House breaker pops when amp is off - sometimes

[LooseChange]

I have a dilemma... A DIY Princeton Reverb.  Plug it in (Amp is off) at one house and the breaker blows immediately.  I put it in my shop and nothing blows. Changed the power cord thinking it might be shorted or something. Still does not blow in my shop. Send it back to the other house and it blows the breaker immediately. Checked the wiring at the other house and it's good, just like my shop.

What is going on here? Anyone???

Thanks!

[John]

Have you tried different outlets and circuits at the customer's house?

[LooseChange]

Have you tried different outlets and circuits at the customer's house?

Yes... Three different zones.

[John]

Hmm. Something's got to be shorting the hot to neutral, or to ground for that matter... it's puzzling why it doesn't do it at your shop. Then again, when does the car ever "make a funny noise" at the mechanics, ya know? It's doubly strange that the amp isn't even on and kicks it. If it's not too much trouble, I'd try your bulb limiter at the house just to see what happens.

[Tiny_Daddy]

Is the amp tripping ground-fault breakers? Or does it really short?

[RicharD]

Is the breaker in question AFCI or GFCI?  Does the amp have a "death cap" or polarity switch? 

[LooseChange]

The breaker is a regular breaker switch on the power panel.
No death cap or polarity switch.

[RicharD]

You said you checked the wiring in the other house and it's fine.  Double check for correct polarity.  Big blade is neutral, little blade is hot, round blade is ground.... duh.  Regardless if the house is miswired, that shouldn't happen.  Here's where I'm confused, you say it happens with the amp switched off correct?  Check your continuity from the 3 plug blades to the chassis.  Neutral and hot should NOT read any continuity.  I've gotten a green blue brown power cord before which was not polarized correctly (green= ground, blue=neutral, brown=hot).  Check for a cracked fuse holder or power switch.  If you do read continuity between the chassis and either the neutral or hot, start dismounting or disconnecting thangs such as the power switch & fuse.  There is also the possibility that you have a primary short in the PT.  My gut instinct tells me you have a neutral to chassis short and the customer's house has some reverse polarity receptacles.  It could be something as simple as bad insulation somewhere in your line power.  When belly up on your bench it's fine but when upright in the cabinet it shorts.  The big suspects are the power switch and fuse holder or something floating around inside the amp between a board and chassis.  I certainly hope it's not an internal primary PT short.  Good luck.

-Richard

[phsyconoodler]

I recently had a customer that had the same issue.He brought me an old sound city head that kept blowing fuses.
  I looked it over and modded the bias supply because it didn't have enough negative voltage.It worked fine at my house and my shop but every time he plugged it in at home it blew the fuse in less that 30 seconds.
  I looked at it three times and even left it on a load box with a signal into it for 6 hours and it never even breathed hard.
  He takes it back and it blows the fuse in 30 seconds.So I go check his house and his wiring is whacked.The hot and neutral are switched.
The way the sound city was wired made it blow because the bias supply would not work if the hot and neutral were switched like that.
  He lent it to a friend and it blew his breaker immediately as well.
 Very odd.
I haven't looked at it since as he has no time.I'm willing to bet there is something wonky with either his house wiring or the hot/neutral on the power cord of your amp.

[PRR]

+1 on some difference between test-bench and user site. I had a box test fine when open but spark on-site. Turned out some idiot ran the case-screw into the transformer.

And GFI and arc-sense breakers will trip on things which did not used to be faults.

Otherwise: There has to be TWO problems. Yes, Friend may have reverse black/white, but the amp should work fine this way. So there is some white/black/green mix-up in the amp, in a way which only works with "legal" outlets. That is not acceptable because 60% of outlets are white/black reversed (in one small study of a typical idiot-wired kitchen).

[gar13]

Easy way to check, I have one of these in my toolkit. They only cost a couple of bucks at the hardware store. Let's you know if the hot and neutral are interchanged, as well as a few other wiring mix-ups/problems.

Tell him to check his outlets with it, at least you'll know if these is the problem or not.

[LooseChange]

The house where the circuit is blowing was tested with one of those devices and is wired correctly.... All sockets.
Just a reminder that the amp blows the circuit with the amp OFF.

[bnwitt]

  This is somewhat perplexing.  How is this amp wired?  Does the on off switch break both the hot and neutral legs or only the hot leg?  If only the hot leg, does the cord's neutral wire go straight to the PT primary side wiring?  Is the only grounded wire the green wire of the cord or is the neutral wire of the PT grounded too?  Is there a separate neutral bar in the service panel or a common bar for both neutral and ground.  If there is a separate neutral bar is there voltage present on the neutral to the ground buss inside the panel?  Have you placed and AC ammeter with peak hold funtion to determine at what current level the breaker is tripping?

[sluckey]

Just a reminder that the amp blows the circuit with the amp OFF.

Does it trip that breaker if it's plugged into another outlet on that same circuit? Does it trip another breaker if it's connected to another outlet on a different circuit?

Disconnect the power cord green wire from the chassis. Still trip the breaker?

[plexi50]

Have you  removed the on switch and checked it out? This is one of those great mysteries /

[RicharD]

"plug Bug" testers are known to lie.  I've pitched 2 or 3 of them in my day.  You might want to test the tester by miswiring a receptacle on the bench.  Regardless, an amp should work with line polarity reversed and as PRR stated, miswired receptacles are common.  This is a good argument for leaving "death caps" in a properly grounded amp.

