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I've got an iMac desktop computer. Love it. I wish to connect it to my LCD TV using HDMI. There is no HDMI output on the iMac so i had to buy one of these bad boys :-

alt text

So now I can output video (via the mini Display Port) and sound (via USB) through this box, to my LCD.

Works great ... with a single direct cable.

I have another 3 or 5 metre cable inserted into my wall, so i do not have to have a silly hdmi cable floating in the air between my iMac and my LCD TV. When I do this, there is no picture.

To better explain all of this, I've made a quick video explaining my problem in detail, so you can exactly see what is going on/wrong.

I've also tried changing the output format for the TV from 1080i down to 720p and even lower .. incase the cable in the wall doesn't allow 1080i.

here's the video with the full explanation :-

(NOTE: I incorrectly said in the video that the hidden wall cable is 10 metres long. me == fail. It's 3m or 5m...).

Can someone please watch it and suggest some ideas to getting it working?


Eeks. the vid was marked as private. It's been marked as public so all can view it, now. Sincere appologies people.

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Can't watch the video - it's marked as private. – ChrisF Apr 27 '10 at 15:20
Ack. Sincere appologies. I've not marked it PUBLIC. Yes, i'm a YT noob :( – Pure.Krome Apr 28 '10 at 7:09
up vote 0 down vote accepted

Try to see if you can get it working with just a basic short hdmi cable to see if length is a possible issue. Once you got that working, then starting adding to the chain and see what happens.

HDMI has its specifications, but that is with just straight hdmi cables. Adapters and multiple segments can greatly reduce the specified useable distance of a cable. This is also a reason you will not find certain types of cables in long lengths.

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@Troggy - have u looked at my video? that's the first step, in the video. And the short cable works. TV <-> short HDMI cable <-> iMac. I'm starting to wonder if this has something to do with the adapter then... ??? – Pure.Krome Apr 29 '10 at 2:59
@Pure Sorry, was at work when I first read this question. I noticed that adapter is USB powered. My guess is that adapter might not allow the use of longer cables because it might not provide enough power to send the signal that far. I am guessing the only way to power that adapter is through USB, so not wall connection to boost the signal option here. I notice you also have a what looks like a female/female connection in between the two cables. What happens if you connect the black wall cable directly to the adapter? So you only have computer-->adapter-->Wall HMDI cable-->TV. – Troggy Apr 29 '10 at 14:42
i know this is a late reply, etc.. but I've been using the short cable to connect between the adapter and the tv. This weekend, I've connected the tv->built in wall HDMI cable -> 5meter extension -> ATI HD5850 HDMI port .. and it works 100% fine! this means the wall cabling is fine. The issue is definately the breakout box I purchased (and pictued in the OP). Looks like it can't send enough power along the longer cable. Sorry mac - looks like the PC is the new media center :) – Pure.Krome Aug 8 '10 at 5:22
@Pure Good to hear you came to some sort of conclusion/answer. I will keep this question in mind if I ever run across a similar setup. – Troggy Aug 10 '10 at 15:03

Check out the Wikipedia article on HDMI:

Although no maximum length for an HDMI cable is specified, signal attenuation—dependent on the cable's construction quality and conducting materials—limits usable lengths in practice. HDMI 1.3 defines two cable categories: Category 1-certified cables, which have been tested at 74.5 MHz (which would include resolutions such as 720p60 and 1080i60), and Category 2-certified cables, which have been tested at 340 MHz (which would include resolutions such as 1080p60 and 2160p30). Category 1 HDMI cables are to be marketed as "Standard" and Category 2 HDMI cables as "High Speed". This labeling guideline for HDMI cables went into effect on October 17, 2008. Category 1 and 2 cables can either meet the required parameter specifications for interpair skew, far-end crosstalk, attenuation, and differential impedance, or they can meet the required nonequalized/equalized eye diagram requirements. A cable of about 5 meters (16 ft.) can be manufactured to Category 1 specifications easily and inexpensively by using 28 AWG (0.081 mm²) conductors. With better quality construction and materials, including 24 AWG (0.205 mm²) conductors, an HDMI cable can reach lengths of up to 15 meters (49 ft.). Many HDMI cables under 5 meters of length that were made before the HDMI 1.3 specification can work as Category 2 cables, but only Category 2-tested cables are guaranteed to work.

So if you've got Category 2 cables you should be OK, but if they're only Category 1 you're at the limit. As HDMI is digital you don't get degradation - it's all or nothing.

share|improve this answer
@ChrisF so your suggesting that a 3m or 5m cable is the limit for Cat 1 (assuming .. and it's a good assumption, mind you ... that it is Cat 1) ? If so, why would the HD Camera work but the iMac not work .. if it's at the limit? that box i'm using might drop some power? – Pure.Krome Apr 28 '10 at 7:14
@Pure - This is pure speculation: If the Cat 1 is at it's limit the camera might be putting out a signal that the upper limit of the spec which gets through, while the Mac is putting out a signal that the lower limit of the spec which doesn't. – ChrisF Apr 28 '10 at 11:33
and is there anyway to .. check this? multimeter or something? – Pure.Krome Apr 28 '10 at 14:06

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