Yamaha Stagepas 300 no left channel

[nosaj]

Both modules read about 195mv DC in either slot. I'll hunt down that resistor to disable the protection circuit then read the DC offsets again.

Thanks,
nosaj

Ok after pulling out the magnifying glass was I able to fin d r877 and tac a wire from it to ground. Using a variac to ramp up voltage I'd get almost 4v - or positive depending on which channel it was plugged into. This is with both modules left and right plugged in. I notice that after it has shutdown visually(no lights) it will still retain .5vdc on the output.


Also since it still shuts down as it did previously Did it matter what side of r877 needed to be tac'ed to ground and what ground? ( I used the ground from one of the fans).
thanks so much for helping,

nosaj

[nickb]

Ok after pulling out the magnifying glass was I able to fin d r877 and tac a wire from it to ground. Using a variac to ramp up voltage I'd get almost 4v - or positive depending on which channel it was plugged into. This is with both modules left and right plugged in. I notice that after it has shutdown visually(no lights) it will still retain .5vdc on the output.


Also since it still shuts down as it did previously Did it matter what side of r877 needed to be tac'ed to ground and what ground? ( I used the ground from one of the fans).
thanks so much for helping,

nosaj

One side if R877 is already grounded, so yes which side you ground matters. You cannot in general bring up a SMPS with a variac. There are all sorts of complications especially with a class D amp too. Don't do it as it's not helping due to too many unknowns.

[nosaj]

One side if R877 is already grounded, so yes which side you ground matters. You cannot in general bring up a SMPS with a variac. There are all sorts of complications especially with a class D amp too. Don't do it as it's not helping due to too many unknowns.

Ok soldered it to the other side turned on . The ammeter is bouncing between 0 and .2amps
VUmeter led's bouncing from 0 to +3db(5 leds)
Lchannel dc bouncing from .99 to .147 vdc
Rchannel dc bouncing from -.93 to -.151vdc

This is with no Load connected.


Thanks,

nosaj

[nickb]

Ok soldered it to the other side turned on . The ammeter is bouncing between 0 and .2amps
VUmeter led's bouncing from 0 to +3db(5 leds)
Lchannel dc bouncing from .99 to .147 vdc
Rchannel dc bouncing from -.93 to -.151vdc

This is with no Load connected.


Thanks,

nosaj

I would say the power supply is the root issue. When you have both modules in it doesn't work properly. I would now put the power supply on a dummy load and check it out. These Stagepasses are so compact thet are not easy to work on.

[nosaj]

I would say the power supply is the root issue. When you have both modules in it doesn't work properly. I would now put the power supply on a dummy load and check it out. These Stagepasses are so compact thet are not easy to work on.

-.001 vdc and .000 vdc on the channels. This afternoon I think I should check output on IC 804 and IC 802 top249y IC's.
I have an isolation transformer I've been using , are there any gotcha's I should be wary of doing this? I see it's separated with a line primary/secondary earlier you schooled me on using grounds from the same side whether it's primary or secondary. Any other things I should be watching for? No burnt looking components on board.

Thanks,
nosaj

[nickb]

The primary purpose of an isolation transformer is to allow you to connect earthed equipment like a scope to the power supply under test. It does reduce the chance of lethal shock a little at there is only a leakage path current path through the transformer to live and then to earth.

It sounds like the power supply may be cycling on and off - a fairly common behaviour when excess current is detected.

The reason for suggesting dummy loads it will allow you to test the power supply on its own. It could be that the combination of the two modules is the real culprit, drawing excessive current. The problem with testing in situ is the load is going to have a rather complex current/time voltage relationship making it hard to understand what is going on. Another approach is to power the amp from a bench variable voltage power supply and test that.

Given the power supply does substantially work would not lead me suspect the TOP249Y's first.

[nosaj]

The primary purpose of an isolation transformer is to allow you to connect earthed equipment like a scope to the power supply under test. It does reduce the chance of lethal shock a little at there is only a leakage path current path through the transformer to live and then to earth.

It sounds like the power supply may be cycling on and off - a fairly common behaviour when excess current is detected.

The reason for suggesting dummy loads it will allow you to test the power supply on its own. It could be that the combination of the two modules is the real culprit, drawing excessive current. The problem with testing in situ is the load is going to have a rather complex current/time voltage relationship making it hard to understand what is going on. Another approach is to power the amp from a bench variable voltage power supply and test that.

Given the power supply does substantially work would not lead me suspect the TOP249Y's first.

The Bench supply I have is a 30volt one. I guess I can check the lower voltages and hope I get lucky.


Thanks,
nosaj

[nosaj]

The Bench supply I have is a 30volt one. I guess I can check the lower voltages and hope I get lucky.


Thanks,
nosaj

Ok I went back and measured the voltage regulators 5v good -15v good well 15.6 so not sure. +15 measures 14 ( so I thought that meant something was pulling it down. I subbed a good VR same issue. So I pulled VR and and wired 15v supply into pins 2 and 3 ground and output. Amp comes up fine. Removed the ground for r877 still comes up fine. Both modules plugged in. Put a load on both channels measuring just under a 100 mv. So this says the issue is before the +15VR.

