I've got an alpine mrv1000 with no output.It powers up fine but just doesn't play.I have found two shorted transistors in one channel and the other channel looks fine.My question is that if the transistors are shorted how come the fuse didn't blow?And if the fuse didn't blow why doesn't the other channel work?Does this amp have a different protection circuit than normal?Also just wanted to check a couple part numbers real quick before I buy.Is an A1265N the same part as an 2SA1265N?And like wise with the C3182N.Would a 2SC3182N be the same part?
2SA1265N is the correct part number.
The amp has independant power supplies. Are you sure the supply for the dead channel is operating (producing rail and regulated voltages)?
Each supply is independently fused.
If the amp has good protection circuits, the fuse won't blow because the supply will be shut down when a fault is detected.
The amp has independant power supplies. Are you sure the supply for the dead channel is operating (producing rail and regulated voltages)?
Each supply is independently fused.
If the amp has good protection circuits, the fuse won't blow because the supply will be shut down when a fault is detected.
I'm getting some real funny ohm readings off of the fets in the power supply of the channel with the shorted output transistors.I'm thinking they are dead or not far from it.The two diodes(rectifiers?they look like transistors) right next to them are reading differently than the ones in the other channel but i'm not sure if that is because of the fets or not.when the fets are removed from the board will they read like a transistor from leg to leg as far as resistance is concerned?
With...
Meter set to DC volts
Power applied to the amp (including remote)
Black meter lead on the chassis ground terminal of the amp
What voltage do you read if you touch the red lead to the center leg of the FETs?
What voltage do you read if you do the same on the center leg of the rectifiers?
Meter set to DC volts
Power applied to the amp (including remote)
Black meter lead on the chassis ground terminal of the amp
What voltage do you read if you touch the red lead to the center leg of the FETs?
What voltage do you read if you do the same on the center leg of the rectifiers?
Heres what I found Perry.With the Black meter lead on chassis ground,meter set to dc volts, and red lead on the center leg of the fets I'm getting 12.7 volts on all fets.The rectifiers are a different story.In the channel without any shorted output transistors I'm getting -34 volts on the center leg of the first rectifier(F10P20FR) and on the second rectifier in that channel i'm getting nothing.That part is a F10P20F.Now onto the other channel with bad output transistors.I'm getting nothing out of the center leg of the F10P20FR.Same goes for the other part on that side(F10P20F).I also noticed a bulging cap on the side of the amp with good outputs right near the rectifiers.16 volt 220 microfarad
On the side with -34v, I'd suspect a broken connection on the rectifier (either a broken leg or a bad solder connection).
Using the same setup as before, measure the voltage on the first and third legs of the FETs in the supply that has no output. If the voltage on the first legs are near B+ voltage, and the third leg is near ground (0 volts), the FETs have failed. If the voltage on the first leg is almost precisely 1/2 B+, switch your meter to AC volts and measure the voltage on the 4 outer legs of the rectifiers in that channel.
Using the same setup as before, measure the voltage on the first and third legs of the FETs in the supply that has no output. If the voltage on the first legs are near B+ voltage, and the third leg is near ground (0 volts), the FETs have failed. If the voltage on the first leg is almost precisely 1/2 B+, switch your meter to AC volts and measure the voltage on the 4 outer legs of the rectifiers in that channel.
well the FETs in the channel with bad outputs are done.12 volts on the first leg and 0 on the third.The resistors feeding the fets all have funny readings.Is that because of the bad fets or should these resistors be replaced as well?The ones in the other channel all read right around 100 ohms and the ones in the bad channel are all over the place.Even though the fets didn't measure half battery voltage I checked the ac voltage anyways.It was approximately .280 volts. The rectifiers in the good channel all measured 46.5 ac volts on their outer legs.Is there a better component available to replace the irfz44n FETs?Originals are easy to find just wondering if there is any room for upgrade as long as I'm inside.Also I was wondering if that -34 volt reading could have anything to do with the shorted capacitor that is in close proximity to the rectifiers?
Remove the defective FETs and measure the resistance of the 100 ohm gate resistors. If any are out of tolerance, replace all 4.
There are two 110 ohm resistors that pull the gate voltage down. One or both of them may be burned.
The drive circuit in this amp is weak. I wouldn't recommend using a substitute FET.
the -34v is the negative rail voltage. I'm not sure what it's supposed to be. I'd expect it to be a bit closer to ±50v but ±35 could be correct. Did you find the reason you didn't have the +35v on the other rectifier in that channel? You may have to remove it from the board to see if the leads are broken. Sometimes they break inside the plastic and don't look broken until you pull on them individually.
Caps often overheat when there is too much ripple current. If the rectifier is defective, that could cause high ripple current.
