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Was wrestling with my 3rd generation (Blue/Red) B&K St-140, using spade lug connectors (large ones) and managed to let the + and - on the R channel touch.
Fired it up, right channel MIA. Checked the connectors. Crap! Checked the speaker fuse. Blown. Replaced speaker fuse with correct value (5 amp, 250 V fast blo) and fired the 140 up again.
Right channel back but very distorted. Guess the fuse didn't blow fast enough to overcome my stupidity. Have no idea what was damaged. hoping to find a repair tech in the northern Virginia area who knows B&K amps.
Just hope it's not one of the 4 MOSFETS on that channel because those puppies aren't easy to find.
I repeat. Grrrrrr.
Opus 33 1/3
Follow Ups:
I blew out the left channel on my PS Audio 4.5 back up preamp. I left the system on because I was changing TT's, I thought I was pulling the power plug on the TT. Turns out it was the pre power cord. I feel ya buddy......
I have a couple B/K ST 140 amps. I believe there are internal fuses as well. The earlier on had them on the power supply board and the later on each channel board? It is best to unplug the unit and let it set for several hours before doing a internal inspection if you are not familiar with the potential dangers.
power supply rail fuses, but i doubt they would cause distortion in the one channel.
Opus 33 1/3
I am guessing there is a fuse for the positive and negative voltage for each channel. I am wondering if the loss of one might do it? I always try to start simple before buying parts. Good luck.
But since he will be opening the unit up, might as well replace the PS caps since I think they are originals.
Opus 33 1/3
Good idea. If you took out a channel it might be cheaper to buy another unit? Just swap the entire channel board/transistors.
Opus 33 1/3
Did exact same thing with my Conrad Johnson MF2300A amp. Blew two MOSFETS on the left channel. Fortunately I was able to find a good technician Audio Specialties in Portland, OR that fixed the amp at a reasonable cost ( a little over $200)
Do not EVER fiddle around with your power amp while it is connected to AC power. And even after you've disconnected the AC feed you should allow sufficient time for the caps to discharge, probably 15 minutes or so...
-RW-
The amp was unplugged while I connected the spades to the binding posts. I simply was not careful to be sure the wide spades were not touching. When I plugged in and hit the switch, there was no pop, smoke or anything, just no sound from the right channel. I immediately powered down and checked the speaker fuses. The right had blown. I checked the spades, saw the two for the right channel were touching, fixed that and replaced the fuse.
Powered up and the R channel was back but distorting badly.
Opus 33 1/3
I guess the lesson here is "Make sure you've made a proper connection before applying AC power to the amp." Sorry for your troubles, it happens to the best of us once in a while...
-RW-
Opus 33 1/3
...may be cheaper than the repair.
I thought I was the only one in history to have done that.......I blew an amp channel and a woofer on the speaker. Not my finest moment. I hope your repair goes well.
See link.
MOSFET Breakthrough!
Maybe you can be the first to try them.
Seriously, I hope your repair goes well.
Opus, I don't recall the name but Sam Tellig is friends with one of the principles from B&K. I happened to go on Sam's last Russia tour promoted through Stereophile and that guy was one of the group.
Since he retired I've seen Sam (Tom actually) posts a bit on General so you might reach out to him there. Hopefully that connection can suggest a tech for you.
"You can't know what the "best" is unless you have heard everything, and keep in mind that given individual tastes, there really isn't any such thing." HP
Opus 33 1/3
"Right channel back but very distorted. Guess the fuse didn't blow fast enough to overcome my stupidity.
Did it have the correct fuses, equipment is designed to use ether a fast or slow blow fuse, it is safe to use a fast blow fuse in equipment designed to use a slow blow unless the fuses keep blowing.
Regards,
Mike.
B&K specified 5A/250V fast blo and that's what was installed. There are 4 power supply fuses inside, but I doubt the issue is there. More likely what airtime suggested.
Opus 33 1/3
It is VERY difficult for a fuse to pop faster than the semiconductor to which it is connected.
To that end I've seen ULTRA fast blow fuses which CAN react fast enough to save a semiconductor.
Something like I've linked MAY have helped save your output devices.
Replace 'em ALL at once, not just the one that popped.
Too much is never enough
If it's playing but distorted you may have just blown out the driver transistors and spared the outputs. Either way don't push it by playing it.
Driver transistors are typically more common and many still available. Been there with a Vintage Marantz - TWICE!!!!!
Opus 33 1/3
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