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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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TEAC Receiver with shorted analog switch chip
Recently I was asked to fix a TEAC home receiver/amplifier and I was able to
do so. I don't work on these things often, so I was surprised to find that all of the RCA jack inputs (CD, tape, etc.) are routed through a couple of integrated circuits that are essentially analog switches. This is how the tin-can pushbutton switches on the front panel effectively choose which inputs to amplify, instead of a direct mechanical switch selection. One of these analog switch chips shorted out, making the right audio channel put out much lower volume than the left -- no matter which audio source you picked. Replacing the chip fixed the problem, but I'm still wondering what caused the chip to fail in the first place. My question is this: Because of these analog switch input chips, is it now a good idea to turn off the power to the amplifier when installing or removing the input audio cables? Perhaps a static spike zapped the chip; I dunno. This unit didn't belong to me and I don't know the story of how the thing failed. Thanks! |
#2
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TEAC Receiver with shorted analog switch chip
It's always been a good idea to have the power OFF when plugging /
unplugging cables. Better still to have the piece unplugged from the wall entirely. Mech switch models still had the potential to loud pops or buzz when the plugs were inserted or removed, and you've just reminded us of one possible problem with digital switch IC's used this way. More likely your friends' problem was caused by lightning/surge or plugging some other device in there, like an electric guitar or an amp output which exceeded the voltage rating of that input. Or the chip may have simply failed for no good reason. Wouldn't be a bad precaution to try to ground oneself to the chassis when plugging in the inputs in the future - I may consider it after reading your post. One could simply touch the metal chassis while at the same time touching the outer ring of the RCA connector 'til one of them is seated. That would prevent most problems that might arise from this. Mark Z. "Matt J. McCullar" wrote in message . com... Recently I was asked to fix a TEAC home receiver/amplifier and I was able to do so. I don't work on these things often, so I was surprised to find that all of the RCA jack inputs (CD, tape, etc.) are routed through a couple of integrated circuits that are essentially analog switches. This is how the tin-can pushbutton switches on the front panel effectively choose which inputs to amplify, instead of a direct mechanical switch selection. One of these analog switch chips shorted out, making the right audio channel put out much lower volume than the left -- no matter which audio source you picked. Replacing the chip fixed the problem, but I'm still wondering what caused the chip to fail in the first place. My question is this: Because of these analog switch input chips, is it now a good idea to turn off the power to the amplifier when installing or removing the input audio cables? Perhaps a static spike zapped the chip; I dunno. This unit didn't belong to me and I don't know the story of how the thing failed. Thanks! |
#3
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TEAC Receiver with shorted analog switch chip
On Thu, 06 Nov 2003 11:30:57 GMT, "Mark D. Zacharias"
wrote: It's always been a good idea to have the power OFF when plugging / unplugging cables. Better still to have the piece unplugged from the wall entirely. I would think you would be better having all the equipment plugged in so they are all at the same ground potential. -Chris |
#4
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TEAC Receiver with shorted analog switch chip
It probably wouldn't make any difference - especially if the Teac has a
"hard" power switch, but it's always been good advice to keep the receiver unplugged from the wall until all your connections are made. Just reduces the chances of anything _bad_ happening. Mark Z. wrote in message ... On Thu, 06 Nov 2003 11:30:57 GMT, "Mark D. Zacharias" wrote: It's always been a good idea to have the power OFF when plugging / unplugging cables. Better still to have the piece unplugged from the wall entirely. I would think you would be better having all the equipment plugged in so they are all at the same ground potential. -Chris |
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