Short in amp: house circuit breaker pops, amp fuse does not.

[slidincharlie (Carlo P)]

I hope the post subject is clear enough...
I did overall maintenance, total cap job and a few tone stack mods in my 1482 two years ago. The amp has worked normally ever since.
Now there seems to be a short somewhere: as soon as I insert the mains plug into the wall socket (or a few seconds later) the house circuit breaker pops BUT the amp fuse does not blow.
What should I check? Is there a step-by-step troubleshooting to chase a possible short?
I have subbed in a new rectifier to no avail.
Amp schematic is in attachment, as well as a picture of the chassis. The power supply section is a little messy because I had to use single filter caps instead of an expensive cap can. But again, the amp has been working fine until now.
The power transformer is a replacement with 230V primary.
TIA,
Carlo

[Steve Conner]

Is your house circuit breaker the earth leakage type? GFI, RCD, ELCB, whatever it's called in your country, you can recognize it by the presence of a test button that trips the breaker when pressed.

If it's one of these, then it's probably tripping because current is leaking to earth. It only takes a few mA of leakage to trip them, which won't pop any fuses.

This implies that you've used a faulty component somewhere on the primary side of your PT (maybe even the PT itself has bad insulation?) or made a wiring mistake, most likely getting neutral and earth mixed up, or the neutral wire is touching the chassis somewhere.

[52 Bill]

Could you have a problem with the ac cord itself? Maybe a frayed wire at the plug end?

Just a thought.

[Don Moose]

Originally Posted by Steve Conner

neutral wire is touching the chassis somewhere.

I'm thinking Hot and Neut reversed or Hot touching Chassis - it appears the amp doesn't even have to be ON.

[slidincharlie (Carlo P)]

Originally Posted by Don Moose

I'm thinking Hot and Neut reversed or Hot touching Chassis - it appears the amp doesn't even have to be ON.

Right, the amp doesn't even have to be ON to make the house breaker pops.
And yes, the house circuit breaker has a test button. Is there a way to detect current leakage to the chassis?
Re: faulty parts or bad insulation on PT: the amp has worked alright in the last two years. Maybe a component (filter cap? power lamp?) has gone south? I'll check the power supply area, connections and cord.

[izzybell2810]

I'm with Steve and bill on this one. I'd put money on it being the power cord causing a fault current to earth. Anything over 30ma will or should trip an RDC as 30ma at 230v is enough t kill you in the right conditions. At least you know your RCD is working!

[slidincharlie (Carlo P)]

Originally Posted by izzybell2810

I'm with Steve and bill on this one. I'd put money on it being the power cord causing a fault current to earth.

The plug is a sealed "schuko" (a.k.a. as "German") plug. I can't open it to check. Anyway I'll install a new cord and see what happens.
Thanks,

[Enzo]

Your schematic shows a cap from mains to chassis, is that still there? Get rid of it.

[slidincharlie (Carlo P)]

Originally Posted by Enzo

Your schematic shows a cap from mains to chassis, is that still there? Get rid of it.

No, I tossed it long ago. Now that end of the fuse goes directly to ground and to the PT. Is that the correct configuration?

[loudthud]

I noticed that there is no strain relief where the line cord goes thrrough a hole in the chassis. Is there any damage to the cord there? If you ohm from either side of the line plug to the chassis do you get anything less than over-range?

[slidincharlie (Carlo P)]

loudthud,
this is just what I was thinking about...
I'm going to bed now... Tomorrow I'll post the results of my job.

[Albert Kreuzer]

Originally Posted by slidincharlie (Carlo P)

No, I tossed it long ago. Now that end of the fuse goes directly to ground and to the PT. Is that the correct configuration?

No. Just leave the cap out. The PT primary should not have a direct connection to ground.

Cheers,
Albert

[slidincharlie (Carlo P)]

I have just installed a new power cord (with the ground wire lifted for now). The result: neither the house breaker pops NOR the amp turns on! The mains AC is on the power switch but the amp stays totally off. No tension anywhere. It's like the PT does not receive the mains AC or it does not deliver it to the rectifier...
Maybe the PT is dead?

