HDMI - how to measure it - Page 1
Forum section: electronics / general

author: Jane
author_rank: Frequent Contributor
timestamp: November 07, 2012, 09:21:50 am
content: Is there any way how to check the HDMI output from a TV receiver is working correctly ?When I plug HDMI output of the receiver into HDMI input of TV, there is no good signal( picture) on TV.I was thinking about using oscillosckope and measuring each pin of HDMI connector, but it did not seem to work.Must be the HDMI connected with another HDMI device before I can measure useful values on HDMI pins? What frequency I should measure on HDMI pins?Any further help would be appreciated.

author: poptones
author_rank: Frequent Contributor
timestamp: November 07, 2012, 09:36:07 am
content: Yes, this is a "feature" of HDMI. You see, because consumers are thieves, HDMI was designed to "protect" media from scurrilous consumers and thei evil intents of piracy. As a result, sometimes equipment gets blacklisted (their HDMI licene revoked so the equipment essentially becomes bricked) or sometimes it just behaves "badly."You might try another cable. Or make sure the source material you're trying to view isn't copy protected - like maybe the output of your desktop. Good luck.

author: JuKu
author_rank: Frequent Contributor
timestamp: November 07, 2012, 10:01:53 am
content: You can't see anything meaningful from HDMI lines with ordinary equipment. As noted, this is intentional. Without specialized equipment, you are pretty much limited to trying combinations of changing TV, player, cable, input of TV etc.

author: Sionyn
author_rank: Frequent Contributor
timestamp: November 07, 2012, 10:05:41 am
content: yes hdmi is brokenhttps://www.schneier.com/blog/archives/2010/09/master_hdcp_key.htmlyou can buy a plethora of 'stripping' devices or build a bruteforcer your selfor like my tv poor implementation of hdmi the buses inside my tv send hdmi unencrypted (thanks hitachi)as for testing do what any other would first do and read the spec

author: amyk
author_rank: Super Contributor
timestamp: November 07, 2012, 10:23:15 am
content: HDMI uses a 340MHz clock and TMDS signaling at 3.3V. A DMM may show a voltage, but to see any of the bits (which are encoded) you'll need a high-end scope and differential probe.

author: Jane
author_rank: Frequent Contributor
timestamp: November 07, 2012, 10:53:31 am
content: Not sure If I put my question in a correct way.To explain here again.From time to time I get a receiver that has faulty HDMI output to repair it.It maybe for different reasons such as : faulty HDMI connector, faulty CPU, or a path from CPU to HDMI connector.So my question again( slightly modify):Is there a way how to find out where is the fault ( whether HDMI connector or CPU or between)?Thank you again for help

author: Sionyn
author_rank: Frequent Contributor
timestamp: November 07, 2012, 10:59:22 am
content: wait a minuet what is this device ? what hdmi solution are they using

author: Jane
author_rank: Frequent Contributor
timestamp: November 07, 2012, 11:42:55 am
content: @Sionyn:It is a satelite receiver. Can you please explain what you mean by"what hdmi solution are they using"?There is a Broadcom main chip

author: JuKu
author_rank: Frequent Contributor
timestamp: November 07, 2012, 12:44:21 pm
content: Quote from: Jane on November 07, 2012, 10:53:31 amNot really. On the other hand, >90% it is the cable or the connector.

author: Sionyn
author_rank: Frequent Contributor
timestamp: November 07, 2012, 03:56:04 pm
content: by solution i mean what devices your sat box is using for instance this sagecom box is using a nxp solution for hdmiwithout the Broadcom SoC datasheets you won't get very far Broadcom also don't hand stuff like that out with signing a NDA contract

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 07, 2012, 04:15:31 pm
content: I also have a feeling that to minimise RFI & power draw, HDMI ports disable their outputs when there is nothing connected. From memory I think it's an LVDS type interface which needs a load resistance as it operates more like a current source than voltage.

