Hello experts!
This might be a silly question but I need to ask it anyway 🙂
I'm am trying to sort out this amplifier that was dead when got it. To start the standby transformer was dead, also faulty diods on the input board had fried stuff but thats all sorted now. The amp has been in protection mode from the get go and still is. I have removed the amp boards and input board so that only PSU remains. All elyt caps replaced as well as the speaker protection relay. Measuring 54v on both coil pins on the protection relay and on the TA7317 protection IC202 I read 0v on both pin 1 and 2 (since the amp boards are removed this is expected) Still in protection. But then I started wondering, will I ever be able to get i out of protection mode without the amp boards connected? My initial thought was to first resolve the issues on the PSU board, get it out of protection and then add one amp board at a time.
Up until now I have searched a lot in the area around the RL201 and the protection ciruit to figure out where these 54v come from.
Anyone that knows or have other suggestions on how to exclude parts and isolate the problem? 🙂
Thanks a lot!
Daniel E
This might be a silly question but I need to ask it anyway 🙂
I'm am trying to sort out this amplifier that was dead when got it. To start the standby transformer was dead, also faulty diods on the input board had fried stuff but thats all sorted now. The amp has been in protection mode from the get go and still is. I have removed the amp boards and input board so that only PSU remains. All elyt caps replaced as well as the speaker protection relay. Measuring 54v on both coil pins on the protection relay and on the TA7317 protection IC202 I read 0v on both pin 1 and 2 (since the amp boards are removed this is expected) Still in protection. But then I started wondering, will I ever be able to get i out of protection mode without the amp boards connected? My initial thought was to first resolve the issues on the PSU board, get it out of protection and then add one amp board at a time.
Up until now I have searched a lot in the area around the RL201 and the protection ciruit to figure out where these 54v come from.
Anyone that knows or have other suggestions on how to exclude parts and isolate the problem? 🙂
Thanks a lot!
Daniel E
The service manual diagrams are bit difficult to follow but it appears that seeing 54 volts on both sides of the relay coil is to be expected if you remove the power amp boards.
It looks like should have 54 volts applied to the relay
which then loops through the power amp boards with each board adding a thermal switch in series with that line. Finally it comes back to the TA7317 and there pin 6 should be at zero volts. If pin 6 is zero then one side of the relay should be zero as well.
So removing the power amp boards (one or both) will give what you are seeing.
It looks like should have 54 volts applied to the relay
which then loops through the power amp boards with each board adding a thermal switch in series with that line. Finally it comes back to the TA7317 and there pin 6 should be at zero volts. If pin 6 is zero then one side of the relay should be zero as well.So removing the power amp boards (one or both) will give what you are seeing.
Hi Mooly and thanks for your input!
This is good advice and now that i'm thinking about it, there was a post about making sure the path from pin 6 all the way thru 2 thermal switches to R229 (just before pin 8 on the relay) was intact! That as you say, is not the case when the amp boards are disconnected. 👍
Tweaking the question al little 🙂
So for me to understand, the TA7317 is putting out 54v on pin 6 when it senses dc current over an acceptable level on pin 1 and/or pin 2. Wouldnt this mean that pin 6 should be 0v at all times when the amp boards are removed? (Since there are no signal at all on pin 1 and 2 then) Because mine puts out 54v
I will connect everything and see what happens. Maybe TA3717 is sensing there is no signal on pin 1 and 2 and therefore it stays HI on pin6?
or am I jumping to conclusions 🙂
Cheers,
Daniel E
This is good advice and now that i'm thinking about it, there was a post about making sure the path from pin 6 all the way thru 2 thermal switches to R229 (just before pin 8 on the relay) was intact! That as you say, is not the case when the amp boards are disconnected. 👍
Tweaking the question al little 🙂
So for me to understand, the TA7317 is putting out 54v on pin 6 when it senses dc current over an acceptable level on pin 1 and/or pin 2. Wouldnt this mean that pin 6 should be 0v at all times when the amp boards are removed? (Since there are no signal at all on pin 1 and 2 then) Because mine puts out 54v
I will connect everything and see what happens. Maybe TA3717 is sensing there is no signal on pin 1 and 2 and therefore it stays HI on pin6?
or am I jumping to conclusions 🙂
Cheers,
Daniel E
Not exactly, the chip does not put out any voltage, rather it connects pin 6 to ground thus completing the circuit. Think of it as a switch. You are seeing 54 volts on pin 6 because the switch is 'open'.
