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Post subject: Blues Jr. III fat switch problem
Posted: Wed Nov 13, 2019 7:45 am
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The FAT switch on my Blues Jr. III is inop.
Any suggestions for bringing it back to life?
Any advice is much appreciated~!


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Thu Nov 14, 2019 2:44 am
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Did Fat fonction work with pedal ?

1- If yes the issue is the Fat switch (on amp front plate) : issue are contacts or solder .

In both case you may need to open the amp and remove the circuit from the amp face and check solder/ reheat and / or spray Deoxit contact cleaner in the switch IF it is not sealed.

Don't do if you don't know what you are doing
Lethal voltage in tubes amp, and printed circuit are "fragile ".

2- If no Fat function with both pedal and switch amp mus see a amp tech. Solid state circuit ssue or if lucky solder issue


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Thu Nov 14, 2019 11:49 am
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stratele52 wrote:
Did Fat function work with pedal ?...


Yep, try unplugging the foot switch. :wink:

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Thu Nov 14, 2019 1:12 pm
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I recapped the amp, and installed a larger output transformer. I added a Celestion speaker as well. The amp sounds great. The FAT switch was working fine before the cap job, so I am unsure where the problem is. My test equipment consists of a multi tester, and that is it...


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Thu Nov 14, 2019 2:06 pm
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You may have damaged the the Fat switch when working on the circuit ?
Or printed circuit ?

Or it is a Hazard, coincidence ? Fat switch will have this issue anyway ?

You will have to look inside the amp and read Fat switch contacts, how they work


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Thu Nov 14, 2019 2:47 pm
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I can hear a faint click ‘signal’ when I actuate the switch. I was wondering what is involved with that particular circuit? I used a .47uF non polarized poly cap for c-20 to replace the polarized cap. I don’t think that would have anything to do with it, but I’m fishing for straws at this point. I used stock values othwise, except I used a 100uF cap to replace the 47, in the power supply


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Fri Nov 15, 2019 2:12 am
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" I used a .47uF non polarized poly cap for c-20 to replace the polarized cap.."
-quarteraw

Replace by a polarized. Mouser Electronic have this cap

Why did you replace this cap ? What whas the issue ?

Did you do other error like that somewhere in the circuit ?


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Fri Nov 15, 2019 6:36 am
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stratele52 wrote:
" I used a .47uF non polarized poly cap for c-20 to replace the polarized cap.."
-quarteraw

Replace by a polarized. Mouser Electronic have this cap

Why did you replace this cap ? What whas the issue ?

Did you do other error like that somewhere in the circuit ?

I replaced all of the electrolytic caps. Those IC branded caps are known to be of very poor quality. The non polarized cap should work, whereas replacing a non Polarized cap with a polarized cap will not. I was just wondering if there was some quirk in the circuit that required a polarized cap @ c-20.
The non polar cap was the only one that I had of that value, and that’s why I used it. I still have the original cap, and I just might stick it back in the amp, to see what happens.


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Fri Nov 15, 2019 6:55 am
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I know IC caps, Illinois Corp .

Most modern amps use them and most of the time they work fine for many many years.
Most modern amps use so many cheap parts to keep price down. It is not the caps I'll replace first.

Put the wrong cap is worse than leaving the low quality one.

" if it's not broken don't fix it "


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Sat Nov 16, 2019 10:03 am
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Its not so much a difference between polarized and non polarized.
Its more about the difference between an electrolytic and a poly cap.
In my experience, poly caps sounds more articulate.
Electrolytics are usually chosen for cost reasons, not performance. I recommend replacing electrolytics with poly caps if they fit. They sound better.


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Sat Nov 16, 2019 1:44 pm
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Tim di you say quartersaw should leave the non polarized cap there ?

I have so much to learn... :oops:


Last edited by stratele52 on Sat Nov 16, 2019 1:56 pm, edited 1 time in total.

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Post subject: Re: Blues Jr. III fat switch problem
Posted: Sat Nov 16, 2019 1:47 pm
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stratele52 wrote:
I know IC caps, Illinois Corp .

Most modern amps use them and most of the time they work fine for many many years.
Most modern amps use so many cheap parts to keep price down. It is not the caps I'll replace first.

Put the wrong cap is worse than leaving the low quality one.

" if it's not broken don't fix it "

The IC caps were *very* warm to the touch, when I first acquired this amp. I removed all of them.


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Sat Nov 16, 2019 1:48 pm
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TimsAudio wrote:
Its not so much a difference between polarized and non polarized.
Its more about the difference between an electrolytic and a poly cap.
In my experience, poly caps sounds more articulate.
Electrolytics are usually chosen for cost reasons, not performance. I recommend replacing electrolytics with poly caps if they fit. They sound better.

Agreed! :-)


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Sat Nov 16, 2019 1:54 pm
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I found the issue today.
I have a Hakko 808 solder sucker, and it inadvertently removed the circular trace for the (New Nichicon) 22uF cap @ V1. Interesting, because the solder joint looked nice, and clean. I scraped down the trace, and extended the wire from the (replaced again) cap. and all is well!! Fat switch sounds knarly!
Thanks to everyone for your feedback! :-)


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Post subject: Re: Blues Jr. III fat switch problem
Posted: Sat Nov 16, 2019 2:01 pm
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Good news,

2 days ago I wrote;

"You may have damaged the the Fat switch when working on the circuit ?
Or printed circuit ? "

:lol:


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