Can I fix this circuit board? Resistor ID help.

[drnickriviera]

So the garage door open for my shop went out. Does nothing, no lights or relays clicking. Open it up to find this:

Built in 97' and I can't find any used boards for sale. The U7 is a KA317 voltage regulator. I don't know what the resistor is. It reads 30.2 ohms, but that doesn't seem to match the colors. Plus i can't even tell what the colors really are. Does a resistors value change if it is overheated? What wattage would it be rated for? Anyone think if I replaced those 2 parts, that may fix it?

 

[Red Squirrel]

I would measure it out of circuit, by measuring it in circuit you are reading whatever it may be in parallel with as well. It is quite possible it burnt out and value changed or it open circuited as well. It may be the regulator that blew too. Resistors don't tend to fail on their own.

I think those yellow things are tantelum capacitors, if they are I would check all of those too, maybe one failed shorted which caused cascading failures. They tend to fail that way.

 

[deadlyapp]

Looks to me it's banded brown, orange, black, with gold tolerance, which makes it a 13 ohm 5% resistor. Can't be more than a 1/4w or 1/2w looking at the size, but its pretty easy to get 1W rated ones.

 

[PowerEngineer]

Looks to me it's banded brown, orange, black, with gold tolerance, which makes it a 13 ohm 5% resistor. Can't be more than a 1/4w or 1/2w looking at the size, but its pretty easy to get 1W rated ones.

My guess is pretty close to this, but to my eyes the tolerance band also looks black so perhaps 13 ohm 20% resistor. But my eyes aren't what they used to be. 🤓 It is hard to judge the size, but think it is at least 1/2 watt rating.

Impossible to tell without a diagram of the board circuitry, but the KA317 spec sheet suggests to me that this could be the short circuit limiting resistor (as does the resistor's odd resistance and higher rating). It showing signs of extreme heating is something I would expect if the KA317 chip failed (around which there are also signs of heating).

Frankly, I'd be tempted to just replace a 24 year old garage door opener. IMHO the new belt drive ones are so much nicer.

But I think there is a reasonable chance that replacing the KA317 would breath new life back into it. The resistor is probably fine, although testing it with one lead lifted out of the board (as Red Squirrel suggested) is a good idea. You'll need to be careful soldering in the new KA317 (or perhaps LM317) to not let the heat travel up the leads into the core of the chip; you can use metal alligator clips between the lead and the chip to add thermal mass that should slow heat transfer to the chip.

Good luck!

 

[sciencewhiz]

Given the discoloration of the PWB, there may also be damage to the PWB.

 

[drnickriviera]

Given the discoloration of the PWB, there may also be damage to the PWB.

PWB?

Thanks for the info. I did remove the resistor and it still reads 30 ohms, but those are the colors I thought they were Brown, Orange, Black and possibly Silver. I'm just going to give it a try to see if I can get more life out of it. If this were a normal Depot/Lowes special opener, i'd just replace it, but it's a 9' door commercial opener. I shall report back with my results

 

[dullard]

PWB = Printed Wiring Board, an older term for PCB

My guess is 13 ohm, 5%, 1 W. If you are reading 30 Ohm, then it has gone bad. I thought most resistors fail with a lower resistance, but that is outside my knowledge. I'm not certain on the wattage. And since you can get 2 W resistors for nearly the same price as 1 W, you might as well go up in power rating:

https://www.mouser.com/ProductDetail/KOA-Speer/MO2C130J?qs=sGAEpiMZZMtlubZbdhIBIEXFIcKpl4X8VCyyZ6OYA00%3D

Even 3 W is cheap if it fits your size needs:

https://www.mouser.com/ProductDetail/Panasonic/ERG-3SJ130?qs=sGAEpiMZZMtlubZbdhIBINC8EtgKGA%2F6WBSBZ1jdrhU%3D

I bet U7 is bad. Voltage regulators tend to fail a lot, and there is no cooling added to that that component (where the screw hole is). The newer ones are far less heat producing, so you might as well replace it even if it hasn't failed.

Your Potter and Brumfield relay also has indications of heat in that round hole on top (it looks slightly burnt). But I can't tell if it is functional or not. Putting it right next to the other two hot components was a poor design choice.

 

[Scarpozzi]

I bet U7 is bad. Voltage regulators tend to fail a lot, and there is no cooling added to that that component (where the screw hole is). The newer ones are far less heat producing, so you might as well replace it even if it hasn't failed.

Your Potter and Brumfield relay also has indications of heat in that round hole on top (it looks slightly burnt). But I can't tell if it is functional or not. Putting it right next to the other two hot components was a poor design choice.

I concur. I'd say, if conditions were right and the door either got in a bind somehow or when up and down too many times back to back, you could have an issue where the motor drew too much current and caused excessive heat. You can also have issues on "hot parts" with solder joints that fail over time and cause arcing on the high voltage leads.

You can test the transistor to see if it's working before you replace it, but if you're going to just order the parts first and swap based on how the board looks, I'd start with the U7 and assume that the relay itself could be good or bad. Based on that, consider ordering 2 new transistors in case the relay is stuck closed and a new replacement transistor blows again. Might be cheaper than shipping it twice.

 

[Muse]

I guess I could never work in electronics because I'm color blind. BBROYGBVGW, I'm lost.

I hooked up my Insignia Blu-ray player a couple months ago and it wouldn't eject the tray. Removed cover, was about to give up and did an online search and found a forum thread where a cool guy who had the same player posted that he'd found that a large capacitor had gone bad and it had the same problem as mine. He indicated the spec capacitor that would work and I ordered off Ebay. 2 of them, because that was the best price and the brand was excellent. Didn't fit exactly, but lying on its side, I made it fit and soldered it into the circuit board. It works again! It's Best Buy's brand. I got it partly because with a certain configuration tweak and firmware version it supports Region 2, and I have some Region 2 Blu-rays. Crazy thing is it doesn't support Region 2 DVDs.

 

[Captante]

Fixing things feels good doesn't it?

Especially when the crappy companies that make this plastic junk so obviously don't want us to!

 

[Muse]

Fixing things feels good doesn't it?

Especially when the crappy companies that make this plastic junk so obviously don't want us to!

I love to fix stuff!

 

[Captante]

I love to fix stuff!

They would rather we just throw it away and buy a new one!

 

[Muse]

They would rather we just throw it away and buy a new one!

Don't I know it. I had a GF who kind of chastised me, saying "you want everything to last forever." I had no answer, but yeah, planned obsolescence has always rubbed me the wrong way. I have stuff I've fixed many many times. I had a golf pull cart, a cheapie from Costco that broke several times. I obstinately refused to buy another golf cart, but figured out a way to fix it every time. So many miles on that sucker. I finally bought a push cart... I was talked into it. It really is way better. I gave my old one to a fellow golfer.

Fixing things can be very gratifying. It challenges your creativity. Your imagination. I have my limitations, though. I don't know much about cars. Nor electronics, particularly. I have lots of tools and hardware of all kinds. My house is partly a mini-hardware store. My hoarding habits have been a big help in this pandemic. The few things I don't have I can order.