Puzzling IR remote control problem

[NeverExpectPowerAlways]

I hope I've come to the right place to get some helpful hints.

I am working on a Mitsubishi TV, model CS-2056R, made in 1988,
specifically, the IR remote receiver circuitry.

The remote function for this unit began failing some time ago. At times,
it would just up and quit working and then just as suddenly, it would
start working again. At first, there did not seem to be a pattern, but
after some months, one appeared. The remote would never turn the machine
on or control it for the first 10 minutes or so, sometimes for much
longer but mostly only for the first ten minutes. After this "warmup"
period the remote control function would kick in, but it would die and
come back to life without hint or warning.

I finally decided to see if I could fix it. Without going into detail, I
am 100% sure that the handheld unit is not the problem. After searching
the web and the newsgroups and spending several hours tracing the traces
on the tuner board of the TV and taking readings with a multimeter, I
decided to try changing some of the larger electrolytic caps used to
filter the AC and anything over 100 microfarads or 50 volts (BTW, I
don't do this stuff for a living, just a part-time hobby). I also
changed a resistor that looked like it had failed.

I also took apart the IR receiver module and changed the three tiny
electrolytic caps within. About this time the remote function ceased
entirely. No matter how long I let the unit warm up, the remote would
not function.

Today, after more web and newsgroup searching, I decided to buy a four
dollar Radio Shack IR receiver module and guess what, it worked! I
mounted the Radio Shack module on the tiny stock IR receiver circuit
board and soldered the three pins to the appropriate spots, held my
breath and hit the "power on" button on the remote and the TV turned on.
I watched an old episode of Perry Mason and then turned it off.

Now, some four or five hours later, the TV will not respond to the
remote. The Vcc voltage to the IR receiver module is 5 volts and the
Radio Shack unit is rated at between 2.4 and 5.5 volts.

At this point, my next idea is to change all the little electrolytic
caps and maybe any small transistors that I find in the IR receiver
circuit. The last step will be to change the 42 pin IC that receives the
signals from the remote and activates the appropriate circuits. I don't
think that is the problem, though as everything worked okay when I put
in the new IR receiver module.

I have a sneaking suspicion that there may be some AC leaking into the
IR receiver circuitry, but I really don't even know if that is even a
valid concept.

If you have read this far and think you may have some insight, please
feel free to post it as a reply to the news group.

Thanks,
Jack

 

[PeterD]

If you have read this far and think you may have some insight, please
feel free to post it as a reply to the news group.

Suggestions like: if you don't know what you are doing, don't try to
fix it?

 

[NeverExpectPowerAlways]

Suggestions like: if you don't know what you are doing, don't try to
fix it?

Yeah, let's all never learn anything new.

Would that have been your advise to Tesla or Edison?

Let's all just get warm around the lightning fire until it burns out.

 

[ian field]

Yeah, let's all never learn anything new.

Would that have been your advise to Tesla or Edison?

Let's all just get warm around the lightning fire until it burns out.

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.

 

[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

 

[ian field]

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 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.

 

[NeverExpectPowerAlways]

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

 

[ian field]

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.

 

[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.

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

 

[PeterD]

Yeah, let's all never learn anything new.

Would that have been your advise to Tesla or Edison?

Let's all just get warm around the lightning fire until it burns out.

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...

 

[Yukio YANO]

I hope I've come to the right place to get some helpful hints.

I am working on a Mitsubishi TV, model CS-2056R, made in 1988,
specifically, the IR remote receiver circuitry.

The remote function for this unit began failing some time ago. At times,
it would just up and quit working and then just as suddenly, it would
start working again. At first, there did not seem to be a pattern, but
after some months, one appeared. The remote would never turn the machine
on or control it for the first 10 minutes or so, sometimes for much
longer but mostly only for the first ten minutes. After this "warmup"
period the remote control function would kick in, but it would die and
come back to life without hint or warning.

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

 

[NeverExpectPowerAlways]

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...

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.

 

[Homer J Simpson]

It turns out that my 12 Volt DC Fluorescent Lighting System would Block
the Remote Control System.

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

 

[Franc Zabkar]

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

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

- Franc Zabkar

 

[Franc Zabkar]

I hope I've come to the right place to get some helpful hints.

I am working on a Mitsubishi TV, model CS-2056R, made in 1988,
specifically, the IR remote receiver circuitry.

The remote function for this unit began failing some time ago.

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

 

[**THE-RFI-EMI-GUY**]

Why don't you try powering the receiver from a battery and isolating it
from the sets PS circuitry. I had a Sony that acted similarly and I
suspect the power supply filters were getting weak and the AC ripple was
disturbing the receiver circuit. Thankfully I gave the set away and so
did not get into repairing it. Also be aware when electrolytics fail
they can dump invisible electrolyte on the board causing nearby,
electrically unrelated circuitry to act up. You might need to wash the
PC board.

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

--
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

 

[NeverExpectPowerAlways]

Why don't you try powering the receiver from a battery and isolating it
from the sets PS circuitry.

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.

 

[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

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:

http://groups.google.com/group/sci....on+electrolytic&rnum=2&hl=en#aea8b6d332f0380f

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

 

[Franc Zabkar]

The picture is still fantastic.

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

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:

http://groups.google.com/group/sci....on+electrolytic&rnum=2&hl=en#aea8b6d332f0380f

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

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

 

[NeverExpectPowerAlways]

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

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.