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Short circuit connecting preamp with amp (RCA)

elgrillo

elgrillo

El Grillo
Hi guys , need some help here from the experts please. Im trying to connect a Marantz 3200 preamp and a marantz 32 power amp, but im getting shortcircuit in the main box of the house (Triped circuit in the box).

The preamp alone powers up with out a problem, and the power amp either. But when y connect them with a pair of RCA cables , they generate a tripped circuit breaker at the main panel box.

Anybody knows what could be happening? , what should I check first?

Thanks in advanced and sorry for my poor english!
 
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I'd guess that one of them has a hot chassis for some reason. Either the power cord has been changed so that it can be plugged in backwards, or one of the pieces has a fault that is making the chassis hot (has AC voltage on it from the outlet). Some equipment is designed to use polarized plugs. On these, one of the blades that plugs into the wall outlet is widder than the other so that the plug only goes in one way. If someone swapped the cord with a non-polarized, then you can get a hot chassis.
I suppose it is also possible that the outlet is wired wrong.

Terry
 
TerryS said:
I'd guess that one of them has a hot chassis for some reason. Either the power cord has been changed so that it can be plugged in backwards, or one of the pieces has a fault that is making the chassis hot (has AC voltage on it from the outlet). Some equipment is designed to use polarized plugs. On these, one of the blades that plugs into the wall outlet is widder than the other so that the plug only goes in one way. If someone swapped the cord with a non-polarized, then you can get a hot chassis.
I suppose it is also possible that the outlet is wired wrong.

Terry
Click to expand...

Hi Terry, thanks for your help. In fact the pre amp has a 3 wire plug ( original ) , and the marantz 32 just a 2 wire plug ( not original ).

I tried puting the 2 wire plug in both ways , and the same story in both cases ( short circuit in the house)

There is a way to find if I have a hot chassis? with a digital volt meter? . Just to know what component is wrong, and try to,find the problem easier.

Thanks a lot!
 
does one have a ground cable to the wall plug and the other one not ? if so the one without is faulty and needs looking at . there will be a capacitor at the power switch that's going short circuit .
that's my theory anyway
 
petehall347 said:
does one have a ground cable to the wall plug and the other one not ? if so the one without is faulty and needs looking at . there will be a capacitor at the power switch that's going short circuit .
that's my theory anyway
Click to expand...

Hi Peterhall347, Yes the preamp has a plug with earth , and the power amp dont.

So you think the power amp is the one with the problem? There are some caps in the amp boards , in the relay board , and also the big filter caps. You think that i have to see the relay boards caps? I just jave a digital volt meter, so,I can't check the caps.

There is a way to check if the chassis is hot? with the DMM?
 
Do you have a voltmeter? If so, plug each unit in separately and check for AC voltage between the chassis and the ground socket of the wall outlet. It should be 0. I suspect the one with the non-original cord is the problem. Someone did that rather than actually fixing the problem.
 
Does the breaker trip if the two are connected together but neither is turned on? Obviously not, or you could just turn one on at a time to see which is causing the issue.
With a DMM, use the Ohms function to measure from the RCA outer ring to the hot blade of the power cord (not plugged in). If you look at an outlet, the two slots are not the same. One is wider (taller) than the other. The narrow one is hot (carries the AC power) and the wide one is neutral (acts as the return path for the power). The roundish one is ground (safety).
So on the pre-amp, measure from the outside of the RCA jack to the power cord blade that would go into the narrow slot. It should not be shorted. On the power amp, it should not connect to either blade.
If those check out OK, it could be your house outlet is wired wrong. Not unheard of. Since most things you plug in don’t care about the polarity, you can go for years with an outlet wired wrong and not know anything is wrong.

BTW, there is nothing else connected right? Just the amp and preamp?

Terry
 
I really don't think that preamp came with a three prong plug to begin with, at least here in the US. My 7C doesn't, nor did my Model 8.
 
It wouldn't be capacitors on the amp boards or the big filter capacitors, it would be a small blue or brown disc shaped capacitor that is attached to either the on/off switch or at the power plug inside the amp and/or preamp inside before the switch.

You say that they both work without the RCA jacks connected, so then you should measure to see if there is voltage between both chassis's without connecting the RCA jacks.

If you are getting 120 (or 240) across both chassis without the patchcords connected, then it is most likely the disc capacitor me and pete are talking about at the switch or plug in either the preamp or the amp.
 
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toxcrusadr said:
Do you have a voltmeter? If so, plug each unit in separately and check for AC voltage between the chassis and the ground socket of the wall outlet. It should be 0. I suspect the one with the non-original cord is the problem. Someone did that rather than actually fixing the problem.
Click to expand...

Im sure it's not the original cable, but Im sure also , that this unit originaly didnt came with a ground wired plug. This is a early marants power amp.

Im going to try that with the power amp. So if
i understand right I have to connect the voltmeters ( voltmeter in ac mode)black lead to the ground socket wall outlet , and the red lead directly to the chassis? And power up the amp?

The voltmeter Ac in : 2,20,200 or 750?

Thanks a lot!
 
Markw said:
I really don't think that preamp came with a three prong plug to begin with, at least here in the US. My 7C doesn't, nor did my Model 8.
Click to expand...

