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Post subject: Blues Deluxe Reissue Blowing Fuses
Posted: Fri Dec 13, 2013 4:35 am
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Greetings,
Please advise. I have a Blues Deluxe Reissue which is blowing fuses.

After checking this thread: viewtopic.php?f=13&t=61086 about a similar problem, I tried the advice given there and removed the power tubes - with power on / standby off; the preamp tubes glow and the fuse is fine until the standby switch is put to ON and the fuse blows again.

I checked the 500v caps C31, 33, 35 and 36 with an ESR meter - C31 and C33 showed as "leaky / in circuit", 35 and 36 showed as good. I disconnected one leg of C31 and C33 to test them out of circuit and they both tested good so I reconnected them.

Any suggestions where I should look / test next? I'm going to look for shorts to earth, what sort of resistance would still be considered a short?

I've noticed that the positive side of the caps (bottom leg as seen from the rear of the amp) are at approx 130 volts just after the fuse blows, dropping to zero volts over a long period if left alone. They could be reaching a higher voltage and losing charge before I test them - the first time I checked they were at 100V and falling, but this was quite a while after the fuse blew. (I safely discharge them before working on them). I'm guessing this charge is just how much charge could build up before the fuse blows.

Cheers, Steve


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Post subject: Re: Blues Deluxe Reissue Blowing Fuses
Posted: Fri Dec 13, 2013 6:11 am
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First , include schematic when you work in amp ;

here ;

support.fender.com/schematics/guitar_amplifiers/BluesDeluxe_Reissue_2004_schematic_Rev-A.pdf

1- Checking capacitor in circuit do not work , need to remove at least one end , sometimes boths side

2- Capacitor voltatge after fuse blow mean nothing

3- Any mods donein the amp or any work on the amp before this trouble ?

Ok resume ; no power output tubes , power ON Stanby PLAY= fuse blow , Yes ?

If yes ;

4- Remove ALL other tubes 12XX7 same test ; fuse blow ? See 5
If No ; check those tubes

5- Fuse blow ; you should isolate power supply output . See schematic . Disconnect Power Supply output where arrow B+ ( TP37 )
Disconnect arrow Z Y X
Keep 12XX7 tubes removed for these test .

Do those test and come back . It is very important to do these test in order I show AND answer in order too.

If this done right you have only the power supply in circuit .

6- If fuse blow , disconnet P13 P14 P15 P16 at the sencondary of Power Transformer.

A usefull tool to save fuse when checking a short is to put a 100 bulb lamp in SERIES with wall outlet and amp . NOT in parallèle .

I try to find you a sketch .


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Post subject: Re: Blues Deluxe Reissue Blowing Fuses
Posted: Fri Dec 13, 2013 6:29 am
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Look here , the middle when scroll down . There is a sketch with 100 watts bulb . Use old style bulb , not halogene or neon. Input go to wall outlet , output ; plug your amp power cords.

If lamp dim very bright ; there is a short on the amp . Try to work in the amp to find where is the short . Because of the bulb all voltage read lower than normal. this circuit will save your fuse. The glow lamp act as a current limiter.

if no short bulb will glow half bright . Try on good working amp you'll see.


www.decdun.me.uk/gaincloneFAQ.html


A video here to show how it work . The guy test a power transformer , You must plug all the amp at same output.
www.bristolwatch.com/load_lamp.htm


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Post subject: Re: Blues Deluxe Reissue Blowing Fuses
Posted: Fri Dec 13, 2013 6:42 am
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Output transformer could be short too .

You must disconnet it from circuit and power on the amp to see if short isalways there .

Keep all tubes removed


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Post subject: Re: Blues Deluxe Reissue Blowing Fuses
Posted: Fri Dec 13, 2013 6:58 am
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SteveJo,

Welcome to the Forum! :D

Before doing any tests, I suggest draining the amp's caps and pulling the amp out of the cab. Now, carefully look for any visual damage in the PSU area and the output section. Look for damaged or burnt tracings. And burnt components. If you don't see anything obvious --- proceed with tests, as Stratele pointed out.


Added suggestions:

You may want to check the choke (L1) for shorts from the leads to the metal frame of the choke. Also, there are two "flyback" diodes (D4 & D5) on the anodes of the 6L6GC's. Check if they are shorted to ground.

I'd look carefully at the electrolytic caps in the PSU. Esp C31 and C33. Check for shorts, using the DC resistance setting on your meter. Do this with the amp unplugged and the caps drained. Place the red DVM lead onto each lytic cap's (+) side and the black to ground. You should get a slow decreasing resistance value (as the caps charge up from your DVM's battery). If the resistance is zero --- pull the cap and replace.

If the amp passes the light bulb test and there are no shorts in the main filter caps, then check the B+, X, Y, & Z DC voltages. With tubes out of amp. They must be within 25% tolerance of values on the schematic. And decrease in relative fashion from B+ to X. If the DCV doesn't follow the pattern of nominal voltages on the schematic, you prolly have a bad cap(s). And/or bad power rail resistor(s) (R 74 or R75).

You may have bad rectifier diode(s). In which case, you won't get a good B+ value.

http://support.fender.com/schematics/gu ... _Rev-A.pdf

Good luck! Keep us informed.


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Post subject: Re: Blues Deluxe Reissue Blowing Fuses
Posted: Fri Dec 13, 2013 7:02 am
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Power Transformer could be short too .

Easy to check ; disconnect all of the secondary wire from the amp ; If fuse blow ,or bulb lamp glow full bright , transformer is short.
These wires are all plug in as I see on schematic.


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Post subject: Re: Blues Deluxe Reissue Blowing Fuses
Posted: Fri Dec 13, 2013 8:38 am
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Many thanks for your quick responses statele52 and BMW2002Ti,
You've given me plenty to look into, and I'll make the light bulb current limiter / indicator.
I think I should get my camera and get some photos before I start disconnecting things. I only get a short amount of time per day to work on gear (during quiet times at work) so I may be a while investigating this and getting back to you. I'm very grateful for your advice and tips.


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Post subject: Re: Blues Deluxe Reissue Blowing Fuses
Posted: Fri Jun 20, 2014 6:01 am
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I know it's an old thread, but I just thought I'd give an update in case anyone else has a similar problem. It took a few months before I had a chance to look at this again, hence the delay.

After trying multiple tests as recommended previously, with no obvious faults found, I went back to looking for shorts to ground in the power supply circuit that is switched in when the standby is put to on - as this was when the fuse was blowing. Again I found nothing with my continuity tester so started removing parts (just one leg) and testing them individually. I eventually found one of the 1N4006 diodes (D6-9) was leaky in the reverse direction, just not enough to indicate a short on my multimeter. I replaced all 4 of them and the amp came back to life. I'm not sure if the fault was caused by something else, but the amp has been working now for a few weeks so I guess that was it.


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Post subject: Re: Blues Deluxe Reissue Blowing Fuses
Posted: Fri Jun 20, 2014 7:30 am
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Thank's for your come back , good to know how you fix it .


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