I got this amp and every power supply transistor was fried. Also, the three rectifiers on the negative side were shorted as well. I thought maybe the outputs may have been bad so I checked.. none were shorted, on either channel. 😕 I checked the large capacitors after removing the bad rectifiers and power supply mosfets and none were shorted.
After replacing all the power supply mosfets and the negative rectifiers (the positive side are ok) I attempted to power the amp up. It lights up and then clamps down on the voltage and the negative rectifiers short out again.😕 Just in case one was bad new, I replaced the rectifiers again, and after trying to power up, it still has the same issue. The power supply mosfets all read ok, none shorted, and all mosfet input lead resistors are reading ok. I can't find any shorted transistors on the audio side of the pcb, so I am stumped.
The rectifiers were UF16C20A and the power supply mosfets were IRFZ48V. I replaced them with SR1603A and IRFZ46 because I couldn't find them for sale through any of the places I normally buy, and the specs seemed to be the same.
If anyone has a clue, I'd appreciate the help. I don't have an oscilloscope or any other expensive test gear. Only a few decent DMMs and a couple of DC power supplies (8A and 40A) I know the amp isn't great, but I'm trying to get it back up and running for a guy who claims it just "smoked". He probably just ran it at too low of a load, but I'll have to check that out later.
Thanks
After replacing all the power supply mosfets and the negative rectifiers (the positive side are ok) I attempted to power the amp up. It lights up and then clamps down on the voltage and the negative rectifiers short out again.😕 Just in case one was bad new, I replaced the rectifiers again, and after trying to power up, it still has the same issue. The power supply mosfets all read ok, none shorted, and all mosfet input lead resistors are reading ok. I can't find any shorted transistors on the audio side of the pcb, so I am stumped.
The rectifiers were UF16C20A and the power supply mosfets were IRFZ48V. I replaced them with SR1603A and IRFZ46 because I couldn't find them for sale through any of the places I normally buy, and the specs seemed to be the same.
If anyone has a clue, I'd appreciate the help. I don't have an oscilloscope or any other expensive test gear. Only a few decent DMMs and a couple of DC power supplies (8A and 40A) I know the amp isn't great, but I'm trying to get it back up and running for a guy who claims it just "smoked". He probably just ran it at too low of a load, but I'll have to check that out later.
Thanks
Well the transformers both look fine, no discoloration, and the none of the caps read a short. Thing is, the rectifiers are after the transformers, so I would think something upstream like maybe something in the lower audio stages causing the outputs to clamp or maybe even the power supply voltage jumping up to high when powering up and killing the rectifiers. I'm wondering if using the irfz46 instead of the irfz48v is causing it, but the rectifiers were shorted when I got the amp. Hey, don't you sell amps? I recognize your screen name from ebay. You sell some very nice amps. They don't make them like that anymore.
Nawh the Z-46's are not the problem, But you must have a dead short somewhere around that single diode that is being taken out everytime.
try running the amp without that single diode and see what happens.
try running the amp without that single diode and see what happens.
The amp has six to220 rectifiers, three on the positive side, and three on the negative side. For each side, all three are paralleled, and when I first got the amp I believe at least two of the negative ones were fried. After swapping them, I ended up toasting only one each time. I will double check, but I believe they are paralleled and that is part of the reason I am baffled. Thanks for checking back.
look at the inducer coil......I have a similair problem in my audiobahn amp because the coil had broken and fired.
The amp has two coils. They both read .9 ohms across any lead on either side. They are also both isolated from the primary to secondary side, so I don't see any short problems. I had a problem with a ppi pc2350 I used to own where the coil was faulty, but all I had to do was move the winding and epoxy it because one had rubbed through from the vibration of the coil. After that it was aok. This amp is different, it has two coils, both read exactly the same and neither are shorted from the primary to secondary side. Maybe one of the caps could be shorting when the voltage ramps up, but while they are in the circuit they all read fine. I hope I don't have to remove all of them and test them individually, they are all glued to the board.
You need to power it up through a current limiter. Some people use an automotive headlamp. I use 2 ohm resistors. When powered up through a limiter, you can check a few things that you can't check when the amp is drawing excessive current. Even with the current limiter, you need to have the components clamped to the heatsink so they don't overheat and fail.
With a current limiter in series with the B+ power line, measure the DC voltage across EACH of the emitter resistors. At idle, there should less than 1mv across each of the emitter resistors. If you find one or more with significant voltage (more than 1mv) across them, you know the general area of the problem.
With a current limiter in series with the B+ power line, measure the DC voltage across EACH of the emitter resistors. At idle, there should less than 1mv across each of the emitter resistors. If you find one or more with significant voltage (more than 1mv) across them, you know the general area of the problem.
The emitters of the audio output transistors? I could try that I guess. So maybe one of them is acting up only when voltage is applied? Its amazing the amp's "protection" circuits don't detect this problem, especially when the rectifier diodes are rated at about 8 amps per leg. 😕
Yes, the emitter resistors on the output transistors.
