>From Ray (08.2000)
Fix for TubeFex motor/pot "chatter" problem

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If you're encounter that annoying "chatter" from the motor/pot when changing presets on your TubeFex, there is a possible fix for it. The following applies to any versions before v1.5. 

Also, when you upgrade to v2.0 from one of these older versions, the "chatter" may be more noticeable due to some needed programming changes that control the motor/pot movement.

If the following fix does not eliminate the "chatter", then you may need
to change out the motor/pot assembly. Since this is beyond the scope of 
this text, I would suggest getting in touch with Peavey's Service Department, or taking the unit to a qualified technician.

THE FIX:

It's simply a matter of changing out one resistor!

If you feel comfortable with working on your own unit, I'll explain the process. On the other hand, if you are not familiar with working on PCB's and doing clean soldering jobs, do yourself a favor and take it to a qualified technician.

Also, you'll have to do some disassembly to get to the bottom of the board to solder. The part certainly won't cost much, and the labor shouldn't be much. A qualified technician should be able to perform the modification within a half hour.

So, to accomplish the task: First, locate the resistor in question (R1431).

To do so, take the top off of the unit and have the front facing you. Look over near the right/front of the circuit board. Locate the (3) large capacitors. These are parallel (vertical) and glued to one another. From the middle capacitor, follow straight down (toward the front). You should see a diode and then (2) resistors all in parallel (horizontal) to each
other. The resistor in the *middle* is the one to change out. (R1431)

Change that resistor to a 1.3k ohm 1/4 watt. The existing one should be a 1.8k ohm 1/4 watt. 

Note: If you have a unit that you bought used, you might want to check first to see if the resistor change has already been made. It'll save you some time and trouble. Also, there is an alternate fix from Peavey. It involved soldering a 4.7k ohm 1/4 watt resistor in parallel with 1.8k ohm.

If you find you have the correct resistor(s) in place, then there is something else wrong with the unit. See a qualified technician.

Unfortunately, the bottom of the TubeFex doesn't come off. So, you'll have to attack the situation from above. You may wish to remove your tubes before starting so they don't get damaged.

Remove all screws from the bottom. These hold the circuit board to the case. Remove the screws located on each side of the back of the unit. There are (2) on each side. Remove the (2) screws/nuts holding the heatsinks on the right/front side. Unplug all of the ribbon connectors and pull all of the knobs off of the front pots. You should now be able to *carefully* pull the entire circuit board up from the back to get underneath.

If the board doesn't come up easily, you've missed a screw somewhere. Double check and try again. Do NOT force the board. It should come up with little resistance.

Anyway, there are two short wires (red and black) that are soldered to the board and to the front display unit. You'll have much better and easier access to the bottom of the board if you unsolder these two wires from the main circuit board. Be certain to remember what order they were in, so
you can solder them back properly when done.

Carefully remove the old resistor from the board and solder in the new 1.3k ohm. Take your time, and do a clean solder job!

Now, reverse the procedure to put the unit back together. Make sure you resolder the red and black wires, plug all ribbon cables back, and get all screws back in place and tightened.

That's it! Turn the unit on, and hopefully you'll have the same good results I did.

If you're fairly proficient and comfortable with working on electronic equipment, it shouldn't take much more time to actually perform the procedure than to read the above explanation.

I hope this helps some of you. Good luck, and please post your results on the TubeFex list or Peavey forum when you've done the modification.