Yes, that was the output of the transistor. Q711 in this case. Ground probe I'm leaving it on the main ground and measured on the emitter of the Q711. But I've just remembered that I didn't replaced it's counter part, the Q710. Will do that now.
From the transistor, trace goes under the board straight to the fets, so I'm assuming that the other transistor is all that could be at this point.
From the transistor, trace goes under the board straight to the fets, so I'm assuming that the other transistor is all that could be at this point.
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A transistor doesn't have an input or output. The output can be taken from either the emitter or collector.
Why do you think there is a problem with the wavewform? Was your probe switch set to 10x?
Why do you think there is a problem with the wavewform? Was your probe switch set to 10x?
No, probe is set to 1x.
I'm thinking there is a problem with the voltage as it will probably won't drive the FET. The other bank has 4.38V, as far as I know should be the same.
I'm thinking there is a problem with the voltage as it will probably won't drive the FET. The other bank has 4.38V, as far as I know should be the same.
Do you have about 10v on the collector of the NPN driver transistor?
Do you have the same signals on the base of all 4 driver transistors?
Do you have the same signals on the base of all 4 driver transistors?
Yes, there are 12v on the collector of the NPN
Yes, signals are the same on all 4 of them.
I've just replaced the Q710 and it was indeed faulty. I have 4v going to the FET's on that bank as well now.
There is still a difference of 0.2v between banks but I assume that could be because of the different revisions of the transistors maybe. Old one, from the other bank, is outputting 4.2v on the emitter. I guess this part should be done now and I need to start on the FETs, probably need to order some new ones as they are gone.
Yes, signals are the same on all 4 of them.
I've just replaced the Q710 and it was indeed faulty. I have 4v going to the FET's on that bank as well now.
There is still a difference of 0.2v between banks but I assume that could be because of the different revisions of the transistors maybe. Old one, from the other bank, is outputting 4.2v on the emitter. I guess this part should be done now and I need to start on the FETs, probably need to order some new ones as they are gone.
The other drivers show signs of overheating by the discoloration in the center of the face. I'd replace them.
Will do, I have plenty of them at the moment anyway.
Is there anything I can look for on the output section before I fit the rectifiers?
Is there anything I can look for on the output section before I fit the rectifiers?
Shorted output transistors. You should check for shorted output transistors when you first open a damaged amp. They often fail and cause the power supply to fail. When they fail, they often take out many of the driver components and can make the amplifier far more difficult to repair. This is important to know, especially if you're repairing for someone else.
The output transistors are shorted for sure. I did check them when I first opened the amp. I know they are the most often reason.
The driver section for the output looks a bit more complicated taking the fact that is just a class D mono amp.
The driver section for the output looks a bit more complicated taking the fact that is just a class D mono amp.
Thank you for all the help at the moment, greatly appreciated. I will get back with updates after I have the parts.
Allright, so the power supply section is happy. The output on the other hand, has a couple of issues, it was to be expexted probably.
Now, I have rail voltage in places I'm not sure I should. I have a KIA7812a regulator marked as IC705 that is very hot. Not sure if it's supposed to be. Taking the fact that has rail voltage on one of it's pins and delivers 12V on other, I would say it does.
The output FET's on one bank don't have the correct voltage to work, I"m assuming that's because of the transistors that drive them. They are some KTC1027 and A1023, marked as Q105-108. Should them have rail voltage passing through?
Also the IC IRS2092S hase rail voltage on one pin. But can't seem to find any drive wave anywhere.
The output FET's are removed at the moment and my 2A power suppy isn't able to put the amp in idle. With a bigger one, it does somehow idle, as the LED is both red and blue with the odd time being blue for a short moment.
Any thoughts? Thank you.
Now, I have rail voltage in places I'm not sure I should. I have a KIA7812a regulator marked as IC705 that is very hot. Not sure if it's supposed to be. Taking the fact that has rail voltage on one of it's pins and delivers 12V on other, I would say it does.
The output FET's on one bank don't have the correct voltage to work, I"m assuming that's because of the transistors that drive them. They are some KTC1027 and A1023, marked as Q105-108. Should them have rail voltage passing through?
Also the IC IRS2092S hase rail voltage on one pin. But can't seem to find any drive wave anywhere.
The output FET's are removed at the moment and my 2A power suppy isn't able to put the amp in idle. With a bigger one, it does somehow idle, as the LED is both red and blue with the odd time being blue for a short moment.
Any thoughts? Thank you.
When checking voltage regulators like the 7812, place the black probe on the regulator's ground terminal.
These ICs are difficult/impossible to check without the outputs in the circuit. They shut down because they measure the Drain-source voltage when the IC is driving the low-side FET and without the FET, it appears that there is an over-current situation. If someone knows how to prevent this from happening, please post it.
These ICs are difficult/impossible to check without the outputs in the circuit. They shut down because they measure the Drain-source voltage when the IC is driving the low-side FET and without the FET, it appears that there is an over-current situation. If someone knows how to prevent this from happening, please post it.
I have some new FET's. I haven't installed them yet because of that difference I've noticed between banks. I don't mind taking a chance, I'm learning anyway.
If you power the amp up through a limiter (a 2 amp supply may be enough of a limiter) and clamp all FETs to the heatsink (or a temporary heatsink), you significantly reduce the chance of damaging FETs.
Without the FET's, the 2A power supply doesn't seem to be enough. The rail voltage is rising to only about half the value, around 25v.
Yes, I've used a computer power supply and that one seems to do the job. Though, even with that one, as far as I've seen, not all the big capacitors are charging.
That, and measured the output terninals at some point, without the FET's I had DC voltage on them. About 4.4v
That, and measured the output terninals at some point, without the FET's I had DC voltage on them. About 4.4v
Is the 2092 getting hot?
Did you check the outputs (high and low) to see if either had leakage to its respective power supply terminals?
If you connect a load across the speaker terminals (If a speaker, something robust). does the 4v drop to 0v? Does the amp draw more current with the load?
You need a limiter with the computer power supply. Most are good for 35 amps or more on their 12v output.
Did you check the outputs (high and low) to see if either had leakage to its respective power supply terminals?
If you connect a load across the speaker terminals (If a speaker, something robust). does the 4v drop to 0v? Does the amp draw more current with the load?
You need a limiter with the computer power supply. Most are good for 35 amps or more on their 12v output.
No, it is not, I did check at some point.
How do I do that exactly? I did a test at some point and connected another 1.5A power supply next to the 2A one. After around 15 seconds or so, it did enter the idle state that it does with the computer power supply. I removed the 1.5 one, leaving just the 2A and it did stay in idle with the correct voltage so I assumed that it just needs a bigger power supply until idle else it drains it somewhere.
I don't think I have anything that I could use as a load on this type of amp. I have a speaker but I wouldn't risk it.
This is an old power supply. Only does around 8-10A on the 12v output.
How do I do that exactly? I did a test at some point and connected another 1.5A power supply next to the 2A one. After around 15 seconds or so, it did enter the idle state that it does with the computer power supply. I removed the 1.5 one, leaving just the 2A and it did stay in idle with the correct voltage so I assumed that it just needs a bigger power supply until idle else it drains it somewhere.
I don't think I have anything that I could use as a load on this type of amp. I have a speaker but I wouldn't risk it.
This is an old power supply. Only does around 8-10A on the 12v output.
