In my home workshop I have a RISCOS computer and a PC sharing a monitor and keyboard etc via a DVI KVM switch. The DVI feed to the monitor goes through a DVI HDMI splitter to feed a second monitor - actually a TV. Worked a treat. The TV is above the workbench so handy for following a circuit diagram when working on something without having to print it out.
After buying a new TV for elsewhere decided to use the one it replaced in the workshop as it is newer and bigger than the existing one.
Tried both the HDMI sockets on it which both worked OK as previously used.
But it only shows the RISCOS picture. Swap to the PC on the KVM switch and blank screen. And no picture on the main monitor either. Unplug the HDMI to the TV and all reverts to normal.
I'm guessing the later HDMI on the TV sends back a signal the KVM switch or PC video card doesn't like (since it beeps at you). Is there a device which strips off any such signal being sent back to the PC?
Temporarily plug the TV straight into the PC, and set up the refresh rate and resolution in the display driver, to be compatible with the rate/resolution of the other monitor that is connected to the DVI splitter.
Then physically set it all back to how you want to use it.
I'll have a play later. At the moment the PC is set to the monitor recommendation - 1920 x 1080 while the RPC is 1600 x 900. And both worked just fine on the old TV. Seems odd a much newer one isn't happy?
DVI and HDMI are not the same. You can feed DVI into an HDMI display, it'll detect it and fall back to DVI mode. But it is possible that the signal path through the switch is not handling this correctly somehow. For example the PC is outputting HDMI which the DVI switch isn't handling correctly.
HDCP is another possibility, if the PC output has HDCP enabled since the DVI switch won't understand it. Maybe there's a way to turn it off?
I had to buy a new video card when I upgraded the motherboard not that long ago. Had to pay quite a lot to get one with both DVI and HDMI outputs. The KVM switch is DVI for the old Acorn machine - for PS2 too. As I wanted to keep the Acorn keyboard.
As I said, everything worked just fine with the old TV via its HDMI inputs.
One question I would have, would be concerning your knowledge of OSD responses to input.
If you ask the TV to accept input from a port with nothing connected, does the OSD say "No signal" ?
There are several responses possible. A TV set could "refuse to consider" a VGA connector, if it senses nothing is there, and pushing an "advance" button to go through all possible inputs, may stop offering the VGA input as an option. Whereas other sets would let you select the VGA, and then the OSD would say "No signal", which is useful info for the user.
A port having no sync signal on it, may say "No signal".
A port having sync but no modulation or colour content, may remain black and consider what is happening to be "normal". It could be there is synchronization being extracted, but something about the signal is still suppressing colour content.
A lack of HDCP support gives "coloured snow" on screen. A PC sending unencrypted monitor output, that shows as coloured snow.
A TV should not switch to HDCP, unless the two ends agree on the key, and the TV is using a particular key to decode the encrypted signal.
There are a ton of failure modes, and we would hope that a thoughtfully designed OSD would help us with some of them. Even a "No signal" or "Out of Range" is helpful at times like this. "Out of Range" is when the accepted frequency range of some part of the signal does not meet the specs of the set. The EDID serial bus content from monitor/TV to computer, tells the computer exactly what range is valid. In other words, it takes some "stupid stuff", such as using custom modelines, to break the connection like that.
On Windows, you can use Entechtaiwan "moninfo" and the "real-time info" to determine what the EDID is sending to the PC end. On Linux, there are packages for EDID handling as well. If in a bind, you could connect a Windows PC to the TV set, then ask for the RealTime EDID.
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On the old Apple computers, there were some pin encodes for selecting resolution. Using a dongle adapter, I could request 1152x870 using switches on the adapter. So not every computing device has used EDID tables for this function. But this is irrelevant to getting your TV to work (fortunately).
You can buy "EDID faking boxes" for situations where the peripheral end does not have EDID output. Some projection devices for multimedia situations, run at 1024x768, but do not send EDID to that effect to the source device. Using an "EDID faker", you can send a request for 1024x768 and then the NVidia video card sends 1024x768, but the projector and screen know nothing of the drama involved. The projector could have, for example R, G, B, H, V coax cables and that is all. A projector with five coax cables has no EDID to send. And the PC will be clueless as to what to do. EDID faker boxes used to cost around $50 USD. Some of the famous suppliers are out of business. Each attempt to find one now, is an adventure.
And when puzzled about a situation, review Wikipedia, and the connector pinout. Do you understand what the pins are for ? Could CEC backchannel do it [No] ? And so on. I'm not trying to be flippant with this suggestion, just as a way of estimating "how mysterious is this stuff". Pins 13 to 17 look interesting.
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Pin 15 SCL (I2C serial clock for DDC) \___ EDID, from TV to computer Pin 16 SDA (I2C serial data for DDC) /
I think I have said before how I find KVM switches unreliable!
This utility will check monitors attached to the PC
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provide EDID and spec.
It should also work if the power to the monitor is off.
What it might do is show the DDC/I2C coms are working through the KVM switch. Without that the PC may simply sit there and not think the monitor is connected.
Obviously you will need another monitor to see it's output, unless you can remote into the PC.
But it only has a reason to read EDID, if the impedance sensing detects connected cables. It can sense 75 ohm single ended terminations on RGB on a VGA connector, or it can sense 100 ohm diff terminations on cable standards that use digital methods. On the diff termination case, it can sense stray capacitance near the connector and mistake that for a device. The VGA might have been a bit more bulletproof.
