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Thread: 2009 Fender Blues Deluxe Reverb Hum and... A poor past repair??

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    2009 Fender Blues Deluxe Reverb Hum and... A poor past repair??

    Hey ya'll,

    A 2009 Blues Deluxe came to me with a gnarly hum issue. After visual inspection it looks like someone scratched off the trace to C53, a 750pf cap. looks like a coupling cap for one of the preamp stages. additionally theres an 844 ohm resistor soldered between one leg of R9 to negative leg of C36, a 22uf 500v cap.

    Schematic can be found here: https://www.thetubestore.com/lib/the...atic-Rev-A.pdf

    I'm wondering why someone would do this? If someone could provide some insight, that would help me a lot! I will ultimately end up disconnecting this resistor and reconnecting the trace for this 750pf cap, but curious to know if there is a reason someone might have done this. Thanks!

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    The 844R resistor, is that connected from the junction of R9/R52 to ground? If so, that attenuate the signal significantly.

    Which side of C52 is the trace removed? Show specifically on the schematic which trace was cut. There are too many possibilities to guess.

    If it was mine, I'd replace everything to stock and reevaluate.

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    Some "killer new mod" someone probably read on the net done by someone who shouldn't have.

    I've seen several.

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    Don't forget the joker g1's Avatar
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    Aside from the hum, was the amp working properly, both channels? Because with the mods as described, I would not expect it to.
    If it is working right aside from the hum, I'd suggest retracing the mod before undoing anything.

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    Quote Originally Posted by The Dude View Post
    But, I did learn something. There are protons, neutrons, electrons, ............ and morons.

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    Hereís some images of what Iím talking about. I wouldnít really expect it to work either. Apparently the amp has been working fine for years

    https://ibb.co/H77fyd3
    https://ibb.co/d0RRsg0

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    Bringing it back to stock will not be difficult, but itís kinda crazy how itís been functioning normally.. but maybe Iím missing something here.

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    The value of R9 has been changed from the schematic value of 270K, and what I see is a 240K resistor which would be the value of R52.

    As for the cut trace, I'd like to know what is under the board. If that trace has been cut, there would be no signal path for the clean channel signal to get to through to the output. There may be added wires or components on the back side of the pc board.

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    Iím pulling the board the check whatís underneath now. Will update

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    No rewiring or bridged connections under the board.. Iím going to remove this resistor and repair the connection on the top of the board and see where we are

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    I pulled the 270k resistor and repaired the trace. No effect. I started signal tracing early on in the circuit and a 1k signal looks pure far past the first few preamp stages. Iím thinking it could be the power supply, or output stage.

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    Quote Originally Posted by 52 Bill View Post
    The value of R9 has been changed from the schematic value of 270K, and what I see is a 240K resistor which would be the value of R52.

    As for the cut trace, I'd like to know what is under the board. If that trace has been cut, there would be no signal path for the clean channel signal to get to through to the output. There may be added wires or components on the back side of the pc board.
    Itís a 240k for a deville 150k for deluxe, so itís a 150k in this case

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    Signal looks good across all controls. So itís somewhere between the output stage and Output. Voltages on the power supply look normal. From 345-360v across all electrolytics. You can see the hum clearly on P19, primary for the OT, so itís not a problem across the OT but could it be an open primary winding? Thinking it could be something on the output board too but thereís nothing that visually stands out. Hoping someone who knows these amps really well can nudge me in the right direction! Iíve already tried another pair of output tubes.

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    Supporting Member The Dude's Avatar
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    The Illinois electrolytic caps in those are notorious for being bad. Take a known good cap of similar value properly voltage rated and clip it across each cap in the amp, one at a time, to see if the hum goes away.

    Also, will the amp bias properly?

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    Last edited by The Dude; 01-12-2019 at 02:43 AM.
    ďYeah, well, you know, thatís just, like, your opinion, man.Ē

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    Those are not mods. There were problems with the circuit board design and that is the way it came out of the factory. I'd suggest you put it back how it was so you do not introduce problems that are not immediately noticeable.
    You should also find that the proper spot marked "R52" on the circuit board (far side of K2 relay) has a jumper instead of a resistor.

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    Quote Originally Posted by The Dude View Post
    But, I did learn something. There are protons, neutrons, electrons, ............ and morons.

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    Senior Member Pedro Vecino's Avatar
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    I had never seen it but the cut on the track does not necessarily mean that the 750p capacitor is deactivated because the boost channel would not sound.
    It can be to avoid the path of the signal until reaching R52, or to assign another ground point.
    It seems to correspond to the original construction but I do not know why because the original design in that same version (the modern one) has no problems.

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    Quote Originally Posted by The Dude View Post
    The Illinois electrolytic caps in those are notorious for being bad. Take a known good cap of similar value properly voltage rated and clip it across each cap in the amp, one at a time, to see if the hum goes away.

    Also, will the amp bias properly?
    Thanks for your suggestion. It looks like the 47uf 500v filter cap is the source of all of this. Unfortunately I donít have one in stock (which sucks I thought I did!) but when I clipped 2 22uf caps across in parallel, the issue was gone. Still kind of noisey, but completely in the right direction.

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    The Takeaway: Illinois Crapacitors gotta go! It completely sucks that an amp made in 2009 has a bad cap in it...

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    Did you check whether R52 is stuffed with a resistor on the circuit board? If it is not, and you remove the 'mod' version, the circuit will have issues.


    Click image for larger version. 

Name:	R52.jpg 
Views:	15 
Size:	37.3 KB 
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    Quote Originally Posted by The Dude View Post
    But, I did learn something. There are protons, neutrons, electrons, ............ and morons.

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    Yup, R52 is unpopulated

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    Iím tempted to do this out of convenience... but I do have 2 22uf 500v caps. Would it be feasible to use them in parallel as a permanent replacement? Itís a time sensitive repair unfortunately, but I figured the value is similar enough to be totally fine. Has anyone done this?

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    Yes. If you can mount them so nothing is hanging loose or flopping around, I don't see any problem using 2 caps paralleled like that.
    I hope you are going to restore the factory mod?

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    Quote Originally Posted by The Dude View Post
    But, I did learn something. There are protons, neutrons, electrons, ............ and morons.

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    Already done! dang trying to get this out of here TODAY

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