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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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#1
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Technics SA5160 distortion on one channel
Greetings.
I wonder if anyone has some insight into this problem. This receiver uses two STK0177 power amplifier "blocks", each with 10 in-line connectors. The LH channel is highly distorted, the RH channel is perfect. The distortion is present on FM, AM and AUX (with sig, gen. input) so it's not the FM demodulator - it's definitely in the audio stages. The DC voltages on each of the two STK0177's power amplifier pins are as follows (with 115 VAC supply): Pin # RH channel LH channel (volts) 1 +0.251 +0.229 2 +0.002 +0.002 3 +0.255 +0.229 4 -26.90 -26.77 5 -1.272 -1.288 6 -28.29 -28.28 7 +0.060 +0.20 8 +28.23 +28.22 9 +1.309 +1.257 0 +26.95 +26.77 (I hope the columns hold together!) I have not yet put a 'scope on each STK0177 line to watch for clipping or drive distortion (pin-out not known.) Nothing gets too hot and there is no perceptible difference in temperature between the two heat sinks (but they are thermally connected do some degree, so that's not conclusive.). Do people think this is a failed STK0177? Or is there another candidate component? Unfortunately, I do not have the schematic. Also, does anyone have a pointer or URL to the pinout and/or spec sheet for the STK0177? I did a quick Google but with no success. BTW, this unit is very difficult to service since all the electronics are on one large PCB and you can't access the bottom of this PCB without disconnecting just about everything and lifting it up (unlike other Technics models where you can take out the metal floor plate.) Thanks for all comments. Cheers, Roger |
#2
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Technics SA5160 distortion on one channel
I'm not at all sure the voltages are far enough off to suggest a problem
with an output IC. Have you just tried manipulating the various controls and switches to eliminate them first? If you swap the output IC's, that would be the final test. That's an odd STK number though, you might have trouble finding one. I use East Coast Transistor parts for old STK's - they can usually suggest a good sub number if one exists. Mark Z. -- Please reply only to Group. I regret this is necessary. Viruses and spam have rendered my regular e-mail address useless. "Engineer" wrote in message ... Greetings. I wonder if anyone has some insight into this problem. This receiver uses two STK0177 power amplifier "blocks", each with 10 in-line connectors. The LH channel is highly distorted, the RH channel is perfect. The distortion is present on FM, AM and AUX (with sig, gen. input) so it's not the FM demodulator - it's definitely in the audio stages. The DC voltages on each of the two STK0177's power amplifier pins are as follows (with 115 VAC supply): Pin # RH channel LH channel (volts) 1 +0.251 +0.229 2 +0.002 +0.002 3 +0.255 +0.229 4 -26.90 -26.77 5 -1.272 -1.288 6 -28.29 -28.28 7 +0.060 +0.20 8 +28.23 +28.22 9 +1.309 +1.257 0 +26.95 +26.77 (I hope the columns hold together!) I have not yet put a 'scope on each STK0177 line to watch for clipping or drive distortion (pin-out not known.) Nothing gets too hot and there is no perceptible difference in temperature between the two heat sinks (but they are thermally connected do some degree, so that's not conclusive.). Do people think this is a failed STK0177? Or is there another candidate component? Unfortunately, I do not have the schematic. Also, does anyone have a pointer or URL to the pinout and/or spec sheet for the STK0177? I did a quick Google but with no success. BTW, this unit is very difficult to service since all the electronics are on one large PCB and you can't access the bottom of this PCB without disconnecting just about everything and lifting it up (unlike other Technics models where you can take out the metal floor plate.) Thanks for all comments. Cheers, Roger |
#3
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Technics SA5160 distortion on one channel
See below...
