Zener or TVS? - Page 1
Forum section: electronics / repair

author: k-krzych
author_rank: Newbie
timestamp: July 21, 2025, 05:47:10 pm
content: Hello,I have these two diodes marked 12-12 opened. Can't find any indication on what exactly they could be. The 12-12 suggests 12v Zener or TVS. But are they? Can you guys help me out to determine? For now even chat GPT can't do :-DRegards

author: Kwakerman
author_rank: Regular Contributor
timestamp: July 21, 2025, 07:49:12 pm
content: No help with the ID but they look to be in series, can you reverse engineer the PCB layout to make a circuit diagram of that area? Might help in identifying their function.

author: Harry_22
author_rank: Frequent Contributor
timestamp: July 21, 2025, 07:54:46 pm
content: Only this similar photo for BYD17K, 135 NXPPSSeems this is SMPS.Yes, some kind of reverse engineering is required.

author: k-krzych
author_rank: Newbie
timestamp: July 21, 2025, 08:47:36 pm
content: Quote from: Harry_22 on July 21, 2025, 07:54:46 pmYes I saw that photo. Also investigated NXP. It's like looking for a needle in a haystack. Seems an obsolete version of some diode.I will make some scheme in following day. Thank you guys in the mean time.

author: Kwakerman
author_rank: Regular Contributor
timestamp: July 21, 2025, 09:27:19 pm
content: Another thought, some PCBs mark Zeners as 'ZD x' on the silkscreen printing. Are there any ZD markings elsewhere on the PCB? If so then those diodes are unlikely to be Zeners (a bit of reverse logic).

author: benj38
author_rank: Frequent Contributor
timestamp: July 21, 2025, 10:37:30 pm
content: Quote from: k-krzych on July 21, 2025, 05:47:10 pmBoy, that is a tough one. Even ChatGPT is helpless. I would simply give up then!Do you really expect us mere humans to be able to do something an LLM can not?More to the point if, as suggested by @Kwakerman, you trace that part of the circuit we may be able to offer more help.

author: temperance
author_rank: Super Contributor
timestamp: July 22, 2025, 12:23:42 am
content: You will not be able to find much about those. The SOD87 package has been taken out of production long ago. My guess: Philips BZD27 series zener diode.Edit: the package has been taken out of production in 2006. An affected component list might help:https://cache.nxp.com/wcm_documents/products/eol/dn56_availabilitysod87.pdf

author: k-krzych
author_rank: Newbie
timestamp: July 23, 2025, 07:07:52 pm
content: Hello,Thank you for your answers. Help a lot. I did small schematic of the smps part. It is obvious now, that those diodes D49 and D50 are not any Zeners. Fast Recovery, Schottkey, Ultrafast? What would be your bet on it?There is another question I would ask. The D36 is shorted. MiniMelf and it has a blue band,so should be Zener. Seems that it is the for protection of base of Q20? Do you think 1.5v of the zener shoul be ok?Forgive the questions of an amatour

author: Harry_22
author_rank: Frequent Contributor
timestamp: July 26, 2025, 05:12:09 pm
content: See the purpose of zener diodes D49, D50 here:Also I found the similar self-oscillating converter.PSIt would be good to redraw your diagram in a clear form and try to compare.

author: k-krzych
author_rank: Newbie
timestamp: July 26, 2025, 09:56:09 pm
content: Quote from: Harry_22 on July 26, 2025, 05:12:09 pmThank you Harry_22 for help and advice.This is very educating. It is indeed very similar circuit. Looks like I have to make another purchase for parts :-) About the 13003, looks like I was too much in the safe side. But this was the small problem, and I was going to adjust it with trials.The big deal are those D49 and D50.I will check the pcb and my drawing for errors and rearrange the layout.