With all connected up you need to check that the DC offset of each power amp is close to zero. If either or both channels have any significant voltage at their output then the chip will keep pin 6 'open'.
That makes so much sense, thanks for clarifying!
Everything connected now. Having -0.450v on pin1 an -0.693v on pin2 so there are dc offset on both channels
Since all caps are replaced and diodes and resistors are checked I will start till measure voltage one Q at a time and compare it to the other channel.
All voltages coming from PSU are dead on.
Starting point is emitter side of the power transistors as the reading should be 0v there.
Is it ok to set idle current pots to fully anti clockwise as I can not have the heat sinks attached when taking measurements?
/Daniel E
Everything connected now. Having -0.450v on pin1 an -0.693v on pin2 so there are dc offset on both channels
Since all caps are replaced and diodes and resistors are checked I will start till measure voltage one Q at a time and compare it to the other channel.
All voltages coming from PSU are dead on.
Starting point is emitter side of the power transistors as the reading should be 0v there.
Is it ok to set idle current pots to fully anti clockwise as I can not have the heat sinks attached when taking measurements?
/Daniel E
yep, ok to set idle/bias current to zero until you sort out the offset issue.
Measure at emitter then base of outputs then same at drivers following the increaing voltage.
Measure at emitter then base of outputs then same at drivers following the increaing voltage.
Thanks,
This is the first amp I have tried to repair thas has different ground points. I had connected PSU GND to both amp boards but not signal GND when I did that the offset went away on both cards and they started to measure the same!
.02v on pin1 and 2 🙂
But still 52v on pin6... is IC202 bad?
pin 4 (ground) is verified working
Having these values on IC202
(all in V pin 1-9)
-0,667
-0.02
-0.02
0
-0.77
52
0.41
0.41
3.2
anything else to try before trying to find a replacement for the TA7317?
Really appreciate the time you take to answer my beginner questions! Really like these NADs since they have good SM sometimes even with voltages written in the schematic. And the sound nice 🙂 PSB build quality isnt the best though 😉
Thanks,
Daniel E
This is the first amp I have tried to repair thas has different ground points. I had connected PSU GND to both amp boards but not signal GND when I did that the offset went away on both cards and they started to measure the same!
.02v on pin1 and 2 🙂
But still 52v on pin6... is IC202 bad?
pin 4 (ground) is verified working
Having these values on IC202
(all in V pin 1-9)
-0,667
-0.02
-0.02
0
-0.77
52
0.41
0.41
3.2
anything else to try before trying to find a replacement for the TA7317?
Really appreciate the time you take to answer my beginner questions! Really like these NADs since they have good SM sometimes even with voltages written in the schematic. And the sound nice 🙂 PSB build quality isnt the best though 😉
Thanks,
Daniel E
Yes 🙂 Check everything else around the chip before even suspecting the IC has failed. We go around every pin and make sure we see what we would consider a reasonable voltage.
First easy checks are to look for parts that are highly stressed. Look at pins 5 and 9 and lift one end of R230 and R235 which are 18k's and check these are OK.
Check fusible resistor R252. If it reads 100 ohm in circuit it's probably fine, no need to lift. This part of the circuit is used as 'AC or power detection' and ensure a fast dropout of the relay when power is removed. If the expected voltage isn't seen the relay will not engage.
C226 is a critical part and highly stressed. If you haven't a scope then you need to substitute it.
R240, a 180k is also to be checked. Lift one end.
Although the IC may be faulty it is the least likely suspect at this point.
