Hola Rolando,
so it seems that the problem is solved - congratulations
It's not a mistake to exchange C11 with a non polarised electrolytic cap despite the fact that the plus/minus voltage swing on C11 is not that big, in all channels to be on safe side.
Concerning R504 in parallel with R506 (which is already a wire wound resistor with higher dissipation) it may make sense to parallel an additional 8k66 resistor, but this will not really change much as these resistors (R504 and R506) in parallel are already about 1,09k total resistance; it may keep the zener CR504 a bit more in its working area.
Finally I would also resolder the pcb's of all amps to run for more years to come!
atentamente
Dieter
so it seems that the problem is solved - congratulations
It's not a mistake to exchange C11 with a non polarised electrolytic cap despite the fact that the plus/minus voltage swing on C11 is not that big, in all channels to be on safe side.
Concerning R504 in parallel with R506 (which is already a wire wound resistor with higher dissipation) it may make sense to parallel an additional 8k66 resistor, but this will not really change much as these resistors (R504 and R506) in parallel are already about 1,09k total resistance; it may keep the zener CR504 a bit more in its working area.
Finally I would also resolder the pcb's of all amps to run for more years to come!
atentamente
Dieter
I hope now is a good time now to bring the discussion back to the problem with my ML 432 😊. My progress has been slow because of other commitments.
But first I would like to thank LJYS and Dieter for their help, I am hoping this thread is helping not only myself but also others with a similar problem …
Here is a summary of what I have done/tried so far.
First I tried Dieter's suggestion to run the amp with only one channel inserted to locate where the problems comes from. If I try this the amp will go into an error mode immediately as I power it on, even before I take it out of standby. So it seems a better way to locate which channel is at fault was described by LJYS, measuring the voltage at the RED binding post. Having said this, myself I am not sure where to find this RED binding post.
Anyway, next I changed the voltage setting from 240V to 230V - as expected this did not fix the problem.
Then I loaded the large capacitors with 20V and left them for about 1 hour. They all kept their charge within 0.1V so I assumed they are likely to be okay. I am however contemplating buying a voltmeter that can measure capacitance up to 30 millifarat to test the capacitors properly.
While waiting for parts to arrive for testing optocoupler U3 I tested what I thought I had tested before, the resistance between each of the pins of all the transistors attached to the cooling conductor. This time around I found something interesting. On the left channel, different to the right channel, the pin 2 (Vin) and pin 3 (Vout) of the positive voltage regulator LM317T (VR1) are a pass though (no resistance) and also the pin 2 and pin 3 of the negative voltage regulator LM337T (VR2) are a pass through. So either the diodes CR1/CR2 are broken or the voltage regulators LM317T and LM337T are broken. I assume it is more likely to be the voltage regulators to be broken, because these regulators work at a voltage that is higher than usual, up to 37V would be normal. The regulated voltage I tried to work out prior to reading the post from LJYS and I had worked out that the regulating resistors are rated 562 ohm (R3) on one side and 36,5k ohm (R1) plus a variable 10k ohm (R2) on the other side. Using an online LM317T calculator with these values told me that the output voltage is set to a value of around 84,6V.
This calculated voltage could be about right because it seems to be near the value of 87,5V at TP3 which was given by LJYS.
I now wonder how a Vin/Vout pass though of the voltage regulators can trigger the amp to shut itself down. Would it not just work at a higher/unregulated voltage instead? Is it likely that the problem is somewhere else and the broken voltage regulators are just a side effect of that other problem?
In other words I do wonder which other parts may have been broken in the signal chain, before or after the voltage regulator, if any. Are there any obvious parts I should check?
I do get different values for the capacitors C1 to C4 when I compare left and right channel board, but some of this will be normal because the voltage regulators have a pass through on the left channel causing the values to be different when I test these in circuit.
What I also find interesting is that the positive as well as the negative regulator appear to have broken at the same time, is this a natural reaction when the voltage regulators breaks on one side it takes the other side with it because of the voltage imbalance this creates?
Apologies for my inexperience - I am a software engineer with very little knowledge of electronics.
This leads me on to another question I have, does anyone know what value I should expect to see for the unregulated voltage?
