Burned out Power Supply

[Migs 31]

Hi there,

One of those cheap multiple voltages Wallwart PS made its way to me.
Apparently it was used on a Guitar Pedal at 9V, wrong polarity (simple change of connector side).
And the Magic White smoke came out, but was disconnected quickly by the Metal Head operating it.

I open it up and I can see a big 1 Watt or 2 Watt resistor is fried on the surface.
I measured it and it reads around 1.895 KΩ. in circuit.
Is it safe to Ass-ume that a partially fried Resistor will still keep it's resistance?
Is it safe to replace with a similar 1.8K resistor or should I go up to 2K ?!?
Or take it out of circuit and re-measure?

Please don't ask me for a schematic, I doubt any company would ever post a Schemo.
of this State of the Art Multitap Variable El Cheepo.

What do you think? Any advice?
Kind regards
M

 

[JohnRoberts]

With simple circuits like that you can trace out a schematic to help understand what is going on. Original resistance may be much lower than 2k...

JR

 

[Migs 31]

With simple circuits like that you can trace out a schematic to help understand what is going on. Original resistance may be much lower than 2k...

JR

Thank you JR,

I took the burned resistor out yesterday. It now reads 2.4/2.5K .

When burning out/degrading, is a resistor more likely to go up (closer towards open) or more likely to go down in value?
I try tracing a quick Schemo. to understand more, when I have time.

PS: Ok, scratched the burned surface and it went from 2.4K to 2.7K then 35K then to open circuit

Thanks.
M

 

[JohnRoberts]

There is no predetermined pattern of resistor degradation for all resistors. Some recover close to original resistance when they cool down. Some are designed to open up like a fuse.

If you scrape off the carbon film there is less conductive media and the resistance will increase.

JR