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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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Sansui receiver repair - xformer coil resistances?
Hey all;
I'm working on a Sansui receiver that shuts down as soon as I switch it on - no lights or anything. I've taken it apart and inspected the power supply section, and found that there is a very low resistance in a couple of the transformer's output wires. If I measure between either of the reds (there are 2) and the black (which is connected close to the reds, so I'm assuming that these taps go together) the meter reads about 0.6 or 0.7 ohms. Is it possible that this is the correct reading for this, or should I take that to be a dead short? I get somewhat higher readings on the other taps - more like 2.5 or 3 ohms. Also, has anyone had experience with a reciever with similar symptoms? Any tips? Thanks --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 |
#2
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The low resistance you measure may be normal. Some Sansui receivers had bad
1 ohm resistors in the power supply. There's lots of possibilities. Model number would help. Mark Z. "tempus fugit" wrote in message ... Hey all; I'm working on a Sansui receiver that shuts down as soon as I switch it on - no lights or anything. I've taken it apart and inspected the power supply section, and found that there is a very low resistance in a couple of the transformer's output wires. If I measure between either of the reds (there are 2) and the black (which is connected close to the reds, so I'm assuming that these taps go together) the meter reads about 0.6 or 0.7 ohms. Is it possible that this is the correct reading for this, or should I take that to be a dead short? I get somewhat higher readings on the other taps - more like 2.5 or 3 ohms. Also, has anyone had experience with a reciever with similar symptoms? Any tips? Thanks --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 |
#3
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do you know how to measure for voltages, do ya have a drawing, can get
one from Sams on-line. Xforms outputs do read low, ya going from AC high input to AC low output. |
#4
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I know how to measure voltages in audio equipment, tv's and the like. I
think I'd stay out of x-ray equipment, radar, very high voltage and the like until I studied up on them a bit more. I don't have any Sansui literature readily available. What is the model number? Mark Z. "Pathogen" wrote in message ups.com... do you know how to measure for voltages, do ya have a drawing, can get one from Sams on-line. Xforms outputs do read low, ya going from AC high input to AC low output. |
#5
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Sorry bout that - should've put that in m OP. It's a Sansui RZ-590.
There are a number of 1 ohm resistors (they are marked FR and have the symbol of a fuse in series with a resistor?). I know how to measure voltages, but as I said in my OP, the unit is dead - it shuts down immediately after power up, so there are no voltages to measure. There are 3 secondaries - a pair of reds with a black, a pair of blues with a white, and a pair of browns. The one in question is the reds and black, which I assume is for the high(er) voltage supply to the output IC, as they are connects to 50v electros. Also, on further inspection, I found that the output IC, although mounted well, doesn't have any of the pins actually soldered to the board. I don't know if this could cause the fault, and I don't know if they have been desoldered for a reason. thanks "Mark D. Zacharias" wrote in message ... The low resistance you measure may be normal. Some Sansui receivers had bad 1 ohm resistors in the power supply. There's lots of possibilities. Model number would help. Mark Z. "tempus fugit" wrote in message ... Hey all; I'm working on a Sansui receiver that shuts down as soon as I switch it on - no lights or anything. I've taken it apart and inspected the power supply section, and found that there is a very low resistance in a couple of the transformer's output wires. If I measure between either of the reds (there are 2) and the black (which is connected close to the reds, so I'm assuming that these taps go together) the meter reads about 0.6 or 0.7 ohms. Is it possible that this is the correct reading for this, or should I take that to be a dead short? I get somewhat higher readings on the other taps - more like 2.5 or 3 ohms. Also, has anyone had experience with a reciever with similar symptoms? Any tips? Thanks --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 |
#6
