Fender Frontman 25R - Same Channel Switching problem

[nwguy]

I have had the same channel switching problem as some others who posted here. After doing my research, determined that Q1 was the culprit. Replaced it and everything worked fine....for about 1/2 hour. Then heard some scratching sounds and back to only the drive chanel. Looks like something caused the "new" Q1 to blow. Any ideas where to look now? Beginning to think this might not have been the best $20 I could have spent.

[g1]

Further down this page, under 'Similar Threads' there are 4 or 5 threads about the same type of issue for this model. Have you checked them for ideas?
And please post the schematic.

[nwguy]

Hi G1.... I have checked them out and in fact allowed me to fix it the first time. Problem is after 1/2 hour of great operation, the Q1 FET failed. Not sure why or what to do next. Schematic below

http://www.electronicstudio.net/sche...ematic_653.pdf

[g1]

Are you positive that the fet has failed and it's getting it's correct switching signal? If not, try swapping it with Q2 and see if the problem follows the fet or remains at the Q1 position.

[Enzo]

Or put another way, in what manner is the JFET failing?

A normal good JFET measures some low resistance between source and drain, then the gate acts like a diode to those.

[nwguy]

Replaced Q1 again and it is now working ok. Guess we'll see what happens

[Jazz P Bass]

One of the ways to kill a jfet is too much applied heat when soldering.
Particularly on the gate lead.

Soldering components is an acquired skill.
The tip type, the solder diameter, the tip temp & the technique all come in to play.

Just throwing that out there.