Nothing In Particular

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Ant
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Re: Nothing In Particular

Post by Ant » Sat Dec 07, 2019 7:36 pm

Curiouser and curiouser.
The Cole phono stage has just tripped the breaker on my balanced mains unit.
I built it following our ali's advice to fit the double pole breaker on the secondary side. This will trip if there is a 40ma imbalance between the 2 sides. Its never tripped before, I wondered what on earth had caused everything to shut down, I thought it was the consumer unit that had tripped but no. Forgot it even had the breaker on it until I had a think.

The Cole has a mains transformer in a separate box that plugs into the main unit via an umbilical. I think the bmu when it tripped could only 'see' the primary side of that transformer. I don't know if it's a split primary, I. E 115 - 0 115-0 connected in series, I'll have to have a look, but obviously one side of the winding was pulling more than the other....
Good job I fitted the breaker. If the Cole is plugged in even when switched off, it immediately trips. This might explain the earlier failure if the mains TX has a problem.
Didn't show up when plugged into a normal socket. Rather indicative of some deeper problems with the unit.

Any ideas?
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Nick
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Re: Nothing In Particular

Post by Nick » Sat Dec 07, 2019 9:55 pm

Well, the only way you can get a imbalance is for the current to go somewhere, and the only place is earth. Likely there is a short somewhere to earth. Check for any caps on the incoming mains to earth, Should be type Y2, but worth checking.
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Mike H
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Re: Nothing In Particular

Post by Mike H » Sat Dec 07, 2019 9:56 pm

EDIT: what he said :D

You got a leak to earth? I.e. live to the case? Short between neutral and earth? Altho I might be out of touch with how modern stuff behaves nowadays.
 
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Nick
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Re: Nothing In Particular

Post by Nick » Sat Dec 07, 2019 11:23 pm

Short between neutral and earth?
Yep, you won't notice that unless you have a new fangled breaker (or you swap live and neutral !!!), but the differential ones in the balanced unit will spot that.

In a moment of stupidity some years ago, I built a linear with neutral and earth swapped over on the iec. Worked fine here, but took David’s breaker out the moment he tried it on his newer mains installation.
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Ant
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Re: Nothing In Particular

Post by Ant » Sun Dec 08, 2019 12:03 pm

OK so I've opened up the TX case, there are no caps at all in there. It's just the TX itsself. It's a toroid, and have had a really good look over it and there appears to be no damage, all the rubber mounting washers are there, all connections in and out are insulated properly too, so there doesn't appear to be any sort of obvious fault I can see in that bit.
Interestingly, there is no earth wire in the umbilical, all that is connected to the iec earth pin is the box itsself.

In the stage, the is a burned out section of the psu board where a resistor was. Burned the tracks clean off the board and burned all the way through to the topside. I knew about this already, it was obvious when it was opened up before and looks to have been repaired before Nigel got the unit in the first place. this is a crc setup and the resistor is r1 in the power supply (after c1 a 6.8uf 630v obbligato) . The resistor that burned out, probably a kiwame as all the rest are, has been taken out and replaced with a 330r welwyn. Which promptly fell off when I looked at it funny.
The rest of the caps are 150uf 350v black gates.
The earths in the unit itsself appear to all be connected to the phon sockets, there is no mains earth........ And the centre tap of the 300 0 300 winding of the mains transformer is also connected to the same earthing scheme.
Not sure why it has been built like this, seems like it would have been easy enough to build it with a mains earth.
Doesn't explain the trippy breaker though
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jack
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Re: Nothing In Particular

Post by jack » Mon Dec 09, 2019 5:00 pm

Latest bench - designed by Clem Churchill. This one's going to Chartwell. Got to make three more.
IMG_20191209_155824-1008x756.jpg
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Mike H
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Re: Nothing In Particular