Hi markw , in fact the preamp is the 3200 (e) this is a european model, im in france by the way.

thx for the help.
 
have been looking at the schematic and i dont see a cap at the power switch .doesn't mean to say there isn't one though . also both units only show 2 pin plugs .
will look again and see if there is a european schematic as it might be slightly different .
n.b there is a 2.2 meg resistor from power to ground but i wouldn't think it could be a problem with the house breaker

looks like i have been looking at the wrong manual .. computer user error strikes again ..:tears:
 
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century tek said:
It wouldn't be capacitors on the amp boards or the big filter capacitors, it would be a small blue or brown disc shaped capacitor that is attached to either the on/off switch or at the power plug inside the amp and/or preamp inside before the switch.

You say that they both work without the RCA jacks connected, so then you should measure to see if there is voltage between both chassis's without connecting the RCA jacks.

If you are getting 120 (or 240) across both chassis without the patchcords connected, then it is most likely the disc capacitor me and pete are talking about at the switch or plug in either the preamp or the amp.
Click to expand...

Hi century tek, thanks for the help.

The power amp doesnt have a power switch. And no caps at the power plug.
and yes both worked independly, but when conected by the rca's ... kaput!

To mesure the voltage between chassis i have to put red lead to one chassis and black one to the other? ac or dc?

thanks for the help!
 
petehall347 said:
have been looking at the schematic and i dont see a cap at the power switch .doesn't mean to say there isn't one though . also both units only show 2 pin plugs .
will look again and see if there is a european schematic as it might be slightly different .
n.b there is a 2.2 meg resistor from power to ground but i wouldn't think it could be a problem with the house breaker

looks like i have been looking at the wrong manual .. computer user error strikes again ..:tears:[/QUOT

The pre amp is the 3200 (e), european version with 3 wired plug.

The power amp is 2 wired plug.
Click to expand...
 
am downloading model 32 manual now ..its being very slow coming
no useful information on the schematic ..
as suggested plug in both units and test volts in AC between the rca outer metal rings . set meter to 750v AC
don't touch the units at the same though with your bare skin ..in fact don't touch any of them for now .
 
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TerryS said:
Does the breaker trip if the two are connected together but neither is turned on? Obviously not, or you could just turn one on at a time to see which is causing the issue.
With a DMM, use the Ohms function to measure from the RCA outer ring to the hot blade of the power cord (not plugged in). If you look at an outlet, the two slots are not the same. One is wider (taller) than the other. The narrow one is hot (carries the AC power) and the wide one is neutral (acts as the return path for the power). The roundish one is ground (safety).
So on the pre-amp, measure from the outside of the RCA jack to the power cord blade that would go into the narrow slot. It should not be shorted. On the power amp, it should not connect to either blade.
If those check out OK, it could be your house outlet is wired wrong. Not unheard of. Since most things you plug in don’t care about the polarity, you can go for years with an outlet wired wrong and not know anything is wrong.

BTW, there is nothing else connected right? Just the amp and preamp?

Terry
Click to expand...

Preamp test: I used the DMM in conectivity mode and put one side to the outside of the RCA , and the other in the right side of the plug ( o beep ) the to the left side of the plug ( o beep ) and finaly to the earth ( it made a beep )

Power amp test : un side to the rca the other to the right side ( beep ) , then tryed to the other side of the plug ( beep agian)

to answer your last question , yes the amp and the power amp were the only components conected when i got the short circuit.

Thaks for the help!
 
elgrillo said:
hi century tek, thanks for the help.

The power amp doesnt have a power switch. And no caps at the power plug.
And yes both worked independly, but when conected by the rca's ... Kaput!

To mesure the voltage between chassis i have to put red lead to one chassis and black one to the other? Ac or dc?

Thanks for the help!
Click to expand...

ac.
 
petehall347 said:
am downloading model 32 manual now ..its being very slow coming
no useful information on the schematic ..
as suggested plug in both units and test volts in AC between the rca outer metal rings . set meter to 750v AC
don't touch the units at the same though with your bare skin ..in fact don't touch any of them for now .
Click to expand...

Thanks Petehall347, at the moment I cant make any test conecting the components , my wife is whatching TV at the moment :S and she' s being very supportive with this , so i dont want to bother her , now.

So if i got Ac in the meter? between the Rca's of the pre amp and the amp? what should be the next step?

thanks a lot for the help!
 
elgrillo said:
Preamp test: I used the DMM in conectivity mode and put one side to the outside of the RCA , and the other in the right side of the plug ( o beep ) the to the left side of the plug ( o beep ) and finaly to the earth ( it made a beep )

Power amp test : un side to the rca the other to the right side ( beep ) , then tryed to the other side of the plug ( beep agian)

to answer your last question , yes the amp and the power amp were the only components conected when i got the short circuit.

Thaks for the help!
Click to expand...

Sure sounds like the power amp is the problem then. Measuring the voltage from chassis to chassis just told us that one of the chassis was hot like we thought. Now measure from either chassis to the ground pin of an outlet. that will tell you for sure which chassis is hot.

Also, it may be that the breaker is a GFI (ground fault interupter), in which case it may not take much current at all to trip it. It this is the case, to find which chassis is causing the fault, I would use an RCA cable connected to the chassis and touch the shield of it to the ground pin of the outlet. This will pop the breaker when done to the 'bad' component.
 
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