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Post subject: HELP!! my Fender Dual Showman Red knob wont turn on? Ideas?
Posted: Sun Sep 15, 2013 1:02 pm
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HELP!! my Fender Dual Showman SR Red knob wont turn on? Anyone have any Ideas? The fuse says it is supposed to be a 7A 125V slo blo the one in there says Buss MDQ 7 250V could this possibly be the problem? no led power light coming on? no tube glow. there where 2 fried resistors R302 R303 (47 ohm 1/2 watt) that i replaced and there was a loose wire that i re soldered..only other possible problem i see is a bent potentiometer on the front control panel. can send pix too..thanks anyone out there that could help me out.


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 1:16 pm
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Buss MDQ 7 250VDC = correct fuse. Can you check the continuity across the fuse with a DVM?


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 1:21 pm
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yes it is good it has continuity..thanks!


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 2:00 pm
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R302 and 303 are ground lifting resistors on the the heater line. For them to blow out would indicate a short in your heater line. The heater line also powers the LED.

You must have a discontinuity in the heater line, after you replaced those resistors. Check this part of the circuitry.

http://www.webphix.com/schematic%20heav ... _schem.pdf


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 2:48 pm
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someone told me maybe it took out a nearby capacitor?


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 2:51 pm
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Caps generally short which in turn usually blow the fuse. You haven't had that issue (yet).

Why don't you start with the simple checks first?

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 2:58 pm
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could you give me a hint about what to test ? That would be really cool!..I know about discharging and safety...I did check the fuse holder and the other internal fuse both seem ok..I checked nearby resistor and a couple other things nearby...thanks! JL


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 3:03 pm
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Did you read and understand this......?

BMW2002Ti wrote:
R302 and 303 are ground lifting resistors on the the heater line. For them to blow out would indicate a short in your heater line. The heater line also powers the LED.

You must have a discontinuity in the heater line, after you replaced those resistors. Check this part of the circuitry.

http://www.webphix.com/schematic%20heav ... _schem.pdf


There's your starting point.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 3:08 pm
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yes i read it about ten times and.. no i dont understand what a heater line is? thanks..i am learning as i go


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 4:21 pm
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hi..I just read up on heater lines and checked all the way throught o the last tube all seems ok? could it be a short in the PT?


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 5:25 pm
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jimi, Nope. Because if you blew the two lifting resistors, the PT had to be working. I'm pretty sure it's in the wiring --- after the PT.


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 5:37 pm
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that is good news..i am looking at the 4 diodes and i trace a beep all the way to the first set then i get nothing on second set d-301-304 ? could that be something..thanks ..jim


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 5:56 pm
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d-307 measures the same both ways? (147) but it is connected to the board still should i remove one end and test?


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Sun Sep 15, 2013 6:12 pm
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You need to pull one leg of the diodes and resistors before reading continuity/resistance.

The diodes are NOT in the heater circuit. The heater runs 6.3VAC. Not VDC.

If the resistance measures the same across the that diode going both direction --- you need to change ALL the diodes in the rectifier. Use good quality UF5408. Faifchilds or Vishays are cheap and very quiet.


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Post subject: Re: HELP!! my Fender Dual Showman Red knob wont turn on? Ide
Posted: Mon Sep 16, 2013 4:46 pm
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thanks for the help..i will be doing a complete check of all soon..will do a follow up..i also took some photos..it seems like there was a mod done and i took a photo of it..also there is a switch that has been removed and hard wired ..could be looked at to tell me if it looks ok..will try and figure out how to post pic tonight..


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