Post by Mike H » Mon Dec 09, 2019 5:50 pm

Ant wrote:
Sun Dec 08, 2019 12:03 pm
OK so I've opened up the TX case, there are no caps at all in there. It's just the TX itsself. It's a toroid, and have had a really good look over it and there appears to be no damage, all the rubber mounting washers are there, all connections in and out are insulated properly too, so there doesn't appear to be any sort of obvious fault I can see in that bit.
Interestingly, there is no earth wire in the umbilical, all that is connected to the iec earth pin is the box itsself.
. . .
Doesn't explain the trippy breaker though
Possible it has a short between turns or insulation that doesn't manifest until a high Voltage is applied, and certainly won't show on a multimeter Ohms range.
 
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Mike H
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Re: Nothing In Particular

Post by Mike H » Mon Dec 09, 2019 5:52 pm

jack wrote:
Mon Dec 09, 2019 5:00 pm
Latest bench - designed by Clem Churchill. This one's going to Chartwell. Got to make three more.

IMG_20191209_155824-1008x756.jpg
Mega impressed. :notworthy:
 
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jack
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Re: Nothing In Particular

Post by jack » Tue Dec 10, 2019 11:19 am

Mike H wrote:
Mon Dec 09, 2019 5:52 pm
jack wrote:
Mon Dec 09, 2019 5:00 pm
Latest bench - designed by Clem Churchill. This one's going to Chartwell. Got to make three more.
Mega impressed. :notworthy:
Ta. The back is very complex as it has loads of joints that are curved and at odd angles. In terms of man-hours, we're looking at about 100-150 and about 600 quid for the wood (all FSC joinery oak, delivered rough-sawn). Commercially, they'd sell for around 4,500 quid but we charge an NT "internal rate" so the other NT properties get them at about 1/3rd of that - bargain! They're built like tanks as they get a fair amount of abuse and are heavily used. Whilst we don't go for cabinetry standards, we get very close to that - far better than almost any commercial offering.

The bits that look like the ends of tenons are nearly all fake (originally, it was all mortise & tenon) - the only genuine ones are where the front legs meet and come up through the arm rests. We use Festool Dominos for most of the joints - stronger and quicker - the dummy tenon ends are to keep the "look" - the NT are pretty strict about the look - we can make structural changes but nothing that the users can see, i.e. it must appear to be original.

We also put sacrificial oak pads on each leg so that we don't have to repair them so often. This is the 13th such bench made in these workshops - here's an image of one of the others in situ at Chartwell:
IMG_3072.jpg
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Dave the bass
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Re: Nothing In Particular

Post by Dave the bass » Tue Dec 10, 2019 11:33 am

Lidl sometimes doing good seasonal deals on cheap benches, I'll ring up the NT next time I see them on 'special' down in Dirtfud. :)
Last edited by Dave the bass on Tue Dec 10, 2019 11:40 am, edited 1 time in total.
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jack
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Re: Nothing In Particular

Post by jack » Tue Dec 10, 2019 11:34 am

Dave the bass wrote:
Tue Dec 10, 2019 11:33 am
Lidl sometimes doing good seasonal deals on cheap benches, I'll ring up the NT next time I them on 'special' down in Dirtfud. :)
Good idea! BTW, how's the job?
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Dave the bass
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Re: Nothing In Particular

Post by Dave the bass » Tue Dec 10, 2019 11:40 am

I'll let you know :)
"One pound of middle cut pork leg joint,
Stew my foot and call me Brenda".

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jack
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Re: Nothing In Particular

Post by jack » Thu Dec 12, 2019 8:53 pm

Election results under a full moon on Friday 13th? What could go wrong...
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IslandPink
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Re: Nothing In Particular

Post by IslandPink » Thu Dec 12, 2019 10:05 pm

Oh god, I just heard the exit poll results ....
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Scottmoose
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Re: Nothing In Particular

Post by Scottmoose » Thu Dec 12, 2019 10:30 pm

Tierra del Fuego is calling me.

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