If one channel (or one transistor) is passing too much current (due to a defect in the driver circuit or a defective transistor), it will show up as a voltage drop across one or more emitter resistors.
If one channel (or one transistor) is passing too much current (due to a defect in the driver circuit or a defective transistor), it will show up as a voltage drop across one or more emitter resistors.
I tried the voltage drop test and apparently none of the outputs are clamping or drawing current. I think its because there is no load connected to the speaker output terminals to complete the circuit. That is part of the reason I am puzzled. Its like the output voltage of the power supply never even jumps high enough to destroy anything, yet there aren't any shorted components after the rectifiers, man this sucks.
Still destroys rectifiers, and like I said above, it doesn't even power up long enough to reach a voltage that seems capable of destroying anything. Maybe I will try powering it up for only a couple of seconds without the heatsink so maybe the bad device will get hotter and be more easy to find.
It's strange that it's still blowing rectifiers if you're using an inline current limiter.
If you have a variable power supply that will go to zero volts, remove the rectifiers and connect the supply between the secondary ground and the output of the negative rectifiers. Since it's the negative rectifiers, the positive of the supply will have to go to the secondary ground. The ground of the supply will go to the output terminal/pad of the negative rectifiers. This will allow you to bring up the voltage slowly and make it easier to determine where the excess current is flowing.
If you don't have a variable supply, you can do this with your bench supply but you'll need to use an inline current limiter.
If you do this, NOTHING else can be connected to the amplifier (no RCAs, no other power supply wires).
If you can't find anything getting hot with this setup, you can find the current flow by measuring the voltage across the traces. Traces that have current flowing through them will have a voltage drop across them. Traces with no current flow will not have voltage across them. As the circuit branches off, you can find branches with/without current to find the defective part of the circuit. You need to measure along the longest lengths of the traces to see the most voltage drop. Keep in mind that the voltage drop is going to be very small. You may see only a couple of millivolts of difference across the trace leading to the defective component.
If you have a variable power supply that will go to zero volts, remove the rectifiers and connect the supply between the secondary ground and the output of the negative rectifiers. Since it's the negative rectifiers, the positive of the supply will have to go to the secondary ground. The ground of the supply will go to the output terminal/pad of the negative rectifiers. This will allow you to bring up the voltage slowly and make it easier to determine where the excess current is flowing.
If you don't have a variable supply, you can do this with your bench supply but you'll need to use an inline current limiter.
If you do this, NOTHING else can be connected to the amplifier (no RCAs, no other power supply wires).
If you can't find anything getting hot with this setup, you can find the current flow by measuring the voltage across the traces. Traces that have current flowing through them will have a voltage drop across them. Traces with no current flow will not have voltage across them. As the circuit branches off, you can find branches with/without current to find the defective part of the circuit. You need to measure along the longest lengths of the traces to see the most voltage drop. Keep in mind that the voltage drop is going to be very small. You may see only a couple of millivolts of difference across the trace leading to the defective component.
Well, I still hadn't tried using the current limiting resistor on the battery lead, just tested by connecting for a short period of time. Just long enough that it should be powering up. I am going to go mess with it now.... I dread messing with that thing again makes me want to 
it
makes me want to it??????
Just got finished removing all three of the negative rectifiers, like you were suggesting. Now the amp will power on without drawing a crapload of current and the opposite voltage rail is working perfectly. I can't understand how it fried all three diodes. I'm kind of thinking they are somehow the wrong type, but the pin configuration is exactly the same as the originals. 😕 The oem and aftermarket diodes both have terminal id's. ARgggh...
Original : UF16C20A ~ - ~ pinout
Replaced : SR1603A ~ - ~ pinout
😕 😕 😕
Just got finished removing all three of the negative rectifiers, like you were suggesting. Now the amp will power on without drawing a crapload of current and the opposite voltage rail is working perfectly. I can't understand how it fried all three diodes. I'm kind of thinking they are somehow the wrong type, but the pin configuration is exactly the same as the originals. 😕 The oem and aftermarket diodes both have terminal id's. ARgggh...
Original : UF16C20A ~ - ~ pinout
Replaced : SR1603A ~ - ~ pinout
😕 😕 😕
STILL stumped
Anyone know where I could readily purchase the original version of the rectifiers? I would like to see how they behave, I'm getting tired of frying the generic replacements. UF16C20A is the model number
Anyone know where I could readily purchase the original version of the rectifiers? I would like to see how they behave, I'm getting tired of frying the generic replacements. UF16C20A is the model number
I looked those rectifiers up previously and the data I found said they were 200v diodes. I looked it up again and it appears that they may be 30 volt schottky rectifiers. If they are the latter, that's your problem.
If the rectifiers have the negative output on the center leg, you can use MUR1620CTRs as the replacement.
If the rectifiers have the negative output on the center leg, you can use MUR1620CTRs as the replacement.
So I was using schottkys or they should be schottkys? Are they latching maybe because the voltage is too high? That would explain it if true. ???? I'm about to head to work, I will definately check back when I get home tonight. I am anxious to get this big ugly amp out of my house
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