I would like to check if things are okay up to the point where the voltage is regulated.
To proceed I decided it would be best if I would make up an extension cable for the P100, P103, P104 connectors and for the 3 power lines P301/302/303, P304/305/306, P307/308/309 as well as the ground connection. With this I can run the amp with the left and right channel boards “folded up”, allowing me to get to the test points with a voltmeter. I am still working away on making the cables as I write this. Or is there another way of getting to these test points – Dieter, how did you solve this did you solder in cables to get to these test points or did you make up cables for the connectors as per my plan?
Once I am finished with the cables I need to build up the courage to cut off the legs of LM317 (VR1) and LM337T (VR2) and solder new replacement regulators onto these legs on for a trial. For me this the hard part because I am not 100% sure my diagnosis is accurate since both my knowledge of electronics and my tools are limited and I don’t want to destroy this piece of art...
But first I would like to thank LJYS and Dieter for their help, I am hoping this thread is helping not only myself but also others with a similar problem …
Here is a summary of what I have done/tried so far.
First I tried Dieter's suggestion to run the amp with only one channel inserted to locate where the problems comes from. If I try this the amp will go into an error mode immediately as I power it on, even before I take it out of standby. So it seems a better way to locate which channel is at fault was described by LJYS, measuring the voltage at the RED binding post. Having said this, myself I am not sure where to find this RED binding post.
Anyway, next I changed the voltage setting from 240V to 230V - as expected this did not fix the problem.
Then I loaded the large capacitors with 20V and left them for about 1 hour. They all kept their charge within 0.1V so I assumed they are likely to be okay. I am however contemplating buying a voltmeter that can measure capacitance up to 30 millifarat to test the capacitors properly.
While waiting for parts to arrive for testing optocoupler U3 I tested what I thought I had tested before, the resistance between each of the pins of all the transistors attached to the cooling conductor. This time around I found something interesting. On the left channel, different to the right channel, the pin 2 (Vin) and pin 3 (Vout) of the positive voltage regulator LM317T (VR1) are a pass though (no resistance) and also the pin 2 and pin 3 of the negative voltage regulator LM337T (VR2) are a pass through. So either the diodes CR1/CR2 are broken or the voltage regulators LM317T and LM337T are broken. I assume it is more likely to be the voltage regulators to be broken, because these regulators work at a voltage that is higher than usual, up to 37V would be normal. The regulated voltage I tried to work out prior to reading the post from LJYS and I had worked out that the regulating resistors are rated 562 ohm (R3) on one side and 36,5k ohm (R1) plus a variable 10k ohm (R2) on the other side. Using an online LM317T calculator with these values told me that the output voltage is set to a value of around 84,6V.
This calculated voltage could be about right because it seems to be near the value of 87,5V at TP3 which was given by LJYS.
I now wonder how a Vin/Vout pass though of the voltage regulators can trigger the amp to shut itself down. Would it not just work at a higher/unregulated voltage instead? Is it likely that the problem is somewhere else and the broken voltage regulators are just a side effect of that other problem?
In other words I do wonder which other parts may have been broken in the signal chain, before or after the voltage regulator, if any. Are there any obvious parts I should check?
I do get different values for the capacitors C1 to C4 when I compare left and right channel board, but some of this will be normal because the voltage regulators have a pass through on the left channel causing the values to be different when I test these in circuit.
What I also find interesting is that the positive as well as the negative regulator appear to have broken at the same time, is this a natural reaction when the voltage regulators breaks on one side it takes the other side with it because of the voltage imbalance this creates?
Apologies for my inexperience - I am a software engineer with very little knowledge of electronics.
This leads me on to another question I have, does anyone know what value I should expect to see for the unregulated voltage?
I would like to check if things are okay up to the point where the voltage is regulated.
To proceed I decided it would be best if I would make up an extension cable for the P100, P103, P104 connectors and for the 3 power lines P301/302/303, P304/305/306, P307/308/309 as well as the ground connection. With this I can run the amp with the left and right channel boards “folded up”, allowing me to get to the test points with a voltmeter. I am still working away on making the cables as I write this. Or is there another way of getting to these test points – Dieter, how did you solve this did you solder in cables to get to these test points or did you make up cables for the connectors as per my plan?