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On Sun, 12 Dec 2004 13:18:19 -0500, "tempus fugit"
put finger to keyboard and composed: Sorry bout that - should've put that in m OP. It's a Sansui RZ-590. There are a number of 1 ohm resistors (they are marked FR and have the symbol of a fuse in series with a resistor?). These are fusible resistors. I know how to measure voltages, but as I said in my OP, the unit is dead - it shuts down immediately after power up, so there are no voltages to measure. There are 3 secondaries - a pair of reds with a black, a pair of blues with a white, and a pair of browns. The one in question is the reds and black, which I assume is for the high(er) voltage supply to the output IC, as they are connects to 50v electros. Also, on further inspection, I found that the output IC, although mounted well, doesn't have any of the pins actually soldered to the board. I don't know if this could cause the fault, and I don't know if they have been desoldered for a reason. This IC is probably a hybrid amp (STKxxxx ?). The previous tech probably desoldered it to isolate the source of a short circuit. Be prepared to replace it. thanks "Mark D. Zacharias" wrote in message ... The low resistance you measure may be normal. Some Sansui receivers had bad 1 ohm resistors in the power supply. There's lots of possibilities. Model number would help. Mark Z. "tempus fugit" wrote in message ... Hey all; I'm working on a Sansui receiver that shuts down as soon as I switch it on - no lights or anything. I've taken it apart and inspected the power supply section, and found that there is a very low resistance in a couple of the transformer's output wires. If I measure between either of the reds (there are 2) and the black (which is connected close to the reds, so I'm assuming that these taps go together) the meter reads about 0.6 or 0.7 ohms. Is it possible that this is the correct reading for this, or should I take that to be a dead short? I get somewhat higher readings on the other taps - more like 2.5 or 3 ohms. Also, has anyone had experience with a reciever with similar symptoms? Any tips? Thanks --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. |
#7
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Thanks Frank.
What is a fusible resistor? The IC is an STK 4161 which I can;t find a data sheet on. This was one of my first suspects, but now that I see that it is desoldered, I assume the problem must be somewhere else. It's kind of tricky to test something that you can't power up. I think my next step is to desolder the xformer and see if the low resistance is still there to see if the problem in the xformer (if the low resistance is a problem) or somewhere on the board (I'm assuming that the resistance from the DC + to ground shouldn't be quite that low, otherwise it'd need to source 50 - 75A, which seems unlikely). Any other thoughts? Thanks "Franc Zabkar" wrote in message ... On Sun, 12 Dec 2004 13:18:19 -0500, "tempus fugit" put finger to keyboard and composed: Sorry bout that - should've put that in m OP. It's a Sansui RZ-590. There are a number of 1 ohm resistors (they are marked FR and have the symbol of a fuse in series with a resistor?). These are fusible resistors. I know how to measure voltages, but as I said in my OP, the unit is dead - it shuts down immediately after power up, so there are no voltages to measure. There are 3 secondaries - a pair of reds with a black, a pair of blues with a white, and a pair of browns. The one in question is the reds and black, which I assume is for the high(er) voltage supply to the output IC, as they are connects to 50v electros. Also, on further inspection, I found that the output IC, although mounted well, doesn't have any of the pins actually soldered to the board. I don't know if this could cause the fault, and I don't know if they have been desoldered for a reason. This IC is probably a hybrid amp (STKxxxx ?). The previous tech probably desoldered it to isolate the source of a short circuit. Be prepared to replace it. thanks "Mark D. Zacharias" wrote in message ... The low resistance you measure may be normal. Some Sansui receivers had bad 1 ohm resistors in the power supply. There's lots of possibilities. Model number would help. Mark Z. "tempus fugit" wrote in message ... Hey all; I'm working on a Sansui receiver that shuts down as soon as I switch it on - no lights or anything. I've taken it apart and inspected the power supply section, and found that there is a very low resistance in a couple of the transformer's output wires. If I measure between either of the reds (there are 2) and the black (which is connected close to the reds, so I'm assuming that these taps go together) the meter reads about 0.6 or 0.7 ohms. Is it possible that this is the correct reading for this, or should I take that to be a dead short? I get somewhat higher readings on the other taps - more like 2.5 or 3 ohms. Also, has anyone had experience with a reciever with similar symptoms? Any tips? Thanks --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 |