Originally Posted by Albert Kreuzer

No. Just leave the cap out. The PT primary should not have a direct connection to ground.

Albert, I have simply tossed away the cap from mains to the chassis and left the wire that goes from there to the PT (see red arrow in the photo below). But there is continuity between that pole of the fuse holder and the chassis (i.e. between the PT primary and the chassis).

[Albert Kreuzer]

Originally Posted by slidincharlie (Carlo P)

I have just installed a new power cord (with the ground wire lifted for now). The result: neither the house breaker pops NOR the amp turns on! The mains AC is on the power switch but the amp stays totally off. No tension anywhere. It's like the PT does not receive the mains AC or it does not deliver it to the rectifier...
Maybe the PT is dead?

Or maybe this time the fuse blew before the house breaker...

Originally Posted by slidincharlie (Carlo P)

Albert, I have simply tossed away the cap from mains to the chassis and left the wire that goes from there to the PT (see red arrow in the photo below). But there is continuity between that pole of the fuse holder and the chassis (i.e. between the PT primary and the chassis).

Yes, I can see it on the picture - you did it right. If there is still continuity between primary and secondary, you may have a shorted PT. Disconnect all PT wires and measure between primaries and secondaries.
Just had one like this last week. Exactly the same symptoms.

Cheers,
Albert

[slidincharlie (Carlo P)]

Originally Posted by Albert Kreuzer

If there is still continuity between primary and secondary, you may have a shorted PT. Disconnect all PT wires and measure between primaries and secondaries.

With all PT wires disconnected (including the central taps) there IS continuity between one primary wire (the one coming from the fuse holder) and each of the two high tension secondaries a well as their central tap.
There is NO continuity when the other primary wire (the one coming from the power switch) is checked. Also there is NO continuity between the two primary wires!
Is there a short? How did it happen? Could a faulty power cord cause such short in the PT?

[Don Moose]

Since it did used to work, we can't take the path saying the PT was in ... um, sideways.

It sounds like the primary broke in a way that shorted it to the secondary.
(you already figures that out)

That PT is toast.

There are a couple of ways that could happen ... I think. High temperatures come to mind, but don't seem very likely. A voltage spike big enough to break down the insulation _and_ make an open doesn't sound very likely either.

How about 10 posts of wild speculation while Carlo orders a replacement?

[Steve Conner]

Wild speculation... The transformer wires got mixed up during the rebuild? Remember that transformer wire colours were only standardized in America.

[slidincharlie (Carlo P)]

Originally Posted by Steve Conner

Wild speculation... The transformer wires got mixed up during the rebuild? Remember that transformer wire colours were only standardized in America.

I don't think so... the amp has worked quite fine for about 2-3 years after PT rebuild.
Please help this dumb self-taught-tech-wannabe understand:
since I have no tension on the secondaries when mains AC is applied to the primary, I wonder: where does all the current go?
Furthermore:
this PT was built ex-novo by a local manufacturer according to specs from the amp schematic. Is it possible that poor craftsmanship (or poor quality components) results in a transformer failure after 2-3 years of faithful job?

[52 Bill]

Originally Posted by slidincharlie (Carlo P)

Please help this dumb self-taught-tech-wannabe understand:
since I have no tension on the secondaries when mains AC is applied to the primary, I wonder: where does all the current go?

There is no path for the current to flow, because the primary winding is open. The current is not going anywhere.

Originally Posted by slidincharlie (Carlo P)

Furthermore:
this PT was built ex-novo by a local manufacturer according to specs from the amp schematic. Is it possible that poor craftsmanship (or poor quality components) results in a transformer failure after 2-3 years of faithful job?

Yes, anything is possible.

I have a question for you about the way the wiring was done. You stated that one of the primary wires was attached to ground? Please explain, as there should never be any ac wire directly connected to ground.

