Sansui 8080DB odd behavior, but first of protection LED.

saabracer23

saabracer23

Super Member
I have an 8080DB that is having some very odd behavior, which I’ve sorted a lot of it on my own, but wanted to confirm this issue on the protection LED. This receiver comes out of protection, pretty quickly, maybe three seconds after power up. If I’m remembering correctly, they’re supposed to be a blinking red light and then it turns green. This receiver I’m working on obviously has a double anode diode in it so it would have two colors.

I’m getting no blinking red light and the green light is pretty dim. You can’t tell by the photo, but in person, the green diode is barely lighting.

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I measured the voltage at that diode and I’m seeing about 1.3V. It doesn’t say anywhere on the schematic what I’m supposed to be seeing here so I’m trying to figure out what is wrong, is it the diet itself or the circuitry? I still have a few things to do. I’ve got bias and offset squared away, so I’m going to go through passing a signal and such but thought I would post this to see if maybe someone would have an idea, is that voltage too low?

IMG_2120.jpeg

Dan
 
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I think I figured a portion of it out, a previous tech had miswired the protection board. I was checking voltages, and they just seemed off, and noticed that they had miswired the relay. The previous person that was in this or one of the people that have been in this thing absolutely butchered this protection board.

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Many traces where the relay goes in have been lifted and what they did as they tried to wire in a standard four contact relay by sticking it to the back and running a bunch of wires. So anyway, I’m getting the red blinking now which is a good thing but it still seems like the green LED is a bit dim. It now has 2 V across it. Is that still too low? If you look at the schematic above when the protection circuit was wired incorrectly, I was only getting about 10V on the cathode of D03. I’m supposed to see 28V. Now that I have corrected the wiring, I am seeing 29V there. So that looks good, but there are no more voltage reference numbers on the schematic so I don’t know if 2V is appropriate for the LED. Maybe it’s just a dying LED.

Dan
 
saabracer23 said:
I don’t know if 2V is appropriate for the LED. Maybe it’s just a dying LED.
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It is. It looks like that with 28 V and 1.5k in series it got some 20 mA through it and that is a lot for a LED like this. Just get a new three-legged two color LED and you should be good to go. You may even have to increase the value of R12 because new LEDs usually are very bright.
 
What a shame, that is a really P-Poor repair job. I think @PE9ZZ has the right idea, the LED is probably old and tired.
 
I have seen these LED’s fail. Also had problems with the circuit. Test the resistors and replace the transistors also the large diode and caps
 
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