#8
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On Sun, 12 Dec 2004 17:30:57 -0500, "tempus fugit"
put finger to keyboard and composed: Thanks Frank. What is a fusible resistor? It's a safety resistor that is designed to fuse under fault conditions. The IC is an STK 4161 which I can;t find a data sheet on. Is this the one? http://www.satel.hu/file/document/El...K/STK4161V.pdf This was one of my first suspects, but now that I see that it is desoldered, I assume the problem must be somewhere else. You should test for shorts between the load side of each of the fusible resistors and ground. You will always measure a short on the winding side. If after desoldering the STK4161 IC there are no longer any shorts on the load side, then the IC must have been the culprit. Just to be sure, test for shorts between pins 10 & 11, 10 & 9, 13 & 14, and 13 & 11. It's kind of tricky to test something that you can't power up. I think my next step is to desolder the xformer and see if the low resistance is still there to see if the problem in the xformer (if the low resistance is a problem) or somewhere on the board (I'm assuming that the resistance from the DC + to ground shouldn't be quite that low, otherwise it'd need to source 50 - 75A, which seems unlikely). Any other thoughts? Thanks The transformer is the last place I would look. In any case you will always measure close to zero ohms on the secondary side. "Franc Zabkar" wrote in message .. . On Sun, 12 Dec 2004 13:18:19 -0500, "tempus fugit" put finger to keyboard and composed: Sorry bout that - should've put that in m OP. It's a Sansui RZ-590. There are a number of 1 ohm resistors (they are marked FR and have the symbol of a fuse in series with a resistor?). These are fusible resistors. I know how to measure voltages, but as I said in my OP, the unit is dead - it shuts down immediately after power up, so there are no voltages to measure. There are 3 secondaries - a pair of reds with a black, a pair of blues with a white, and a pair of browns. The one in question is the reds and black, which I assume is for the high(er) voltage supply to the output IC, as they are connects to 50v electros. Also, on further inspection, I found that the output IC, although mounted well, doesn't have any of the pins actually soldered to the board. I don't know if this could cause the fault, and I don't know if they have been desoldered for a reason. This IC is probably a hybrid amp (STKxxxx ?). The previous tech probably desoldered it to isolate the source of a short circuit. Be prepared to replace it. thanks "Mark D. Zacharias" wrote in message ... The low resistance you measure may be normal. Some Sansui receivers had bad 1 ohm resistors in the power supply. There's lots of possibilities. Model number would help. Mark Z. "tempus fugit" wrote in message ... Hey all; I'm working on a Sansui receiver that shuts down as soon as I switch it on - no lights or anything. I've taken it apart and inspected the power supply section, and found that there is a very low resistance in a couple of the transformer's output wires. If I measure between either of the reds (there are 2) and the black (which is connected close to the reds, so I'm assuming that these taps go together) the meter reads about 0.6 or 0.7 ohms. Is it possible that this is the correct reading for this, or should I take that to be a dead short? I get somewhat higher readings on the other taps - more like 2.5 or 3 ohms. Also, has anyone had experience with a reciever with similar symptoms? Any tips? Thanks --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. |
#9
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Thanks a lot Frank. The IC says STK4161II, but I'm sure this is probably the
