How do i determine the value of a burnt resistor?

Thats right...also chck the nearby diode and opto connected to the resistor. these work together to "fire" the SCR at Q1. ;o)

jatinah
March 2016

522 ohms is an unusual value - not a regular resistor - 510 Green Brown Brown may well be easier to find.

The 1% rating allows for plus or minus 5 ohms i.e. from 517 to 527. I do not understand quite why the value is so precise - in your place I'd shoot for 510 Ohms.

Just because the old resistor was burnt do not necessarily expect a new resistor to solve the problem.

Continuing good luck...
January 2016

Thank you so much for the info. I found the value of R17 in the schematic diagram from a site, it's 522 ohms 1 % tolerance. I'll try RadioShack. Any suggestions as to where I could get this? Thank you so much. God bless!

Danny
January 2016

You could even just go OUT for a walk

XXX
January 2016

Either from the circuit schematic which you will probably not have or from the colour bands - sometimes on a burnt resistor the top is burnt but some of the colour is still visible on the underside - you have to unsolder and lift the component to see any remaining colour.

Also - just because it's burnt that does not mean that it's no longer a resistor - lift one end and measure the value.

If this doesn't work for you then take a guess - bung in something around 33K (three orange bands) and see what happens.

As for the burning - either the resistor wattage was under rated and the resistor has slowly burnt with the passage of time - or - something has gone wrong with the circuit containing the resistor and it has been subjected to a higher voltage than normally expected.

A burnt resistor does not necessarily mean a bad resistor - just that it got too hot

If you do go ahead with a new resistor you can put in one of the same resistance value but with a higher wattage rating - physically bigger- to stop the cooking.

Good Luck...
January 2016