Rowe CD100B amplifier pop at power on

vpkc

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Recently acquired a CD100B which emits what sounds much like a gunshot when the amplifier powers on. Unnervingly loud and I'm guessing it can't be "normal". There's a slight "thump" as the amp powers off, however it pales in comparison to the god awful "crack" when it powers up.

Internal speakers only and the remote wiring, etc. appears to be at factory defaults although there is some evidence of it having been used at one time. There is some noticeable distortion in the right channel while playing and the overload indicator does flicker briefly on the right channel but only during the initial power on/firearm salute. I can't tell for sure whether the pop is occurring in both channels or only the right. Upon closer inspection of the amp I discovered mismatched 10A and 14A fuses in the right driver board which I replaced with the correct 8A ones. Somewhat to my surprise they have yet to blow, so whatever was once overloading the amp must no longer present. The large caps look to be okay visually.

In reading the posts here I'm compiling a list several known issues (cold solder joints, crossover issues, etc.) to check for on this unit, however I'm hoping these distinct symptoms passing through the right pair of knowledgeable eyes here might help to point me in a particular direction.

Thanks much!
 
I know some of the vinyl boxes had that pop at powerup. There was a set of diodes installed somewhere, maybe in the power supply or on the crossover board? I don't remember what the purpose was but Rowe eventually quit doing it. It was harmless, just annoying as hell. I'm wondering if maybe yours has something like that in it. Is it possible that older parts were used in the CD boxes?
 
Thanks, Doughbroz. A little more digging and I now see the loud "pop" is normal for these Rowe boxes:

http://forums.arcade-museum.com/showthread.php?t=159057

Anyone have any tips as to how I might isolate the right channel distortion? Assuming they're nearest the top of the heatsink the right channel output transistors appear to be new(er) whereas the left appear to be the originals. I'm thinking the next step may be to flip-flop the driver boards in the amp and see if the problem follows. From what I've read the speakers in these boxes rarely fail, although it sure sounds a lot like a fried voice coil.
 
Yes the loud pops at turn on/off are normal.

Check all the boards in the amplifier and the crossover board for any cold solder joints.

Recap the preamp board and both driver boards.

Set the bias on the driver boards.
 
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