Once I am finished with the cables I need to build up the courage to cut off the legs of LM317 (VR1) and LM337T (VR2) and solder new replacement regulators onto these legs on for a trial. For me this the hard part because I am not 100% sure my diagnosis is accurate since both my knowledge of electronics and my tools are limited and I don’t want to destroy this piece of art...
Hi ML432,
the red binding post is simply the red (hot) V_OUT speaker connector
your info about the large caps seem to me that they are ok - if they would be faulty, you would find some electrolytic fluid or cap deformation.
The VR1 and VR2 short circuit you should check a bit more: desolder one pin of CR1 and CR2 and then measure again the VR`s as well as the CR`s and you will find out the faulty parts. The VR´s are able to handle max 37V, but the circuit keep them "floating", which means that the voltage difference between the three pins will never exceed 37V. As the circuit diagram is for the 431, and R1, R3, R4, R6 maybe a little different due to higher voltages in the 432. Check also the trimmers R2 and R5 if they are well working / have stable contact.
Your statement "I now wonder how a Vin/Vout pass though of the voltage regulators can trigger the amp to shut itself down. Would it not just work at a higher/unregulated voltage instead? Is it likely that the problem is somewhere else and the broken voltage regulators are just a side effect of that other problem?" is a good question which I am not able to answer; the preamp circuit part seem to be well constructed and this little plus in POS_REG and NEG_REG voltage should not destroy this part. Nevertheless check the parts for burning signs.
The regulated voltage of plus/minus 87,5V - according to LJYS - makes it necessary that the UNREG should be at least plus / minus 95V to have stable regulating behaviour of VR1/2 even under high amp output power.
As I have not had fault problems with my 431 it was not necessary to provide extension cables - I took out the amps, resoldered them completely and put them back into the housing.
good luck!
Dieter
the red binding post is simply the red (hot) V_OUT speaker connector
your info about the large caps seem to me that they are ok - if they would be faulty, you would find some electrolytic fluid or cap deformation.
The VR1 and VR2 short circuit you should check a bit more: desolder one pin of CR1 and CR2 and then measure again the VR`s as well as the CR`s and you will find out the faulty parts. The VR´s are able to handle max 37V, but the circuit keep them "floating", which means that the voltage difference between the three pins will never exceed 37V. As the circuit diagram is for the 431, and R1, R3, R4, R6 maybe a little different due to higher voltages in the 432. Check also the trimmers R2 and R5 if they are well working / have stable contact.
Your statement "I now wonder how a Vin/Vout pass though of the voltage regulators can trigger the amp to shut itself down. Would it not just work at a higher/unregulated voltage instead? Is it likely that the problem is somewhere else and the broken voltage regulators are just a side effect of that other problem?" is a good question which I am not able to answer; the preamp circuit part seem to be well constructed and this little plus in POS_REG and NEG_REG voltage should not destroy this part. Nevertheless check the parts for burning signs.
The regulated voltage of plus/minus 87,5V - according to LJYS - makes it necessary that the UNREG should be at least plus / minus 95V to have stable regulating behaviour of VR1/2 even under high amp output power.
As I have not had fault problems with my 431 it was not necessary to provide extension cables - I took out the amps, resoldered them completely and put them back into the housing.
good luck!
Dieter
In the meantime I gave up on my earlier plan to make cables to run the amp folded up. Doing this turned out to be too time consuming and also it would open up the potential for an error in the wiring and I do not want to destroy the amp. Instead I decided to solder cables on the back of the left and right channel capacitors where these are connected to TS3 and TS4 so that I can measure and adjust the regulated voltage without needing to directly get to TS3 and TS4.
Next I measured the voltages outlined by LJYS – This I did after cutting off the legs of the voltage regulators VR1/V2 and soldering replacement regulators onto the legs. The old legs are still in place because I will leave the proper repair to a professional once I have located the problem:
Left channel:
Right channel:
The above came a bit of a surprise to me. Because of a very prominent white discoloration on the inside of the cover just above the left channel voltage regulator. However looking at the information form LJYS it seems the right channel is at fault – maybe I had two problems to start with.
