Raspberry Pi -- HDMI question

There are some useful suggestions at the RasPi Troubleshooting Wiki: http://elinux.org/R-Pi_Troubleshooting#Display.  I find my display blanks out if TP1-TP2 voltage drops too low.

Is TP1 and TP2 where you can connect a volt meter and test the Pi to see if it has sufficient voltage going thru?

Yes -- there's a nice photo showing how to do it at the RasPi Hardware Wiki: http://elinux.org/Rpi_Hardware#Power_Supply_Problems.

Tested with SD card inserted and tested TP1 and TP2. My voltmeter read 4.84v. So its between 4.75v and 5.25. Maybe it should be around 5.xx?

Tested with SD card inserted and tested TP1 and TP2. My voltmeter read 4.84v. So its between 4.75v and 5.25. Maybe it should be around 5.xx?

When I use a composite video cable it comes in fine.  Not sure why the HDMI doesn't work though. 

4.84V is just barely enough voltage to drive the board. With all of those loses, as soon as you start using more stuff on the pi, such as the HDMI output, you'll see the voltage drop. More current used == more voltage drop over resistive devices such as the polyfuses and bad cables and terrible PSU's. Your second post shows us the results.

You should see all of the other power problems manifest as well: failing keyboards/mice, network sketching out, hdmi not working. Suggest during your testing (hope you can get a spare PSU to try) that you utilize ssh to remotely connect to the pi and diagnose its problems from a perfectly working computer which has no unknown problems. There's a lot to be said for a working keyboard and display when troubleshooting.

There's many more guides to be referring to when it's about power problems. Just remember that sometimes HDMI problems are actually power problems. Sorry for not posting links but it's too late at night here. Good luck!

David Harrison wrote:

 

Tested with SD card inserted and tested TP1 and TP2. My voltmeter read 4.84v. So its between 4.75v and 5.25. Maybe it should be around 5.xx?

4.84V at TP1-TP2 should work fine.  My board works at 4.65V (DVI-D monitor fails at 4.60V), but that's a matter of having peripherals that are happy with lower voltages.

I suggest looking at other causes at the RasPi Troubleshooting Wiki: http://elinux.org/R-Pi_Troubleshooting#Display.  My DVI-D monitor works without config.txt, but a lot of people need to create config.txt and try various display options.

Well I tried the troubleshooting routines suggested on the RasPi Troubleshooting Wiki and without the config.txt.  I guess it's the voltage because I get a 'no signal' message on the screen.

David Harrison wrote:

 

Well I tried the troubleshooting routines suggested on the RasPi Troubleshooting Wiki and without the config.txt.  I guess it's the voltage because I get a 'no signal' message on the screen.

Here's the remaining things I'd check before RMA:

1.  Make sure your HDMI cable and monitor work from an HDMI source other than RasPi.

2.  If you know someone with a working RasPi w/ HDMI, try using his or her HDMI cable and monitor.  That way you can tell if the problem is RasPi or monitor compatibility.

3.  There are many config.txt options: http://elinux.org/RPi_config.txt#Video_mode_options.  Maybe some combination of these work, or your monitor requires a combination of options not yet discoverd.

4.  Check raspberrypi.org forum threads about HDMI problems.  There are lots of them.  One of the moderators (I think dom) has soliticited details of problems in the past and used them to fix bugs.

5.  Otherwise you may just have a RasPi with defective HDMI, and it's time for RMA.

I found out going to the Raspberrypi.org.   I went to the forums and found a section called Basic setup and Usage.  Under that was a post by Gert Von loo called 'Setting up HSMI Ouput'. 

"If you are unsure what formats are supported, set the output format to VGA 60Hz and then follow the instructions below to parse the EDID to find out what formats are supported."

So I created a new config.txt file and picked the following VGA 60 setting from the list given in the 'Setting up HSMI Ouput' text.

hdmi_group=2

hdmi_mode=HDMI_DMT_VGA_60=0x4

I suggest this since no keyboard or mouse is needed to simple find out if your HDMI works.