Need Help Identifying This DIODE mounted on a Frigidaire oven control PN:316131600

[DennisH]

This diode is mounted on a Frigidaire electronic oven control PN:316131600. This diode runs hot enough that the PCB is showing slight burn marks (black soot looking area on PCB above the diode). It looks to me to be coming from the body of the diode.

The oven control is 22 years old and still works, but I can't get a new replacement, so I'm doing preventative maintenance and replacing a few parts on it that I think could fail - and this is one of them.

Can any of you identify this diode (see pic) and suggest a replacement that can handle more heat - or if not, can you identify this one and tell me what to order to replace it? There is no other writing on it other than "231." It is actually very small - I zoomed in on it quite a bit.
Regards,
Dennis

[stj]

it may be getting hot because of another part - show the full board

[DennisH]

stj: Thanks for the suggestion! There are many of this model of oven control board for sale on eBay. All of them show this diode and a TO-92 size "78L08" IC appear to run hot and cause "scorch" marks on the PCB. Mine is has fainter scorch marks, but these marks are there only at these two component locations. I don't think my oven control has a bad part (yet). It still works fine. I'm trying to prevent it failing if possible by replacing these two parts that appear to run hot. I ordered the 78L08 IC from Mouser as well as a TO-92 heatsink. What I want now is to get a beefier version of that diode that can handle the heat better - or maybe put two of that diode in parallel so each shares the heat.

Next is a picture from eBay of one of these same oven control boards. I put two red arrows so you can see where these parts are and you can see what looks like scorch marks above. This one looks like the entire board overheated (notice the coating on the transformer looks like it reflowed). Mine is nowhere near this bad, but it does have fainter marks in the same 2 spots.



Next is a picture of my oven control board. You can see the same two scorch marks.

[petehall347]

5.1v zener ..measure voltage across it to confirm

[DennisH]

Are you sure it's a zener diode and all I have to do is measure the voltage across it and buy one with that same voltage?

Thanks

[petehall347]

i am not sure of anything but measuring the voltage might make me somewhat sure or not .

[eccerr0r]

If the zener diode failed, you won't get a voltage, it'd (usually) be shorted.
If you get a voltage then likely it's still good unless it's open...

[mon2]

Coming to the same conclusion, 5v1 zener.

Part # 1N5231B looks to be a match. Onsemi at Digikey is available.

[redwire]

I agree it's a 1N5231 zener 1/2W 5.1V
They're not scorch marks, it's just soot buildup on the board due to convection air currents around hot running parts, after many years. It would wipe off or a q-tip and IPA can clean the board.
The diode is not easy to cool as most of the heat is dissipated through the leads to the PC board. Even putting in a 1W part it would run near the same temperature.
For the age, I would replace all the 6 electrolytic capacitors esp. CapXon ones.

[DennisH]

Originally Posted by redwire

I agree it's a 1N5231 zener 1/2W 5.1V
They're not scorch marks, it's just soot buildup on the board due to convection air currents around hot running parts, after many years. It would wipe off or a q-tip and IPA can clean the board.
The diode is not easy to cool as most of the heat is dissipated through the leads to the PC board. Even putting in a 1W part it would run near the same temperature.
For the age, I would replace all the 6 electrolytic capacitors esp. CapXon ones.

Thanks for the tips. ALL 6 of the caps on this control board are CapXon. I will try to find replacements.

I think I'd rather replace that diode with one that is 1 watt. Can you help me find the 1 watt version.

Here's a link to the original .5 watt diode:
https://www.mouser.com/datasheet/2/3...04-1917989.pdf

And here's a link to what I think is a 1 watt equivalent:
https://www.mouser.com/ProductDetail...UnYSfA8g%3D%3D

Did I pick the correct 1 watt equivalent? If not, can you help me find the right one?

Also, the "soot" did come off with IPA and a q-tip - thanks for the idea.

Thank you!