Which I will go back and verify d804, and D830, I believe that D829 and D814 will be ok because of what was just observed.

I think if it comes to the transformer it's a goner, no?
Again just guessing.

Thanks,
nosaj

[nosaj]

Ok I went back and measured the voltage regulators 5v good -15v good well 15.6 so not sure. +15 measures 14 ( so I thought that meant something was pulling it down. I subbed a good VR same issue. So I pulled VR and and wired 15v supply into pins 2 and 3 ground and output. Amp comes up fine. Removed the ground for r877 still comes up fine. Both modules plugged in. Put a load on both channels measuring just under a 100 mv. So this says the issue is before the +15VR.

Which I will go back and verify d804, and D830, I believe that D829 and D814 will be ok because of what was just observed.

I think if it comes to the transformer it's a goner, no?
Again just guessing.

Thanks,
nosaj

Ok lifted legs on d804, d830, d829, d814. Diodes check good . Resoldered them back in.
Here's where I loose what I'm reading.

D804 and D830 Can read 15vdc and 15.4 vdc on one side. Now I can't see any ac though I know it should be there.

D829 and D814 .4 and .5vdc.

Just a reminder this is with +15VR removed and PS tacked in. both amp modules on with a load plugged in. and R877 protection re-enabled.

Not sure what to do at this point. One thing I am sure about is I do not know if taking voltages on a SMPS transformer is the same as a Linear PT.

Thanks so much,
nosaj

[The Dude]

Are you using a scope or multimeter? The SMPS will be high frequency- not 60hz. I suspect that if the input to your +15V regulator is low, you have a bad capacitor there at the input (maybe C802). The attachments in this thread are only a block diagram and don't show the whole story. If you don't have the full schematic, you can get it here.

http://www.go-gddq.com/upload/2014-0...2721337905.pdf

P.S.- I doubt it's a bad transformer.

Edit: I wrote this assuming that the input to the regulator was low. Looking back through the thread, I don't see that we have that info. You should check the input voltage first to verify that this is the case. It can only regulate if there is enough supply to regulate.

[nickb]

Ok lifted legs on d804, d830, d829, d814. Diodes check good . Resoldered them back in.
Here's where I loose what I'm reading.

D804 and D830 Can read 15vdc and 15.4 vdc on one side. Now I can't see any ac though I know it should be there.

D829 and D814 .4 and .5vdc.

Just a reminder this is with +15VR removed and PS tacked in. both amp modules on with a load plugged in. and R877 protection re-enabled.

Not sure what to do at this point. One thing I am sure about is I do not know if taking voltages on a SMPS transformer is the same as a Linear PT.

Thanks so much,
nosaj

As Dude says, it requires the right equipment to measure the voltage coming out of the transformer as there are both high frequencies and complex waveforms. Also for these same reasons its very hard to verify the high frequency diodes are working correctly. You need about 18V into the 7815 to be sure it regulates so check that.

The design is unusual in that there are two switching front ends and they both supply current to the +15 and -15 rails. This means that a faulure of either diode 804 or 830 or the cap could C802 could cause a problem.

A transformer failure is very unlikely.

A

[nosaj]

Are you using a scope or multimeter? The SMPS will be high frequency- not 60hz. I suspect that if the input to your +15V regulator is low, you have a bad capacitor there at the input (maybe C802). The attachments in this thread are only a block diagram and don't show the whole story. If you don't have the full schematic, you can get it here.

http://www.go-gddq.com/upload/2014-0...2721337905.pdf

P.S.- I doubt it's a bad transformer.

Edit: I wrote this assuming that the input to the regulator was low. Looking back through the thread, I don't see that we have that info. You should check the input voltage first to verify that this is the case. It can only regulate if there is enough supply to regulate.

It was a 15.6 input 14v output I'm using a meter for those checks.

nosaj

[nosaj]

As Dude says, it requires the right equipment to measure the voltage coming out of the transformer as there are both high frequencies and complex waveforms. Also for these same reasons its very hard to verify the high frequency diodes are working correctly. You need about 18V into the 7815 to be sure it regulates so check that.

The design is unusual in that there are two switching front ends and they both supply current to the +15 and -15 rails. This means that a faulure of either diode 804 or 830 or the cap could C802 could cause a problem.

A transformer failure is very unlikely.

A

Ok will checkout the cap this afternoon. Thanks guys,

Jason

[nosaj]

Ok will checkout the cap this afternoon. Thanks guys,

Jason

Replaced the cap Fires up and plays both left and right channels. put it back in the case power supply and outputs screwed in Preamp still loose not screwed in . Symptom comes back. It was dropped pretty hard is what I was told. Solder joints all looked good. I'm wondering if I could be looking at a pcb problem since it is working out of the shell but not in it.

thanks,
nosaj

[The Dude]

When you replaced the cap, did it change the input voltage to the regulator?

Also, some of those Yamaha powered mixers need to be assembled to run, or else ground wires clipped in for testing. The preamp to power amp section ground is carried by a foil that is connected by screws when assembled. I'm not sure if this is one of those.