Puzzling IR remote control problem

On Sat, 03 Mar 2007 03:38:22 GMT, NeverExpectPowerAlways

The symptom does have some similarities to an electrolytic with ESR issues, if you are going to get into fault finding you really do need to invest in an ESR meter such as the Dick Smith ESR meter, changing caps in a random manner is more likely to result in damage to PCB tracks or solder bridges which would certainly make the fault become permanent.

Thanks, ian

There WAS a damaged track on the board. I say this because the signal voltage between ground and the track that connected the IR receiver to the 42 pin IC fluctuated erratically between 2 and 4 volts when the unit was plugged in but not powered on. I thought that I had located the problem on the track and made a careful repair, but the erratic voltage remained. Just this morning I severed the track at both ends and used an insulated wire to reconnect. The voltage is now rock solid. The track was not being used for any other purpose but to connect the signal from the IR receiving module to the IC that apparently controls the switches for the various functions that the remote is supposed to control.

I just measured the signal voltage and it measures +3.7 volts to ground with an analog meter and +4.75 to ground with a digital meter. I don't understand that. In addition to the signal line, the IR receiver module has a +5 volt line and a ground line running to it. The +5 volt line measures +5 volts with both meters.

The unit is still not responding to the remote, however, and I am off to radio Shack to buy another $4 IR receiver module to see if that revives it again. Perhaps the first one was damaged by the faulty track or it was just a faulty unit. The fact that it worked when first installed is heartening. It would seem to indicate that the 42 pin IC is not at fault.

Thanks again, Jack

The two different meters respond differently to a train of pulses, the analogue meter probably gives a reasonable indication of mark-space-ratio if you know the value of both ground and Vcc, depending on individual design the ADC in some DMMs is confused by pulse trains and can give completely nonsensical readings.

I don't know if it makes a difference, but the measurements were taken without any signal being sent from the handheld unit.

Is it common for the signal out line on an IR receiver to have standing voltage on it?

Jack

The IR sensor might be picking up the 50/60Hz (actually 100/120 half cycles/second) from domestic lighting, but they normally have a 38 or 40kHz bandpass filter in addition to an optical filter.

ian,

I fixed it.

You hit right on the problem.

The original IR receiver unit was mounted on a small PCB, 1 1/2" square. When I removed the old module and soldered on the new one from Radio Shack I may have fried one of the tracks where the pin from the IR module poked through. When I went to remove the Radio Shack module to try a new one, I noticed that the copper track around the little hole was gone. The solder around the pin must have made contact with what was left of the track, but it came lose when the unit warmed up.

I replaced everything with wire and it works again.

Thanks a ton for the feedback.

If I ever decide to get serious about repair work, I will look into an ESR meter. That and a bit more education.

Jack

just shotgun replacing parts is not a learning experience. What it is, is a waste of time and money.

Instead useing proper debugging techniques to determine where the fault lies is learning.

That said, IR remote receivers can be tricky things to work on...

My Flaky Remote Control Experience !! In my Motor Home, I was having severe Intermittent problems using my Remote Controller driving my Bell Express-Vu Satellite Receiver. It turns out that my 12 Volt DC Fluorescent Lighting System would Block the Remote Control System. By Shading the RX sensor from the direct illumination of the fluorescent fixture,I cleared up the problem .

I think the 15 KHz 12Volt DC Ballast was modulating the fluorescent Tube ! Although the Light output from the fluorescent lamp is far from the ~

900uM IR spectrum I suspect it was still strong enough to overwhelm the IR output from the Remote Controller. I have NEVER had any problems using this system with my Domestic setup using 60 Cycle ballasted fluorescent lighting !!!

I no longer have access to the Mobile Setup so I cannot use my Scope to confirm the frequency of the Fluorescent Fixture or the output of the Remote Controller.

INTERMITTENTS are the bane of troubleshooters !! If you don't understand the intermittent, you don't understand the problem !

Yukio YANO

Replacing $10 worth of 20 year old electrolytic caps is hardly throwing money away.

A $4 Radio Shack IR receiver module solved it the problem.

Now how did I know to swap that out, clueless as you take me to be.

Try going to help someone you can impress with your superior knowledge and condescension.

It doesn't block it, it over drives it.

On Sun, 04 Mar 2007 03:42:39 GMT, "Homer J Simpson" put finger to keyboard and composed:

To be fair, he does go on to say that the IR interference "overwhelms" the sensor.

- Franc Zabkar

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Please remove one 'i' from my address when replying by email.

On Sat, 03 Mar 2007 03:38:22 GMT, NeverExpectPowerAlways

I have (had?) an intermittent IR fault with a Mitsubishi set of slightly earlier vintage. The problem has not recurred since I replaced the caps in the IR module.

Anyway, I just wanted to ask whether your picture tube is still good after all these years. The contrast in mine seems sharper than many new sets.

- Franc Zabkar

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Please remove one 'i' from my address when replying by email.

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Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money"  ;-P

That thought had crossed my mind once or twice. But as it turned out the problem was not with the power supply but with the original IR receiver module and my poor job of soldering in the replacement unit from Radio Shack. The solder made the connection at first but when the set warmed up and then cooled down, the expansion and contraction of the solder, the trace and one of the pins from the new unit caused the connection for that pin to be open. Once I saw that and resoldered all the connections for the new unit, the remote control function began working like new.

The picture is still fantastic. It's seems as good as new. That is why I tried to resurrect the remote control function rather than junk the set.

I, too, thought that it may be the electrolytic caps and I replaced the three that I saw in the IR module plus about 10 or 12 on the main board. Past experience and the post linked below led me to try that first:

In my case, though, a $4 Radio Shack IR receiver module finally did the trick.

On Mon, 05 Mar 2007 04:30:25 GMT, NeverExpectPowerAlways put finger to keyboard and composed:

That's been my experience with the majority of AWA/Mitsubishi sets. IMO CRT technology seems to have taken a retrograde step.

My set uses a "discrete" sensor based on an M51014L IR receiver/demodulator. To use a modern sensor, I would have to redesign the PCB. Fortunately the IC is still available for around AU$4.

- Franc Zabkar

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Please remove one 'i' from my address when replying by email.

I cannot comment on that, except that it seems CRTs are on the way out for television reception. I just installed a digital TV tuner in my computer and I am amazed at the number and clarity of free digital broadcast stations in the San Francisco Bay Area. From what I have seen, all new television sets being sold that are capable of receiving digital broadcasts are either LCD or plasma or some other non-CRT technology. Analog CRT sets are dirt cheap and few people seem to be aware that analog broadcasting is scheduled to end in the United States in early 2009.

The tuner card I bought is more prevalent in Oz then in the US. It's a TwinhanDTV ATSC D+A, bought on eBay for $58us delivered. The OZ model would be TwinhanDTV DVB-T (D+A), I believe.

The hardware works fine, but the user interface software for controlling the hardware is poorly designed.