[slidincharlie (Carlo P)]

Originally Posted by 52 Bill

I have a question for you about the way the wiring was done. You stated that one of the primary wires was attached to ground? Please explain, as there should never be any ac wire directly connected to ground.

Bill you are right, my statement was misleading.
I measured continuity between one primary and chassis with the PT leads still connected - because actually there is continuity between that primary wire and the HT secondary (and their CT). Actually, contrary to what I stated, there is no continuity between the fuse holder lugs and ground. Sorry about that.
Now a replacement power tranny is the only way to go, or can the current PT be repaired?
EDIT: I'll talk to the guy who built this PT and ask if he can check and possibly rewind it

[Don Moose]

The tranny can be repaired, but I would want a complete rewind - primary and secondaries - since it sounds like insulation on both was less than adequate.

It should be OK for your transformer guy to re-use the laminations, and _maybe_ the bobbins (are there bobbins?), but all new wire - preferably with better insulation is a must.

I do wonder if the labor of disassembling old one would cost him more than a fresh-from-scratch unit (which would give you the comfort of knowing all the wire is new).

Hope this helps!

[Dave Curtis, dB AudioTech]

Originally Posted by Albert Kreuzer

Or maybe this time the fuse blew before the house breaker...



Yes, I can see it on the picture - you did it right.
Cheers,
Albert

Well, kinda. The blue wire (neutral) should go directly to one side of the PT primary, and the brown wire should go through the fuse (backside first) and then to the switch. Although in Europe, they normally switch both the neutral and the hot with a 2 pole switch.

You don't want to fuse the neutral. If you switch it, the switch must also open the ungrounded conductor (hot).

[icefloe01]

Originally Posted by Dave Curtis, dB AudioTech

Well, kinda. The blue wire (neutral) should go directly to one side of the PT primary, and the brown wire should go through the fuse (backside first) and then to the switch. Although in Europe, they normally switch both the neutral and the hot with a 2 pole switch.

You don't want to fuse the neutral. If you switch it, the switch must also open the ungrounded conductor (hot).

I agree with this and was going to post likewise until I looked at the schematic. I would not fuse the neutral either, but that's how the schematic is drawn: Live wire to switch to PT, PT to fuse to Neutral. It's just not what I'm used to seeing.

Eric.

[slidincharlie (Carlo P)]

Thank you Dave and Eric for addressing this issue. I did not know that I should fuse the hot wire instead of the neutral. Actually nobody cares about where the hot and the neutral go in Europe as far as I know, or if the hot is blue or brown. Well, maybe electricians care about it, but not common people who make their own small house works, like replacing an old plug and the like.
Don, I'll inquire for the costs of such job and post here my decision.

[slidincharlie (Carlo P)]

Originally Posted by Dave Curtis, dB AudioTech

Well, kinda. The blue wire (neutral) should go directly to one side of the PT primary, and the brown wire should go through the fuse (backside first) and then to the switch (...)

Dave, I have thought about it a little bit, and I can tell you that definitely this rule does not apply here in Italy, and possibly in most European countries. In fact I can insert a plug into a wall socket either way, so one wire (the blue for example) can be hot or neutral anytime, and there is no way to make sure that you are always fusing the hot wire.

[icefloe01]

Originally Posted by slidincharlie (Carlo P)

Thank you Dave and Eric for addressing this issue. I did not know that I should fuse the hot wire instead of the neutral. Actually nobody cares about where the hot and the neutral go in Europe as far as I know, or if the hot is blue or brown. Well, maybe electricians care about it, but not common people who make their own small house works, like replacing an old plug and the like.
Don, I'll inquire for the costs of such job and post here my decision.

The difference between U.S. and European color codes below

The U.S. code for single phase (like a regular power cord) is typically:

Black = Live or "Hot" and goes to the narrow blade of a power plug.
White = Neutral or "Cold" and goes to the wide blade.
Green = Ground or Earth and goes to the long round pin of a three prong plug.

The European code is my experience has been:

Brown = Live or "Hot"
Blue = Neutral or "Cold"
Green w/ Yellow stripe = Ground or "Earth"

Personally, I think the European code makes more sense when you associate color with temperature.