same thing more or less. The transformer is the last place I would look. In any case you will always measure close to zero ohms on the secondary side. This was something I wondered about. I'll do some more testing. Thanks "Franc Zabkar" wrote in message ... On Sun, 12 Dec 2004 17:30:57 -0500, "tempus fugit" put finger to keyboard and composed: Thanks Frank. What is a fusible resistor? It's a safety resistor that is designed to fuse under fault conditions. The IC is an STK 4161 which I can;t find a data sheet on. Is this the one? http://www.satel.hu/file/document/El...K/STK4161V.pdf This was one of my first suspects, but now that I see that it is desoldered, I assume the problem must be somewhere else. You should test for shorts between the load side of each of the fusible resistors and ground. You will always measure a short on the winding side. If after desoldering the STK4161 IC there are no longer any shorts on the load side, then the IC must have been the culprit. Just to be sure, test for shorts between pins 10 & 11, 10 & 9, 13 & 14, and 13 & 11. It's kind of tricky to test something that you can't power up. I think my next step is to desolder the xformer and see if the low resistance is still there to see if the problem in the xformer (if the low resistance is a problem) or somewhere on the board (I'm assuming that the resistance from the DC + to ground shouldn't be quite that low, otherwise it'd need to source 50 - 75A, which seems unlikely). Any other thoughts? Thanks The transformer is the last place I would look. In any case you will always measure close to zero ohms on the secondary side. "Franc Zabkar" wrote in message .. . On Sun, 12 Dec 2004 13:18:19 -0500, "tempus fugit" put finger to keyboard and composed: Sorry bout that - should've put that in m OP. It's a Sansui RZ-590. There are a number of 1 ohm resistors (they are marked FR and have the symbol of a fuse in series with a resistor?). These are fusible resistors. I know how to measure voltages, but as I said in my OP, the unit is dead - it shuts down immediately after power up, so there are no voltages to measure. There are 3 secondaries - a pair of reds with a black, a pair of blues with a white, and a pair of browns. The one in question is the reds and black, which I assume is for the high(er) voltage supply to the output IC, as they are connects to 50v electros. Also, on further inspection, I found that the output IC, although mounted well, doesn't have any of the pins actually soldered to the board. I don't know if this could cause the fault, and I don't know if they have been desoldered for a reason. This IC is probably a hybrid amp (STKxxxx ?). The previous tech probably desoldered it to isolate the source of a short circuit. Be prepared to replace it. thanks "Mark D. Zacharias" wrote in message ... The low resistance you measure may be normal. Some Sansui receivers had bad 1 ohm resistors in the power supply. There's lots of possibilities. Model number would help. Mark Z. "tempus fugit" wrote in message ... Hey all; I'm working on a Sansui receiver that shuts down as soon as I switch it on - no lights or anything. I've taken it apart and inspected the power supply section, and found that there is a very low resistance in a couple of the transformer's output wires. If I measure between either of the reds (there are 2) and the black (which is connected close to the reds, so I'm assuming that these taps go together) the meter reads about 0.6 or 0.7 ohms. Is it possible that this is the correct reading for this, or should I take that to be a dead short? I get somewhat higher readings on the other taps - more like 2.5 or 3 ohms. Also, has anyone had experience with a reciever with similar symptoms? Any tips? Thanks --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 |
#10
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Ok I did some more poking around. There are no shorts on any of the pins you
suggested on the IC. Also, I couldn't find any shorts to ground near the filter caps/PS area - everything seems to check out OK there. There are 2 taps from the big xformer - I'm wondering if I should disconnect 1 of them and see if the unit will power up then, to save me checking every single connection. Is it safe to do this (I can't see why it wouldn't be)? Also, is it possible that the unit is shutting down because the output IC is disconnected (again, I don't know why this would be, so I'm wondering if you've had experience with anything that did)? Thanks "Franc Zabkar" wrote in message ... On Sun, 12 Dec 2004 17:30:57 -0500, "tempus fugit" put finger to keyboard and composed: Thanks Frank. What is a fusible resistor? It's a safety resistor that is designed to fuse under fault conditions. The IC is an STK 4161 which I can;t find a data sheet on. Is this the one? http://www.satel.hu/file/document/El...K/STK4161V.pdf This was one of my first suspects, but now that I see that it is desoldered, I assume the problem must be somewhere else. You should test for shorts between the load side of each of the fusible resistors and ground. You will always measure a short on the winding side. If after desoldering the STK4161 IC there are no longer any shorts on the load side, then the IC must have been the culprit. Just to be sure, test for shorts between pins 10 & 11, 10 & 9, 13 & 14, and 13 & 11. It's