Resistor Identification Help

[Mosquito]

Hi, I am trying to repair my Guitar Amp. I have discovered this burnt resistor but cannot identify it as the colours have changed or burnt off. Any help?

Further info:
Reverb stopped working after a fall. and Amp only produced buzz when reverb knob turned. (spring reverb kind) it made a heck of a noise as the spring reverb does when it's bumped. I assume this must have shorted or something and burned this resistor out. Everything else on the board and reberb circuit seems fine, just this resistor. I cannot locate any information or schematic on the amp as it is a discontinued brand and from korea. Everything else works fine.

 

[Mosquito]

Sorry for the quality of the picture, and I am unable to provide a better one as I removed it and all the coating came off.

 

[jpanhalt]

Are you referring to the big resistor or the little one with glare from the flash that obscures any chance of reading the color code?

John

 

[edeca]

Two things to think about. Firstly when something blows like this it might have done damage that you can't see to other components. So you might replace the resistor and it still doesn't work.

Secondly think about the component in context. It could be a super critical 1% resistor with a tiny temperature coefficient that controls something excatly. Or it might just be ballast, there to load down another part of the circuit enough so it works.

Consider the difference between:

- a resistor that controls an LED, replace it with something similar and it will be slightly brighter or dimmer
- a resistor as part of a critical tuning circuit, replace it exactly or it wont work!

So with that in mind, can you sketch out a little bit of the circuit? What does the resistor connect to? Imagining the circuit as a series of functional blocks, what do you think that block is?

 

[colin55]

I cover this in my eBook <snip: spam link>
All you have to do is scrape away the paint and measure between one end and the spiral track on the resistor. Then do the same with the other end. Add the two together and allow for a small amount for the part that has been vapourised. This will give you a value as close as you will ever get.

 

[Mosquito]

thanks for your assistance with this, i appreciate it!

yeah I saw that Colin, but couldn't get it to work right no matter where i put it on the resistor, kept giving me a .88K (even when making contact from both ends maybe it's my multimeter or i'm not doing it right... and am i right in saying that the multimeter shouldn't pick up anything from the body on the resistor i.e only from the spiral?? cause it seems to?.?.

In closer inspection i suspect this resistor has nothing to do with my reverb issues, .. It appears this resistor is in series with a capacitor (green next to the resistor in the pic) [yes john the small one in the middle with the two burnt lumps on each side] it creates a bridge between what appears to be a common ground and the positive line between the transistor and the speaker (the speaker wire point on the board and a prong on a transistor. looks like this: common ground - capacitor - resistor - positive speaker line...I'll try to sketch it up... it seems weird to me to bridge across like that, but my knowledge is only basic

the lumps on each end of the burnt resistor were scorched- and i could only make out two bands in the middle which appeared to me to be white and gold?!?(seems wrong maybe it's orange).. after i removed the resistor on the underside on one lump was what appeared to be a gold band.

 

[DerStrom8]

I would desolder it from the circuit and see if you can measure the resistance with a multimeter. If it's broken, the full 360 degree view around the resistor might show the bands a little better. If it does work, or if you can see the bands correctly, just re-solder it (or the replacement) to the board. It's worth a try, anyway.
Good luck!
Der Strom

 

[4pyros]

Have you looked for a schematic for your amp? Or maybe someone has the same amp. The problem is that resisters dont just blow and you may have other problems like a bad transister that burned the resister. You may what to check your outputs.