Ben e Boy
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Re: Did the Pi somehow break my TV?

Wed May 09, 2012 12:03 pm

Sorry for the long post, but I wanted to include all the detail. My flatmate and I cant wait to use the Pi, but our first concern is repairing/replacing an expensive TV and knowing whether any of these components are safe to use again without breaking the replacement.

My Samsung LE32R88BD TV went pop last night when was trying to get the Pi to work and now it refuses to do anything once taken off standby. There are three candidate causes, so I thought I"d discuss the setup here to warn others as well as find answers to these questions:

1) What caused the TV to break?

2) Is it likely to be repairable?

3) Is the Pi still safe to use on another TV?

4) Is the powered USB hub safe to use?

5) Is my 4-way mains adapter safe to use?

I"d managed to get the Pi to boot with debian6-19-04-2012 connected to my TV via HDMI, but it was not accepting responses from either of two simple wired keyboards. It didn"t make a difference whether I had a wired optical mouse plugged into the other port or not, nor which port I used. The keyboard was apparently not receiving power from the USB port at all, as the caps/num/scroll lock indicators never lit up. Unfortunately, I didnt have a voltmeter handy, so I couldn't measure the voltage, but I tried two working phone charger cables (one was 5V, 1A, the other was 5V, 700ma). Ill try to measure the voltage tonight and post that here. Whatever the voltage, the mouse, when connected, was receiving power as the red light underneath was lit.

Thinking that power might be the problem, I plugged a powered 7-port USB hub (http://tinyurl.com/7bra564) into the Pi and into the mains and connected the mouse and keyboard through that. Still nothing from either keyboard, so I was unable to login. However, I noticed that sometimes when I disconnected the Pi from the mains, it would remain on by apparently drawing power back through the USB peripheral cable from the powered USB hub. This only happened once, and I didnt leave it on for long, but I thought it might be important.

Also potentially important: the TV, Pi and USB hub, when plugged into the main, were all plugged into the same 4-way UK extension cable/splitter, which is fused to 13A.

Ok, so here"s the bit where it turned to the worse. I continued to try various configurations and eventually had the following situation:

Pi is turned off (not connected to mains)

Pi connected to Samsung LE32R88BDTV HDMI port 1

Pi connected by USB to 7-port powered USB hub

Wired optical mouse and simple wired keyboard plugged into USB hub

USB hub and TV plugged into same 13A-fused 4-way UK mains extension

When I reached forward to plug the Pi back in, as I had safely done before, before the mobile phone charger was even close to the 4-way socket extension there was an electrical flash and the AC power went off in the flat. Given that I hadn't yet plugged the Pi in, the suddenness of the flash must have been from nudging one of the already-connected cables. After my flatmate reset the circuit breaker, the TV was broken. It now buzzes (as if shorting-out) from the area where both the power and HDMI cables connect to it.

So which of these happened when the cables were nudged?

1) The Pi drew power from the powered USB hub and a surge passed up through the HDMI to the TV? Is this possible? I don"t know how the HDMI connectors work but I"d already seen that the Pi could receive power from the Hub.

2) The hub shorted internally, causing a power surge that broke the TV via the shared 4-way extension before the circuit breaker tripped.

3) Movement on the HDMI cable caused a short in the HDMI socket on the back of the TV, causing a surge.

Note that the 13A fused extension didn't blow. I"ll post the Amp rating of the circuit breaker tonight.

jamesh
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Re: Did the Pi somehow break my TV?

Wed May 09, 2012 12:32 pm

If only all bug reports were as detailed.

My initial thought is that I cannot see how the Raspi (unpowered) could have caused the problem. The buzz from the TV implies it's the power circuitry on the TV that has failed. The fact that the power in the flat went off implies a catastrophic failure in the TV/supply to TV taking out the mains - I cannot see any way that the rest of the devices could do this, providing they are correctly wired.

As the fuse didn't go in the power plug, that would indicate a short which tripped the circuit breaker (or RCD?) faster than the fuse could blow - earth leakage?

I suppose there is a possibility that the TV got a signal from the Raspi (but it's was unpowered at the time..) that told it to go to some weird state that shorted out it power circuitry, but that sounds too bizarre to be true. But then it is a Samsung...

