Hello,
i have a guitar pedal that is not working. the light comes on and thats it. no sound or display in the lcd screen. i tested voltages at points on the circuit board. these points were indicating 8v which measured 6.4v, 5v which measured the same and 3.3v which is the component that is heating up. it is a lm317t. i replaced this component and the same thing happened. i am not sure where to test to find the problem. i can not find the schematic
any help or advice would be great.
thanks
simon

 

the component that is heating up. it is a lm317t. i replaced this component and the same thing happened.

So you probably need to look 'downstream' of the 317 for a shorted component which is pulling the voltages down. With the unit switched off, try a check (with a DMM on its continuity or diode test setting) of semiconductor junctions and electrolytic capacitors. You might strike lucky, but without a schematic finding the culprit could be difficult.

 

i can not find the schematic
any help or advice would be great.

Some pictures of both sides of the circuit board might help. I'd bet that it's a shorted capacitor.

 

gravy! going on the hunt now!
cheers buddies

 

So you probably need to look 'downstream' of the 317 for a shorted component which is pulling the voltages down. With the unit switched off, try a check (with a DMM on its continuity or diode test setting) of semiconductor junctions and electrolytic capacitors. You might strike lucky, but without a schematic finding the culprit could be difficult.

sorry but, downstream? so after the component, find where the component is fed from and go where the component is feeding?? not sure where this is on a lm317?

 

Here's a datasheet for the LM317:

http://www.ti.com/lit/ds/symlink/lm317.pdf

Page 4 shows the pinout.