Raspberry Pi HDMI Cutting Out

My guess is that while your power supply is fine, your Micro USB cable may have very thin conductors which can cause a substantial voltage drop when RasPi's CPU needs extra current.  Another possibility is excessive drop over polyfuse F3 when the current is high.

There are other possibilities as well.  Take a look at the RasPi Troubleshooting wiki: http://elinux.org/R-Pi_Troubleshooting#No_HDMI_output_at_all

Thanks John.  I will check out that link.  What would cause the current to be high?  If the devices attached are using too much power?  Is there a limitation to what can be attached to the Pi?  I'll see if I can dig up another micro-usb cable to try too.

Thank you!

Ray Price wrote:

 

Thanks John.  I will check out that link.  What would cause the current to be high?  If the devices attached are using too much power?  Is there a limitation to what can be attached to the Pi?  I'll see if I can dig up another micro-usb cable to try too.

 

Thank you!

Here's what the RasPi Hardware Wiki has to say about power: http://elinux.org/Rpi_Hardware#Power

Basically, RasPi model B uses up to 700 mA though it's unclear whether that includes 100 mA each for two low-powered USB devices and any budget for the GPIO.  Your 1A supply should be fine.

However, if your Micro USB cable or polyfuse F3 is iffy, the normal 700 mA could cause enough of a voltage drop across one or both components to drop RasPi's 5V below its minimum 4.75V.  Measuring the voltage between TP1 and TP2 as shown in both the wikis I linked to will tell you if your 5V is below spec.  Even if the 5V is low, you might be able to fix your HDMI problem with "config_hdmi_boost=4" as suggested in the Troubleshooting Wiki linked above.

When I was first trying out my RasPi I had an iffy power supply and cable.  My DVI-D monitor worked fine at 4.65V and above, but below that it would first show random dot patterns and then blank out completely.  Sometimes it would be fine unless I compiled, and then the extra CPU activity dropped the voltage enough to show random dots, which would vanish when the compile completed.  Kind of a cute "feature", actually.

Ray Price wrote:

 

Thanks John.  I will check out that link.  What would cause the current to be high?  If the devices attached are using too much power?  Is there a limitation to what can be attached to the Pi?  I'll see if I can dig up another micro-usb cable to try too.

 

Thank you!

Here's what the RasPi Hardware Wiki has to say about power: http://elinux.org/Rpi_Hardware#Power

Basically, RasPi model B uses up to 700 mA though it's unclear whether that includes 100 mA each for two low-powered USB devices and any budget for the GPIO.  Your 1A supply should be fine.

However, if your Micro USB cable or polyfuse F3 is iffy, the normal 700 mA could cause enough of a voltage drop across one or both components to drop RasPi's 5V below its minimum 4.75V.  Measuring the voltage between TP1 and TP2 as shown in both the wikis I linked to will tell you if your 5V is below spec.  Even if the 5V is low, you might be able to fix your HDMI problem with "config_hdmi_boost=4" as suggested in the Troubleshooting Wiki linked above.

When I was first trying out my RasPi I had an iffy power supply and cable.  My DVI-D monitor worked fine at 4.65V and above, but below that it would first show random dot patterns and then blank out completely.  Sometimes it would be fine unless I compiled, and then the extra CPU activity dropped the voltage enough to show random dots, which would vanish when the compile completed.  Kind of a cute "feature", actually.

When I first got my Pi, the 1A supply worked at first, then wouldn't.

A few versions later, I finally got one that would work reliably.

Even the USB outlet type models had issues, and that included the 2A version I got with the Toshiba Tablet.

I seriously believe most of these aren't designed as Power supplies, but chargers for the battery which is most likely a 3.6v LiOn or similar.

I did check most of the cables, and while they have a very small voltage drop, the biggest drop was the Polyfuse.

The HDMI boost didn't seem to help me, but it might be worth a try.

Interestingly, my son could run his from the USB outlet on his Netbook.!

Mark