I've spoken to Gert, but he want to think about it before posting.

Where did the Flash come from? If it was the extension block, I'd be looking at that as as the cause of the problem. Worth taking apart  (if you feel comfortable doing it) to see if there are any scorch marks inside that might point to an issue.
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Re: Did the Pi somehow break my TV?

Wed May 09, 2012 12:33 pm

NOTE : Please PLEASE remove extension board from mains prior to examining it!!!
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Ben e Boy
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Re: Did the Pi somehow break my TV?

Wed May 09, 2012 12:45 pm

The flash came from the extension block. The devices were connected to the extension block in this order:

1) TV

2) Nintendo 64 (turned off throughout)

3) <empty> (this is where I'd been connecting the Pi)

4) USB hub

The flash appeared to come from the empty socket, but might have been from the end (near the USB hub). I'll disconnect it and examine it for scorch marks tonight, as well as checking the voltage across the Pi while it's not connected to anything else other than the mains (directly)

bredman
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Re: Did the Pi somehow break my TV?

Wed May 09, 2012 4:58 pm

From the very detailed description, I would assume you have a loose connection inside your extension block. Some slight movement seems to have disturbed this loose connection and shorted live to neutral.

This seems to have been a massive short-circuit if it tripped the main circuit breaker. I assume the breaker that it tripped did not have a test button on the front marked "T".

The short seems to have blown something in the Switched Mode Power Supply in your TV, resulting in the buzzing noise. If you are adventurous, you could open the TV to see if there is a fuse blown somewhere on the power supply board. Don't open your TV if you don't have a clue what you're doing!

In summary, it seems that the fault was caused by a fault extension block. To confirm this, disconnect it from the mains and check if there are scorch marks inside.

Your TV won't fix itself. You will probably need to have the power board replaced.

I hope you have home insurance to cover this. You will be glad to know that the RPi is CE certified, so the RPi will not void your insurance. CE certification is actually useful for some things.

Sorry for the bad news, but you probably had low hopes anyway.

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Gert van Loo
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Re: Did the Pi somehow break my TV?

Wed May 09, 2012 7:32 pm

It is very difficult to find a fault theoretically. I often say: 'There is only one way for things to go right but there are many ways in which things can go wrong'.

So here is where I start speculating: You had a short from a power cable to probably ground. That short caused your ground to carry a very short but very high spike. If all the grounds are connected the spike will traveled through all your circuits. Especially you can have a high voltage difference between the TV ground and the TV HDMI cable ground.

Now what goes against this is that officially the ground of the USB supply and HDMI should not be connected to the ground of the extension cable.

If you have an ohm meter try the following:

1/ UNPLUG THE EXTENSION COURD FROM THE WALL SOCKET.

2/ Plug the TV and the USB supply in the unconnected extension sockets, the PI with HDMI in the TV, No PI power as when the error occurred.

3/ Measure the big ground pin of the extension socket plug against the various metals: - Housing of the PI plugs USB, Ethernet HDMI. Etc.

There should be no connection. If there is: you have a llikely cause.

Phil Spiegel
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Re: Did the Pi somehow break my TV?

Wed May 09, 2012 8:49 pm

Although in this case, from the description of the dynamic situation, it is probably a fault in the extension sockets,  something to be wary of, is the plugging together of equipment powered by a mixture of Double-Insulated 2-wire power supplies, and 3-wire with ground connection back via the mains ground/earth ! {Not all are connected by opto-isolators or capacitor-isolation [as with TV aerial inputs]}

With 2-wire equipment, the exposed terminals are probably at 'mid-rail' via very high-impedances – this constraining the voltage range experienced! (instead of floating freely) … if a lead from such a device is connected to a device where ground is referenced to the mains-earth, then there might be a 120V difference … a quick discharge may occur on connection … this is one reason why equipment instructions advise that connections should be made with the Power OFF: there is then NO voltage difference/ current flow, and when power is applied, the current through the high-impedance is usually insignificant (and safe).

HOWEVER , when many-such devices are connected together in a single area (with us it was an Edit/Training suite), the sum of the individually acceptable currents MIGHT be enough to trip an RCCB, especially with the surges experienced at switch on!

