burned resistor on old Mercedes auto-dimming rear view mirror PCB

[neverending]

Hello,

I have a 1997 Mercedes-Benz SL-320 with an auto-dimming rear view mirror that I am attempting to repair. There was a burned resistor on the board I was able to remove, so was trying to see if I could identify it so I could get a compatible replacement. The markings on it show "15Ω • J" I may need to add jumper wires to reconnect it as the mounting holes are in pretty bad shape. Not sure if it is 15 or 150 ohm, or what wattage it would be. I believe the "J" marking means it has a +/- 5% tolerance. The resistor itself is just shy of 12mm.

I am a novice to electronics, but feel confident in my soldering ability to get a new one installed. Any advice on what type of resistor I should try to find and where might be a good place to look? Thank you in advance! Here are some photos:

 

[Nigel Goodwin]

It's very clearly marked as 15 ohms, and it's a wire wound resistor, from the size, 2.5W or 3W - go with 3W.

 

[neverending]

Thank you for the help. Would this work?

mouser.com

 

[starLED]

There was a same issue someone posted long time ago:

Rear view mirror electronics smoking - PeachParts Mercedes-Benz Forum

Hi All, I had smoke coming from my rear view mirror yesterday and found a burnt resistor on one of the circuit boards (see pics) inside. It looks like

www.peachparts.com

 

[Tony Stewart]

The Caps shows signs of slight lid pressure from heat and may or may not need to be replaced but the cause of the 15 ohm R failure is secondary. The root cause may be a short in the power transistor DARLINGTON TIP122.
Just guessing. A diode test in a DMM would be useful for the transistor then test the resistor, it might still be working ( proving it was not the cause of failure) but a bit higher in value from heat stress.

So my guess is if TIP122 has any shorts, replace that + 12 Ohm 1/2W WW 5%

 

[Tony Stewart]

 

[Nigel Goodwin]

Thank you for the help. Would this work?

mouser.com

Yes, but as others have said you need to repair what caused it, otherwise the new resistor will overheat as well.

 

[neverending]

Ok, so found my digital multimeter and tested the power transistor on diode setting. Here are the results:

R1 B2 .771
R3 B2 .577
R1 B3 .889

Reversing leads:

B1 R2 OL
B3 R2 OL
B1 R3 .837

Resistor shows 72 when set to 200 ohm

If I understand correctly, there should be no reading between 1 and 3, so I'm guessing the power transistor is bad?

If so, is this a suitable replacement: mouser.com?

Better photo of capacitor here. Should I replace this as well?

Thanks again for the help.

 

[starLED]

Capacitor is bulged, should be replaced.

 

[Nigel Goodwin]

Capacitor is bulged, should be replaced.

More domed than bulged, and some capacitors are like that - however, as it's been next to such a hot resistor, and the plastic sleeve has partially melted, I would certainly replace it.

 

[Ian Rogers]

When I worked at AUDI some years ago.. the reason resistors burnt out was the elements became corroded and used tons more current
The big one was the internal heating fan.. Remember these things are designed to be just so. ie there is no room for maneuver.. If its a 3W resistor just work out how much current flow there is. The switching transistor ( looks like a t220 device) will also be working too hard 3W is a few amps at 12v that's if the mirror circuit is. power, element, resistor, ground.

 

[starLED]

More domed than bulged.

"Domed" not familiar word in my English dictionary, sorry, "bulged" more knowing.

More domed than bulged, and some capacitors are like that -has partially melted, I would certainly replace it.

PCB looks pretty burned, traces and pads should also be checked.
I am very shocked how it got such burns on both sides.

 

[Nigel Goodwin]

When I worked at AUDI some years ago.. the reason resistors burnt out was the elements became corroded and used tons more current
The big one was the internal heating fan.. Remember these things are designed to be just so. ie there is no room for maneuver.. If its a 3W resistor just work out how much current flow there is. The switching transistor ( looks like a t220 device) will also be working too hard 3W is a few amps at 12v that's if the mirror circuit is. power, element, resistor, ground.

Yes, it's not got that hot without something causing it - that needs sorting before changing the resistor.

 

[neverending]

Ok, so I should replace these components (transistor, capacitor and resistor), correct?

If so, are these the correct items?

Transistor:
https://www.mouser.com/ProductDetail/STMicroelectronics/TIP122?qs=ljbEvF4DwOPuWPwhe20bIQ==

Capacitor:
https://www.mouser.com/ProductDetail/Nichicon/UKW1J101MPD?qs=kArNe9LFxXk23csYyqnfAw==

Resistor:
https://www.mouser.com/ProductDetail/KOA-Speer/MOS3CT631R150J?qs=%2BP4npbOQ5kUy%2BGnKLyltTA==

The traces are pretty bad, so my plan is to put jumper wires going to where the traces lead.

Again, I am a total novice, so all help is appreciated!

 

[Ian Rogers]

What we are saying... the resistor has cooked... replacing it will work but will be short lived.. the device the resistor / transistor is supplying is worn and no longer efficient, the resistor will burn again.