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Post subject: problems with 4 button footswitch Twin amp
Posted: Thu Jan 17, 2013 4:32 am
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Hi all,

I have some problems with the 4 button footswitch schematic of the pro tube Twin Amp: http://support.fender.com/schematics/gu ... ematic.pdf

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I have build this footswitch because the guy that sold me the twin amp couldn't find it anymore. But it is not working, I'm pretty sure it's build the right way (I'm using a guitar cable to connect it). A technician here at work is sure the schematic is wrong.

Does anybody know what could be wrong? Polarity of all the diodes are correct, I'm using latching footswitches. Can anybody maybe explain the working of the footswitch?

If anyone has a picture of the inside of the original, it would be appreciated.


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Post subject: Re: problems with 4 button footswitch Twin amp
Posted: Thu Jan 17, 2013 5:39 am
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Don't want to sound too negative here but if you built it yourself and you don't understand how it works, that's really not a strong indication that the schematic is wrong. It's very rare that a manufacturer leaves an incorrect schematic on the internet.

When you say it's not working, what exactly is it doing or not doing? Have you checked all the voltages specified at the test points on the schematic? Those are a good way to quickly find where a fault lies.

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Post subject: Re: problems with 4 button footswitch Twin amp
Posted: Thu Jan 17, 2013 5:47 am
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I can follow a schematic and build it without really understanding how it works :p
I've made dozen of (working) guitar pedals without really understanding them, hehe..
It's just that one of the only decent technicians here at work is convinced the schematic doesn't serve a purpose.. That's why I want to know how the pedal works to achieve the channel/effect/.. switching.

*Edit: When I connect the footswitch, the leds don't light up.. switching doesn't work..
Btw: I don't see any voltages on the footswitch schematic?


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Post subject: Re: problems with 4 button footswitch Twin amp
Posted: Thu Jan 17, 2013 7:24 am
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*pictures removed*


Last edited by slowrider on Thu Jan 17, 2013 1:59 pm, edited 1 time in total.

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Post subject: Re: problems with 4 button footswitch Twin amp
Posted: Thu Jan 17, 2013 10:33 am
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slowrider wrote:
I don't see any voltages on the footswitch schematic?


The schematic's full of labels like this:

TP51
CH1: -15.2VDC
CH2: +14.7VDC

"TP" means "Test Point"

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Post subject: Re: problems with 4 button footswitch Twin amp
Posted: Thu Jan 17, 2013 12:03 pm
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But these are all from the amp schematic, not the footswitch part..

Anyway I got it kinda working :) Switched the black wire from the jack to the unused lug on the jack.. Now I can switch channels (led works), I can switch tremelo (led works) but channels switches to drive when I switch tremelo on... I can switch the effect loop when the reverb is in off position (then effect loop led works).. Turning on reverb does nothing (reverb led doesnt light) and effect loop (and led) turns off.


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Post subject: Re: problems with 4 button footswitch Twin amp
Posted: Thu Jan 17, 2013 1:56 pm
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Ok fixed :) Had an orange led for the reverb instead of a red one, the cause of all the problems :x


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