Other problems that might occur (and have done within multi-power-rail equipment) are voltage-reversals on electrolytic capacitors during a connection discharge (or power-rail decay when turning off) .. the capacitor then fails, and so does (your TV) ??????

Ben e Boy
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Re: Did the Pi somehow break my TV?

Thu May 10, 2012 9:21 pm

Sorry for not replying to this with any follow-up information yet. I haven't got my hands on a Voltmeter since the accident.

I'll try to get some answers up on here tomorrow.

Ben e Boy
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Re: Did the Pi somehow break my TV?

Sun May 13, 2012 9:33 pm

First of all, thank you for everyone's help and hypotheses so far.

Here's what I can now add to the discussion:

Using a voltmeter, I found completely different voltages with the same phone charger able but two different HTC 3-pin adapters (both labelled 5V 1A). With one I got a steady 3V from TP1 to TP2. The other gave a varying voltage around 1V. So that probably explains why the keyboard wasn't doing a lot.

As far as the 4-way mains extension goes, there are no scorch marks inside that I can find. There also doesn't seem to be any way that any two of Live/Neutral/Ground could have shorted. I'll post photos of the inside if that will help.

All of the ground pins are connected, so if there was a surge through any of the ground pins, it would have been sent across the circuit. However, the TV is the only plug (apart from the N64, which was off) with a metal ground pin.

I also used an Ohmmeter and found that the ground of the extension is not only connected to the TV ground, but seemingly both ends of the plugged-in HDMI cable. In fact, with the TV and Pi connected via HDMI (and nothing else connected to anything), the TV ground pin shows a connection to virtually everything on the Pi (USB housing, circuit components, Pi power socket etc).

Should that be so? What does this suggest or eliminate as a possible cause? Unfortunately, my contents insurance expired just over a month ago and I've been waiting to buy a new smartphone before shopping around to renew it, which sucks.

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Re: Did the Pi somehow break my TV?

Mon May 14, 2012 4:12 pm

Obviously I am unable to say whether this was anything to do with the problem or not, but personally I would not be too happy using a powered 7 port USB hub (with an unspecified output) which is being sold on EBay for £3.69 including 'free' delivery.

Purely my personal opinion though, which I fully accept that others may not necessarily agree with!

Isn't this one of the type which is being mentioned on http://elinux.org/RPi_VerifiedPeripherals as being a problem hub anyway? Better to stick with reputable brands I think!

Ben e Boy
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Re: Did the Pi somehow break my TV?

Mon May 14, 2012 6:20 pm

I don't think you can risk putting too much faith in that list. I've tested the exact HTC and Samsung adapters mentioned, but they give only 3V across TP1 and TP2. While they might work enough to power the Pi, they aren't giving the recommended readings.

I am eagerly anticipating a response regarding the connection between the TV plug ground pin and the entire Pi when connected by HDMI. I just don't know enough about electronics, but it suggests to me that the Pi is faulty, drew a power signal the wrong way through the connection to the USB hub and transmitted it up the HDMI cable to the TV.

I don't mind replacing the USB hub, but I'd really like some confirmation one way or the other regarding the Pi itself, since I'm already out of pocket now and can't afford to risk damaging another TV.

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Gert van Loo
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Re: Did the Pi somehow break my TV?

Mon May 14, 2012 11:56 pm

Ben e Boy wrote:First of all, thank you for everyone's help and hypotheses so far.

Here's what I can now add to the discussion:

.........., the TV ground pin shows a connection to virtually everything on the Pi (USB housing, circuit components, Pi power socket etc).

Should that be so? .....
All metal parts of a piece of electrical equipment with mains, are connected to ground. (Unless you have a so called double-insulated device indicated by two nested square boxes)
But also I prefer to have my sensitive electronics equipment NOT connected to that same ground.
As others have mentioned even without a resistive path, capacitive couplings will still pass voltage spikes. So I think something, somewhere shorted and cause a voltage spike which has entered your TV and killed it. I believe the HDMI cable is a potential candidate and allowed the spike to travel between your TV and the USB HUB (Or vice versa). I don't think this has anything to do with the Pi, it could have happened with any equipment which is connected using an HDMI cable.

