 3/4 to watch the cable box output? Regardless of this problem, that is the worst possible quality connection, especially for a TV that large.

The problem could be with the new TV, likely either the tuning section (i.e. too much jitter) or NTSC decoding section -- but the composite circuitry or RF remodulator in the cable box could be partially or completely at fault.

It is quite common inside modern digital NTSC decoders to have a 'color killer' signal when they can't cleanly lock to the color carrier within the combined signal. Conversely, many older TVs will have essentially a hard-programmed cut like "<3 mhz=Luma,>3Mhz = Chroma", and therefore always show a color picture (albeit a much lower quality one).

The bottom line: You can determine if the new TV's tuner section is deficient by connecting the coax cable directly to the TV, bypassing the box. If the problem doesn't happen with analog channels (i.e. 2~70), the TV is fine.

Whether or not you need to replace the TV, you should change the cable box->TV connection to the best signal possible -- from best to worst:
- HDMI / DVI (many pins, pure digital connection)
- Component (3xRCA jacks, Green/Red/Blue, usually labeled YPbPr)
- S-Video (Round 4-pin connector)
- Composite (Single yellow RCA jack)

Except for composite, all of the above mean the chroma and luma signals are sent separately, so the TV's comb filter does not come into play at all. Even with the combined composite signal, though it will still be split in the comb, you at least avoid the signal losses and noise from the box's RF remodulator and TV's tuner.
posted by SpookyFish at 10:27 AM on January 2, 2007