Peavey Basic 112 went kaput - Help!

[xilefone]

Last night my Peavey Basic 112 broke. Below are some symptoms.

1) When I plugged in headphones to the headphone jack it made a high pitched squeal through the headphones. (frightened the cats sleeping in another room but I digress)

2) I unplugged the headphones. Now when the instrument is plugged in, there is no sound from the speaker except when I touch the strings it generates a buzzy hum. There is no correlation between the volume knob setting and the volume of the buzzy hum.

Hoping for suggestions on diagnosis, etc.

[The Dude]

Possibly a bad switching jack. Plug your guitar into the "PWR AMP IN" jack. Do you get anything? Also try running a jumper from the "PREAMP OUT" jack to the "PWR AMP IN" jack, plug in your guitar. Does the amp then work?

[nickb]

Is this the Basic 60? It sounds like the power amp could be oscillating. An oscilloscope is really the best instrument to check for this. You could try a meter set to ACV across the speaker terminals but check for close to zero DCV first. The problem with than is many meter are not reliable above 200Hz or so. If it more than a 100mVAC or so it's probably oscillating. The cause might simply be that R42 has gone open circuit. You check that with a meter on ohms range.

Peavey_Basic_60_Schematic.pdf

[xilefone]

Thank you for the reply. Yes, it's the Basic 60. I'll take a look, as best I can.

[olddawg]

Just a guess.. But it sounds like an open ground path on the input jack to me.

[xilefone]

Just a guess.. But it sounds like an open ground path on the input jack to me.

I replaced the input jack, pilfering the external speaker jack, and now it seems to be fixed.


Thanks for your ideas!