One of the problems with swapping the neutral and hot leads in a piece of equipment is that everything that was originally tied to the neutral line is now hot all the time, even when the power switch is opened. Just something to be aware of.

Eric.

[slidincharlie (Carlo P)]

Originally Posted by icefloe01

The difference between U.S. and European color codes below
The U.S. code for single phase (like a regular power cord) is typically:
Black = Live or "Hot" and goes to the narrow blade of a power plug.
White = Neutral or "Cold" and goes to the wide blade.
Green = Ground or Earth and goes to the long round pin of a three prong plug.

I see. Unfortunately in Italy (as well as in many other European countries) the holes in the sockets are exactly the same, as well as the plug pins, so there is no way to know which pole is hot and which is neutral...
Thanks for clarifying the subject anyway

[Albert Kreuzer]

The fact that you can insert the plug either way is the reason for the obligatory two-pole switch.
The blue/brown rule still applies in house wirings, where the blue (neutral) has to be on the left and the brown (hot) on the right side of the socket (well, at least in theory...)

Cheers,
Albert

[slidincharlie (Carlo P)]

Originally Posted by Albert Kreuzer

The fact that you can insert the plug either way is the reason for the obligatory two-pole switch.
The blue/brown rule still applies in house wirings, where the blue (neutral) has to be on the left and the brown (hot) on the right side of the socket (well, at least in theory...)

Well, sockets here have three holes arranged vertically
Seriously... is there any trouble using an amp built on US specs like this one, with European (well, Italian actually) AC wiring? Please consider that, except maybe a few marginal cases, electrical circuits here always have ground wiring.

[Dave Curtis, dB AudioTech]

Originally Posted by slidincharlie (Carlo P)

Dave, I have thought about it a little bit, and I can tell you that definitely this rule does not apply here in Italy, and possibly in most European countries. In fact I can insert a plug into a wall socket either way, so one wire (the blue for example) can be hot or neutral anytime, and there is no way to make sure that you are always fusing the hot wire.

Hence, the use of a 2-pole switch to open the neutral and the hot at the same time.

[Dave Curtis, dB AudioTech]

Originally Posted by icefloe01

I agree with this and was going to post likewise until I looked at the schematic. I would not fuse the neutral either, but that's how the schematic is drawn: Live wire to switch to PT, PT to fuse to Neutral. It's just not what I'm used to seeing.

Eric.

And it was legal in the era when it was made. That's why codes change; to make things safer.

[Twist]

This may be a bit off the subject but...... Isn't Palermo, Italy where they have a huge tomb full of exposed corpses. I would love to go there to see them.

[slidincharlie (Carlo P)]

Originally Posted by Twist

This may be a bit off the subject but...... Isn't Palermo, Italy where they have a huge tomb full of exposed corpses. I would love to go there to see them.

Yep! All people who died because of bad electrical wiring
Call me if you ever come here!

[J M Fahey]

Hi Carlo.
I live in Argentina, which usually follows European Standards by default (generally DIN).
We use Blue as Hot , Brown as Cold and Green/Yellow as neutral.
Around ´95 the old European two-round-pins was forbidden (I think you still use it) to avoid what´s happening to you, easy Hot/Cold unknown swapping.
Now we use 3 angled flat pin plugs and for not-so-dangerous equipment a 2 angled flat plug.
Maybe Italy will follow soon with a similar new standard.
Ciao caro amico.

[slidincharlie (Carlo P)]

Hi JM,
in Italy most electronic equipment (radio/hifi sets, hair driers, tv/dvd sets, etc) come with a two-pin-in-a-row plug. Actually all house sockets have three pins in a row (central is for ground) and there is no way to know which one is hot and which is neutral. High current equipment like refrigerators, washing machines, etc. come with the round German-type ("schuko") plug, that needs an adapter fo fit house sockets. Clearly electrical circuits in Italy are built in a way that does not require a precise plugging direction.