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Zener diode?

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simon1979

New Member
Hi all, I'm new here and would like some help. I have a PCB board off an appliance. I've noticed a zener diode(?) Is damaged. Does anyone know what value or number it could be? Hope the pic is clear enough. The damaged one is on the right Thank u. IMG_20161122_195909_230.JPG IMG_20161120_205155_785.JPG IMG_20161120_205155_785.JPG IMG_20161122_195909_230.JPG
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Zener diodes usually have their voltage printed on the casing, so a blurred picture without any writing on it offers no clues.

A picture of the entire board might offer some clues?, as would knowing what the zener actually does?.
 

simon1979

New Member
I can't see a single thing printed on them . I can put a whole pic up of the board. A new PCB from aga/Rayburn is nearly £700!
 

DerStrom8

Super Moderator
Most Helpful Member
Why such blurry photos? It's not that difficult to hold a camera still. Set it on something if you have to, but the pictures you are providing are not helping at all.
 

cowboybob

Well-Known Member
Most Helpful Member
Welcome to ETO, simon1979!

Tough PCB to find, but:

upload_2016-11-22_17-40-18.pngSource: https://www.aga-spares.co.uk/index...._id=1315&virtuemart_category_id=76&Itemid=495. A Rayburn "Sequence Controller".
No schematic that I could find.

But from your pix, the diodes have been, obviously, carrying quite a lot of current. But few traces. Maybe zeners in series?

Could you get a good, focused pic of the underside of that section of the PCB to help us see how they're wired?

As for replacing them, and if they're zeners, I suspect that they're all the same value/type. What value may be tough to determine.

<EDIT> Also, see this: (400G/L PX (PF): http://www.rayburn-web.co.uk/Prodin...urn 400GL PF instal 08-13 EINS 512531 (2).pdf - page 18.
 
Last edited:

pfofit

Active Member
Howdy.
What makes you think they are Zeners. Elsewhere on the board, red circle, there is a zener clearly marked as zd1.
They're not always labeled zd but if there is one marked zd then i would hope any others as labelled the same.
Also what is all that stuff everywhere, it might be conductive ? Is it just dust? Looks like corrosion or carbon.
What environment is it in? Either way needs to be cleaned up

Cheers
123.JPG
 

JLNY

Active Member
Maybe I'm completely wrong on this, but I'm not sure I can see any polarity markings on D4 or D6? Are we sure they aren't surge protection diodes of some kind?
 

cowboybob

Well-Known Member
Most Helpful Member
Maybe I'm completely wrong on this, but I'm not sure I can see any polarity markings on D4 or D6? Are we sure they aren't surge protection diodes of some kind?
Could be. Odd that they're stuck off all alone the way they are.

And the heat signatures around them certainly indicate a lot of heat.
What makes you think they are Zeners. Elsewhere on the board, red circle, there is a zener clearly marked as zd1.
Good catch, pfofit.

So, anyway, could use a pic of the underside for the traces. Might at least show how they're wired. Need a really close look at the the "diodes", whatever they are.
 

DerStrom8

Super Moderator
Most Helpful Member
What are the wires coming out from beneath the diodes? What do they go to?

I expect these diodes are, indeed, some sort of protection diode, be it TVS (transient voltage suppressor) or even just flyback to protect against voltage spikes when an inductive load switches off.

That whole board needs a good cleaning. Get some isopropyl alcohol and a stiff-bristled toothbrush to clean it off.
 

simon1979

New Member
Yes will give a good clean. Tha nks for all the replies! I'm beginning to think I've rub markings off the diodes! And they are diodes not zener diodes! Will get a pic up later of underneath the board. I'm think the other diodes away from the area in question are the same type. They have 3 bands on them.
 

Scott Marshall

New Member
Have you actually tested them? They may be OK, just dirty.
I'm familiar with Rayburn (er) systems, and they are usually oil or gas industrial heat exchanger burners. (I spent a few years in a potato chip plant as plant engineer, and subsequently have run an industrial controls business)
The oil burners especially produce so much "gunk" it's often attracted by electrostatic charge and will occasionally make components look burned when they are in fact, only dirty. The pattern around the diodes looks like this effect.

I've seen a pair of series diodes used as a flame out indicator before as well, and wonder if that may be the case here. (they react rapidly to temperature changes). Does that board tab face the burner thru an opening in the burner box? If so that may be the function of the diodes. Rayburner always held onto old tech way past it's prime, as the diode flame detector was a very 1940-50s kind of technology. Then again I could be totally wrong with that assumption...

Hope I helped a little...

Scott
 
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