I don't know the SB-220 at all so I don't know where the subject resistor
is in the circuit. But if a 0.82 ohm 2W metal film resistor was taken out
by an event, there must have been greater than 2.5 amps flowing through it
(or, > than 2 volts across the resistor). 2.5 amps would dissipate 5W
through this resistor, and it probably would be able to take that for
several seconds before failure. Since it failed quickly, there must have
been more current than that. Replacing it with a larger wattage resistor
to "see if it keeps blowing " maybe no wiser than putting a penny in a fuse
box ( the "younger" folk here won't what that means).
What voltage and current is normal at this location in the circuit? What
would have to happen in the circuit to place > 2 volts and/or > 2.5 amps
across this resistor ?
I'm afraid that's all the help I can offer - no SB-220 experience here.
Phil
>---------------- Begin Forwarded Message ----------------
To: <amps@contesting.com>
>Date: 03/18 10:00
>Received: 03/18 10:05
>From: William L. Fuqua III, wlfuqu00@pop.uky.edu
>To: Jon Ogden, jono@enteract.com
>
>A high current transient will open a film resistor but
>not a wire wound or carbon comp. resistor. Sometimes
>a film resistor can be blasted open with no visable signs
>of damage.
>
>73
>Bill wa4lav
>
>>
>>Don't know why a 2W wirewound would have more dissipation capability than
>>a 2W metal film. I'd put in a bigger wattage value anyhow if that's what
>>keeps blowing.
>>
>--------------------------------------------------------------------------
>Jon Ogden
>
>>
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