Pioneer GM-X304

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anatech

anatech

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Joined 2004
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Hi,
I have a Pioneer GM-X304 in for service. The RCA ground is open to the amp ground. There is a 10V DC offset between the RCA inputs and everything else.

I'm guessing a resistor is open, unless they are using a referenced active ground.

Any ideas?

-Chris
 
anatech

anatech

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Joined 2004
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Hi Perry,
I am not familiar with the new Pioneers for sure, but what you say makes some sense. I'll test the regulator tomorrow AM.

If it helps, all speaker outputs are within mV of common ground. The previous tech (unknown) has replaced all the op amps, looks like twice.
The amplifier does not go into protection either.

Are the inputs referenced to ground via the car chassis? Right now there are left floating on the bench.

Thanks very much for the reply.

-Chris
 
anatech

anatech

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Joined 2004
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Hi Perry,
After some testing I have determined the following.

Both 15V regulators are running fine, but getting warm. The main supplies are + / - 25VDC.

The op amps on the input are not getting any supply power. The entire mess is sitting around 10 above ground.

-Chris
 
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dce

Member
Joined 2005
gmx304

anatech,

Did u check if there is a coil in the rca ground line...usually a green
one and very small... if there is check to see if they are open.
some pioneer amps the rca is not directly connected to chasis ground, it gets the ground fron the head unit, the rca ground on some models pass through a coil and goes to the one input of the opamp....can u take a picture of the heatsink and the inside
of the unit, maybe i have a service manual with similar model that we can compare. Ive got some late 90's service manual here.
I wish I can help you more.

dce
 
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dce

Member
Joined 2005
gmx304

anatech,

thanks
I got the pictures, to me, the inside is look like gmx922 or 1022.
I am looking right now on my files.
It would be nice if you can take a picture of the top cover(heatsink) so I can find it easily on my files.
usaually if they have the same heatsink they are under the same series. thanks

dce

:)
 
P

Perry Babin

Member
Joined 2003
bcae1.com
I found a schematic and it looks like the isolator section (the front-end op-amps IC 851-854) will float to 10 volts if there are no RCA inputs or if the RCA input shield grounds are floating (not connected to chassis ground). From that point on, the op-amps seem to be referenced to chassis ground.

The secondary ground is connected to chassis ground.
 
anatech

anatech

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Hi Perry,
Thank you so much for that. The amp does run okay with the RCA's grounded. I'm not okay with running DC current through the signal leads. Oh well.

Is there a way to send a copy of the schematic to my email? If not, that's okay. Just eternal curiousity.

-Chris
 
anatech

anatech

Administrator
Joined 2004
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Hi Danny,
Thanks for looking. I did get it.

Now the last problem. Previous gorilla has stripped many mounting holes in the heatsink. Too bad Pioneer didn't use machine screws instead of fine pitch self tappers.

The amp is running fine, thanks very much to all.

-Chris
 
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