Sunn Beta Lead Footswitch Issue

[EastCoastRocker]

Hello Friends.

I just dug up a beta lead foot switch, and I have an issue:

Although both channels of my Beta lead work fine from the amp itself,(red,green,or both depending on what input I plug into) When I hook up my footswtich, it will only turn on the RED channel or the BOTH CHANNELS selection, but won't switch to just the green channel.

Does anyone have any experience with this?

Thanks.

[george]

I'm assuming you can manually switch between channels and the issue is with only the foot switch?

[EastCoastRocker]

>I'm assuming you can manually switch between channels and the issue is with only the foot switch?

Correct.
All channels work as they should by plugging a guitar into the corresponding input on the amp itself.(green,red,or both)

When the footswitch is installed, The footswitch will allow operation of both channels at once or the red channel itself, but it won't switch to the green channel.

[loudthud]

When the footswitch is installed, The footswitch will allow operation of both channels at once or the red channel itself, but it won't switch to the green channel.

So are you using the Both input when using the footswitch?

[EastCoastRocker]

>So are you using the Both input when using the footswitch?

Yes.

[george]

I'm doing this from memory - I believe there are two diodes on the red LED leg and just the LED on the green circuit. Do both red and green LEDs work?

[EastCoastRocker]

>I believe there are two diodes on the red LED leg and just the LED on the green circuit. Do both red and green LEDs work?

Thank you so much for your reply. I'm playing a guessing game, but I think I know where you're going with this..... I quickly scanned the schematic notes, and saw that the switching logic gets it's "state" from a voltage drop across the LED's in the footswitch. So I was thinking that maybe the voltage wasn't getting through the green LED. I hadn't even thought about the diodes, I'm not that smart! (wait a tick...LED's are diodes! LOL)

I'm not sure about the footswitch circuit. I don't have an original schematic for that, just the DIY one. I can open it up and look at the layout if you tell me what to look for.

I'll test the switch tonight, but from memory, the green LED on the pedal itself does NOT work, but the red and yellow do. Would a bad green LED cause this type of thing?

I'll post again later once I look. All  help is GREATLY appreciated!

UPDATE: The red and yellow footswitch lights light, but green footswitch LED does not,
even when the amp is in "both mode". While in "both" mode, both channels work, and both LED's on the AMP light. I think you are on the right track George, where do I go from here?

Thanks, ECR.

[loudthud]

If the Red LED in the footswitch goes off, that means that the switch is working. If the Green LED does not come on, it could just be a bad LED, but the amp should still switch channels.

I have edited the schematic to include expected logic levels that you would measure in the footswitch. Note that according to the spec sheet for the chips in the amp, the logic levels from the footswitch are not guaranteed to be valid for the chips. A guaranteed high on an input is 12.5V and a guaranteed low is 2.5V when the power supply is 15V.

Edit: 2013NOV10 replaced schematic

[EastCoastRocker]

Thanks for the Schematic! I needed that.

I have the foot switch apart right now, but if memory serves me, the red light does not go off when I work the switch.
I'll have to re assemble the switch and test that.

While I have the switch apart, how can I test it ? Can I hook up a voltage supply to the connector pins and check values at the switch?
I'd rather not connect it to the head for testing. I don't want to risk anything that would damage the head. ( or is that not a concern?)

I would guess that the issue is that I'm not getting the voltage in the switch to change from -10.2 to -2.5, does that seem reasonable?

I would guess that I can check the diode with my multimeter. I seem to remember (?) that I need to remove at least one leg from the circuit to do that.
If I get continuity in both directions, it's a bad diode,correct? I can then switch to diode mode and check for value, correct?
There's not too many parts in this thing, I would think that we can all successfully brainstorm through this.

BTW, how do I get the footswitch plug apart? I want to check for loose pins,wires,etc.
Does the top just unscrew, I don't want to break it. Can you still buy those plugs from allied (or elsewhere?)

Please keep the info and suggestions flowing.

Thanks,
ECR.

[loudthud]

Working inside the footswitch is safer than working inside the amp. The only thing that could damage the amp is if you shorted the P or S lines to ground. A momentary short is ok but long term, R136 or R138 will get hot and leave a burn mark on the PCB.

If the red LED does not go off, the switch could be bad or the green LED is bad.  You can check the switch with an ohm meter when the amp is off or the footswitch disconnected. The green LED would have to be an open circuit if the switch is ok. Your ohm meter may not be able to check the LED. Replace it or connect a 100 ohm resistor (1/4W) across the terminals to check that the red LED goes off.

If the red or green LED goes on, the wiring is ok through the connector.

[EastCoastRocker]

Thanks so much for the reply, that's just the kind of info that I need.
I'll do some tests and report back.

Cheers,
ECR

[EastCoastRocker]

Thank you everyone for staying with me on this!
>Your ohm meter may not be able to check the LED. Replace it or connect a 100 ohm resistor (1/4W) across the terminals to check that the red LED goes off.

Just to clarify, I'm shorting the green LED wires with the resistor, correct?

Update/questions:

I noticed that If I exercise the channel button on the switch, the green LED comes on sometimes, but doesn't stay lit or switch channels. This "flickering" is mirrored on the amp's green LED. It may very well be the mechanical on/off switch or that connection on the plug.

Is the "normal" state for the red channel on/of fswitch "closed" , and for green channel "switch open" ? If so, I can lift one side of the on/off switch out of the circuit, and the green channel should go on, correct?

Update2:
Continuity tester indicates that the switch opens and closes like it should.
I can hear the continuity tone shut off and on as I operate the switch.
The green LED flickers, but won't change channels. Opinions Please...

[EastCoastRocker]

Good news.

I shorted the Green LED with a 100 ohm 5 watt resistor (5 watt is all I had).
The results were good, but not quite what I expected. With the resistor in place, the switch works, and not only does the red LED go off, the green LED works!

I am SOOOO exited about this. I'm guessing that the next step is to replace the green LED?
does anyone know the specification on that part?

Thanks,
ECR

[loudthud]

Your narration suggests to me that there is some kind of intermittent connection inside the footswitch. Most likely a broken solder connection or other open circuit fault like a fractured PCB trace. It has to be somewhere between ground, the switch, the green LED and to the "S" wire. Could be inside the LED. You know you have a good connection as far as CR5 otherwise the red LED would never come on. Re-solder all the connections, add a little fresh solder and check continunity of any wire or PCB trace.