No Sound From Rear Speakers

[Artaban]

I just purchased a second hand system from a neighbor. It is an old 1995 Pioneer CX-770 and M-770 set (receiver and amp joined by flat black cable). It came with a tape deck, CD player, two tower cabinets (3ch), a center speaker and two rear speakers (all pioneer). The receiver has Dolby Pro Logic Surround, which as I understand is used when using a VHS, or in today's age a DVD player, provided the media has the Dolby Digital logo.

I was originally trying to have sound coming from all speakers though upon further research realized that isn't how it works. However, there is a option to do a speaker test, whereby static noise plays through each channel from L-C-R and then S (both surround speakers at once). When I do this I can see on the receiver display which channel noise should be coming through and when, but when it cycles through the surround speakers no sound at all comes from them. I tried different wire, plugging the rear in the middle slot and cycling through but to no avail. I also tried plugging the center in the rear which gave no sound, but when switched back to center worked fine.

I purchased this whole thing to use with a turntable I just purchased but haven't even gotten to setting it up because I am fixated on figuring out why I can't get any sound from the surround speakers.

Any and all suggestions or comments are welcome and I thank you for taking the time to read this!

 

[Dan Madden]

Sounds to me like bad wiring to the surrounds OR......the surround speakers are fried. The fact that you connected your surrounds to the center channel out and they STILL didn't work tells me that there is a problem from the wires to the surrounds or the surrounds themselves and not the surround amp!

 

[Artaban]

Thank you for your response! Troubleshooting I have tried:

- Tried new wire from speakers to system.
- Tried rear speakers in center channel (no sound, so this tells me speaker/wire issue but I already switched the wire)
- Tried center speaker in rear channel(s) (no sound which tells me issue with amp in the rear channels)

Perhaps with the previous owner there was an "event" that somehow shorted out the inputs and speakers attached to it?

 

[TLS Guy]

Sounds to me like bad wiring to the surrounds OR......the surround speakers are fried. The fact that you connected your surrounds to the center channel out and they STILL didn't work tells me that there is a problem from the wires to the surrounds or the surrounds themselves and not the surround amp!

He did not get sound from the working center plugged into the rear either. My bet is that this old unit does not have proper DC off set protection and the rear channels failed and fried the rear speakers as they failed.

OP, connect a battery to the rear speakers and connect and disconnect the battery and see of you get a popping sound. Better get an ohm meter and see if the surround speakers have DC resistance. I bet they are open circuit.

Those old prologic receivers were never much use and now well passed their sell by date.

I will give it to you upstrate. You have just paid for someone's worthless old junk and saved them the gas to the recycling center.

 

[Artaban]

Thanks TLS Guy, I knew this thing wasn't much of it after my first Google search after getting it home.

I will do the battery test soon; however, I don't have an ohm meter. I may run to the hardware store for a look as well.

If if the speakers are toast, and there is a problem with the rear channels... Is there any way to open up the amp and replace the components causing the rear channel fail?

He did not get sound from the working center plugged into the rear either. My bet is that this old unit does not have proper DC off set protection and the rear channels failed and fried the rear speakers as they failed.

OP, connect a battery to the rear speakers and connect and disconnect the battery and see of you get a popping sound. Better get an ohm meter and see if the surround speakers have DC resistance. I bet they are open circuit.

Those old prologic receivers were never much use and now well passed their sell by date.

I will give it to you upstrate. You have just paid for someone's worthless old junk and saved them the gas to the recycling center.

 

[TLS Guy]

Thanks TLS Guy, I knew this thing wasn't much of it after my first Google search after getting it home.

I will do the battery test soon; however, I don't have an ohm meter. I may run to the hardware store for a look as well.

If if the speakers are toast, and there is a problem with the rear channels... Is there any way to open up the amp and replace the components causing the rear channel fail?

Yes, there is but not you. To service it you need some experience and a battery of test gear. We do not encourage service by the inexperienced because of the danger. You are working round high voltages and you need a variable output isolating transformer to be safe just for starters.