Most audio amplifiers now have 2 separate power supplies. A very small one powers the microcontroller and control circuits, the main power transformer is for the audio amplifier. So there is always power to the control circuits while ever the amp. is plugged into the mains. This is necessary so that power amplifier can be operated completely via remote control or the front panel logic level switches.
So standby is the normal state of the amp. but the microcontroller should always be capable of responding by switching on the mains power to the power amplifier via a relay. After perhaps 15 years of constantly being switched on, I think you can understand why the control circuits may fail before the amplifier, which may only see 10 hours intermittent use per week or even less.
So standby is the normal state of the amp. but the microcontroller should always be capable of responding by switching on the mains power to the power amplifier via a relay. After perhaps 15 years of constantly being switched on, I think you can understand why the control circuits may fail before the amplifier, which may only see 10 hours intermittent use per week or even less.
As long as you plan to do something about it soon, I don't think being powered up is going to cause further damage in the short term, if that's what your concern is. The present problem has likely been there for some time but CMOS logic circuits operate at very low current and only when commands are entered and the clock is running. This gives the control circuits some immunity to damage even when operated as it likely has been, with intermittent power, no clock etc.
However, we can't be certain this is the case without your performing the supply voltage measurements. These would give us confirmation of what is currently happening and whether the controller is then likely to function correctly if the power to it is improved.
However, we can't be certain this is the case without your performing the supply voltage measurements. These would give us confirmation of what is currently happening and whether the controller is then likely to function correctly if the power to it is improved.
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Today I have made some measurements - and it looks like D45 (rectifier) might be faulty.
I measured the same values in both stand by and power on mode: 0V on one side and 0,1V on the other. I compared it with D25 (2V/2V in stB mode and 26V/50V in pw mode.
Also compared with D18 and D19 - both 0V/14V in stB mode and also 0V/14V in pw mode.
According to service manual (page 14) I tried to follow the line from D45 to Q42 and to Q55 - but I can not find Q42 and Q55.
Now I wonder if it is D45 that is faulty - or if instead could be Q42 or Q55. (I wish I could find those - two. I have found several others like Q41 etc - but not 42 and 55).
D45 is placed close to Z6 - but in the service manual it is shown close to Z7.
I wonder if there might be some errors in the service manual. In the area with Z6 or Z7 - I can't find the Q42/Q55 - and neither in other areas on the print board.
I measured the same values in both stand by and power on mode: 0V on one side and 0,1V on the other. I compared it with D25 (2V/2V in stB mode and 26V/50V in pw mode.
Also compared with D18 and D19 - both 0V/14V in stB mode and also 0V/14V in pw mode.
According to service manual (page 14) I tried to follow the line from D45 to Q42 and to Q55 - but I can not find Q42 and Q55.
Now I wonder if it is D45 that is faulty - or if instead could be Q42 or Q55. (I wish I could find those - two. I have found several others like Q41 etc - but not 42 and 55).
D45 is placed close to Z6 - but in the service manual it is shown close to Z7.
I wonder if there might be some errors in the service manual. In the area with Z6 or Z7 - I can't find the Q42/Q55 - and neither in other areas on the print board.
OK - thanks.
Do you see something from the measurements.
It's not easy to trace the power to/from D45. D45's pins are not soldered to a print lane as the D25 pins are.
I assume that it is ok - that D18 and D19 has 0V on one side and 14V on the other.
But I'm not sure about neither D45 or D25.
Should D25 not be 0V on one side. And should D45 not have voltage on one of the sides?
The amp was functioning perfectly when I made the measurements.
Maybe I should wait - and make a comparison later - when I have had a chance to measure the components - when the amp will not power on.
Do you see something from the measurements.
It's not easy to trace the power to/from D45. D45's pins are not soldered to a print lane as the D25 pins are.
I assume that it is ok - that D18 and D19 has 0V on one side and 14V on the other.
But I'm not sure about neither D45 or D25.
Should D25 not be 0V on one side. And should D45 not have voltage on one of the sides?
