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Carver TFM-35X testing recommendations

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  • Carver TFM-35X testing recommendations

    I have a Carver TFM-35X that I am attempting to repair. I received it with a blown right channel. This was done when the amp was being used in bridged mono mode. It physically blew up several parts. Miraculously, the circuit board appears unharmed. I found that 2 of the output transistors were dead shorts, along with an open emitter resistor, 2 shorted diodes on the + and - 25 volt rails. 2 of the bias/balancing transistors were apparently in the path of doom and got taken out along with their attached resistors. I tested the other small transistors for shorts and they measured OK. For good measure I replaced all of the power transistors attached to the heat sink.

    Unfortunately this thing is a mechanical nightmare, so I'm trying to make sure that I have all my ducks in a row before I power it up for testing.
    I've always found the group in this forum to be very knowledgeable so I was hoping for some advice on a couple of questions.

    1. There was no thermal grease between the power devices and the heatsinks, only the insulating rubber pad. Is it recommended to add the grease or go with the original insulator material?

    2. Is it wise and/or safe to bring this device up for testing on either a variac or dim bulb tester? There doesn't seem to be tons of info on this amp online, so I can't find a straight answer on this.

    I'm attaching the schematic. I can list out the parts that I found as bad and replaced (along with the power transistors that did test OK and were replaced).

    Thanks in advance for any thoughts on this.

    Dave
    TFM-35x Service.pdf

  • #2
    Those rubber insulators are sil-pads and do not use heatsink grease. Make sure none are nicked or damaged in any way.
    By all means use a variac or dim bulb and power up with no load until you verify there is no DC on both channel outputs.
    Originally posted by Enzo
    I have a sign in my shop that says, "Never think up reasons not to check something."


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