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Re: Did the Pi somehow break my TV?

Tue May 15, 2012 11:48 am

Is this a fault that can be covered by the TV manufacturer? I mean if this has happened is it classed a manufacturing / design fault of the TV? or is it something that is hard to protect from.

From memory my flatscreen is double insulated, it uses a figure of 8 connector
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Ben e Boy
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Re: [UPDATE] Did the Pi somehow break my TV?

Wed May 16, 2012 11:12 pm

UPDATE

I've independently tested each of the other components: the 4-way extension, powered USB hub, charger and cables and all are working normally. However, the Raspberry Pi is faulty.

I know this because my friend received his Raspberry Pi yesterday and tonight I helped him to set it up. He is using the charger recommended and sold by RS Components. The voltage across his Pi is exactly 5V when tested. Using my charger on his Pi, the voltage comes to 4.8V.

My Pi, using either charger, measures only 3V. The power light stays on for a while, but if the Pi is nudged, it either flickers or goes out. All other connected components (keyboard, mouse, HDMI, SD card) were identical. So something is damaged and inconsistently shorting on my Pi. This explains how, when no connections were changed, a nudged cable could cause my Pi to send power up the HDMI cable.

I was happier when I thought the problem was a dodgy cheap USB hub, but now that I know my Pi is faulty I feel pretty miffed.

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Re: [UPDATE] Did the Pi somehow break my TV?

Wed May 16, 2012 11:25 pm

Ben e Boy wrote:UPDATE

I've independently tested each of the other components: the 4-way extension, powered USB hub, charger and cables and all are working normally. However, the Raspberry Pi is faulty.

I know this because my friend received his Raspberry Pi yesterday and tonight I helped him to set it up. He is using the charger recommended and sold by RS Components. The voltage across his Pi is exactly 5V when tested. Using my charger on his Pi, the voltage comes to 4.8V.

My Pi, using either charger, measures only 3V. The power light stays on for a while, but if the Pi is nudged, it either flickers or goes out. All other connected components (keyboard, mouse, HDMI, SD card) were identical. So something is damaged and inconsistently shorting on my Pi. This explains how, when no connections were changed, a nudged cable could cause my Pi to send power up the HDMI cable.

I was happier when I thought the problem was a dodgy cheap USB hub, but now that I know my Pi is faulty I feel pretty miffed.
To be fair, you pi might have also been damaged along with the TV and what you're seeing is the result of the pi having been damaged rather than the culprit. Not ruling out the possibility of the pi, just saying it's possible this is an effect as opposed to a cause
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Ben e Boy
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Re: Did the Pi somehow break my TV?

Wed May 16, 2012 11:56 pm

I'd considered that, but the light that light up now (power, but no ethernet) and the fact that the low mA keyboard wasn't receiving power before, when the Pi was boxfresh, suggest that it was never receiving enough power, despite the adapter and cable now being shown to be fine.

tonycollinet
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Re: Did the Pi somehow break my TV?

Thu May 17, 2012 4:50 pm

In order to get a flash near the power adaptors, then there must have been a failure in somthing connected to the mains.

It is most unlikely that 5V could have caused what you saw. This means either the PSU in the TV blew up (just randomly by chance - unlikely)

Or the very cheap USB hub power supply flashed over, possibly as a result of being overloaded. I've seen video on youtube of one of these cheap chinese PSU's melting the internal insulation (in the switching transformer) even when running slightly less than rated load. The melted insulation then caused the device to fail in a way that shorted out the mains to the low voltage side = dangerous.

For me, this is the most likely explanation for the failure. (Edit - having read your description, that is unlikely if the PSU is still working)

Ben e Boy
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Re: Did the Pi somehow break my TV?

Thu May 17, 2012 5:22 pm

All components except the Pi and the TV are working. The Pi still turns on, but for brief times or until nudged. It doesn't illuminate Ethernet when plugged in (even if that's the only thing connected other than power), but it never did before, either.

I wish I'd tested the voltage when I first had it booting, so I'd know for certain that the Pi was always the faulty component. A very simple 75mA keyboard failed to work in it, though, and I know that the PSU is sufficient and working, so it can't have been drawing 5V. The keyboards have also both been seen working.

