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Author Topic: Blown fuse [Resolved]  (Read 787 times)

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Offline tubenoob

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Blown fuse [Resolved]
« on: March 20, 2020, 03:37:18 PM »
Resistance checks looked correct (see below).  Plugged in power to complete the final voltage check and immediately blew the fuse.  I'll need to purchase more fuses tomorrow if the coronavirus hasn't shut everything down by then.  I've triple checked my wiring, but could use another set of eyes as I'm not seeing any issues.  I did wind up having to replace my power switch after doing the earlier transformer, glow and voltage tests due to trying to clean up a messy solder connection on the power switch and ruining it by getting it too hot.  The previous tests (prior to the final resistance test) all checked out fine; however, again I replaced the power switch between those tests and the final voltage check. 




Resistance test results:




1. .0L

2. .0L

3. .001

4. .0L

5. .0L




6. .001

7. 2.95

8. .000

9. 2.95

10. .000




12. .000

13. .0L

14. .000




20. .000

22. .000




B3 2.95

B6 2.95




RCA Jacks

Center Pin R - 103.8 B - 97.6

Ground tab R - .000 B - .000
« Last Edit: March 21, 2020, 05:17:04 PM by tubenoob »

Offline Paul Birkeland

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Re: Blown fuse
« Reply #1 on: March 20, 2020, 04:12:30 PM »
Could you post some close up photos of all the UF4007 diodes? 

What kind of solder was used to build the kit? (was any extra flux used?)
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline tubenoob

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Re: Blown fuse
« Reply #2 on: March 20, 2020, 04:36:43 PM »
Thanks for the quick reply.  Requested pics are attached. Solder used was 60/40 lead core.  I did use flux.  Should I not have? I don't recall seeing anything in the manual advising against it, but may have missed something.

Offline tubenoob

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Re: Blown fuse
« Reply #3 on: March 20, 2020, 04:43:28 PM »
Sorry, misspoke on the solder type. 60/40 rosin core.

Offline Paul Birkeland

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Re: Blown fuse
« Reply #4 on: March 21, 2020, 05:39:47 AM »
Could you post a photo of the packaging for the flux?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline tubenoob

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Re: Blown fuse
« Reply #5 on: March 21, 2020, 06:12:58 AM »
attached

Offline Paul Birkeland

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Re: Blown fuse
« Reply #6 on: March 21, 2020, 06:23:10 AM »
Thank you for posting that.  In recent years, it has gotten somewhat more common for builders to use brazing flux or repair flux on their kits, and this flux is conductive and causes a whole ton of issues.  I could tell in your photos that some extra flux had been used, so I thought it was worth asking.  The rosin core in the solder you used is the flux, so you don't need to use any extra. 

With your black meter probe grounded, what DC resistance do you get between each end of each 270 ohm 5W resistor? 

I would also assume that all of the measurement tests before the final one were done without the fuse blowing? 

Generally what I expect when someone reports a fuse blowing immediately upon powering up a Crack is that a UF4007 diode is installed backwards, the leads of two diodes that go to two different terminals are touching, a 220uF/250V cap is installed backwards, a black ground wire is installed into an improper terminal, or a 270R/5W resistor is installed into an improper terminal.  I don't see any of this going on in your photos. 

We can split the circuit in half for the purposes of testing though.  You can remove the red wire at terminal 13 and bend it up and out of the way, then fire up the amp and see if the fuse holds (I would be surprised if the amp was suddenly happy, but it's worth the cost of the fuse to see). 

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline tubenoob

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Re: Blown fuse
« Reply #7 on: March 21, 2020, 07:02:20 AM »
Thanks for helping me out with this. I’m obviously inexperienced and appreciate your patience.

Resistance seems to be all over the place when I measure the 270 ohm 5W resistors. It seems to decrease gradually during measurement and not hold

The fuse held up through all previous tests without issue.

I can try splitting the circuit as described next if you feel that’s appropriate. Thanks again.

Offline Paul Birkeland

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Re: Blown fuse
« Reply #8 on: March 21, 2020, 07:25:50 AM »
Yes, go ahead and pop that red wire out, then see if a fuse holds.

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline tubenoob

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Re: Blown fuse
« Reply #9 on: March 21, 2020, 07:46:18 AM »
No luck. Red wire @ terminal 13 removed and the fuse still blew when power was applied. I do need to note that I was only able to locate fast acting 1a fuses here locally to replace the original shipped with the kit. I have slow burn 1a ordered but they won’t be here until Thursday.

Offline Paul Birkeland

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Re: Blown fuse
« Reply #10 on: March 21, 2020, 08:06:42 AM »
Can I see some close ups of the other 6 lug terminal strip (the one with terminals 11-16)?

The fuse blowing here means that something is awry on one of the 6 lug strips.  It could be an untrimmed lead poking through and touching something it shouldn't, debris, etc.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline tubenoob

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Re: Blown fuse
« Reply #11 on: March 21, 2020, 08:20:00 AM »
As requested
« Last Edit: March 21, 2020, 08:28:33 AM by tubenoob »

Offline Paul Birkeland

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Re: Blown fuse
« Reply #12 on: March 21, 2020, 08:53:18 AM »
Can you unhook the red wire from power transformer terminal 11, then see if the fuse holds?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline tubenoob

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Re: Blown fuse
« Reply #13 on: March 21, 2020, 09:01:04 AM »
The fuse held after removing the red wire from terminal 11 on the transformer

Offline Paul Birkeland

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Re: Blown fuse
« Reply #14 on: March 21, 2020, 09:46:11 AM »
Well, I'm looking over everything you've posted as closely as I can.  This is all I can see that might cause that problem.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man