2. amps-preamps
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Changing rail fuses inside a B&K amp. Is it safe?

I need to change the rail fuses inside my B&K 200.5 amp. I have two channels which sound very fuzzy, almost no output, at any volume level. I changed the fuses in the back of the amp, for each channel, and it fixed a previous channel which was exhibiting the same behaviour. The two giving me grief now, were not fixed by changing the speaker output fuse, and I assume might be due to the internal rail fuses which are also a 6 amp slow blow.

The amp is probably nine years old.

My big concern is working around high voltage circuitry, and if it is safe to go in and change the fuses. Is this something I can and should do myself?
mar
6 responses Add your response
czarivey
5,946 posts
 
If unit keeps on blowin' fuses I believe the problem should be elsewhere. Once you open your unit take a look at output transistors tight onto the heat sink and the tac is greasy and not dry and chipping off. Otherwise transistors needs re-tac with new tac to the heat sink.
Quiet fan next to amp may buy you some time.
mar OP
8 posts
 
Thank you for the replies. I will do the change soon and post my results.
czarivey
5,946 posts
 
Yep it's something like that.
rlwainwright
1,904 posts
 
Just disconnect the amp for an hour before you change the fuses. No worries then...

-RW-
mar OP
8 posts
 
Thank you. When you say zap slightly, you mean a small arc when placing a new fuse back into the rail fuse holder?
czarivey
5,946 posts
 
nothing is lethal once you disconnect amp... however if you want to be completely safe, you can discharge filter caps(they may zap slightly if not completely discharged) with 1MOhm resistor, but do not short them. short caps with 1MOhm resistor and hold it for 5...10s. to verify and visualize you're actually discharging caps, you can also connect resistor terminals to the voltmeter.
all that discharge is only to reassure that zap won't happen.
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