"Mark D. Zacharias" wrote in message ... I'm not at all sure the voltages are far enough off to suggest a problem with an output IC. Have you just tried manipulating the various controls and switches to eliminate them first? Yes, all OK. If you swap the output IC's, that would be the final test. Good point! But that is a VERY difficult job on this board (see below in my text.) I may have to do it, though. That's an odd STK number though, you might have trouble finding one. I use East Coast Transistor parts for old STK's - they can usually suggest a good sub number if one exists. Thanks for that idea - will file it for future use. Mark Z. -- Please reply only to Group. I regret this is necessary. Viruses and spam have rendered my regular e-mail address useless. "Engineer" wrote in message ... Greetings. I wonder if anyone has some insight into this problem. This receiver uses two STK0177 power amplifier "blocks", each with 10 in-line connectors. The LH channel is highly distorted, the RH channel is perfect. The distortion is present on FM, AM and AUX (with sig, gen. input) so it's not the FM demodulator - it's definitely in the audio stages. The DC voltages on each of the two STK0177's power amplifier pins are as follows (with 115 VAC supply): Pin # RH channel LH channel (volts) 1 +0.251 +0.229 2 +0.002 +0.002 3 +0.255 +0.229 4 -26.90 -26.77 5 -1.272 -1.288 6 -28.29 -28.28 7 +0.060 +0.20 8 +28.23 +28.22 9 +1.309 +1.257 0 +26.95 +26.77 (I hope the columns hold together!) I have not yet put a 'scope on each STK0177 line to watch for clipping or drive distortion (pin-out not known.) Nothing gets too hot and there is no perceptible difference in temperature between the two heat sinks (but they are thermally connected do some degree, so that's not conclusive.). Do people think this is a failed STK0177? Or is there another candidate component? Unfortunately, I do not have the schematic. Also, does anyone have a pointer or URL to the pinout and/or spec sheet for the STK0177? I did a quick Google but with no success. BTW, this unit is very difficult to service since all the electronics are on one large PCB and you can't access the bottom of this PCB without disconnecting just about everything and lifting it up (unlike other Technics models where you can take out the metal floor plate.) Thanks for all comments. Cheers, Roger |
#4
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Technics SA5160 distortion on one channel
"Engineer" bravely wrote to "All" (16 Jun 04 23:04:54)
--- on the heady topic of "Technics SA5160 distortion on one channel" En From: "Engineer" En Greetings. En I wonder if anyone has some insight into this problem. En This receiver uses two STK0177 power amplifier "blocks", each with 10 En in-line connectors. The LH channel is highly distorted, the RH channel En is perfect. The distortion is present on FM, AM and AUX (with sig, En gen. input) so it's not the FM demodulator - it's definitely in the En audio stages. En The DC voltages on each of the two STK0177's power amplifier pins are En as follows (with 115 VAC supply): En Pin # RH channel LH channel (volts) En 1 +0.251 +0.229 En 2 +0.002 +0.002 En 3 +0.255 +0.229 En 4 -26.90 -26.77 En 5 -1.272 -1.288 En 6 -28.29 -28.28 En 7 +0.060 +0.20 En 8 +28.23 +28.22 En 9 +1.309 +1.257 En 0 +26.95 +26.77 En (I hope the columns hold together!) En I have not yet put a 'scope on each STK0177 line to watch for clipping En or drive distortion (pin-out not known.) Nothing gets too hot and En there is no perceptible difference in temperature between the two heat En sinks (but they are thermally connected do some degree, so that's not En conclusive.). En Do people think this is a failed STK0177? Or is there another En candidate component? Unfortunately, I do not have the schematic. En Also, does anyone have a pointer or URL to the pinout and/or spec En sheet for the STK0177? I did a quick Google but with no success. En BTW, this unit is very difficult to service since all the electronics En are on one large PCB and you can't access the bottom of this PCB En without disconnecting just about everything and lifting it up (unlike En other Technics models where you can take out the metal floor plate.) En Thanks for all comments. En Cheers, En Roger With a lot of obvious distortion a scope will just confirm it but it could be useful to locate where it starts. If Pin 7 is the output to the speakers then 0.20 volts on the left channel is certainly cause enough for distortion. The +Vcc is also a little low compared to -Vcc. This unbalance indicates the IC is sourcing significant current from the positive supply into the speaker. Try and measure the same voltage without the speakers. If it goes way up then the IC could be bad. However, a leaky coupling cap can also unbalance the IC or high ESR can cause a parasitic oscillation though the latter isn't as likely. Good luck and be careful! A*s*i*m*o*v .... KPLA: Klingon Radio: All Klingon Opera, All The Time. |
#5
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Technics SA5160 distortion on one channel
See below...
"Asimov" wrote in message ... "Engineer" bravely wrote to "All" (16 Jun 04 23:04:54) --- on the heady topic of "Technics SA5160 distortion on one channel" En From: "Engineer" En Greetings. En I wonder if anyone has some insight into this problem. (snip) With a lot of obvious distortion a scope will just confirm it but it could be useful to locate where it starts. That was my plan. If Pin 7 is the output to the speakers then 0.20 volts on the left channel is certainly cause enough for distortion. Damn, that's a typo! It's actually 0.020 VDC, a bit less than the RH channel. I don't know the pin-out but I plan to measure the voltage across the speaker termimals with and w/o a speaker connected, RH and LH channels. The +Vcc is also a little low compared to -Vcc. This unbalance indicates the IC is sourcing significant current from the positive supply into the speaker. Try and measure the same voltage without the speakers. If it goes way up then the IC could be bad. However, a leaky coupling cap can also unbalance the IC or high ESR can cause a parasitic oscillation though the latter isn't as likely. Good luck and be careful! Thanks. A*s*i*m*o*v ... KPLA: Klingon Radio: All Klingon Opera, All The Time. Cheers, Roger |
#6
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Technics SA5160 distortion on one channel
"Engineer" wrote in message
... Greetings. I wonder if anyone has some insight into this problem. (snip) Pin # RH channel LH channel (volts) 1 +0.251 +0.229 2 +0.002 +0.002 3 +0.255 +0.229 4 -26.90 -26.77 5 -1.272 -1.288 6 -28.29 -28.28 7 +0.060 +0.20 Typo! It's 0.020 VDC 8 +28.23 +28.22 9 +1.309 +1.257 0 +26.95 +26.77 (snip) Cheers, Roger |
#7
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Technics SA5160 distortion on one channel
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