MA3600VZ odd distortion on one channel

7 posts in this topic

I've got a 3600VZ on the bench here, with an odd fault on one channel. Basically, it looks like something's going unstable and oscillating in the positive half of the cycle, resulting in this output waveform (photos were taken a while ago):

With no load attached:


With 4 ohm dummy load attached:


I happen to be using a 200Hz sine wave input, but some kind of distortion happens at all frequencies. The trace is shifted down, so the oscillation can be seen on the positive cycle.

Here are some more photos from today, with no load, at different frequencies:







Any ideas?? Note the huge negative spike at the same positive voltage level on every trace... Biases are all in spec and I've swapped everything socketed on the main board to no avail.



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Ok, just done that and the problem is still there with Ch2's VZ module connected to Ch1. So... looks like main or output module fault.

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I've had a similar problem a while ago and had to send the unit back to Crown. (Hey, it happens!)

Apparently, it was a (or perhaps more!) output transistor! Since one the sides appear good, swap output transistors (6 at a time) and determine which set (if discovered!) was faulty. In my problem, the error side didn't generate any distortion. As far as your images demonstrates and if this solution is conclusive, could we have determined the fault with this information?


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I have repaired hundreds of macrotech. Never seen waveforms like those. Possibly the 100hz.

Did you find the fault?

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