I've just got back from work so I'll contact Farnell now regarding a replacement Pi.

edit: tonycollinet: I think the Pi drew power from the hub (which I'd already seen happening, as the pi had remained on while not connected to the mains, a while before it blew), passed it up to the TV due to the intermittent fault/short and probably blew something (a resistor?) in the TV's power board, which resulted in a larger power surge, a flash at TV mains and tripped the circuit breaker.

keylevel
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Re: Did the Pi somehow break my TV?

Sun May 20, 2012 7:08 pm

I assume you checked the fuse in the plug for the TV?

Ben e Boy
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Re: Did the Pi somehow break my TV?

Sun May 20, 2012 8:02 pm

It goes into standby, so it's getting power.

avtsuk
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Re: Did the Pi somehow break my TV?

Sun Jun 03, 2012 9:38 pm

Hi, I feel your pain....

Having read all the posts there are a lot of constructive suggesting and plausable suggestions;

Also though.. if no evidence exists like scorching o the mains sock or the such like, it is quite possible given firstly that even at the low voltages present you're actually dealing with a healthy amount of current and the exposed nature of the pi pcb, it is quite possible that the flash you saw could have been a short between the usb or hdmi or mains adapter etc,

An unwanted voltage applied to the screen of the hdmi cable could easily damage the tv, eg we had samsung 50" plasma at work that a P.A.T inspector with little experiance caused damage to because he failed to disconnect it fully before testing, after he'd tested it it was stuck in standby until we repaired it by reflashing the firmware back into it. If your set has a serial port on it, do a bit of googling for firmware etc, you might get lucky.

Back to the Pi, have you tried rewriting the sd card with the debian image again,it could be the sd card is corrupt?, maybe even try the other image from the downloads and see if you get a picture on thenanalogue output, in either case the OK LED should flash etc..

Video_Liam
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Re: Did the Pi somehow break my TV?

Mon Jun 04, 2012 11:32 am

Hi All,

Very sorry to hear Ben's story, and great to see so many contributions.

Can I also make a suggestion. Has anyone checked the actual wall socket?

You can get a little plug type tester which pluging it to the socket and with three neons will test for basic faults, but I would suggest isolating the ring main, and checking that the actual connections in to the socket are correctly and tightly made... I've seen some suprising results over the years..

BTW what surface was the PI resting on?

Liam

reggie
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Re: Did the Pi somehow break my TV?

Mon Jun 04, 2012 2:01 pm

I have a small amount of experience with those 7 port hubs, another tinkerer and I had these hubs from different places, and other hubs that use the same FE1.1 or FE1.2 chips. Your mileage will most certainly vary on the state of the inside of that hub. Your mileage will vary on the state of the power supply as well. See below for some pics of the inside of one of those hubs.

I would look at the pcb for the hub if you feel comfortable and take a look at the inside of the psu if you feel safe doing so. As mentioned, your mileage will vary, looking at the pcb it will probably be missing some capacitors, mine had 7 missing I believe and you may find that the psu V in and the usb Vbus don't have anything in the way of seperation, mine has a 000 ohm resistor (jumper basically, marked dc1 on the bottom of the hub board, bottom right corner, near the missing decoupling cap) between the 2 supplies, there should be a schottky diode there apparently.

Onto the power supplies, between my friend and I, I got the decent 2amp beefy supply, I believe his was rated on the outside as 2amp but when measured it couldn't sustain more than an amp, it was also missing capacitors. I also had to resolder the ground in mine as it came away from the board when I took the psu pcb out. My power supply also measures 5.25V, which is in spec.

Not sure how much bearing this has on blowing a TV up but it's worth noting that you get what you pay for with cheap usb hubs. The missing caps in mine were a decoupling cap for the whole board and caps on the usb sockets to stop a device when plugging it in dipping the 5v rail for anything else that's already plugged in.

Oh nearly forgot, these hubs also have a tendency to be hard wired to be self-powered, whether they have a power supply plugged in or not.

All in all, if you have a cheap hub and you are getting issues with various devices, I would look there first.
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