Agreed 🙂
I checked all these and they are within tolerance. (17.7 on the 18k, 98 on the 100ohm and the 180k was dead on). C226 is brand new and controlled before mounted. One big risk here is that the PCB leads will brake and cause failures. I look at the schematic and test connection between components after I solder everytime so I dont create new problems.
All boards connected now and when I turn it on, red protection LED goes on and the relay clicks instantly. Power LED i yellow and after 2 sec the pre out relay on the input board clicks and the LED turns green
Feels like I am sooo close! 😱
Could bias current pot set to zero o both channels cause this at this point? I dont have them mounted to the heat sink yet as this makes it impossible to flip the PSU board.
Thanks for all advise. Some problem is still hidden somewhere close to the IC202. Stable voltages from PSU, no DC on outputs, all pins except pint 6 on TA7317 looks right.
This must be the best hobby ever! 😆
I checked all these and they are within tolerance. (17.7 on the 18k, 98 on the 100ohm and the 180k was dead on). C226 is brand new and controlled before mounted. One big risk here is that the PCB leads will brake and cause failures. I look at the schematic and test connection between components after I solder everytime so I dont create new problems.
All boards connected now and when I turn it on, red protection LED goes on and the relay clicks instantly. Power LED i yellow and after 2 sec the pre out relay on the input board clicks and the LED turns green
Feels like I am sooo close! 😱
Could bias current pot set to zero o both channels cause this at this point? I dont have them mounted to the heat sink yet as this makes it impossible to flip the PSU board.
Thanks for all advise. Some problem is still hidden somewhere close to the IC202. Stable voltages from PSU, no DC on outputs, all pins except pint 6 on TA7317 looks right.
This must be the best hobby ever! 😆
The bias has no effect on this unless it was massively high and triggering an over current condition.
The chip looks to at DC offset (pins 2 and 3) while pin 1 looks for presence of AC from the power supply via D211 and surrounding parts with the ability of the Protect line from each power amp being able to override that and instantly cause the relay to drop out.
What voltage do you see here which is the common Protect input from both amps?
I think we should probably use the scope.
That voltage sounds OK tbh. D211 and C226 (note the way the cap is fitted with + to ground) generates a negative bias voltage when mains is present. R234 (47k) is trying to pull pin 1 high and disconnect the relay. The high negative bias across C226 is applied via the 180k and is pulling the pin the opposite way to keep the relay active. Its a tight balancing act with resistor values and voltages chosen to just be below the trigger threshold.
The voltage across C226 will have a high ripple content but will peak at around -50 volts although a meter will probably read a lot lower. Worth measuring for interesting.
It might be worth scoping all these inputs to the chip because a meter doesn't show any ripple or other problems. Pins 2 and 3 should be a clean zero volts. Pin 9 should be clean.
Is R233 connected to pin 8 OK? I think the voltage on pin 8 should rise to that of pin 9 as the cap C224 charges. Check that it does. That R/C time constant will give the on delay.
Pin 1 on the scope I'm going to say should be all negative and not have any peaks in the ripple going above 0 volts. If the peaks in the ripple take pin 1 over zero volts then that might be constantly retriggering the delay and holding the relay off.
That voltage sounds OK tbh. D211 and C226 (note the way the cap is fitted with + to ground) generates a negative bias voltage when mains is present. R234 (47k) is trying to pull pin 1 high and disconnect the relay. The high negative bias across C226 is applied via the 180k and is pulling the pin the opposite way to keep the relay active. Its a tight balancing act with resistor values and voltages chosen to just be below the trigger threshold.
The voltage across C226 will have a high ripple content but will peak at around -50 volts although a meter will probably read a lot lower. Worth measuring for interesting.
It might be worth scoping all these inputs to the chip because a meter doesn't show any ripple or other problems. Pins 2 and 3 should be a clean zero volts. Pin 9 should be clean.
Is R233 connected to pin 8 OK? I think the voltage on pin 8 should rise to that of pin 9 as the cap C224 charges. Check that it does. That R/C time constant will give the on delay.
