i bought this amp as a blown "project", and the input nulling turoid was burnt (see pic) so i replaced it from a spare from a working amp and now i have power through out the output stages but still no led's are lighting up. any ideas what i should do next? i have the other identical amp on the work bench for referance if this will help me. the amp is a phoenix gold ms2125.
An externally hosted image should be here but it was not working when we last tested it.
i'm sure the irfp054's are not blown, they have power on the middle leg and don't have any obvious damage, same for the caps, all looks good.
how do i test a mosfet?
how do i test a mosfet?
if you have a scope, you could check for waveforms on the gate and drain terminals of the mosfets.
if there is totally no waveform, the oscillator is broken.
also, not all blown mosfets have shorted terminals. some may be open.
if there is totally no waveform, the oscillator is broken.
also, not all blown mosfets have shorted terminals. some may be open.
Connect the black lead of your multimeter to the ground terminal of the amplifier. Set the meter to DC volts. Apply power to the amp including remote.
Read the voltage on each lead of the power supply FETs. They're all likely to be the same. Post the readings.
Post the part number on the PWM IC (TLx94, SG352x) and measure the voltage on all pins. Post the readings for all 16 pins.
Read the voltage on each lead of the power supply FETs. They're all likely to be the same. Post the readings.
Post the part number on the PWM IC (TLx94, SG352x) and measure the voltage on all pins. Post the readings for all 16 pins.
right, there's no voltage at any of the 16 pins on the pwm's. on the good amp they vary from around 2-12volts.
on the power supply fets, think i'm doing the right ones (4x irfp054 on each side). i have 12volts on the middle leg only. on the good amp i also have around 0.7volts on the left leg, nothing on the right.
hope this info helps!
on the power supply fets, think i'm doing the right ones (4x irfp054 on each side). i have 12volts on the middle leg only. on the good amp i also have around 0.7volts on the left leg, nothing on the right.
hope this info helps!
power supply ic? erm, not sure! where would i find it in here!
An externally hosted image should be here but it was not working when we last tested it.
The IC will have a number like SG3525 or TL494 (most likely an SGxxxx number). It will be near the power supply. It's very likely to be the two ICs just to the left of the large rail caps in the second photo.
sg2525a, then wrote underneath it, -99141. made by ST.
these are the ones you asked me to check earlier arn't they?
these are the ones you asked me to check earlier arn't they?
hi
Check voltages at the mosfet legs again. The very left leg of the FEt´s are connected to small resistors, usually something arounf 10-100 Ohms. The middle legs are connected to the transformer coils. As you can see, each transformer uses 2 primary coils. So that totals up to 4 primary coils. As there are 8 mosfets, 2 mosfets work in parallel to drive one coil. The other end of the primary coils are connected to +12V . As the coils are very low in resistance, you get a 12V reading with your meter/scope.
The very right leg of the fets is connected to GND. Also check the main GND- curcuit line for burns and cracks.
I think you should start the other way around.
Even if the PWM-controller IC doesn´t work doesn´t have to mean it is broken. Your amplifier is a huge baby and it has more than one protect curcuits. It could also be a broken protect curcuit that will cause the PWM controller not to start.
Usually if there hd been a fault in the SMPS it is a good thing to take alle mosfets out, especially in big amplifiers. As mentioned before, broken mosfets do not always cause a short.
I would take them out and test each FET seperately. With this small test curcuit you can find out if all FETs are ok.
When the Fets are out, you can power up the amplifier. Check the gate resistors with a scope. There should be a nice square wave signal. If there´s nothing follow the curcuit lines from the gate resistors. They will usually end at a all-purpose/small signal transistor (usually PNP-type ) Check those transistors´ base with a scope. if there is no square wave signal either the PWM controllers are disabled or burned.
You will then need to take a look at the datasheet and compare it how this thingy is used in your amplifier. Usually the PWM controller IC´s are disabled via the inbuilt error-amplifiers or the shutdown-connector. You can find those in the datasheet. If the PWM-controller is disabled, there might be something wrong in the protection curcuits, or the music-amplifiers have a problem, or both.
Also check, if the RMT-Signal (+12V) is fed through the parts. Usually there is a diode or a resistor around 10-33Ohms in series, those sometimes burn. If so, the PWM controller doesn´t recognize that it´s supposed to turn on.