I am now not sure where to look on the right channel. The voltage regulator on the right channel seems to be okay. But although the channel circuit diagrams are for the ML431 there are a lot of similarities so I am thinking that I also have +-16V on OPA377P (U101) on the ML432 and I should therefore measure this to see if I really get these 16V.
Dieter, any recommendations?
LJYS, the information you shared has been most helpful. It would be the icing on the cake if you could also share the channel diagrams of the ML432.
Many thanks to both of you in advance, Mischa
Next I measured the voltages outlined by LJYS – This I did after cutting off the legs of the voltage regulators VR1/V2 and soldering replacement regulators onto the legs. The old legs are still in place because I will leave the proper repair to a professional once I have located the problem:
Left channel:
- Unregulated voltage 102,3V/-102,3V
- Regulated voltage 88,6V/-88,1V -> I adjusted these to 87,5V/-87,5V as per instructions kindly shared by LJYS
- Daughter board T8 voltage: 600mV at start going down constantly toward to 479mV, stable at 479mV after about 5 Minutes. Not sure if it is normal to take so long to stabilize. I adjusted this to 500mV as per instructions shared by LJYS.
- Voltage between red and black speaker binding post (after waiting 5 Minutes and after adjusting to 500mV at T8): -1V
Right channel:
- Unregulated voltage 101,8V/-101,8V
- Regulated voltage 88,3V/-88,3V
- Daughter board T8 voltage: about 1,5mV
- Voltage between red and black speaker binding post: about -3V
The above came a bit of a surprise to me. Because of a very prominent white discoloration on the inside of the cover just above the left channel voltage regulator. However looking at the information form LJYS it seems the right channel is at fault – maybe I had two problems to start with.
I am now not sure where to look on the right channel. The voltage regulator on the right channel seems to be okay. But although the channel circuit diagrams are for the ML431 there are a lot of similarities so I am thinking that I also have +-16V on OPA377P (U101) on the ML432 and I should therefore measure this to see if I really get these 16V.
Dieter, any recommendations?
LJYS, the information you shared has been most helpful. It would be the icing on the cake if you could also share the channel diagrams of the ML432.
Many thanks to both of you in advance, Mischa
Hi Mischa,
so it had been faulty VR1 and VR2chips - it looks that the POS_REG and NEG_REG have now the correct value. The supply voltage on U101 should be +- 16V in both (431 and 432) amps, as this chip have a max rating of +-18V. Have you checked that after renewing VR1 and VR2? If not you should also check CR5 and CR6 (16V Zeners)
I am a bit concerned about your offset voltages on the speaker binding posts: the offset there should be as small as possible, typically about +-20mV or so; have you checked at the left channel to get near zero volts at the binding posts by help of adjusting R133?
It seem that the right channel have some problem, maybe short-circuit of CR117/118 or a faulty U101.
These are my 2 cents on your problem; the diagrams of the 432 and 431 are more or less equal - if you look at the output transistors Q301 - Q314, you will see that Q301,302,313,314 are signed with "NU" which means "not used" in the 431; in the 432 they should be used due to the higher output power capabilities.
best regards and good luck
Dieter
so it had been faulty VR1 and VR2chips - it looks that the POS_REG and NEG_REG have now the correct value. The supply voltage on U101 should be +- 16V in both (431 and 432) amps, as this chip have a max rating of +-18V. Have you checked that after renewing VR1 and VR2? If not you should also check CR5 and CR6 (16V Zeners)
I am a bit concerned about your offset voltages on the speaker binding posts: the offset there should be as small as possible, typically about +-20mV or so; have you checked at the left channel to get near zero volts at the binding posts by help of adjusting R133?
It seem that the right channel have some problem, maybe short-circuit of CR117/118 or a faulty U101.
