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Carver MXR130 no sound
Carver MXR130 no sound
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Old 17th July 2019, 06:15 PM   #1
rodner is offline rodner  United States
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Default Carver MXR130 no sound

I just picked up a carver mxr130. I play a 1khz test tone through it and I can measure the same signal on the speaker terminals and show ac voltage around 60v with the volume all the way up. But, when I plug in speakers, I have no sound at all. Any ideas?
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Old 17th July 2019, 09:28 PM   #2
Ylli is offline Ylli  United States
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Have you tried both 'A' and 'B' speakers? First place I'd check would be the speaker relays. You have two of them one to switch between speaker set 'A and 'B' and the other to disconnect the speakers in case of a protection fault.
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Old 18th July 2019, 01:17 PM   #3
rodner is offline rodner  United States
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I'm getting signal through both A&B speakers. Just no sound.
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Old 18th July 2019, 02:54 PM   #4
Ylli is offline Ylli  United States
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My interpretation of your symptoms is that you are seeing the output when looking with a high impedance measuring device, but lose the output when the load draws current. This is indicative of a high resistance in the output path. Primary suspects would be the relays.

When you are trying to drive speakers and are getting no output, measure the AC voltage across the speaker terminals and then measure the AC voltage at the junction of R543 & R545 (or R544 & R546). If you have good signal at the amplifier outputs (R543/R545 or R544/R546) but not at the speaker, then follow the signal path through from the amplifier output to the speakers and see where it is lost.

Note this has an output relay configuration that selects 'A' speakers, 'B' speakers, or 'A & B' speakers. In the 'A & B' position, the speakers are in series and both A and B must be connected for there to be any output. Due to this configuration, you will need to confirm that the speaker output black (-) terminal is at chassis ground when that particular speaker is selected.
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Old 18th July 2019, 02:59 PM   #5
rodner is offline rodner  United States
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Thanks for that! Good insides are welcomed!

I added an 8ohm dummy load to it this morning and the relays went crazy. So, I ordered a pair of them. I can trace the output signal all the way to the relays with the dummy loads installed. I'm going to replace them and see what happens. I'll let you know.
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Old 18th July 2019, 04:51 PM   #6
Mark Tillotson is offline Mark Tillotson
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Relays going nuts indicates the the protection circuitry is likely to be the problem, I doubt its the relays themselves, they just do what they are told.
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Old 18th July 2019, 05:40 PM   #7
rodner is offline rodner  United States
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Good point. But, I can't find any reason for the protection circuits to be active.
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Old 18th July 2019, 06:09 PM   #8
Ylli is offline Ylli  United States
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Connecting an 8 ohm dummy load makes the relays go crazy, but connecting an 8 ohm speaker does not? That's strange.

Could also be a power supply that is sagging under load.
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Old 18th July 2019, 08:11 PM   #9
rodner is offline rodner  United States
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I haven't checked the power supply yet.
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Old 18th July 2019, 11:47 PM   #10
MAAC0 is offline MAAC0  Portugal
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Measure for DC before the relays. If there is DC that indicates a supply fault or presumably blown output drivers.
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