If you have a square wave signal at the gate-resistors and FETs are ok, install the FETs back into the curcuit board. If you turn the amp on and nothing happens there is a fault in the amplifiers/protectors as the SMPS tries to turn on but is immediaetly shut down by the protection curcuit.
Check voltages at the mosfet legs again. The very left leg of the FEt´s are connected to small resistors, usually something arounf 10-100 Ohms. The middle legs are connected to the transformer coils. As you can see, each transformer uses 2 primary coils. So that totals up to 4 primary coils. As there are 8 mosfets, 2 mosfets work in parallel to drive one coil. The other end of the primary coils are connected to +12V . As the coils are very low in resistance, you get a 12V reading with your meter/scope.
The very right leg of the fets is connected to GND. Also check the main GND- curcuit line for burns and cracks.
I think you should start the other way around.
Even if the PWM-controller IC doesn´t work doesn´t have to mean it is broken. Your amplifier is a huge baby and it has more than one protect curcuits. It could also be a broken protect curcuit that will cause the PWM controller not to start.
Usually if there hd been a fault in the SMPS it is a good thing to take alle mosfets out, especially in big amplifiers. As mentioned before, broken mosfets do not always cause a short.
I would take them out and test each FET seperately. With this small test curcuit you can find out if all FETs are ok.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
When the Fets are out, you can power up the amplifier. Check the gate resistors with a scope. There should be a nice square wave signal. If there´s nothing follow the curcuit lines from the gate resistors. They will usually end at a all-purpose/small signal transistor (usually PNP-type ) Check those transistors´ base with a scope. if there is no square wave signal either the PWM controllers are disabled or burned.
You will then need to take a look at the datasheet and compare it how this thingy is used in your amplifier. Usually the PWM controller IC´s are disabled via the inbuilt error-amplifiers or the shutdown-connector. You can find those in the datasheet. If the PWM-controller is disabled, there might be something wrong in the protection curcuits, or the music-amplifiers have a problem, or both.
Also check, if the RMT-Signal (+12V) is fed through the parts. Usually there is a diode or a resistor around 10-33Ohms in series, those sometimes burn. If so, the PWM controller doesn´t recognize that it´s supposed to turn on.
If you have a square wave signal at the gate-resistors and FETs are ok, install the FETs back into the curcuit board. If you turn the amp on and nothing happens there is a fault in the amplifiers/protectors as the SMPS tries to turn on but is immediaetly shut down by the protection curcuit.
You need to get power to pin 15 of the sg2525. Follow the traces back on the board. The trace may go to a transistor. If so, one leg of the transistor should have +B. The trace may also go back to a diode as sdoom mentioned.
You may want to look at the area where the board was burned. The supply voltage for the switching transistor that supplies power to the sg2525 (assuming that there is a transistor that feeds pin 15) could have been connected to that point .
Until you get voltage to pin 15 of the chip, it wil not turn on and that means that the amp can't turn on.
You may want to look at the area where the board was burned. The supply voltage for the switching transistor that supplies power to the sg2525 (assuming that there is a transistor that feeds pin 15) could have been connected to that point .
Until you get voltage to pin 15 of the chip, it wil not turn on and that means that the amp can't turn on.
which is pin 15, 2nd from bottom right?
edit- there are 2 pwm's, hows this work, are they wired up in parallel? or one for each side?
edit- there are 2 pwm's, hows this work, are they wired up in parallel? or one for each side?
If there are two PWM ICs, the amp likely has two independent supplies (essentially a dual mono design).
Perry Babin said:
it is a dual mono design 🙂
also checked the rail fuses and apparantly there should be 35 volts here with the fuses removed........there's very little!
update- i've traced #15 pin on the pwm's (circuit board out job!) and this is where it leads to. you can just make out where i highlighted the 12v trace in red. on my good amp this is 12v. i think things are starting to get complicated! i've ordered 8 new irfp054's as a matter of course as i think it could be a power supply problem.
An externally hosted image should be here but it was not working when we last tested it.
You need to follow the trace back a little more. The point where it stops is a via (feedthrough) to the other side of the board. Find it and follow it. It looks like the remote wire goes into the board very near that via so it should be easy to follow.
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