The amp was functioning perfectly when I made the measurements.
Maybe I should wait - and make a comparison later - when I have had a chance to measure the components - when the amp will not power on.
Here is some measured values for comparison:
A/Amp not working (power switch pushed on - but nothing happens)
B/Amp powered (on and works fine)
C/Amp - on stand by mode
D10,D11,D12,D13 (rectifiers - “Z7 - area"):
A/ 0,3V/0V B/ 50V/0V C/ 1V/0V
D18,D19 (rectifiers - “Z7 - area”):
A/ 0V/14V B/ 0V/14V C/ 0V/14V
D45 (rectifiers - “Z6 - area”):
A/0V B/0,1V C/0,1V
D25 (rectifier - “Z6 - area”):
A/0,3V B/50V/26V C/ 2V/2V
R200 (resistor): A/ 0,3V/0,3V B/ 0,1V/26V C/ 0,5V/0,5V
Is it possible to see from the measured values - if some of the above mentioned components should be replaced.
Or could the measurements be telling something else?
A/Amp not working (power switch pushed on - but nothing happens)
B/Amp powered (on and works fine)
C/Amp - on stand by mode
D10,D11,D12,D13 (rectifiers - “Z7 - area"):
A/ 0,3V/0V B/ 50V/0V C/ 1V/0V
D18,D19 (rectifiers - “Z7 - area”):
A/ 0V/14V B/ 0V/14V C/ 0V/14V
D45 (rectifiers - “Z6 - area”):
A/0V B/0,1V C/0,1V
D25 (rectifier - “Z6 - area”):
A/0,3V B/50V/26V C/ 2V/2V
R200 (resistor): A/ 0,3V/0,3V B/ 0,1V/26V C/ 0,5V/0,5V
Is it possible to see from the measured values - if some of the above mentioned components should be replaced.
Or could the measurements be telling something else?
My amp has improved a lot in the last days.
But I now wonder if this is a correct behaviour:
If the "On/off button is pushed in on the amp - when plugging in power cord - it gets power and goes into stand by mode - and then it can be operated using the remote.
If plugging in power - and first afterwards pushing in the on/off button on the amp - it looks like nothing happens.
But then when toggle on (by remote) - it turns on.
When by remote toggle off - the amps goes into stand by mode. When I the want to turn it of completely using the on/off button on the amp - it stays in standby mode anyway. But then I can toggle off one more time using remote and then the red light on the amp disappears.
I could live with the described way that it functions. I don't think it could harm the unit.
But on the other hand it has the before mentioned rectifier "D25" - that when measured showed 0W both when the amp was in standby and when it was playing. Maybe I should order a new rectifier anyway to see if that will make any difference.
But I now wonder if this is a correct behaviour:
If the "On/off button is pushed in on the amp - when plugging in power cord - it gets power and goes into stand by mode - and then it can be operated using the remote.
If plugging in power - and first afterwards pushing in the on/off button on the amp - it looks like nothing happens.
But then when toggle on (by remote) - it turns on.
When by remote toggle off - the amps goes into stand by mode. When I the want to turn it of completely using the on/off button on the amp - it stays in standby mode anyway. But then I can toggle off one more time using remote and then the red light on the amp disappears.
I could live with the described way that it functions. I don't think it could harm the unit.
But on the other hand it has the before mentioned rectifier "D25" - that when measured showed 0W both when the amp was in standby and when it was playing. Maybe I should order a new rectifier anyway to see if that will make any difference.
The measurements you've got are pretty much only telling you that the main supply is not being turned on when it should be. The main transformer doesnt get connected to the mains until the microcontroller switches it on via RLY7.
Your measurements at D18 and D19 suggest the rectifiers there are OK, so what you want to measure next is the output of Z7, an 8v regulator. If the 8V supply is not present when the amp is "on but not functioning" then that's the smoking gun.
edit: D25 is simply a back-EMF diode across RLY6's coil. This relay is part of the "inrush limiter" system for the main transformer, and is only activated when the power is applied to the main transformer. All you have really confirmed is that when the amp is "on but not functioning", the main transformer is not being turned on when it should be.
