strange diode identification

[electricenthusiast]

This is a failed/ shorted zener diode
I got this from a failed sony dvd (sony_dvp-ns57p) smps. this smps turns on but it is giving out voltage higher than it should .So I removed the optocoupler, checked it, and resoldered it to the board. And now, when I switched on the powersupply( without connecting to the mainboard) it started to cry. So I let the powersupply to run untill the failed component to get hot. And it was this  zener diode which look like a resistor but only 2 color bands. What is the value of this zener diode

[fzabkar]

Service manuals:

https://elektrotanya.com/showresult?what=dvp-ns57p&kategoria=All&kat2=All

[electricenthusiast]

I already have this service manual. It also has the zener listed in it , but no values are given   

Could it be a 46 or 47v zener diode?

Is there any way to find the value using the color ring . I think it is 47v but still not sure

[Swake]

What zener is it in the schematic? There are several.
Why do you think it is 46V (or 47V)?

[electricenthusiast]

by the color rings on it   Yellow and blue
                                       4             6   v    -> 46v   But there is no 46v zener, so it might be 47v ? not sure about that

[fzabkar]

"What zener is it in the schematic? There are several."

[electricenthusiast]

this one

[Swainster]

I'll have a guess and say its a Panasonic MAZ2470. However its function looks like over voltage protection, so if your output is too high and the diode is getting hot then it is just doing its job I.e. it's a symptom and not a cause.

[gamalot]

I'll have a guess and say its a Panasonic MAZ2470. However its function looks like over voltage protection, so if your output is too high and the diode is getting hot then it is just doing its job I.e. it's a symptom and not a cause.

MAZ2470 looks like the most reasonable guess to me. The blue band might just be caused by digital cameras, sometimes they don't capture purple very well.

[electricenthusiast]

yes you are right it was purple . let me try replacing it with that

[electricenthusiast]

Panasonic MAZ2470 zener is no longer available. Can i use 1N4756 zener instead ?

[wraper]

I'll have a guess and say its a Panasonic MAZ2470. However its function looks like over voltage protection, so if your output is too high and the diode is getting hot then it is just doing its job I.e. it's a symptom and not a cause.

Yes, with elevated output voltage defect replacing it won't fix anything.

[electricenthusiast]

But that zener was already shoted/failed

[wraper]

But do you get a normal voltage without it installed? If you don't fix high voltage issue, you will just burn another zener diode when powering on the PSU.

[fzabkar]

ISTM that the zener has +11V on the cathode and -10V on the anode. That's 21V. If a 47V zener is shorting due to a fault, then the overvoltage must be serious.

[electricenthusiast]

I dont know the actual value of the zener, but that zener was already failed/shorted. But how did you found that the zener has +11V on the cathode and -10V on the anode. That's 21V ?

[fzabkar]

But how did you found that the zener has +11V on the cathode and -10V on the anode.

Follow each end of the zener to CN201. There you will see EVER-10V and EVER+11V. The voltage difference is 21V.

[electricenthusiast]

So should i replace it with a 21v zener? there is no 21v zener .So should i use 22v or 20v zener ?

[electricenthusiast]

which should i use ?

[fzabkar]

No, a 21V zener would be on the borderline. There must be a reason that the original zener was 47V, but I can't understand what that could be. I would wait until you repair the circuit, and then examine the voltage between the zener's pads.

[electricenthusiast]

No, a 21V zener would be on the borderline. There must be a reason that the original zener was 47V, but I can't understand what that could be. I would wait until you repair the circuit, and then examine the voltage between the zener's pads.

I'm not at all sure whether that zener is 47v. I'm just assuming it to be 47v based on the color rings on it, with the help of that chart

[electricenthusiast]

No, a 21V zener would be on the borderline. There must be a reason that the original zener was 47V, but I can't understand what that could be. I would wait until you repair the circuit, and then examine the voltage between the zener's pads.

I didn't got a 21v zener, but, I connected 3 zeners in series insted of just one 21v zener. Now there is no increasing voltage problem .The voltage between the zener's pads are 21.7v .
All set
Now I can peacefully go to sleep .  Next day I will connect it to my dvd

[electricenthusiast]

After repairing the smps, when i plugged it to the dvd, after pressing the power switch, the voltage from smps just dropped like 11v ever to 7.11v , 8.8v to 4.9v and so on. Is there any problem with the primary high voltage part ?