Lost TV remote control action...

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Externet
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Lost TV remote control action...

Post by Externet » Thu Apr 01, 2010 11:45 am

Hi all.

Gradually been worsening along several months, the remote control has no response on my TV (Trutech 19"-Target)
Symptom: takes many pushes to get response, getting worse day by day, now to a couple of dozen pushes ! to have a response. After that first response, all commands work perfect.
2 possibilities:
-The remote is bad
-The TV is bad

Replaced the 4MHz resonator in the control. Same thing, no change.
Connected a phototransistor to the oscilloscope leads and showed activity from the emitter all times, 'cold or warm'. But it seemed the waveform period to be different when the TV reacts ('warm') and when it does not. {I still have to measure carefully}

Leaving the remote to 'cool' :???: several hours ends in no TV response again, until multiple pushes whatever clicks-in and starts working flawlessly.

To this point, seems the microcontroller in the remote is changing its 'frequency' after a few hours of not being used. "Universal" replacement remotes have no selection for such brand.
Suggestions ?

Miguel
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CeaSaR
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Re: Lost TV remote control action...

Post by CeaSaR » Thu Apr 01, 2010 12:16 pm

Most no-name brands are built by larger name maunfacturers. In that respect, you can usually program
a universal remote with another code that works. Many have a feature that lets you try each code until
one is found that works. My Comcast remote doesn't have my Dynex TV listed, so I went through their
"try 'em all" process till I found one that worked. You may have to do that.

As for the TV remote, have you checked all caps and solder joints? Battery connections? Button contacts?
Any of these may cause intermittent operation.

CeaSaR
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Dean Huster
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Re: Lost TV remote control action...

Post by Dean Huster » Thu Apr 01, 2010 1:41 pm

Many remotes have a sensor at the opposite end of the IR emitter that is pointed at the user during use. If it senses either weight or a body fat index that's too high, it shuts the remote control down, forcing you to get up off the couch to mess with the TV. The chip used is from National Semiconductor and the following sequence of numbers (the dash indicates the pressing of the "enter" key) entered on the keypad will force the remote back into normal operation for about an hour:

04-01-10

:) Happy April!
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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Re: Lost TV remote control action...

Post by SETEC_Astronomy » Thu Apr 01, 2010 4:23 pm

CeaSaR wrote:As for the TV remote, have you checked all caps and solder joints? Battery connections? Button contacts?
Any of these may cause intermittent operation.
That about sums up my remote troubles. I had a remote that behaved in much the same way. The remote had a cracked lead on the crystal, low batteries and coke under the keypad. I soldered the lead back together, cleaned the board and keypad with alcohol and installed fresh batteries. Good as new.

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Externet
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Re: Lost TV remote control action...

Post by Externet » Thu Apr 01, 2010 7:31 pm

All contacts and buttons are very clean, has never been dropped, no cracks, all solder joints retouched. It is nearly new. There is only one 47µF capacitor in parallel to the 3V supply, the microcontroller, the resonator and the IR led. It works perfectly well when it wants (mostly "warm"). When it does not (mostly "cold"), still shows signals on the scope from a sensing phototransistor placed in front of it. :sad:
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Re: Lost TV remote control action...

Post by SETEC_Astronomy » Thu Apr 01, 2010 7:38 pm

Do you have access to another TV of the same brand? If you do that could at least remove the TV as a possibility. Have you pointed the remote at a digital camera to verify the LED is still good? The LED being bad doesn't fit the symptoms necessarily but the more you eliminate the less you have to look at. Plus it's a simple test.

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Externet
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Re: Lost TV remote control action...

Post by Externet » Thu Apr 01, 2010 7:43 pm

No chance with same TV. Even the dealer does not carry it now. The test on the scope tells the led works. :sad:
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Re: Lost TV remote control action...

Post by SETEC_Astronomy » Thu Apr 01, 2010 7:57 pm

:eek: I didn't pay attention, I thought you had connected the Oscope to the board, not a phototransistor that picks up the real output.

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Bob Scott
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Re: Lost TV remote control action...

Post by Bob Scott » Fri Apr 02, 2010 7:31 am

A very common problem is that the most used push buttons like Vol up, Vol down etc. get intermittent. They are strange rubber contacts with no metal. The problem gets worse and worse until the buttons no longer function. I have an old 1986 Sony like that. At $90 for a new replacement remote control, I instead bought a Sony universal remote for $4 from a discount store.

Trutech is a Target brand. If you can spend an hour or so trying different manufacturer's codes, you will probably find one that works. ie: If Trutech is really made by Toshiba, the Toshiba code should work.
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Externet
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Re: Lost TV remote control action...

Post by Externet » Fri Apr 02, 2010 9:37 am

Thanks, fellows.
Now I have solid data, from repeated measurements. Holding any button pressed,

When the TV does not respond, the remote emits data pulses every 50 mS. (fast)
When it works, the data pulses are every 100mS. (normal operation)
The data period is consequently compressed/expanded with the repetition rate.

Code: Select all

No work-------||||----------||||----------||||---------||||--------
Works ----------------------| | | | -------------------| | | | ----------
Now the question is: Can I sustitute its 4MHz resonator with a 4MHz crystal ?
Something is acting on harmonics or the µC is not dividing properly.

This has nothing to do with contacts, I always get signal from the phototransistor.
Miguel
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Re: Lost TV remote control action...

Post by SETEC_Astronomy » Fri Apr 02, 2010 1:13 pm

Did you add small value caps (15-33pf) on each leg to ground? Should work if you did.

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haklesup
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Re: Lost TV remote control action...

Post by haklesup » Fri Apr 02, 2010 1:25 pm

So it appears your transmit frequency is doubling without excuse.

The resonator is unlikly to double its frequency so that leaves double clocking due to noise like ground bounce coming out of the resonator or the Remote control chip is degrading such that it fails to divide the clock properly under certain conditions of temperature.

Adding or replacing the decoupling caps is a good place to start. It should reduce noise produced by or sensitive to the devices on the board.

I would just get a universal remote and try that. Its pretty likely the codes are in its library. If you have cable with a provided remote, it is already universal and calling customer support will tell you how to program it.

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