So I picked up a nice marantz 105b that works great except every display light was out except for one. I just finished converting it to all led's and all is great except the stereo light is not working. I get 3.2 volts while tuner is powered up all the time. moving the dial doesnt change voltage at all. I know im tuned into a stereo radio station. Any input appreciated. Thanks!
No Stereo light marantz 105b
- Thread starter ls1jay
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Bob_in_OKC
Addicted Member
Yes...the stereo indicator requires a different lamp from the rest, as I recall.
catrafter
Marantz Specialist
Connect the anode of your LED to the trace that goes to J204, connect the cathode of the LED thru a resistor to the trace that goes to J205. The resistor should be between 470 and 2K Ohms depending on how bright you want the stereo indicator to be.
J205 should go to near zero volts when you have a stereo station tuned in. If not then trace the wiring through the mono switch, the FM switch and back to J117, ultimately to pin 4, the lamp driver, on the MPX decoder chip, H114.
If pin 4 of H114 doesn't go to near zero volts when you have a stereo station tuned in and you are sure that you hear the station in stereo, then H114 may be bad. If you hear the station in mono, then H114 may be bad or the decoder may just need an alignment.
Tom
J205 should go to near zero volts when you have a stereo station tuned in. If not then trace the wiring through the mono switch, the FM switch and back to J117, ultimately to pin 4, the lamp driver, on the MPX decoder chip, H114.
If pin 4 of H114 doesn't go to near zero volts when you have a stereo station tuned in and you are sure that you hear the station in stereo, then H114 may be bad. If you hear the station in mono, then H114 may be bad or the decoder may just need an alignment.
Tom
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Im an obvious Newbie at this stuff, but I can normally get it done with lots of thought and some help. Just out of curiosity, How can the led light if j205 goes to zero volts. Does that trace supply the ground for the light? IF its a ground why does it normally have voltage running through it? Im not a wiring diagram expert but im tryin to learn. Thanks for the help, much appreciated.
catrafter
Marantz Specialist
Set your meter to read DC volts. Connect the black meter lead to the chassis and the red meter lead to J204. Turn the tuner on in FM mode.
You should read several volts. Make sure the mono button is not pressed.
Move the red meter lead to J204.
Now, tune across the dial. When you are off station, you should read several volts on your meter. When you tune in a stereo station the voltage should drop to near zero and the LED should light.
This assumes that you installed the LED and resistor as outlined in my previous post, the FM and mono switches and wiring are good and the MPX decoder is working properly.
A voltage from J204 on the anode of the LED and zero volts (ground) on J205 from the multiplex decoder through the resistor to the cathode of the LED forward biases the LED junction, causing it to produce light.
Read about series circuits here.
Tom
You should read several volts. Make sure the mono button is not pressed.
Move the red meter lead to J204.
Now, tune across the dial. When you are off station, you should read several volts on your meter. When you tune in a stereo station the voltage should drop to near zero and the LED should light.
This assumes that you installed the LED and resistor as outlined in my previous post, the FM and mono switches and wiring are good and the MPX decoder is working properly.
A voltage from J204 on the anode of the LED and zero volts (ground) on J205 from the multiplex decoder through the resistor to the cathode of the LED forward biases the LED junction, causing it to produce light.
Read about series circuits here.
Tom
Thanks for all the great info. I havent gained much so far. If I ground to chassis and probe j204 I get like 7 volts. If i touch chassis with my hand voltage drops to 3.5. What does this tell a guy? if im not touching chassis I get around 6 volts regardless of where tuner dial is and stereo light will not light. Why would me touching tuner chassis give such a huge voltage gain? Im gonna keep messing with this for a little while longer till i finally break down and take it in.
petehall347
the brandy coffee man
what is wrong with original lamp ?
All but 1 lamp was burnt out when I got it, so i proceeded to change them out with led's. All went well except I found out stereo is not working. Im not so much worried about the lamp as i am the stereo function not working properly.
petehall347
the brandy coffee man
i know some stereo circuits rely on the bulb to operate properly . maybe yours is one of them .
NavinJohnson
Professional Amateur
my realistic had a flicker in the stereo light. i know i had to adjust and clean the trimmer for the stereo multiplexer. it did work in my case and was easy but i have no idea how to do this on a marantz. probably similar but i havent done this on that. find the service manual.