[sam_sam_sam]

Would it be possible to use a 7805 and modify the circuit slightly would this be a better I just asking the question

[DennisH]

Originally Posted by sam_sam_sam

Would it be possible to use a 7805 and modify the circuit slightly would this be a better I just asking the question

I'm going to stick with the 7808 (I already ordered a couple new ones) and try getting a 1 watt equivalent diode - but thanks for the idea.

[petehall347]

use original diode wattage . stand it up off the board a bit if you are worried it might get hot .

[DennisH]

Originally Posted by petehall347

use original diode wattage . stand it up off the board a bit if you are worried it might get hot .

Why not upgrade to higher wattage?

[redwire]

There are two issues with using a higher power zener:
It's leads are fatter and will likely not fit the PC board holes, it's also longer.
It's voltage rating (5.1V) is spec'd at a much higher test current and a circuit operating it at less will end up with a lower voltage. So you'll get less than 5.1V operating and I'm not sure what it's doing in the circuit, what say 4.9V will affect. It could provide filament bias for the VFD display.

For a component to run cooler, you need it to be physically larger (more surface area) and thicker leads for better heat conduction to the PC board pads.
If the part worked for 22 years I don't think it's stressed in a bad way. The capacitors are the components that fail the most.

5.1V 1W 1N4733A is at 49mA, 5.1V 0.5W 1N5231B is at 20mA.

[DennisH]

Thanks Redwire - I will stick with the original diode size and raise it up off the board a little. Thanks everyone else who responded to my post.

Can I get help from one of you in picking replacement caps? I don't know if it's as simple as getting one with the same voltage, temp rating and farad rating as I see choices like "Audio Quality" or "General Use" and the cap details talk about different ripple current ratings - which I don't know anything about.

If you can help me find replacements, here's pictures of the caps and last, a picture of the entire board.

The first pic shows one cap, but there are two identical ones on the board (side by side).
Here's the pic: https://www.dennishunt.com/CAP12.jpg

Here's the second pic (there are two identical caps like this): https://www.dennishunt.com/CAP3.jpg

In the third pic, I'm show two different caps that are mounted side by side. Here's the fourth pic: https://www.dennishunt.com/CAP56.jpg

Last, here's the entire board pic: https://www.dennishunt.com/BOARD.jpg

Thanks!

[stj]

0.47uf is obsolete,
i would use a 470nF 63v polyester/polypropylene film cap

the larger caps, i would use panasonic FR series.
if you can get them cheaper then rubycon ZL are also good quality

[redwire]

I can make a list. What value is C3? U4 is a 78L08?
For appliance repairs, I am using Chemi-con, Nichicon, Panasonic, Rubycon long life 105°C rated capacitors purchased from a decent distributors like Mouser or Digi-Key to avoid fakes. eBay etc. is pretty much all counterfeits.
Long life, these can be little larger size (lead spacing, diameter) and the component shortages is making some hoops to jump through.
I wonder if Badcaps should kit some of these values.

[DennisH]

Originally Posted by redwire

I can make a list. What value is C3? U4 is a 78L08?
For appliance repairs, I am using Chemi-con, Nichicon, Panasonic, Rubycon long life 105°C rated capacitors purchased from a decent distributors like Mouser or Digi-Key to avoid fakes. eBay etc. is pretty much all counterfeits.
Long life, these can be little larger size (lead spacing, diameter) and the component shortages is making some hoops to jump through.
I wonder if Badcaps should kit some of these values.

C3 and C10 are identical, and are 100uf, 16V, 105 degrees C, about 1/4" dia.

C4 is 470uf, 25V, 105 degrees C, about 3/8" dia.

C5 is 1,000uf, 25V, 105 degrees C, about 1/2" dia.

C13 and C14 are identical, and are 0.47uf, 50V, 105 degrees C, about 3/16" dia.

I'd prefer the best caps I can get, and only from good sources. I can compensate if the size is a little different or lead spacing isn't the same.

Yes, U4 is a 78L08. I am going to replace it at the same time and found it on Mouser here: https://www.mouser.com/c/?q=L78L08ACZ

Thanks very much for your help with the caps.

[stj]

you need to include the diameter