These are my 2 cents on your problem; the diagrams of the 432 and 431 are more or less equal - if you look at the output transistors Q301 - Q314, you will see that Q301,302,313,314 are signed with "NU" which means "not used" in the 431; in the 432 they should be used due to the higher output power capabilities.
best regards and good luck
Dieter
Hi LJYS & Mischa,
thanks for the circuit diagram; it is more or less the same - one difference is the value of resistors R6,7,8 which are slightly higher in the 432 due to the higher POS_REG voltage.
I have checked the voltage on the binding posts (speaker output) of my 431 after warm up and as I suggested the DC voltage is only about 10mV offset - this clearly contradicts the adjustment advice to have -1 V at the output. Is there any explanation for this behaviour?
best regards and good luck
Dieter
thanks for the circuit diagram; it is more or less the same - one difference is the value of resistors R6,7,8 which are slightly higher in the 432 due to the higher POS_REG voltage.
I have checked the voltage on the binding posts (speaker output) of my 431 after warm up and as I suggested the DC voltage is only about 10mV offset - this clearly contradicts the adjustment advice to have -1 V at the output. Is there any explanation for this behaviour?
best regards and good luck
Dieter
Thank you once more Dieter and LJYS.
LJYS, in standby after waiting for 5 minutes for the voltages to stabilize I measured the following values on TP6 and TP7 of the daughter audio channel. This was measured against the left/right back speaker binding post:
LJYS, in standby after waiting for 5 minutes for the voltages to stabilize I measured the following values on TP6 and TP7 of the daughter audio channel. This was measured against the left/right back speaker binding post:
- Left channel TP6: +0,526 V
Left channel TP7: +0,513 V
- Right channel TP6: -1,877 V
Right channel TP7: -1,868 V
Hi Mischa,
due to the circuit diagram it should have identical voltage in standby mode - the relay contacts K102 are shortening TP6 and TP7 and should be not far away from zero as the relay K101 put the two TP´s to ground over a 50 ohms resistor R142. I think both values are too much away from zero volt under standby conditions.
I would check Q119 to Q122 as they dissipate under normal conditions about two watts each (therefore they are heat sinked) and become pretty warm. Maybe one of them is faulty.
bets regards
Dieter
due to the circuit diagram it should have identical voltage in standby mode - the relay contacts K102 are shortening TP6 and TP7 and should be not far away from zero as the relay K101 put the two TP´s to ground over a 50 ohms resistor R142. I think both values are too much away from zero volt under standby conditions.
I would check Q119 to Q122 as they dissipate under normal conditions about two watts each (therefore they are heat sinked) and become pretty warm. Maybe one of them is faulty.
bets regards
Dieter
The output -1 V is the voltage value measured with no speaker load.
10MV is correct after the horn is loaded.
What is the value of the red dot voltage when measuring standby?
Is it correct to measure the blue dot resistance value?
Is it bad to measure the purple point 2N5551?
LJYS, Dieter, I cannot thank you enough for your expert help.
First I would like to clarify that my measurements were take in standby (sleep mode off) with no speakers connected. Also I would like to clarify that my TP6 and TP7 daughter audio channel measurements were taken against the black speaker post at the rear of the amp, due to a typo I had written back rather than black. I used the left side black speaker post for left side measurements and right side black speaker post for the right side measurements.
LJYS, I will take out the right channels this evening to measure the points you have identified and to solder in a cable to make a voltage measurement at the red dot in standby. As part of this I will do some “power off” resistance value comparisons between left and right audio channel on all the legs of Q102 to Q122.
First I would like to clarify that my measurements were take in standby (sleep mode off) with no speakers connected. Also I would like to clarify that my TP6 and TP7 daughter audio channel measurements were taken against the black speaker post at the rear of the amp, due to a typo I had written back rather than black. I used the left side black speaker post for left side measurements and right side black speaker post for the right side measurements.
LJYS, I will take out the right channels this evening to measure the points you have identified and to solder in a cable to make a voltage measurement at the red dot in standby. As part of this I will do some “power off” resistance value comparisons between left and right audio channel on all the legs of Q102 to Q122.
Thanks you Dieter for making a comparison measurement. My measurement was taken between the red and the black speaker binding post. The DMM black ground cable connected to the black binding post as per instructions shared by LJYS. This was with no speakers connected and the amp in standby with the dip switch at the back set to "power safe mode off”.