I have a "fake VGA connector", with three termination resistors and no EDID info whatsoever, and the video card will run that as a monitor and send a signal to it. Taking a "desktop snapshot" helps verify what the computer thinks it is sending and what the resolution of each real or fake monitor is.
If it cannot raise an EDID response, it can select 1024x768 for "safety". There was a class action lawsuit years ago, regarding damage to fixed resolution monitors, via some video card problem. It was a result of that suit, that caused the notion of "a safe resolution selection" to be made by the video card driver. That's why, in certain scenarios, you may find higher resolutions blocked.
A TV can have HDMI ports that only respond to SD or HD signals. These may be referred to as multimedia ports or the drawing may show a BR settop player connected to the port.
Certain ports on a TV can have a dotted line around them, suggesting that they are different, and that they might support EDID and have a fuller scaler setup. This allows PC resolutions over and above the SD and HD choices.
Years ago, some TVs refused to go to "native resolution". If your TV set really had 1920x1080 pixels on it, the TV would not list 1920x1080 as an option on the "PC connector". I think eventually they stopped doing that.
And we pay good money for this treatment.
Life is a lot better, if there is a working OSD to use. Even when the messages are cryptic, they help a bit.
Did some playing. PC video output (DVI) fed to either HDMI input on the TV works fine. Using the DVI in DVI and HDMI out passive splitter, but monitor not connected. And at the same resolution as I use with the monitor. In other words, just what I want.
Tried again, monitor also connected. Nothing connected hot. Boot the PC.
Monitor and TV now do display a picture - but changed to the wrong resolution (1024x768) - circles now oval and larger - so a lower res setting. Try a re-boot - same result.
I suppose that at least eliminates the KVM switch.
Further tests with everything still connected but TV switched off. Monitor now correct resolution after booting. Switch on the TV, and picture on the monitor disappears - even with the TV not switched to a HDMI input.
--------| | | KVM |------- Monitor (black picture, no OSD) | | PC ----- passive diff ----------| | to dual single ended ------------------------------- LG 28 inch (black picture, no OSD)
On the passive splitter, only one side of the splitter can have SCL and SDA connected. This means that the EDID comes from the monitor (1440x900?) or from the TV (1920x1080?) but not both. It means one display device gets its preferred value, while the other display device has to "eat what it is sent".
You could have no OSD, if the signal carried synchronization info (DE Data Enable is the equivalent of the old HSYNC and VSYNC). The display devices are being told when valid rows of data are present. And the rate of presentation (the resolution and refresh) must be within range on both devices.
It implies the PC is sending a black signal on purpose.
OK, I have an idea. The output on the PC has been routed to another PC video card connector. The HDMI is not driven with a signal that is usable (it's just black).
I think I've had this problem here, with an NVidia card. Every once in a while, it would start up driving the HDMI and stop driving the DP that had the monitor connected to it. It should not be driving the HDMI, because there are no loads on the diff pairs. And yet, it did.
So perhaps whatever you've got for a video card on the PC side, is driving out on a second connector for some reason.
That means the PC is not getting EDID, and the SCL and SDA signals are not getting to the PC. With no EDID, the PC is allowed to set a signal like 1024x768, but not higher. It could also send 640x480 or 800x600 (these are VESA 4:3 ratio standards).
It shouldn't be a grounding problem, because I think some of these differential interconnect standards are AC coupled. And only the difference is measured (takes the reference out of the picture). Converting differential signals to two single ended signals, makes the grounding an issue again.
Perhaps getting an active 1:2 would work better than a passive 1:2 ? Since HDMI has +5V on it, such an active device may be able to draw power from the PC output.
I see this active example uses a USB cable for power.
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"The OREI HD-102 is a reliable distribution amplifier powered splitter that will take HDMI signal up to 4K@30Hz and duplicate the signal to up to 2 HDMI displays simultaneously, creating an impressive lossless image or audio transmission via HDMI cable."
"If the connected displays do not support the same resolution then the splitter will lower the output resolution to the next best resolution supported by both displays and same goes with the audio signal."
So that device is applying some logic to the two SCL and SDA pairs it receives, and works out what to send back to the PC as the "preferred" resolution.
1024x768 means the SDA and SCL signals are not getting to the PC. It sends out the "safe" res in response.
If the TV sees 1920x1080 coming in, it means the PC received the EDID table OK, the TV indicated 1920x1080 is native, and that's what the PC used when sending out the video.
If everything was "normal", there would always be a picture. The resolution might be wrong, as a function of not receiving EDID. The usage of KVMs or passive splitters, implies "custom" wiring patterns that must be accounted for (figuring out what happens to SDA and SCL).
But you report a black signal, which does not trigger the OSD. That tells you that the image content is suppressed on purpose, as if the crossbar in the PC video card has been told not to send the normal stream of pixels. I don't think of this as being a normal scenario, but it's all I can suggest based on the symptoms.
I've seen a black signal come from my video card. It was when the "normal" output had been redirected to the *wrong*
*unused* connector on the faceplate. It was another connector that then had the correct signal. This only happens on around one-in-five boot cycles or so. It's like the driver has ignored what the impedance sensing is telling it and just applies a "default" crossbar interconnect pattern.
So why just the TV and not the monitor? To me, it means the TV 'signal' is over-riding the monitor one.
Ignore earlier comments. Very likely confused myself. Provided the TV is powered up after the PC, there is always a picture. Correct with the Acorn, but altering the res on the PC to both TV and monitor.
I think that only happened if the TV was powered up first and HDMI selected. Then the PC booted.
There must be a workround, given the older TV worked just fine.
Snag is I'm used to buying black boxes which claim to do something, then don't.
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