Fender Chamion DSP 30 Channel 2 has no volume control

[GuitarJones]

Hello,
This is the second Fender amp that has had problems for me. The first is a champion dsp 30, when channel 2 is switched on, both 1 & 2 volume has no control, the only control is by turning the gain down on channel two. Channel 1 works fine alone. Problem in the DSP card?
The second is a fender fm25 dsp, it has no out put, only when I freeze the dsp card. Is there anywhere I can get a replacement card for each... anyone know?

[Enzo]

Hi, welcome to the forum. If you are just asking about DSP cards, I'd say contact Fender and ask them if they are available as a part and what list prices might be, and ask the part numbers to order. Then any Fender dealer or partseller can get them - if available.

If you need repair assistance, please start a thread for each amp. It gets real confusing trying to fix two things at once in the same thread.


Champion 30 DSP: Look at your schematic. As far as I can see, the DSP card has no way to know what channel you are on. The channel switching is all analog back at the input stages. Your signal comes into U1a, then branches into the two channels. JFETs Q1 and Q2 then are turned off and on to select which branch gets to pass. The two branches then rejoin at U3a. I suspect you have an issue with those JFETs.

If I had to test that, it appears to me that on the DSP card connector, the top left pin (on the schematic, I have no idea which way it faces on the board) is the signal into the card, and the top right is the output from the card back to the amp. Looks like we could remove the card and short those two pins together to bypas the card. And teh amp should work. I see no way for the DSP card to affect which volume controls work.

FM25 DSP: If the amp is silent, but passes signal when you freeze teh card, then the card is involved, and may be bad. But before replacing it, make sure the +5v fed to it is 5 and not higher. And I cannot see where the 3.3v comes from offhand, but it seems to appear at two pins on the card header. Verify that is 3.3 and not higher. The card could be running hot from excess voltage.


The two DSP cards do not appear to be the same.