LJYS, I realized this evening that I can directly measure the voltage at the "red dot" using the middle pin of Q119. The measurements I took are as follows:
Red dot:
Left channel:
Starts at about -4V and then settles at -1,91V after about 2 minutes
Right channel:
Starts at about -4V and then settles at +4,38V after about 5 minutes
Blue dots:
All blue dot resistors on the right channel measure the correct resistance values. Additionally, I measured CR101 to CR108 and they show the expected values.
Purple dots:
Tomorrow I will disassemble the audio boards to get to the back of the daughter audio channel to measure Q102, Q103, Q106, Q107 with a diode tester and compare the left and right audio channel values. Or do you have another suggestion what I should be testing next?
Also a while back I had measured Q119 to Q121 with the diode setting and as far as I remember left and right channel did not show any difference. But I will also test this area once more tomorrow.
Best regards and once more thanks to both of you,
Mischa
LJYS, I realized this evening that I can directly measure the voltage at the "red dot" using the middle pin of Q119. The measurements I took are as follows:
Red dot:
Left channel:
Starts at about -4V and then settles at -1,91V after about 2 minutes
Right channel:
Starts at about -4V and then settles at +4,38V after about 5 minutes
Blue dots:
All blue dot resistors on the right channel measure the correct resistance values. Additionally, I measured CR101 to CR108 and they show the expected values.
Purple dots:
Tomorrow I will disassemble the audio boards to get to the back of the daughter audio channel to measure Q102, Q103, Q106, Q107 with a diode tester and compare the left and right audio channel values. Or do you have another suggestion what I should be testing next?
Also a while back I had measured Q119 to Q121 with the diode setting and as far as I remember left and right channel did not show any difference. But I will also test this area once more tomorrow.
Best regards and once more thanks to both of you,
Mischa
Hi Dieter,
the left channel and the right channel PCBs share the same circuit diagram but unfortunately they are assembled differently (in mirror fashion) and are not interchangeable. On my amp the left and right channel PCBs even have different revision numbers.
LJYS,
I measured Q102, Q103, Q106, Q107 and compared the result of the diode setting on the DMM between left and right channel. Doing this and measuring the pins left to right and right to left I found that Q106 on the right channel is showing an unusual value.
Left channel Q106 (DMM in diode test mode):
Pin 1 to Pin 2: 0,700 V
Pin 2 to Pin 1: Infinite
Pin 2 to Pin 3: Infinite
Pin 3 to Pin 2: 0,700 V
Right channel Q106 (DMM in diode test mode):
Pin 1 to Pin 2: 1,16 V (a value of about 0,7 V is expected)
Pin 2 to Pin 1: Infinite
Pin 2 to Pin 3: Infinite
Pin 3 to Pin 2: 0,700 V
In still need to get a replacement soldered in by someone who is better at this than I am, but I have a good feeling that Q106 really is at fault and that this was the fault I have been chasing. It seems your expert advice has been spot on, I can not thank you enough for this LJYS.
Just to be on the safe side I measured and compared all other Q... transistors and so far only Q106 showed an unusual value. All resistors I measured did show the expected values.
Unfortunately my knowledge of electronics is very limited, but I assume a faulty Q106 explains why I was seeing an excessive positive voltage at the TP8 and at the red dot. Dieter what are your thoughts, can a faulty Q106 explain the excessive positive voltage?
Anyway, I will report back to you all once I have a replacement for Q106 in place.
Best Regards,
Mischa
the left channel and the right channel PCBs share the same circuit diagram but unfortunately they are assembled differently (in mirror fashion) and are not interchangeable. On my amp the left and right channel PCBs even have different revision numbers.
LJYS,
I measured Q102, Q103, Q106, Q107 and compared the result of the diode setting on the DMM between left and right channel. Doing this and measuring the pins left to right and right to left I found that Q106 on the right channel is showing an unusual value.
