Mark IV, FU-3 Lead Channel not Switching

[Rick Finsta]

Okay, I've got a used MkIV (I've had for like ten years) and I'm finally looking into getting an issue fixed. Since I always run EQ on the lead channel I didn't really care until now but here's the skinny:

The switch works for all functions except for Lead. If switching to Lead, the amp goes silent. Rhythm 1 and 2 both work, as does the EQ in/out and the loop in/out. The Lead/EQ works as well, only the Lead button switches on the pedal but then puts the amp in some sort of null state (none of the channel LEDs on the amp are lit after selecting Lead on the pedal).

The FU-3 footswitch changes LEDs and all the IC tests work out, so I don't think it is the footswitch.

I've got another issue with the Recording out not working so I was going to take into a local Boogie tech anyways, but since I build circuits and such as part of some of my hobbies, if it is as simple as poking around with a multimeter and desoldering/soldering some components, I'd rather do it myself.

I'm going to call Boogie today to see what they say as well. I noticed Blueracer, who posted the information I've followed so far, hasn't been active on the board for about two years, so if anyone else can help me out I'd really appreciate it.

Thanks in advance!

 

[Markedman]

There's an alternate 1/4" foot switch spot on the back of the amp where you can use a regular foot switch to test it out. It will help narrow the problem down anyway. Also, what happens when you unplug the FU-3 foot switch and turn the knob to lead?

 

[Rick Finsta]

No matter what channel is selected when the footswitch is plugged in, when I unplug it the amp goes to lead w/ EQ (amp on and in standby mode). With the footswitch plugged in or unplugged, the channel select knob on the back works. Footswitch plugged in or unplugged, if the external switch position is selected, the amp goes to the "null" state.

If I plug a 1/4" cable into the lead switching jack on the back (I don't have an on/off footswitch but since it is logic level I figure it is safe to just use a 1.4" cable and a screwdriver - well actually a BCM firing pin for an AR-15 but whatever) and then select the external switch mode on the rear selector knob, it goes into the "null" state, but then shorting the 1/4" cable activates the lead channel. The same is true with the other channels - the external switch position defaults to the "null" state and then shorting a cable that is inserted into any of the selectors activates that channel/option.

Hope that's helpful!

 

[Rick Finsta]

Any other ideas? Otherwise I'm taking it in to see Jonathan Blick tomorrow or Friday...

I hate paying to get such a simple device fixed after building an ECU for and wiring a race car... :?

 

[Rick Finsta]

$47 and less than 24 hours later the switching issue was just a single resistor and the recording output was just poor contact in that circuit. 8)

New tubes came today, too... :twisted: