Hi
When I turn on the amp, channel 2 relay clicks in about 4 secs and they is sound on this channel. Channel 1 relay takes about 17secs to click in. I have checked all the components on this power amp board and all seem fine. What could cause this delay in turning on. Can someone guide me on what are the components that cause this time delay.
Thanks
When I turn on the amp, channel 2 relay clicks in about 4 secs and they is sound on this channel. Channel 1 relay takes about 17secs to click in. I have checked all the components on this power amp board and all seem fine. What could cause this delay in turning on. Can someone guide me on what are the components that cause this time delay.
Thanks
Download the datasheet and application info on the TA7317 IC check around it for abnormality. Also check the DC voltage at the output stages (R334, 335 and 336, before the relay contact) and see if one takes longer to settle down to near 0V. E
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There is no TA7317 IC on the board(as shown on the schematic), it is replaced by a small PCB with some smd components in it. When the relay turns on, there is appox 1.6V DC across the speaker terminals. I have adjusted SUR301 to get the minimum voltage across the speaker, but there is still 1.6V across the speakers. I cannot get it down to 0V. What can be wrong and how do I get it down to 0V.
Thanks
Thanks
Hi carlosraj,
If I surmise correctly, channel 2 works correctly and only channel 1 has the excessive output voltage? Assuming this is correct, use channel 2 as reference to nominal voltages that should be present on ch 1.
The most likely culprits for excessive output offset are the input pair Q301 and Q067 and a bunch of associated passives, so I suggest some voltage checks toward those parts. But first confirm supply rails are OK at about +/- 72VDC re ground.
There should be about +0.7V across D301, and -0.7V across D302; roughly half those voltages should appear at the ends of SVR301.
You mention +1.6V at output with SVR301 adjusted to extreme. Would you measure wiper voltage you observe? (If wiper is negative, would you report as a negative voltage.)
Next would be some checks of capacitor leakage and bias currents. Check DC voltage across R316; ideally, it will be 0mV. Any DC across R316 indicates leakage in C306; any current flowing elevates the output voltage via R318.
A similar test can check leakage in C302. If you can you conveniently unplug the connector AN104-A, a voltage check across R305 will test leakage current through C302.
If no leaky caps are revealed, next would be some tests of bias currents in Q301 and Q067. Restore connector AN104-A if it was removed. Use a consistent ground for meter ground (eg. Point B near input) and with most sensitive meter range, measure the following circuit nodes:
Wiper of SVR301:
Voltage across C304:
Voltage at base of Q301:
Voltage at base of Q067:
Voltage at amp output (R318):
Objective is to compute voltage across bias resistors and infer the base currents flowing into bases of Q301 and Q067.
Thanks!
If I surmise correctly, channel 2 works correctly and only channel 1 has the excessive output voltage? Assuming this is correct, use channel 2 as reference to nominal voltages that should be present on ch 1.
The most likely culprits for excessive output offset are the input pair Q301 and Q067 and a bunch of associated passives, so I suggest some voltage checks toward those parts. But first confirm supply rails are OK at about +/- 72VDC re ground.
There should be about +0.7V across D301, and -0.7V across D302; roughly half those voltages should appear at the ends of SVR301.
You mention +1.6V at output with SVR301 adjusted to extreme. Would you measure wiper voltage you observe? (If wiper is negative, would you report as a negative voltage.)
Next would be some checks of capacitor leakage and bias currents. Check DC voltage across R316; ideally, it will be 0mV. Any DC across R316 indicates leakage in C306; any current flowing elevates the output voltage via R318.
A similar test can check leakage in C302. If you can you conveniently unplug the connector AN104-A, a voltage check across R305 will test leakage current through C302.
If no leaky caps are revealed, next would be some tests of bias currents in Q301 and Q067. Restore connector AN104-A if it was removed. Use a consistent ground for meter ground (eg. Point B near input) and with most sensitive meter range, measure the following circuit nodes:
Wiper of SVR301:
Voltage across C304:
Voltage at base of Q301:
Voltage at base of Q067:
Voltage at amp output (R318):
Objective is to compute voltage across bias resistors and infer the base currents flowing into bases of Q301 and Q067.
Thanks!
Hi
The amp I am working on is Ver1.2 whereas the schematic is for Ver3.6. I am getting a voltage drop of +0.68 and -0.68 across diodes 302 and 301. Before taking the other readings I decided to check and compare the resistors on both boards. There were 2 differences I noticed. R343 on the OK board is 62K whereas the other board is 82K. R319 is a 10K resistor on both boards, but the reading I get across R319 on the OK board is 470 ohms, and the resistance varies as I vary SUVR302. On the other board it is 10K and does not vary as I vary SVR302. R319(18K on the schematic) is between the emitter of Q308 and one end of SVR302. I do not understand how this is possible. They are connected exactly the same way on both boards. Could this high resistance of 10K, or the difference of resistance of R343 (82K and 62K) be responsible for the slow relay turn on..
Thanks
The amp I am working on is Ver1.2 whereas the schematic is for Ver3.6. I am getting a voltage drop of +0.68 and -0.68 across diodes 302 and 301. Before taking the other readings I decided to check and compare the resistors on both boards. There were 2 differences I noticed. R343 on the OK board is 62K whereas the other board is 82K. R319 is a 10K resistor on both boards, but the reading I get across R319 on the OK board is 470 ohms, and the resistance varies as I vary SUVR302. On the other board it is 10K and does not vary as I vary SVR302. R319(18K on the schematic) is between the emitter of Q308 and one end of SVR302. I do not understand how this is possible. They are connected exactly the same way on both boards. Could this high resistance of 10K, or the difference of resistance of R343 (82K and 62K) be responsible for the slow relay turn on..
Thanks
Hi,
If you're seeing 10K at SVR302 and it doesn't vary, it sounds like the pot has failed. Powered check of voltage across pot element should yield about 0.6V. Check wiper voltage. I wouldn't be surprised if it was about about -0.6V and might account for -1.6V output.
The resistor differences don't seem enough to explain the huge difference in relay activation. I'm hoping that resolving the offset problem will cure delay issue. It may be a different issue; then the small PCB module become an issue.
P.S. I looked again issue of pot wiper voltage. My mental recall had failed me; pot wiper at +0.6V would go part way toward explaining 1.6V at output but not enough. Voltage measurements will help with mysteries.
If you're seeing 10K at SVR302 and it doesn't vary, it sounds like the pot has failed. Powered check of voltage across pot element should yield about 0.6V. Check wiper voltage. I wouldn't be surprised if it was about about -0.6V and might account for -1.6V output.
The resistor differences don't seem enough to explain the huge difference in relay activation. I'm hoping that resolving the offset problem will cure delay issue. It may be a different issue; then the small PCB module become an issue.
P.S. I looked again issue of pot wiper voltage. My mental recall had failed me; pot wiper at +0.6V would go part way toward explaining 1.6V at output but not enough. Voltage measurements will help with mysteries.
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Hi
Its not across the pot, I was measuring the resistance across R319 (a 10K resistor). The resistance across this resistor was showing 470 ohms and as I vary the trimpot SVR302, the resistance across this resistor(R319) also changes. Today I changed the resistor R343 which was 82K to 62K. Now the relay turns on after 13secs. It turns on 4secs earlier than before. I will continue taking the voltage readings as suggested.
Thanks
Its not across the pot, I was measuring the resistance across R319 (a 10K resistor). The resistance across this resistor was showing 470 ohms and as I vary the trimpot SVR302, the resistance across this resistor(R319) also changes. Today I changed the resistor R343 which was 82K to 62K. Now the relay turns on after 13secs. It turns on 4secs earlier than before. I will continue taking the voltage readings as suggested.
Thanks