Resistor Needed

[dazzer]

Hi all, i am looking for a replacement resistor, it is blue and has, from left to right, yellow,brown,black,gold, red. i think it is 41 ohms 2%, where i removed it is an R8 underneath
i am new at this so am not sure what i am looking for as i cant find anything exactly the same.
i have attached a pic of it
thanks for your help

 

[Nigel Goodwin]

Unfortunately the resistor has overheated, so it's VERY likely that the colours have changed - and the colours you suggested make no sense?, gold is a 5% tolerance band, so wouldn't have red as a tolerance band after it. Also 41 ohms isn't a standard E24 (5%) value, or indeed an E48 (2%) value.

 

[dazzer]

Oh i see, thats a shame, then i guess i will never know, time to buy a new fan controller!,
well thank you for taking a look
cheers

 

[Nigel Goodwin]

Do you know what it actually does?, and can you post a picture of the complete board?

 

[dazzer]

I dont, but it did look quite easy to replace as i can solder a little. first picture with it in place and second with resistor removed.
its a swiftair fan controller

 

[Nigel Goodwin]

Is it just a speed controller?, are the two pairs of terminals on the left of the first picture the mains in, and out to the fan? - and what are the terminals at the other end for?.

 

[dazzer]

Apologies, it is a fan speed/temperature controller and yes one pair is mains in and the other to plug the fan in. The terminal at the other end holds the thermostat.

here is the same item on ebay
https://www.ebay.co.uk/itm/253240772012

 

[Nigel Goodwin]

OK, presumably the thermostat is simply a mechanical one?, and simply opens and closes a pair of contacts, which switch the fan ON and OFF.

This site shows typical simple triac speed controller circuits, which as you can see are pretty simple.

**broken link removed**

However, the two small electrolytic's on the board concern me - are there also electronics on the other side of the PCB?. My thought is that it's not a mechanical thermostat, and possibly a thermistor instead - and the electronics for controlling that are on the other side of the board. In which case it needs powering somehow - such as via a transformer-less power supply, using a large yellow capacitor, and a series fusible resistor for safety purposes - the one you've taken out.

In which case it 'could' be that the yellow capacitor has failed (it's a special X rated safety component), which would blow the resistor - or it's simply gradually died because it's been running too warm. Assuming the resistor is just the safety 'fuse', then it's value isn't particularly crtical - the extra band on the end could signify it's flame-proof, or it's temperature coefficient.

 

[sagor1]

Can you still measure the resistor with an ohm meter? it may not be too far off the original value. Another thought I have is that the second band is violet, which when heated a lot may turn more "brownish". That would make it a standard 47 ohm, 2% resistor.
It appears to be a "metal film" type of resistor, and though heated a fair bit, I don't see indications that it is actually destroyed. What makes you think the resistor is the problem? In many cases, where simple solid state devices are used, it is the solid state device that "blows" first.
Are there devices on the other side of the board?

 

[sagor1]

PS: A handy resistance calculator for those that don't have every color code memorized:

Resistor Color Code Calculator - 4 band, 5 band, 6 band | DigiKey Electronics

The resistor color code calculator makes it easy to identify and select resistance and tolerance values for 4, 5, and 6 band through hole resistors.

www.digikey.com

 

[Nigel Goodwin]

Can you still measure the resistor with an ohm meter? it may not be too far off the original value. Another thought I have is that the second band is violet, which when heated a lot may turn more "brownish". That would make it a standard 47 ohm, 2% resistor.
It appears to be a "metal film" type of resistor, and though heated a fair bit, I don't see indications that it is actually destroyed. What makes you think the resistor is the problem? In many cases, where simple solid state devices are used, it is the solid state device that "blows" first.
Are there devices on the other side of the board?

As I suggested in my last post, it 'may' be a safety resistor as part of a transformer-less PSU, in which case a minor change of value would have no effect - it would need to be O/C to prevent the unit working, which is probably what it's designed to do.

 

[dazzer]

hi, i have added more pictures, including bottom of board, i have also tested the resistor and i get 0.05 at 20k Ohms

 

[Nigel Goodwin]

OK, the big yellow capacitor, and the resistor you've removed, are almost certainly a transformer-less PSU, powering the electronics under the board. As the resistor reads 50 ohms, it certainly isn't fault, just slightly discoloured from running warm.

So your fault lies elsewhere, and I'm loath to make suggestions as the entire circuit is live to the mains, so pretty dangerous for someone not used to dealing with it. Repairing equipment doesn't consist of taking pieces out and performing static tests on them, it consists of performing live tests (voltages etc.) with meters and scopes, and this is particularly hazardous with equipment live to the mains such as this one.

 

[dazzer]

Fair enough, a £20 item isnt worth risking my health on. I noticed it didnt work, opened it up and assumed that because the resistor was brown it had burnt out, you live and learn. Thanks all for your input, on this occasion it seems a better idea to recycle it and purchase another.