Your measurements at D18 and D19 suggest the rectifiers there are OK, so what you want to measure next is the output of Z7, an 8v regulator. If the 8V supply is not present when the amp is "on but not functioning" then that's the smoking gun.
edit: D25 is simply a back-EMF diode across RLY6's coil. This relay is part of the "inrush limiter" system for the main transformer, and is only activated when the power is applied to the main transformer. All you have really confirmed is that when the amp is "on but not functioning", the main transformer is not being turned on when it should be.
You mention rly7 an z7 - I guess that they are the same component.
And then - when you mention 8V supply - does it mean that I should be able to measure 8V on some of the pins on Z7 - also when the amp is working?
I'm pretty sure - that I did measure it without any result.
If I shall focus on the components in the same area as the Z7 - I can only see 5 (in the service manual). C48, C85 and C94 on the input side - and C45 and C86 on the output side.
Should these all have the same 8V?
NB: D10, D11, D12 and D13 has 50V on one side - when the amp works
But when it is not working - the 50V are gone.
That is a lot more than the 8V - from Z7. Would there be other components - that could cut of the 50V?
And then - when you mention 8V supply - does it mean that I should be able to measure 8V on some of the pins on Z7 - also when the amp is working?
I'm pretty sure - that I did measure it without any result.
If I shall focus on the components in the same area as the Z7 - I can only see 5 (in the service manual). C48, C85 and C94 on the input side - and C45 and C86 on the output side.
Should these all have the same 8V?
NB: D10, D11, D12 and D13 has 50V on one side - when the amp works
But when it is not working - the 50V are gone.
That is a lot more than the 8V - from Z7. Would there be other components - that could cut of the 50V?
No. RLY7 is, as the designator would suggest, a relay. Z7 is a TO-220 packaged regulator IC. It is mounted on the heatsink marked as HS2NA
You should measure 8V on pin 3 of Z7 when the amp is plugged into the wall. This should ALWAYS be present.
You don't seem to realise that there are TWO transformers producing power in this unit... a small one (labelled TX2 on the schematic), which is always powered when the amp is plugged in, and the main toroidal transformer (TX1, the primary windings connects to SK7 and the secondary windings connects to SK8), which is powered ONLY when the microcontroller closes RLY7's contacts. If the microcontroller doesnt tell RLY7 to switch on, then TX1 doesnt get any power at all and the amp doesn't work.
D10-D13 will ONLY show power on them when the main transformer is powered up. If it isn't then you wont get any voltage. It doesnt mean those parts are faulty.
On C48 you should see ~11V. On C45 you should see 8V.
If those are present, check on C10 for 5V.
My bet is that when the amp is "on but doesnt work" you will find one of those voltages is missing
Thanks jaycee - you are very helpful to me.
I did realise that the amp has two transformers - but I was just wondering if something could cut off the 50V.
But on second thoughts you're right - because when the amp works, I can hear a relay kick in when it is turned on - and when that does not happen I understand that the 50V would probably not be measurable either.
Next step I'll check the components you have mentioned.
But maybe not before next week. The amp still works pretty good.
I did realise that the amp has two transformers - but I was just wondering if something could cut off the 50V.
But on second thoughts you're right - because when the amp works, I can hear a relay kick in when it is turned on - and when that does not happen I understand that the 50V would probably not be measurable either.
Next step I'll check the components you have mentioned.
But maybe not before next week. The amp still works pretty good.
My amp still works great at the moment.
However I wonder how the display should work.
I have seen that it should be possible to let the display stay on - and that it also should be possible to switch it off or dim it.
How to you change the display settings?
My amp only shows the display - when I operate it - or push the control button. But shortly after that it switch off again.
However I wonder how the display should work.
I have seen that it should be possible to let the display stay on - and that it also should be possible to switch it off or dim it.
How to you change the display settings?
My amp only shows the display - when I operate it - or push the control button. But shortly after that it switch off again.
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