Troubleshooting a Technics SU-V9 LED circuit

Thread Starter

bobert.hinton

Joined Sep 17, 2021
2
In the attached schematic image, under normal operation Led's D808-D823 do not light up yet D806 & D807 do illuminate properly. Connection "C" has +5v and "B" & "C" are connected to a SPDT switch which is connected to ground. I have tested each LED and confirmed they are all working, drawing approx 1.6v each. If I power the circuit and ground any of LEDs D808-D812 they light up respectfully. If I ground any of the LEDs D813-D817 they light up respectfully and the switched on LED D808-D812 lights up. Nothing lights up if I ground any of LEDs D818-D823. How do I troubleshoot this circuit? And what is purpose of diode D825?


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Dodgydave

Joined Jun 22, 2012
10,394
You need to narrow it down, by temporary shorting out the J7 and J8 terminals, to see if the rotary switches are causing the problem.
The leds are wired in series via the rotary switches.
 

Thread Starter

bobert.hinton

Joined Sep 17, 2021
2
Solved! Zener Diode D825 had failed. I put it out and tested it. It had equal resistance in both direction. After replacing it all Leds are functioning correctly. I believe Diode D825 and R809 function as a voltage regulator, however, all the schematics I found have a resistor between V+ and the Cathode of the Zener Diode. So I may be wrong about purpose of those components.
 
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