Fender Princeton 65 DSP Problems ???

[Jason]

Hi,
I just recently registered and have a few problems with my amp that I was hoping to get addressed:

1. This amp has 2 channels. I notice that while playing on the CLEAN channel, there is a background distortion (as if the speaker is playing the clean channel loud and the drive channel low) due to the DRIVE of the THE DRIVE channel.

2. There is a slight hum that is louder than most other solid states I've played

3. NEWEST problem: Lately my amp has been cutting out and making that farting noise or sometimes cutting out. AND for some reason, if i smack the amp on the side it goes away (some times).

Any feedback/response would be greatly appreciated

[Twist]

Here's a couple of possibilities. Is your reverb working? On some solid state amps with op-amp driven reverb trays you can hear a small distorted noise in the background while you strum the guitar if the reverb tray is disconnected or the tray is faulty. I've come across this a few times. Another cause may be a problem with your speaker. If you haven't already, try a different speaker.
As far as the hum, do you still hear it if you turn all the controls down? One of the two main filter caps may be breaking loose from the PC board. This may also be causing the distorted noise.
I would pull the PC board out and reflow any cracked or questionable solder joints.

[Jason]

heyy,
Yeah I'm pretty sure the REVERB is working. The DSP uses a chip with some sort of wide thin computer cable. Also, the HUM is there a little when all the knobs are turned down. I guess i would have to check the solder joints..

But, I'm really confused as to why the clean channel has the slight background noise of the GAIN channels when the gain is up on the drive channel. I figured the switch from channel 1 to channel 2 completey isolated each channel separately???

[Twist]

Duh !!! I didn't realize you had digital reverb. Go ahead and check your solder joints and while your at it make sure your "return jack" on the effects loop and "power amp in" are making good contact (if the amp has either one).

[52 Bill]

The channel switching in this amp is done with fets. If there is bleed through of the distortion channel, there may be a problem with the switching circuit, one of the fets, or the power supply.

Seeing how you also say the amp is humming and that it sometimes responds to physical input (thumping), I'd first look at the power supply. Do as Twist suggested, and check the filter cap solder joints, etc. Make sure that the voltages are all up to the levels shown on the schematic, etc.

Next, check the channel switching circuit voltages to see that they are changing as they should, and that they are getting to the gates of the fets.

Then check the fets themselves. The fets work just like switches and are wired to allow the signal to pass or to ground out the signal. If you trace out the signal paths from the schematic you should be able to tell what signal path should be grounded and what signal path should be connected when each of the channels is activated.