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Post subject: Limited Edition Blues Junior Tweed sudden loss sound/power
Posted: Thu Feb 17, 2011 9:52 am
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My Limited Edition Blues Junior Tweed amp is a joy to play through. Its a 2003-2004 amp bought used a year ago and in great shape- like new). Two days ago suddenly it had no sound - no light showing power on etc. Fuses seem good - I swapped out the 2 amp larger fuse (couldn't find a 5 AMP 250 V fuse to replace the smaller one but it appears intact). The power chord and supply at the outlets are good. The transformer has slight smell but nothing that seems unusual. Any advice - anyone else had a problem like this?


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Post subject: Re: Limited Edition Blues Junior Tweed sudden loss sound/pow
Posted: Thu Feb 17, 2011 10:12 am
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Fuse blown, Open primary in the power transformer in those amplifiers where the power indicator is on a secondary,Power cord open - test it with an ohmmeter, Faulty AC power switch - with the amp unplugged, test it with an ohmmeter, Faulty wire or solder joint in the AC power path. Test from AC plug prong to prong with an ohmmeter.


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Post subject: Re: Limited Edition Blues Junior Tweed sudden loss sound/pow
Posted: Thu Feb 17, 2011 2:19 pm
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Hi d. spree,

You will need a good VOM (Volt-Ohm-Milliammeter) and the schematic and some knowledge of the inside of your amp, and the dangers involved when opening it up. You should actually verify whether the fuses are good or not, before just randomly changing them. The type of fuse that is used is very important, not all 2 amp fuses are the same. Here is the schematic, do you have a meter?

http://support.fender.com/schematics/guitar_amplifiers/Blues_Junior_schematic.pdf

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---> "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: Limited Edition Blues Junior Tweed sudden loss sound/pow
Posted: Fri Feb 18, 2011 9:04 am
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shimmilou wrote:
Hi d. spree,

You will need a good VOM (Volt-Ohm-Milliammeter) and the schematic and some knowledge of the inside of your amp, and the dangers involved when opening it up. You should actually verify whether the fuses are good or not, before just randomly changing them. The type of fuse that is used is very important, not all 2 amp fuses are the same. Here is the schematic, do you have a meter?

http://support.fender.com/schematics/guitar_amplifiers/Blues_Junior_schematic.pdf



Thanks for response and for the link to the schematics (which aslo found on line) - I have a meter.


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Post subject: Re: Limited Edition Blues Junior Tweed sudden loss sound/pow
Posted: Fri Feb 18, 2011 10:22 am
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Cool! Before you check anything else, make sure that the amp is unplugged from electricity, and that the capacitors are discharged. You can check the DC voltage across the big gray capacitors to make sure that the voltage is less than 30 volts before proceeding, they won't get to zero and that is OK.

I guess next you should check the fuses continuity with the ohm meter, they should read zero ohms, or very close to zero if good. The 2 amp fuse is for the power transformer, the 5 amp fuse is for the filament (heater) supply for the tubes. You may have lost the filament supply, which also powers the power LED circuit. If the filament supply fuse is blown, it may be from a bad tube, maybe an output tube, but all tubes are suspect until they are checked. If the fuse is blown, pull all tubes out before trying a replacement fuse. If replacing the fuse, with the tubes out, works and gives a power light, then you probably have a bad tube. Just something to check. :idea:

BTW, just comparing the BJr schematic on line to the hard copy that came with my amp, and it looks like the online version is revision A and D, A being the first US version, whereas mine is revision C for the Mex chrome plate version. So, some of the component designations may be different on your amp, but besides the reverb, and the 5 amp fuse not being shown on the on line schematic, they are practically the same thing circuit wise.

_________________
---> "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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