Left channel Q106 (DMM in diode test mode):
Pin 1 to Pin 2: 0,700 V
Pin 2 to Pin 1: Infinite
Pin 2 to Pin 3: Infinite
Pin 3 to Pin 2: 0,700 V
Right channel Q106 (DMM in diode test mode):
Pin 1 to Pin 2: 1,16 V (a value of about 0,7 V is expected)
Pin 2 to Pin 1: Infinite
Pin 2 to Pin 3: Infinite
Pin 3 to Pin 2: 0,700 V
In still need to get a replacement soldered in by someone who is better at this than I am, but I have a good feeling that Q106 really is at fault and that this was the fault I have been chasing. It seems your expert advice has been spot on, I can not thank you enough for this LJYS.
Just to be on the safe side I measured and compared all other Q... transistors and so far only Q106 showed an unusual value. All resistors I measured did show the expected values.
Unfortunately my knowledge of electronics is very limited, but I assume a faulty Q106 explains why I was seeing an excessive positive voltage at the TP8 and at the red dot. Dieter what are your thoughts, can a faulty Q106 explain the excessive positive voltage?
Anyway, I will report back to you all once I have a replacement for Q106 in place.
Best Regards,
Mischa
Hi Mischa,
ok, then it is not possible to interchange the daughter boards; but when they have different revision numbers it looks a bit tinkered to me.
There should not be 1,16V between pin 1 and 2 of Q106 - looks as this will solve the problem - hopefully. Also check the voltage on R120 and 121 - it should be 0,7V each when the current generators (Q108/109 and Q110/111) are working properly.
One more hint: resolder the complete amp this will avoid future problems as some parts are becoming a bit warm and this ages the solder joints over time.
Good luck!
Dieter
ok, then it is not possible to interchange the daughter boards; but when they have different revision numbers it looks a bit tinkered to me.
There should not be 1,16V between pin 1 and 2 of Q106 - looks as this will solve the problem - hopefully. Also check the voltage on R120 and 121 - it should be 0,7V each when the current generators (Q108/109 and Q110/111) are working properly.
One more hint: resolder the complete amp this will avoid future problems as some parts are becoming a bit warm and this ages the solder joints over time.
Good luck!
Dieter
Hola Dieter,
Sigo trabajando con estos amplificadores... Tengo problemas con el +16/-16. Cuando se activan los relés, los +16v caen a +9v. Esto sucede en los 3 canales de este amplificador. He puesto el zener y las nuevas resistencias al 1%.
También tengo uno de 5 canales, estos son casi idénticos al HPA3. Esto no sucede en el canal 5. Cuando los relés se activan, el voltaje permanece estable.
En los 3 canales del HPA cae el +16v. Pulse las resistencias de 8k66 en paralelo y el voltaje subió a +10v.
Thanks!
Hola Symphony,
a pretty interesting behaviour - as I understand all three channels have the same effect that the positive voltage decreases from 16 to 9 Volt; have you measured the POS_REG as well as the POS_PRE_REG voltages under the condition of activated relays in all channels? If there is no substantial decrease in these voltages I would check R506 (its a wire wound resistor with some dissipation) and check the value (1,8kOhm )as well as the soldering around (maybe the solderings are not well contacted due to hot/cold cycles). CR504 is a 5Watt 16V Zener diode which should be pretty robust. Btw, what is the voltage on POS_REG?
When I look at Power supply schematics, the plus/minus voltage for the 5 channel amp should be a bit below 50 V due to the max voltage of the 17000uF caps; is this the same for the 3 channel amp?
atentamente
Dieter
a pretty interesting behaviour - as I understand all three channels have the same effect that the positive voltage decreases from 16 to 9 Volt; have you measured the POS_REG as well as the POS_PRE_REG voltages under the condition of activated relays in all channels? If there is no substantial decrease in these voltages I would check R506 (its a wire wound resistor with some dissipation) and check the value (1,8kOhm )as well as the soldering around (maybe the solderings are not well contacted due to hot/cold cycles). CR504 is a 5Watt 16V Zener diode which should be pretty robust. Btw, what is the voltage on POS_REG?
When I look at Power supply schematics, the plus/minus voltage for the 5 channel amp should be a bit below 50 V due to the max voltage of the 17000uF caps; is this the same for the 3 channel amp?
atentamente
Dieter