Crown D75 monitor amp goes terminal

Happened the other day, took out the monitor speakers too.  I am not sure how this happened, but the production director reported that the speakers began making very loud squeal.  Somebody finally thought to turn off the amp using the conveniently located on/off switch on the front panel.

Crown D75 audio board burned open resistor
Crown D75 audio board burned open resistor

The two watt resistor is burned open.  Also, this got so hot it burned a hole in the circuit board below it.  Truth be told, I think this amp was about 25 years old and due to be replaced when the new studios were built out.

I’ve seen these Crown amplifiers self destruct in the past.

5 thoughts on “Crown D75 monitor amp goes terminal”

  1. Yet further proof that all electronics run on smoke. You let the smoke out, they don’t work any more.

    Heh.

    P.S. To any non-tech types reading this, yes, that was a joke!

  2. I subscribe to the magic smoke theory myself. Of course, higher power stuff like transmitters requires smoke and flame to work.

  3. Crown’s FM transmitters are better than their audio amps. I never liked them. My favorite monitor amp is the Western Electric 124E with 350B tubes. Next pick is the Sansui AU-217 which has about the closest “tube sound” in the solid-state world.

  4. We have lots of Crown amps here in the facility that shall not be named, and they are here for the duration. That resistor does run very hot, and when it goes it will take other components with it. I think part of the reason is that the pots get noisy and that causes voltage surges. New pots are available at Newark if I remember correctly. The D-45 model is worse for the noisy pots. We don’t have a single one with original pots that work. I have begun substituting some real cheapies from MCM (like $1.50 each) and with some heavy modification and complete tear down (they are not the mini size) they work perfectly and don’t get noisy.

  5. I recently repaired a 1986 D75 that did exactly the same thing. R1 went up in flame and almost burned a hole in the fiberglass circuit board. It scorched nearby parts for an inch around and burned out two traces. R2 had overheated as well but hadn’t lit fire yet. U3 (LM339) was also bad, maybe from the flame. Other than soot and discoloration, no other parts were defective.

    Crown recommends installing 910 ohm 3 watt flame-proof (duh) metal film resistors for R1 and R2, and also replacing the two 10V zener diodes D1 and D2 with 1N4740A parts, which are rated at 1 watt.

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