Carver M-400a schematic

Hello Joshua Wells,

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Hum can come from a jillion different places. Is this hum coming from the unit with no speakers connected, or is it heard through the speakers? What sources are being used? What cables? Are thereany common sources of interference near? Troubleshooting is difficult without much information.

this could be related to the power supply it is the
magnetic field variety that has a thyristor controlling its input check if the voltage supply to the amp outputs is varying when the pulsing is heard. if so
the control curcuit could be at fault.

magnetic field supplies are different than conventional types, check that the thyristor is working properly

is that resistor in the line to q12 ? if so it should be in the spec sheet for that device. if you don't have the spec sheet then let me know what q12 part number is.

Carver designs in general are not easy to repair. I would recommend that you send this unit into a Carver authorized service center. The likely problem is the output transistors, but the driver circuits and predrivers are not simple designs and if there is a problem there, it could effect the outputs. Tracing this will require equipment and schematics that I don't believe are available on the net.

Dan

You need an amplifier with at least 200 wpc to get the most out of your BOSE. Look into getting a NAD, ADCOM or CARVER amplifier. I prefer CARVER myself. I am running a CARVER M-500T(251 wpc) on my 901's and they sound incredible.

1-shut down all flourecent lamp and check.
2-check for your cables in a good condition and no touching of wires to the body of amp.
3-connect(ground loop isolator)code number(270-054)from radio shack near you and connect it between your audio device(like cd player and amp)

your going to need this place to download the remedy's for your system http://www.euras.com/repair_tips_1/CARVER/AV505/AV505_CARVER.htm

if it is not working then there is another serious problem , and it could be the amp IC or the volume IC but tests will need to be done to determine what is causing the failure , but it does sound like amp IC as a suspect since the rear were not even working , did the volume seem different when turning it up or down before the center quit or after the center quit?

I just picked up the same amp, a Carver TFM-35x, with the same problem, the bulbs that light up the meters are burnt out. They aren't hard to replace, but I didn't know what bulb to use. I found out today that you need to use 12 volt, .15 amp bulbs (150 milliamp). And it needs to be an axial-type bulb.