One of my 15-1994 remotes stopped transmitting infrared (the red LED worked but there was no IR signal).
I tested this by viewing the LED-end of the working remote through a digital camera - the IR LED on the working remote appeared white/blue through the digital camera / PCcam.
I repaired this by soldering another IR-LED in parallel to the diode. This is the diode on the lower-right corer of Tommy Tyler's schematic...and on the right side of the circuit board when looking at the top of the board when the LED's are facing right.
I was not sure if the diode had failed or if the driver circuit had failed and discovered that a parallel IR LED caused the original to start transmitting.
Two questions:
1) does anyone know why this worked?
2) should both of the LEDs transmit? (I read earlier that on the 15-1994 that one IR LED is transmit and the other is transmit/receive (for learning)...or are these two used for transmit+receive (and not transmit+receive/transmit). Can anyone check this out (use a digital camera to "look" at the IR signals).
thanks
Replacing IR-LED in 15-1994
Moderator: Moderators
schematic
Sorry - I thought I saw the schematic link listed in previous posts - it isn't. I found it at:
http://www.hifi-remote.com/files/schematics/15-1994.gif
It's hard to read the text on the schematice but the LED is on the lower-right side. Only this LED is transmitting (on both remotes - they're old). The one I 'repaired" has a 5-6ft range and my other remote has a 10-15ft range. What items are most likely to go bad - solder joints? resistor, transistor or LED?
A better copy is at:
http://www.hifi-remote.com/forums/dload ... le_id=3849
http://www.hifi-remote.com/files/schematics/15-1994.gif
It's hard to read the text on the schematice but the LED is on the lower-right side. Only this LED is transmitting (on both remotes - they're old). The one I 'repaired" has a 5-6ft range and my other remote has a 10-15ft range. What items are most likely to go bad - solder joints? resistor, transistor or LED?
A better copy is at:
http://www.hifi-remote.com/forums/dload ... le_id=3849
Last edited by jimschott on Tue Nov 14, 2006 10:22 pm, edited 2 times in total.
I don't know whether I'm downloading that wrong or using the wrong programs to view it, or if the original is just too low resolution. But I can't get a good enough view of that to read any of the details.
By "diode on the lower-right" I assume you mean the LED near the lower right in that schematic.
It must have burned out in a way that made it open (pass no current) rather than shorted (pass current generating no light).
The two LEDs are wired so that for transmit current must pass through both of them together. If one of them is open, the other won't work either.
So your repair makes sense. The new LED lets current pass through both itself and the still working one.
If you're currious about the details:
The plus side of the top LED is connected to power (through a resistor). The minus side of the bottom LED is connected to ground.
The transistor between the two acts as a switch to either disconnect them so they're off, or connect the minus side of the top one to the plus side of the lower one to allow current to flow through both.
The other connection between the top LED and that transistor is just for learning. The current through that connection is tiny in transmit mode.
Without seeing all the component values, I can't guess the exact behavior with the bottom LED open. Some of the current that should have passed through the bottom LED would instead go through the base of the transistor. That might put some current through the top LED, in which case I guess it was too weak to control your devices or you wouldn't have known your remote was broken. Possibly enough current leaks through the disabled learning logic that the LED has too little voltage to turn on at all.
By "diode on the lower-right" I assume you mean the LED near the lower right in that schematic.
It must have burned out in a way that made it open (pass no current) rather than shorted (pass current generating no light).
The two LEDs are wired so that for transmit current must pass through both of them together. If one of them is open, the other won't work either.
So your repair makes sense. The new LED lets current pass through both itself and the still working one.
If you're currious about the details:
The plus side of the top LED is connected to power (through a resistor). The minus side of the bottom LED is connected to ground.
The transistor between the two acts as a switch to either disconnect them so they're off, or connect the minus side of the top one to the plus side of the lower one to allow current to flow through both.
The other connection between the top LED and that transistor is just for learning. The current through that connection is tiny in transmit mode.
Without seeing all the component values, I can't guess the exact behavior with the bottom LED open. Some of the current that should have passed through the bottom LED would instead go through the base of the transistor. That might put some current through the top LED, in which case I guess it was too weak to control your devices or you wouldn't have known your remote was broken. Possibly enough current leaks through the disabled learning logic that the LED has too little voltage to turn on at all.
I repaired two 15-1994 remotes by replacing the IR LEDs with Siemens LD271 emitters. One remote had one LED not working; in the other, both LEDs were defective.
To repair:
1) use a digital camcorder or PC-cam to "see" which IR LED(s) are defective (good IR LEDs will appear bright/white if the are emitting IR signals)
2) to open the remote: http://www.hifi-remote.com/jp1/disassemble/
3) solder the new LED to the existing IR LED (connect the anode, long lead, closest to the center of the circuit board).
4) no need to remove the existing IR LED - snip one of the leads of the defective IR LED
5) bend the defective IR LED up and out of the way and bend the new IR LED to align & point it in the right direction)
Siemens Infrared LED (Emitter):
http://www.datasheetcatalog.com/datashe ... D271.shtml
Schematic of the 15-1994 (Tommy Tyler):
http://www.hifi-remote.com/forums/dload ... le_id=3849
IR1 is used for learning and transmitting. IR2 is transmit only. IR1 may lose it's learning (receiving) capability with this repair (not tested).
Thanks to johnsfine & Tommy Tyler for advice.
To repair:
1) use a digital camcorder or PC-cam to "see" which IR LED(s) are defective (good IR LEDs will appear bright/white if the are emitting IR signals)
2) to open the remote: http://www.hifi-remote.com/jp1/disassemble/
3) solder the new LED to the existing IR LED (connect the anode, long lead, closest to the center of the circuit board).
4) no need to remove the existing IR LED - snip one of the leads of the defective IR LED
5) bend the defective IR LED up and out of the way and bend the new IR LED to align & point it in the right direction)
Siemens Infrared LED (Emitter):
http://www.datasheetcatalog.com/datashe ... D271.shtml
Schematic of the 15-1994 (Tommy Tyler):
http://www.hifi-remote.com/forums/dload ... le_id=3849
IR1 is used for learning and transmitting. IR2 is transmit only. IR1 may lose it's learning (receiving) capability with this repair (not tested).
Thanks to johnsfine & Tommy Tyler for advice.