I'm leaning towards an intermittent line short to chassis.  It could be (probably) hot to chassis or neutral to chassis (if the user's house is reversed).  You've probably ruled out the cord itself since you replaced it.  There isn't much connected to the line: fuse, power switch, 120V pilot lamp (if applicable), and the primary of the power transformer.  Under no circumstance should you read continuity between the ground and neutral, or the hot and ground.  With the switch off, you should read no continuity hot to neutral but with the switch on, you should read some resistance (a few ohms) hot to neutral.  Grab 2 ohm meters, tie 1 side of each to the cord's ground pin, one of the remaining to the cord's neutral pin, and the last one to the cord's hot pin.  Now grab the amp and shake it, flip it around, and chop stick the line power circuitry heavily.  See if you can make it beep.  Look for obvious thangs like a chassis screw running into something it shouldn't, or a solder blob under a turret board.  Perhaps there is a rogue nut up in the bell of the PT?  

If you can't find it, take your lamp limiter with you when you go back to the customer's house.  If it blows a breaker with a lamp limiter in line, the you've narrowed it down to premises wiring.  There is the possibility his house wiring was done with with 12/3 home runs and a neutral has come loose somewhere.  This effectively puts the 2 - 120V circuits in series.  This doesn't mean the breaker should trip, but a plug bug doesn't know the difference between 50V, 120V, or 240V.  All it know is polarity.  Sometimes there's no substitute for a real meter.

I'm still leaning towards a bad power switch, fuse, cord, split wire, solder blob, or messed up primary PT wiring in that order.

[Jack1962]

A bad breaker would be my first guess bro 


                                                Rock On

[alerich]

I'd try the amp in a third house. 

[Rev D]

 Does the shop have a bigger breaker than the houses? (i.e. 15 amp vs 20 amp) Quite the conundrum for sure.

D.

[PRR]

> take your lamp limiter with you

May pop without glow. To be for-sure, you need at least 2 of the 3 wires series-lamped. Imagine a Ground to "Neutral" short on an outlet with a white/black cross. We usually lamp the black lead. It would not light-up for a ground to "hot Neutral" fault.

> A bad breaker would be my first guess bro 
> I'd try the amp in a third house.
> Does the shop have a bigger breaker than the houses?

Unless this "other house" has an unrevealed history of odd electric troubles, these are probably red herrings. A Princeton is a small amp, no strain on a 15A breaker. (Anyway it was stated the amp was OFF.) If breaker is bad, other amps and lamps would be popping it. Third house... 2 out of 3 may be a democracy, but most amps work in 999 of 1,000 houses; and is the guy in the third house looking to buy a Princeton?

[LooseChange]

I'm going to get to this this weekend.
Meanwhile, I did bring the amp into my bathroom and tested it at the GFI... It popped everytime with the amp off.... Is this a clue?? Thanks!

[supro66]

I think it has to be the OFTEN ON switch in the amp

It is wired wrong

I bet when the switch is in the off position the white and black wires are connected

do an OHMS test on the plug

[alerich]

Third house... 2 out of 3 may be a democracy, but most amps work in 999 of 1,000 houses.

That would be a better test but who has time to schlep an amp to 988 houses?

I see with LC's GFCI comment that things are pointing toward amp - not house wiring. Road trip cancelled.

[Tiny_Daddy]

It's gotta be flowing current from the Hot (black wire) to chassis. Another thought: For amp applications, the black wire should go to the amp's fuse first, then to the switch. Does it?

[LooseChange]

Figured it out and, of course, it's stupid....

This chassis has the fuse holder on the bottom of the chassis, standing straight up.  The inside of the cabinet has an aluminum shield. They touch sometimes!
Thanks all it was.

Thanks for all the creativity.. Makes you think.

White to fuse, Black to switch on this one.

[RicharD]

>White to fuse, Black to switch on this one.

So you had a neutral to ground short.  That should trip a GFCI under normal conditions or a house breaker if the polarity is reversed.  I suspect your plug bug was lieing and your friend has a reverse polarity circuit in his house.  Real meter > plug bug.  Some folks frown on neutral fusing.  This doesn't stop the fuse from working properly but the circuit will remain hot with respects to ground if the fuse trips.  The down side is if you have a primary hot short to the chassis, the fuse will do nothing.  The fuse will protect anything on the secondary of the transformer but not the power switch, 120V pilot lamp (if applicable) or power cord.  All of this is a good argument for hot fusing and DPDT power switching.  Case -n- point, you were tripping the house breaker and not blowing the fuse.  This is a great "real world" example we can all learn from.  Thanks for sharing.

-Richard

[plexi50]

A great thread. It those little things that just baffle you in the end after finding the problem. Glad you got it figured out.

[John]

yep, I've been checking twice a day at least to find out what the solution was! 

[LooseChange]

Here is the culprit. Circled it.

[Tiny_Daddy]

What are those blue capacitors?

[phsyconoodler]

They look like the new Sozo molded caps.

[theundeadelvis]

Was it shorting out in the cabinet and fine when you had it in the shop out of the cab, or something else?

[LooseChange]

Sozo's for sure.
Shorted when in the cab... Sometimes. That was the conundrum.