kind of tricky to test something that you can't power up. I think my next step is to desolder the xformer and see if the low resistance is still there to see if the problem in the xformer (if the low resistance is a problem) or somewhere on the board (I'm assuming that the resistance from the DC + to ground shouldn't be quite that low, otherwise it'd need to source 50 - 75A, which seems unlikely). Any other thoughts? Thanks The transformer is the last place I would look. In any case you will always measure close to zero ohms on the secondary side. "Franc Zabkar" wrote in message .. . On Sun, 12 Dec 2004 13:18:19 -0500, "tempus fugit" put finger to keyboard and composed: Sorry bout that - should've put that in m OP. It's a Sansui RZ-590. There are a number of 1 ohm resistors (they are marked FR and have the symbol of a fuse in series with a resistor?). These are fusible resistors. I know how to measure voltages, but as I said in my OP, the unit is dead - it shuts down immediately after power up, so there are no voltages to measure. There are 3 secondaries - a pair of reds with a black, a pair of blues with a white, and a pair of browns. The one in question is the reds and black, which I assume is for the high(er) voltage supply to the output IC, as they are connects to 50v electros. Also, on further inspection, I found that the output IC, although mounted well, doesn't have any of the pins actually soldered to the board. I don't know if this could cause the fault, and I don't know if they have been desoldered for a reason. This IC is probably a hybrid amp (STKxxxx ?). The previous tech probably desoldered it to isolate the source of a short circuit. Be prepared to replace it. thanks "Mark D. Zacharias" wrote in message ... The low resistance you measure may be normal. Some Sansui receivers had bad 1 ohm resistors in the power supply. There's lots of possibilities. Model number would help. Mark Z. "tempus fugit" wrote in message ... Hey all; I'm working on a Sansui receiver that shuts down as soon as I switch it on - no lights or anything. I've taken it apart and inspected the power supply section, and found that there is a very low resistance in a couple of the transformer's output wires. If I measure between either of the reds (there are 2) and the black (which is connected close to the reds, so I'm assuming that these taps go together) the meter reads about 0.6 or 0.7 ohms. Is it possible that this is the correct reading for this, or should I take that to be a dead short? I get somewhat higher readings on the other taps - more like 2.5 or 3 ohms. Also, has anyone had experience with a reciever with similar symptoms? Any tips? Thanks --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.818 / Virus Database: 556 - Release Date: 17/12/2004 |
#11
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On Sat, 18 Dec 2004 11:47:14 -0500, "tempus fugit"
put finger to keyboard and composed: Ok I did some more poking around. There are no shorts on any of the pins you suggested on the IC. Also, I couldn't find any shorts to ground near the filter caps/PS area - everything seems to check out OK there. There are 2 taps from the big xformer - I'm wondering if I should disconnect 1 of them and see if the unit will power up then, to save me checking every single connection. Is it safe to do this (I can't see why it wouldn't be)? IME amp problems of this kind have nearly always been due to blown outputs, whether discrete transistors, or hybrid modules. The only other thing I can think of would be leaky rectifier diodes which may not test as shorts under static conditions, but which may cause the filter capacitors to look like shorts under dynamic conditions. Also, is it possible that the unit is shutting down because the output IC is disconnected (again, I don't know why this would be, so I'm wondering if you've had experience with anything that did)? I'm not familiar with your amp, so I don't quite understand what you mean by "shutting down". Does the amp have some kind of uP or overload sensing circuit? Thanks "Franc Zabkar" wrote in message .. . On Sun, 12 Dec 2004 17:30:57 -0500, "tempus fugit" put finger to keyboard and composed: Thanks Frank. What is a fusible resistor? It's a safety resistor that is designed to fuse under fault conditions. The IC is an STK 4161 which I can;t find a data sheet on. Is this the one? http://www.satel.hu/file/document/El...K/STK4161V.pdf This was one of my first suspects, but now that I see that it is desoldered, I assume the problem must be somewhere else. You should test for shorts between the load side of each of the fusible resistors and ground. You will always measure a short on the winding side. If after desoldering the