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Fuse keeps blowing on power on

bnfbmk

Registered
10 Years
Joined
Jan 10, 2012
Messages
13
Location
ng9
Hi all



I wonder if anyone can help with this one - my BK2K is blowing the main fuse on power on.



Having looked in the backbox, the only abnormal finding was this badly burnt connector on the interconnect board, J7 for the insert GI:



View attachment 1457



I know it's a long shot 'cos it seems there's a million and one reasons why a main fuse should blow but does anyone have any ideas if this finding could be linked to the fuse issue?



Thanks a lot in advance

Ted
 
No link at all. Assuming the fuse blows immediately you switch on, and you are using a 5a slow blow fuse, then most likely the input mains filter is short circuit. It is inside the grey box in which the fuse is mounted. Caution. There is exposed mains inside this box.
 
Thanks for that Andy
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OK, so just to clarify - I am using 4A slow blow fuses (as per the label next to the fuse holder) and they are blowing immediately I switch on. However, having fiddled a bit more, it's not every time, just most of the time. I have disconnected everything on the downstream side of the transformer and it still (usually) blows.



So (bearing in mind I am useless at this stuff :oops: ) does this still sound like the mains filter (or could it be eg the transformer) and if so, is there any way to test it to make sure or should I just buy a new one (I see you have them on your website
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)



Cheers, Ted
 
If you feel able, you can take the filter out and bypass it to confirm whether the filter is at fault (99% probably yes). Then either fit a new filter or leave it out. The filter prevents interference going back onto your ring main.
 
Thanks again - I have bypassed the filter as above and tried turning it on with everything downstream of the transformer detached and it blew again. So with the mains plug out I tested with a DMM and found that when the main switch is closed and the transformer is attached there is continuity between the positive and negative wires at the mains input. If I detach the connector upstream from the transformer, there isn't continuity.



So, does this mean there is a short in the transformer? I'm rapidly getting out of my depth here. Lol, when are you next up the East Midlands, Andy???
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Just to check. You have removed the filter from the circuit, not just bypassed it.
 
Yeah, I have desoldered the live and neutral input and output wires from the filter and soldered them directly together and also soldered the component (is it a varistor?) between them. The only thing left attached to the filter is the earth wire from the mains plug. Hope this is what you meant me to do...?
 
Thanks Paul



Not sure how I would test the varistor? I've just tested the resistance across the varistor - it's too high to register on the DMM. The resistance when I close the main switch though (introducing the transformer into the circuit) is 0.9 Ohms. Is this normal for a transformer?



Is there anything else I can test to help with the diagnosis? :confused:



Cheers, Ted
 
Cut the varistor off for now. It is not essential for now You cannot get any sensible reading s from a meter with the transformer attached as you are using dc. A transformer only has resistance to AC voltage.
 
OK, I'm just waiting for some 5A slow blow fuses to arrive now as I've now used up my last pack of 10 fuses! I'll report back soon...
 
Sorry to resurrect this thread but after the longest wait in history for a delivery, the fuses finally arrived the other day and, after removing the varistor, everything pretty much seems fine.

I say "pretty much" because, out of about 30-40 "power-ons" so far, the fuse has blown just once. I'm using 5A slo-blow as suggested rather than 4A this time.

So, I'll pop in an order with Andy for a new varistor and also the bits and pieces for mending the GI connector and see how I go. Really appreciate the help you gave with this one...

Ted
 
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