profuse said:
Pull the board and figure out where the traces go from the pins. With most car audio amps, the boards are double-sided, which makes tracing easy The boards I design have 4 layers and sometimes more. This means that the traces are only on the top and bottom. If the boards had more layers, they would be much harder to fix beacuse some of the traces would be sandwiched between the top and bottom. The board designer should have both pins 13 and 15 shorted together. use the continuity check on your DMM to trace where the +12V is sopposed to come from. Most likely it is going to a PNP transistor. Find that transistor and you will be headed in the right direction. Happy hunting.
First, thanks to oPossum for the link to the schematics.
This amp is different than most amps in that pin 13 has a variable voltage instead of a constant 12 volts. They used PAM (Pulse Amplitude Modulation) instead of Pulse Width Modulation. Orion does something similar and I never understood why they would do that when they had PWM ICs in the circuit.
Applying 12 volts to pin 15 powers the IC's internal circuits. The 5v reg should be producing 5.1v ±1%. The 4.67 volts that you stated earlier is a bit low and could mean that the regulator is being overloaded. If it's within 1% of 5.1v, that's what you want.
The IC should now be producing pulses on pins 4, 5 and 7. Pins 8 and 9 should be near 5v. Pin 10 needs to be at or very near ground.
If all of those voltages are OK, the amp should produce pulses on pins 11 and 14 if you can restore voltage to pin 13. You can't get any useful output from 11 and 14 until 13 has supply voltage. Maybe oPossum can direct you to common failures in the PS.
This amp is different than most amps in that pin 13 has a variable voltage instead of a constant 12 volts. They used PAM (Pulse Amplitude Modulation) instead of Pulse Width Modulation. Orion does something similar and I never understood why they would do that when they had PWM ICs in the circuit.
Applying 12 volts to pin 15 powers the IC's internal circuits. The 5v reg should be producing 5.1v ±1%. The 4.67 volts that you stated earlier is a bit low and could mean that the regulator is being overloaded. If it's within 1% of 5.1v, that's what you want.
The IC should now be producing pulses on pins 4, 5 and 7. Pins 8 and 9 should be near 5v. Pin 10 needs to be at or very near ground.
If all of those voltages are OK, the amp should produce pulses on pins 11 and 14 if you can restore voltage to pin 13. You can't get any useful output from 11 and 14 until 13 has supply voltage. Maybe oPossum can direct you to common failures in the PS.
There is a PNP that supplies pin 15 with power - just as TO-3 suggested. It is a MPSA56. Here is a schematic of a typical switched lead circuit.
You have to find Q54 (most likely labeled something else on you amp). You should see supply voltage on collector and emiter, supply minus ~600 mV on the base. I suspect there will be little if any voltage on the collector, and the transisor will have to be replaced.
Do not connect pin 13 to pin 15, or supply 12 volts to pin 13. The rails will exceed the filter cap rating and damage them. Bad things will happen. This is not a typical 3525 topology!
The low Vref voltage on pin 16 is a bit suspect. The 3525 may indeed be damaged.
Many amps have a bipolar transistor buffer between the PWM chip and the MOSFET gates. It is not unusualy for these buffer transistors to blow along with the MOSFETs. In this case there is no buffer to protect the 3525, so it may have been damaged by MOSFET(s) that failed shorted.
You have to find Q54 (most likely labeled something else on you amp). You should see supply voltage on collector and emiter, supply minus ~600 mV on the base. I suspect there will be little if any voltage on the collector, and the transisor will have to be replaced.
Do not connect pin 13 to pin 15, or supply 12 volts to pin 13. The rails will exceed the filter cap rating and damage them. Bad things will happen. This is not a typical 3525 topology!
The low Vref voltage on pin 16 is a bit suspect. The 3525 may indeed be damaged.
Many amps have a bipolar transistor buffer between the PWM chip and the MOSFET gates. It is not unusualy for these buffer transistors to blow along with the MOSFETs. In this case there is no buffer to protect the 3525, so it may have been damaged by MOSFET(s) that failed shorted.
after reading the thread of another PPI owner that opossum posted, i thinking this is more than i could handle. ill have to step back, here, a bit.
if yall dont mind helping me, lets start forward instead of backward. but b4 that, i need to check to see if i can go forward w/ this process cause i dont want to waste anyones time. if the damage is extent like the other guy have, could i be able to use just my DMM to test it or do i have to get an O-scope?
if yall dont mind helping me, lets start forward instead of backward. but b4 that, i need to check to see if i can go forward w/ this process cause i dont want to waste anyones time. if the damage is extent like the other guy have, could i be able to use just my DMM to test it or do i have to get an O-scope?
alright, after reading some thread, i got to understand a bit more. ill just have to trace the track from the pin 13 or 15 back to the PNP. btw, what is PNP and NPN stand for?
lets say i get the PNP sorted out and then comes to the PWM, if the PWM gets power, then the pin 16 have to have about ~5v, no matter what, right? if not, what else is there that may affect the pin 16?
btw, if the PWM gets power, then the pins 11 14 to the gates should read about ~6v, no matter what, right?
lets say i get the PNP sorted out and then comes to the PWM, if the PWM gets power, then the pin 16 have to have about ~5v, no matter what, right? if not, what else is there that may affect the pin 16?
btw, if the PWM gets power, then the pins 11 14 to the gates should read about ~6v, no matter what, right?
NPN and PNP denote the layering of the doped silicon material of the transistor. To remember which schematic symbol was NPN, think Not Pointing iN (referring to the arrow on the symbol).
If pin 15 has B+ (~12v) on it and pin 12 is grounded, pin 16 should have ~5.1 volts unless it's overloaded or the IC is defective.
The voltage on pins 11 and 14 will be 1/2 of the voltage on pin 13. On a normal PWM circuit, pin 13 will have B+ voltage. Here, the voltage will vary with current demand from the audio section and the B+ voltage feeding the amp. From the other information posted, a PPI amplifier with this type of regulation, operating normally should have ~2vdc on 11 and 14 if you're using a voltmeter.
Remember to do all testing through a current limiter or a small fuse. If the amp has another problem like a shorted transformer or shorted output transistors and you power it up without protection, you can destroy all FETs in just a few seconds (or less).
If pin 15 has B+ (~12v) on it and pin 12 is grounded, pin 16 should have ~5.1 volts unless it's overloaded or the IC is defective.
The voltage on pins 11 and 14 will be 1/2 of the voltage on pin 13. On a normal PWM circuit, pin 13 will have B+ voltage. Here, the voltage will vary with current demand from the audio section and the B+ voltage feeding the amp. From the other information posted, a PPI amplifier with this type of regulation, operating normally should have ~2vdc on 11 and 14 if you're using a voltmeter.
Remember to do all testing through a current limiter or a small fuse. If the amp has another problem like a shorted transformer or shorted output transistors and you power it up without protection, you can destroy all FETs in just a few seconds (or less).
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