STK4161 IC there are no longer any shorts on the load side, then the IC must have been the culprit. Just to be sure, test for shorts between pins 10 & 11, 10 & 9, 13 & 14, and 13 & 11. It's kind of tricky to test something that you can't power up. I think my next step is to desolder the xformer and see if the low resistance is still there to see if the problem in the xformer (if the low resistance is a problem) or somewhere on the board (I'm assuming that the resistance from the DC + to ground shouldn't be quite that low, otherwise it'd need to source 50 - 75A, which seems unlikely). Any other thoughts? Thanks The transformer is the last place I would look. In any case you will always measure close to zero ohms on the secondary side. "Franc Zabkar" wrote in message .. . On Sun, 12 Dec 2004 13:18:19 -0500, "tempus fugit" put finger to keyboard and composed: Sorry bout that - should've put that in m OP. It's a Sansui RZ-590. There are a number of 1 ohm resistors (they are marked FR and have the symbol of a fuse in series with a resistor?). These are fusible resistors. I know how to measure voltages, but as I said in my OP, the unit is dead - it shuts down immediately after power up, so there are no voltages to measure. There are 3 secondaries - a pair of reds with a black, a pair of blues with a white, and a pair of browns. The one in question is the reds and black, which I assume is for the high(er) voltage supply to the output IC, as they are connects to 50v electros. Also, on further inspection, I found that the output IC, although mounted well, doesn't have any of the pins actually soldered to the board. I don't know if this could cause the fault, and I don't know if they have been desoldered for a reason. This IC is probably a hybrid amp (STKxxxx ?). The previous tech probably desoldered it to isolate the source of a short circuit. Be prepared to replace it. thanks "Mark D. Zacharias" wrote in message ... The low resistance you measure may be normal. Some Sansui receivers had bad 1 ohm resistors in the power supply. There's lots of possibilities. Model number would help. Mark Z. "tempus fugit" wrote in message ... Hey all; I'm working on a Sansui receiver that shuts down as soon as I switch it on - no lights or anything. I've taken it apart and inspected the power supply section, and found that there is a very low resistance in a couple of the transformer's output wires. If I measure between either of the reds (there are 2) and the black (which is connected close to the reds, so I'm assuming that these taps go together) the meter reads about 0.6 or 0.7 ohms. Is it possible that this is the correct reading for this, or should I take that to be a dead short? I get somewhat higher readings on the other taps - more like 2.5 or 3 ohms. Also, has anyone had experience with a reciever with similar symptoms? Any tips? Thanks --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.818 / Virus Database: 556 - Release Date: 17/12/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. |
#12
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Thanks Frank.
By "shutting down" I mean I switch the receiver on, and before any lights or display comes on, a relay opens, disconnecting the input 120VAC from the power xformers. I'm not real experienced with repair (although I have managed to get a few things fixed), but I am aware of the practice of using a relay to protect the speakers from DC damage at the audio output. This one, however, has the relay in the power supply section. The PS goes: 120v in = small xformer = relay = big xformer = rectifier stages. I need to look around more in there (I don't have a lot of time to work on it) to see exactly why there are 2 xformers in this arrangement. The small xformer has a CT output with 15v on either side and feeds a 7806, and the big xformer has 3 taps - one that must be +/-15v (because I can see the 78 and 7915s), another that must be in the 40-60v range for the output IC, and 2 brown leads (?). There is some type of surface mount device on the underside of the board, but I'm not sure if it is a uP. As you may have guessed, I have no schematic. I also immediately suspected the output IC, but now that it is completely disconnected from the circuit, and the amp still shuts down, I began to suspect the PS circuitry. "Franc Zabkar" wrote in message news On Sat, 18 Dec 2004 11:47:14 -0500, "tempus fugit" put finger to keyboard and composed: Ok I did some more poking around. There are no shorts on any of the pins you suggested on the IC. Also, I couldn't find any shorts to ground near the filter caps/PS area - everything seems to check out OK there. There are 2 taps from the big xformer - I'm wondering if I should