Tweet
On the two burned resistors: the cheap zener shunt regulator strikes again.
This seems to be the standard way to provide for opamps in an amp like this, and it quite often provides for charring of the PCB and sometimes outright failure.
The simplest way to fix it to better than new is to put in higher wattage resistors and space them up off the PCB. Same-value resistors will dissipate the same amount of heat, but the bigger bodies of a higher-wattage resistor will spread it out so the surface temperature is lower. Spacing it up off the PCB reduces the surface temp at the PCB by the inverse-square law for the radiated heat.
A technically more elegant way is to replace the resistor/zener with some way to get a series regulator in there. I've satisfied myself that the reason they didn't use a three terminal regulator in there is that the input voltage is too high, and zeners are cheap.
This seems to be the standard way to provide for opamps in an amp like this, and it quite often provides for charring of the PCB and sometimes outright failure.
The simplest way to fix it to better than new is to put in higher wattage resistors and space them up off the PCB. Same-value resistors will dissipate the same amount of heat, but the bigger bodies of a higher-wattage resistor will spread it out so the surface temperature is lower. Spacing it up off the PCB reduces the surface temp at the PCB by the inverse-square law for the radiated heat.
A technically more elegant way is to replace the resistor/zener with some way to get a series regulator in there. I've satisfied myself that the reason they didn't use a three terminal regulator in there is that the input voltage is too high, and zeners are cheap.
Comment