Zener Diode identification.

[Steve.B]

Hi people, I am in need of some of your helpful advice again.

I have a SMD Zener diode that is totally naff - dead short. But even with a jewelers eye glass i cannot make out any ID markings on it.

It is from a faulty Proview PL926w power/inverter board that i have had kicking around for ages. The board had 0v on the 5v output pins. I have recapped the board because most of those on it were showing signs of bulging, but that did not solve the no 5v issue.

After a bit of probing i traced the problem back to a small zener diode that sits on the 5v line, it was shorted completely. Lifting the diode from the board restored the 5v output. But obviously that zener serves a purpose, so i would like to replace it.

The diode in question is ZD203, it can be seen towards the top left in the first picture below. I got this photo from another thread regarding this board - https://www.badcaps.net/forum/showpo...90&postcount=1

I hope SBlackfoot does not mind me showing his photos.

The trace runs from one leg of the diode straight to the 5v output pins. The diode sits right next to, and in parallel with R223 and C221.

Would any of you knowledgeable guys know what voltage rating that zener is likely to be? Would that be something you would be able to guess at seeing that it sits on the 5v line?

Thanks in advance.

EDIT: It looks the same as this one on ebay, only with a black band instead of yellow. ebay linky.

[budm]

Re: Zener Diode identification.

That will be 6.2~6.8V 1/2Watts, it is used for protection in case the regulation feedback circuits go wrong and cause the output to go too high and causes damages to the 5V circuits, this will limit the voltage on 5V line not to be higher than 6.2V, normally this Zener will not be conducing due to 5V which is too low to cause the Zener to conduct. And if the output gets really high, the Zener will short out acting like a crowbar protection and cause the SMPS IC to go into shutdown mode. You probably hear the ticking sound from the transformer when this shorted out diode was in the circuits.

[Steve.B]

Re: Zener Diode identification.

Thank you budm, lightning fast response! very much appreciated.

I understand now what it's purpose is, thank you. So, 6.2~6.8v, but could you just clarify the wattage, is that 1/2 a watt, or 1 to 2 watt? Just want to make sure i get the correct replacement.

Cheers.

[jetadm123]

Re: Zener Diode identification.

I think budm already mentioned it as 1/2W.

[budm]

Re: Zener Diode identification.

That size as shown in the picture will more likely be 1/2Watt, since you have room to use axial lead diode instead of surface mounted, just solder the Diode on the solder side of the board. I would get the 6.2V one.

[Steve.B]

Re: Zener Diode identification.

That's brilliant. Thank you for the clarification. I think i have found an exact match on ebay - 6.2v 0.5w. Would you agree?

[Steve.B]

Re: Zener Diode identification.

I think budm already mentioned it as 1/2W.

Yeah, but i just wanted to be sure, he said 1/2watts, it was the watts rather than just watt that i was not sure about, thought he may have meant 1 slash 2 watts. But like you say, it's 1/2 a watt.

[mariushm]

Re: Zener Diode identification.

Why eBay when you can use Farnell or Rs-Online ?

http://uk.farnell.com/diodes-zener-single (pick 6.2v, 500mW or more, sort by price... avoid the ones available from US as shipping kills the deal)

The guy on eBay is probably buying the things from Farnell as well :

http://uk.farnell.com/cdil/cll5234b/...-5w/dp/1466634 (same diode)

[jetadm123]

Re: Zener Diode identification.

The schematic is on post #19 here:

https://www.badcaps.net/forum/showth...ighlight=zd203

[Steve.B]

Re: Zener Diode identification.

Why eBay when you can use Farnell or Rs-Online ?

http://uk.farnell.com/diodes-zener-single (pick 6.2v, 500mW or more, sort by price... avoid the ones available from US as shipping kills the deal)

The guy on eBay is probably buying the things from Farnell as well :

http://uk.farnell.com/cdil/cll5234b/...-5w/dp/1466634 (same diode)

I would do, but Farnell have a minimum order value of £20 when paying by debit or credit card, and R.S charge £4.95 for delivery. So eBay is always my friend when it comes to these one off purchases. But i would most certainly use R.S or Farnell if i needed a large amount of parts that warranted it.

The schematic is on post #19 here:

https://www.badcaps.net/forum/showth...ighlight=zd203

That is fantastic, i have looked for one of these in the past but not found one. Thank you so much. I knew that the board could be found in a couple of different monitors - viewsonic and a philips branded one, never knew about the zerox one.

[Steve.B]

Re: Zener Diode identification.

Just got to say a big thank you to you all again. The help you guys give on this forum is fantastic and invaluable for a novice like myself.

I received and fitted the zener diode that you helped me with identifying, and i now have a fully working psu board again. I have also re-capped the whole board, so hopefully the same problem will not occur anytime soon.

When that board first blew, it took out the logic board with it. I could not find the fault originally on the logic board, so i replaced the whole board. But after reading through some other threads on this forum, i took the advice you guys had given to other people and checked the voltage on the small 3.3v regulator on the logic board. Sure enough, it was only outputting 1.25v. So when i ordered the replacement zener for the power board, i also ordered a replacement regulator for the logic board. Thanks to all the help and advice on this forum, i now not only have a working psu board, but i also have a fully working logic board to keep as a spare.

So thank you once again everyone, the time you all put into this forum, and the knowledge that you share with people like myself is so very much appreciated. In the last 2 weeks alone you have helped me to repair 2 x power supply/inverter boards, a Bestec atx psu, and a logic board. All saved due to the info you guys give so willingly.

[budm]

Re: Zener Diode identification.

Thanks for the feedback and glad to see another monitor saved from going to the landfill.