disconnect 1 of them and see if the unit will power up then, to save me checking every single connection. Is it safe to do this (I can't see why it wouldn't be)? IME amp problems of this kind have nearly always been due to blown outputs, whether discrete transistors, or hybrid modules. The only other thing I can think of would be leaky rectifier diodes which may not test as shorts under static conditions, but which may cause the filter capacitors to look like shorts under dynamic conditions. Also, is it possible that the unit is shutting down because the output IC is disconnected (again, I don't know why this would be, so I'm wondering if you've had experience with anything that did)? I'm not familiar with your amp, so I don't quite understand what you mean by "shutting down". Does the amp have some kind of uP or overload sensing circuit? Thanks "Franc Zabkar" wrote in message .. . On Sun, 12 Dec 2004 17:30:57 -0500, "tempus fugit" put finger to keyboard and composed: Thanks Frank. What is a fusible resistor? It's a safety resistor that is designed to fuse under fault conditions. The IC is an STK 4161 which I can;t find a data sheet on. Is this the one? http://www.satel.hu/file/document/El...K/STK4161V.pdf This was one of my first suspects, but now that I see that it is desoldered, I assume the problem must be somewhere else. You should test for shorts between the load side of each of the fusible resistors and ground. You will always measure a short on the winding side. If after desoldering the STK4161 IC there are no longer any shorts on the load side, then the IC must have been the culprit. Just to be sure, test for shorts between pins 10 & 11, 10 & 9, 13 & 14, and 13 & 11. It's kind of tricky to test something that you can't power up. I think my next step is to desolder the xformer and see if the low resistance is still there to see if the problem in the xformer (if the low resistance is a problem) or somewhere on the board (I'm assuming that the resistance from the DC + to ground shouldn't be quite that low, otherwise it'd need to source 50 - 75A, which seems unlikely). Any other thoughts? Thanks The transformer is the last place I would look. In any case you will always measure close to zero ohms on the secondary side. "Franc Zabkar" wrote in message .. . On Sun, 12 Dec 2004 13:18:19 -0500, "tempus fugit" put finger to keyboard and composed: Sorry bout that - should've put that in m OP. It's a Sansui RZ-590. There are a number of 1 ohm resistors (they are marked FR and have the symbol of a fuse in series with a resistor?). These are fusible resistors. I know how to measure voltages, but as I said in my OP, the unit is dead - it shuts down immediately after power up, so there are no voltages to measure. There are 3 secondaries - a pair of reds with a black, a pair of blues with a white, and a pair of browns. The one in question is the reds and black, which I assume is for the high(er) voltage supply to the output IC, as they are connects to 50v electros. Also, on further inspection, I found that the output IC, although mounted well, doesn't have any of the pins actually soldered to the board. I don't know if this could cause the fault, and I don't know if they have been desoldered for a reason. This IC is probably a hybrid amp (STKxxxx ?). The previous tech probably desoldered it to isolate the source of a short circuit. Be prepared to replace it. thanks "Mark D. Zacharias" wrote in message ... The low resistance you measure may be normal. Some Sansui receivers had bad 1 ohm resistors in the power supply. There's lots of possibilities. Model number would help. Mark Z. "tempus fugit" wrote in message ... Hey all; I'm working on a Sansui receiver that shuts down as soon as I switch it on - no lights or anything. I've taken it apart and inspected the power supply section, and found that there is a very low resistance in a couple of the transformer's output wires. If I measure between either of the reds (there are 2) and the black (which is connected close to the reds, so I'm assuming that these taps go together) the meter reads about 0.6 or 0.7 ohms. Is it possible that this is the correct reading for this, or should I take that to be a dead short? I get somewhat higher readings on the other taps - more like 2.5 or 3 ohms. Also, has anyone had experience with a reciever with similar symptoms? Any tips? Thanks --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.783 / Virus Database: 529 - Release Date: 25/10/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.818 / Virus Database: 556 - Release Date: 17/12/2004 - Franc Zabkar -- Please remove one 's' from my address when replying by email. |
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