Pin 1 on the scope I'm going to say should be all negative and not have any peaks in the ripple going above 0 volts. If the peaks in the ripple take pin 1 over zero volts then that might be constantly retriggering the delay and holding the relay off.
In my experience the standby transformer is not a common failure item. One I did see fail was taken out by lightening strike power surge according to the equipment owner. And there were several other failed components in the standby circuit as well.
I can only suggest you carefully check/test all the semiconductors. Good luck.
I can only suggest you carefully check/test all the semiconductors. Good luck.
Helloo,
It's up and running! Such a great feeling when you finally get to play something on it for the first time! And when the relay clicked, and the protection light stayed off 🙂
I realized that the most probable problem was the low quality of the board itself. Alot of pads had come off when I replaced caps and I had needed to use wires to create new paths etc. a few times.
I focused the search around IC202 and decided to measure all pins for connection out to the next component and there it was. No connection between pin 7 and C223! I also at the same time switched back to the original cap (that measure OK) because it was replaced by a bipolar cap. Don't know if this could be a problem in this case.
After this I followed the signal from pin6 0v thru the first thermal switch and then on the second it stopped. on the other side of the switch, it was 54v. I then found that pin one on the connector cable was broken. Fixed that and the 0v could make it to the relay coil. And the relay clicked. Sweet
In the end it sums up to one 9v transformer, three fusable resistors on the PSU, three diodes on the input board, four transistors on the PSU and two transistors on the source switch front panel plus basically all caps were replaced 🙂
Thanks for all advice. Your great explanations and guidance led me to success, and now I know a lot more about how TA7317 is working 🙂
Only one detail left really and that is that the LED in the volume knob is broken. I tried to replace it with a few different I have at home but the barley even glows if at all.
Anyone know the spec on the original LED or could I adjust a resistor on the Volume board to make it shine a bit brighter?
It's up and running! Such a great feeling when you finally get to play something on it for the first time! And when the relay clicked, and the protection light stayed off 🙂
I realized that the most probable problem was the low quality of the board itself. Alot of pads had come off when I replaced caps and I had needed to use wires to create new paths etc. a few times.
I focused the search around IC202 and decided to measure all pins for connection out to the next component and there it was. No connection between pin 7 and C223! I also at the same time switched back to the original cap (that measure OK) because it was replaced by a bipolar cap. Don't know if this could be a problem in this case.
After this I followed the signal from pin6 0v thru the first thermal switch and then on the second it stopped. on the other side of the switch, it was 54v. I then found that pin one on the connector cable was broken. Fixed that and the 0v could make it to the relay coil. And the relay clicked. Sweet
In the end it sums up to one 9v transformer, three fusable resistors on the PSU, three diodes on the input board, four transistors on the PSU and two transistors on the source switch front panel plus basically all caps were replaced 🙂
Thanks for all advice. Your great explanations and guidance led me to success, and now I know a lot more about how TA7317 is working 🙂
Only one detail left really and that is that the LED in the volume knob is broken. I tried to replace it with a few different I have at home but the barley even glows if at all.
Anyone know the spec on the original LED or could I adjust a resistor on the Volume board to make it shine a bit brighter?
Yes, most LED indicator circuits have a series resistor to limit current through the LED and it's brightness. You may have to just trace it back from the LED to find it. Might be simpler to just piggyback another resistor in parallel with the existing one to reduce the resistance and increase the current/brightness. Trial and error will get you there unless you know the source voltage and LED current requirement - usually about 10-20 mA. I put a trim pot in some of my creations so I can easliy adjust any time.
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Well done 👍
As a general rule 'its never the chip' for low power stuff like this... as you have found out. A non polarised cap should be fine for most small value electrolytics but there really is no need to do that. Electrolytics aren't all bad and often the best part for the job.
Modern LED's are blindingly bright so replacing an LED might be a worthwhile option.
As a general rule 'its never the chip' for low power stuff like this... as you have found out. A non polarised cap should be fine for most small value electrolytics but there really is no need to do that. Electrolytics aren't all bad and often the best part for the job.
Modern LED's are blindingly bright so replacing an LED might be a worthwhile option.