FDP Forum / Sunn Sentura I blowing fuses after replacing two conductor power cable with a three conductor./ 17 messages in thread.

1 to 17 of 17 shown.


Stratmanx

Contributing Member
**********
*******

Memphis, TN

Oct 1st, 2017 10:20 AM        

I went ahead and snipped out the death cap and polarity switch and rewired for the three conductor plug.<br /> <br /> However I keep blowing fuses when turning on the power switch. <br /> <br /> I've blown them with all the tubes in place, as well as removing all of them, including the rectifier tube, so it tells me I'm missing something simple in the 1st stage of the power delivery.<br /> <br /> (Hoping my transformer isn't shot !)<br /> <br /> I would really appreciate if someone could check out if I've done this properly.<br /> <br />



Stratmanx

Contributing Member
**********
*******

Memphis, TN

Oct 1st, 2017 10:21 AM        

<br /> <br /> <br /> <br /> <br />



Stratmanx

Contributing Member
**********
*******

Memphis, TN

Oct 1st, 2017 10:22 AM        

<br />



Stratmanx

Contributing Member
**********
*******

Memphis, TN

Oct 1st, 2017 10:23 AM        

.



willie

Contributing Member
********

Too Near Atlanta GA

Amp Tech Emeritus
Oct 1st, 2017 10:49 AM        

Hard to tell based on your drawing...<br /> <br /> Why not use a 3 amp slow blo fuse?<br /> <br /> Can you take digital photo of the AC mains wiring that you you replaced? Might help...<br /> <br /> Have you tested the transformer primary and secondary windings? <br /> <br /> w



Stratmanx

Contributing Member
**********
*******

Memphis, TN

Oct 1st, 2017 11:35 AM        

I've enclosed this shot, not the best, but coupled with the drawing should give you an idea. <br /> <br /> So the way I've got it wired is the Neutral (White) goes directly to the 2nd connection on the power switch. <br /> <br /> The black (Hot) goes to the fuse, then to the black wire on the transformer, then the other black wire on the transformer goes to the 1st connection on the power switch.<br /> <br /> The Ground (Green) goes directly to the chassis.<br /> <br /> I also ran a hot wire (The red one with the capped off end) to the number three connector on the switch to light the power lamp<br /> <br /> What's the best way to test the primary / secondary windings ?<br /> <br /> Thanks !<br /> <br /> <br />



ECS-3

Contributing Member
**********
**

USA / Virginia

Oct 1st, 2017 01:03 PM        

If you have both the black(hot) and white(neutral) connected to the power switch, then you have a dead short.<br /> <br /> The white (neutral) should go directly to one of the transformer leads.<br /> <br /> The black (hot) should go to the fuse, then the switch, then from the switch to the second transformer lead.<br /> <br />



Stratmanx

Contributing Member
**********
*******

Memphis, TN

Oct 1st, 2017 01:38 PM        

I'll give that a shot.<br /> <br /> Thanks !<br />



Stratmanx

Contributing Member
**********
*******

Memphis, TN

Oct 1st, 2017 02:16 PM        

Tried that as well.<br /> <br /> Still blowing the fuse. <br /> <br /> Transformer fried ?<br />



Stratmanx

Contributing Member
**********
*******

Memphis, TN

Oct 1st, 2017 02:27 PM        

measuring both black leads of the primary gives me 3.2 ohms.<br /> <br /> Measuring both leads individual to ground shows no short.<br />



ECS-3

Contributing Member
**********
**

USA / Virginia

Oct 1st, 2017 02:46 PM        

With all the tubes removed, you still have those 2 diodes (1N2070s) connected to the secondary.<br /> <br /> If either one of those diodes are shorted that would put a heavy load on the transformer. I would check those two diodes, or disconnect them and see if the transformer will idle without blowing a fuse.



ECS-3

Contributing Member
**********
**

USA / Virginia

Oct 1st, 2017 02:49 PM        

The more I think about it, if those diodes are shorted you could have some other failed components downstream, like filter capacitors being exposed to AC instead of DC.<br /> <br /> I'd probably disconnect the diodes and see what happens, and test the two diodes.



Stratmanx

Contributing Member
**********
*******

Memphis, TN

Oct 1st, 2017 04:19 PM        

I unsoldered the red / black wire going from the transformer to the diodes and capped that off and still blowing the fuse.<br /> <br /> All tubes still removed as well.<br /> <br />



Stratmanx

Contributing Member
**********
*******

Memphis, TN

Oct 1st, 2017 05:40 PM        

So with the Red / Black wires from the secondary capped off and then removing the Red / Yellow that goes to Ground from the secondary can capping that off, the fuse stays intact. <br /> <br /> But either of them connected and the fuse blows. <br /> <br /> I can see how the Red / Black from the secondary feeds the circuit and could understand why something down stream of that might blow the fuse, but why when the Red / Yellow is connected to the Ground and its supposed to, with the Red/ Black still disconnected it blows the fuse ?



Roly

Contributing Member
**********
**********
*

Whitehorse Canada

I don't get out much
Oct 1st, 2017 08:24 PM        

Did the amp work before you changed the AC cord?<br /> <br /> What does your meter say (ohms) when measuring from each side of the primary to centre tap (red/yellow).<br />



ECS-3

Contributing Member
**********
**

USA / Virginia

Oct 3rd, 2017 04:49 AM        

I think you just need to disconnect ALL the transformer leads, including the two ground leads. Then start ohming out everything.<br /> <br /> With all the leads disconnected each winding should have an ohms reading but no reading to the frame of the transformer and no reading to any other winding.<br /> <br /> It should ohm out just like the schematic, the yellow winding should have no reading to either of those ground leads or to the frame. The primary should have no reading to either ground lead or the frame.



Roly

Contributing Member
**********
**********
*

Whitehorse Canada

I don't get out much
Oct 3rd, 2017 11:29 AM        

" The primary should have no reading to either ground lead or the frame."<br /> <br /> That's what I was getting at.



Copyright 1999-2003 Fender Discussion Page, LLC. Visit the web site at http://www.fenderforum.com