author: SeanB
author_rank: Super Contributor
timestamp: November 07, 2012, 04:22:13 pm
content: With HDMI most commonly it will be a connector broken, or a driver killed by a shorted cable. connector much more common being either broken by putting the cable in upside down or by it being ripped off the board complete with the pads.

author: free_electron
author_rank: Super Contributor
timestamp: November 07, 2012, 05:26:01 pm
content: Quote from: mikeselectricstuff on November 07, 2012, 04:15:31 pmcorrect. differential signalling over twisted pairs. no 'load means no signal. the transceivers detect 'connection' then signal the source that they can start key negotiation

author: mzacharias
author_rank: Frequent Contributor
timestamp: November 08, 2012, 01:02:44 pm
content: Quote from: Jane on November 07, 2012, 09:21:50 amI work on a significant number of receivers with HDMI problems. Generally the problems not including the jacks themselves come down to the HCMI transmitter IC (VERY common), a HDMI receiver or switch IC.Removal and replacement of the surface-mounted IC's is generally difficult, and some manufacturers/models have more robust foil pads than others.In other words, I'm not always successful replacing these IC's. Often the entire board gets replaced if the unit is under warranty, and the board available. Otherwise mostly uneconomical to repair.

author: tom66
author_rank: Super Contributor
timestamp: November 08, 2012, 07:57:19 pm
content: I've found plenty of main boards from LCD TVs that don't encrypt the RGB signal going to the LCD panel. It's right there, unencrypted LVDS, with a specification in the panel documentation. All that effort of encrypting the data along the cable and the first thing it hits is the decryption engine.

author: amyk
author_rank: Super Contributor
timestamp: November 09, 2012, 06:31:40 am
content: Quote from: tom66 on November 08, 2012, 07:57:19 pmThat's been known for a long time but the HDCP group were targeting consumers, not electronics enthusiasts. You can find LVDS to DVI converters that do this cheaply, but a DVI capture card costs a lot more.Why do they want consumers not to open their electronics? Knowledge is power, they don't want you knowing too much...

author: JuKu
author_rank: Frequent Contributor
timestamp: November 09, 2012, 06:41:26 am
content: They know that you can't stop a dedicated hacker. At some point in processing chain, you just have to have the signal in non-encrypted form. Hack an FPGA into the wires going to the display, and you'll get the digital video. Connect a SPDIF transmitter to the i2s lines going to the DACs, and (with the right pre-amp and right settings,) you get bit-exact audio signal. The exact wording in the HDCP license is "with commonly available tools", meaning it must be more difficult than opening the case and soldering a connector, installing a jumper and so on. This stops the local teenager from putting a copy on the internet. The hacker that puts in the effort and investment to produce counterfeits is in principle, unstoppable by technology.

author: Monkeh
author_rank: Super Contributor
timestamp: November 09, 2012, 02:05:24 pm
content: Quote from: JuKu on November 09, 2012, 06:41:26 amIn other words, they've done it to make things awkward for consumers and to make money, because it has precisely 0 effect on actual piracy.

author: tom66
author_rank: Super Contributor
timestamp: November 10, 2012, 02:41:32 am
content: I would argue that attempting to capture uncompressed 1080p video at 60 Hz across three differential pairs plus clock would in itself be an achievement beyond the average teenager. The storage alone for an uncompressed blu-ray would be in the 2.5TB region. (Ballpark 1920x1080p, 24-bit, 60 Hz, 2 hours.)I did consider doing it as a final year project, but I don't know if there would be repercussions from it, so maybe I'll go with something a little less legally grey. Oh look, it worked on me...

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: November 10, 2012, 09:33:53 pm
content: Quote from: free_electron on November 07, 2012, 05:26:01 pm... and if negotiation fails the transmitter assumes that the receiver is a DVI sink and falls back into DVI mode (no audio, encryption, etc.)Leo

author: JuKu
author_rank: Frequent Contributor
timestamp: November 10, 2012, 10:28:23 pm
content: And no encryption agreement (DHCP fail) means no picture.