If one of the 494s is defective, that may be able to cause current to feed back to the LED. It may also be due to the FETs being shorted. Hopefully, after you pull them, the LED will only light up when remote is applied.
There are two 110 ohm resistors that pull the gate voltage down. One or both of them may be burned.
The drive circuit in this amp is weak. I wouldn't recommend using a substitute FET.
the -34v is the negative rail voltage. I'm not sure what it's supposed to be. I'd expect it to be a bit closer to ±50v but ±35 could be correct. Did you find the reason you didn't have the +35v on the other rectifier in that channel? You may have to remove it from the board to see if the leads are broken. Sometimes they break inside the plastic and don't look broken until you pull on them individually.
Caps often overheat when there is too much ripple current. If the rectifier is defective, that could cause high ripple current.
If one of the 494s is defective, that may be able to cause current to feed back to the LED. It may also be due to the FETs being shorted. Hopefully, after you pull them, the LED will only light up when remote is applied.
just got a look at the solder side of the circuit board and holy crap. Check This out.this ground trace is trashed.I'm surprised it even turns on.How do I go about fixing that?I removed the fets in the bad channel and the gate resistors are ok.I've yet to find any reason why I wasn't seeing 35 volts on that other rectifier.I'll probably take a closer look tomorrow.I'm getting kind of tired of staring at this thing for the day
To repair the trace, I'd recommend laying the foil back down and running 3-4 pieces of desoldering braid over the defective area. Since it's a short trace, I'd suggest overlaying the entire length. Tin the braid and solder it to the foil over the entire length.
If you don't have desoldering braid, several runs of tinned 16g or 18g wire will work.
If you don't have desoldering braid, several runs of tinned 16g or 18g wire will work.
I got the trace fixed and it took care of the problem I was having with the LED.What would have caused that kind of damage anyways?It now only lights up when remote turn on power is applied.Where are those two 110 ohm resistors located that pull down the gate voltage?I'm having trouble locating them.I'm thinking that the one rectifier may be dead.Does it have to be replaced with the exact part or are there others that could possibly work in its place?
If the solder connection at the corner of the board (near the aluminum plate) is a grounding lug, the damage is likely from a 12v power source coming in contact with the heatsink.
The 110 ohm resistors are standing vertically. They are labeled R841-R844. They are probably green.
If you pull the rectifier, you can check it easily. It will read just like two ordinary diodes. The symbols on the case tell you how the diodes are oriented internally. If the positive rectifier is defective, an FEP16DT or an MUR1620CT can replace the original.
The 110 ohm resistors are standing vertically. They are labeled R841-R844. They are probably green.
If you pull the rectifier, you can check it easily. It will read just like two ordinary diodes. The symbols on the case tell you how the diodes are oriented internally. If the positive rectifier is defective, an FEP16DT or an MUR1620CT can replace the original.
well I replaced all components I originally found to be defective.I powered the amp up and heard a click that its never made before.I'm assuming its some sort of relay.Anyways I had it powered up for about a minute and was just beginning to check the new fets and rectifier for voltage when the magic smoke came from the same capacitor that I had just replaced.Its a 16 volt 220 microfarad cap near the rectifiers but I believe that it is connected to the first leg of a small transistor directly next to the rectifiers.
It could be under the cap. One end would be connected to ground and the other end would be connected to the base of the transistor. The emitter of the transistor would be connected to the cap that has failed.
I know you don't want to hear this, but this is often very bad news. In some amps, regulator failure destroys every op-amp that's powered by the failed regulator. If no op-amp shows signs of being defective, you should let the amp play for at least 3-4 hours before returning it to the owner. That should be enough time for any injured op-amps to fail.
I know you don't want to hear this, but this is often very bad news. In some amps, regulator failure destroys every op-amp that's powered by the failed regulator. If no op-amp shows signs of being defective, you should let the amp play for at least 3-4 hours before returning it to the owner. That should be enough time for any injured op-amps to fail.
I've got all the time in the world to let this thing play.Its just another one of my personal projects.I don't plan on trying to make any real money at this until I know more and have the right equipment. Its better for me to start with my own stuff before I try somebody elses.Anyways regardless of the cap that smoked that is still oozing some electrolytic fluid the amp does play cleanly from both channels as well as bridged but I'd really like to find what made that cap die.I'll have to get into it more tomorrow and follow that circuit.
Before replacing the cap, clean the area with acetone and a cotton swab. The electrolyte is corrosive and will cause problems if not completely removed.
Don't power up the amp until you find the problem with the regulator. After you've replaced all the failed regulator components, connect a meter across pins 4 and 11 of the 14 pin op-amp. Set the meter to DC volts and power up the amp. If the voltage goes over ~35 volts, immediately remove power from the amp. It should be ~30 volts.
Don't power up the amp until you find the problem with the regulator. After you've replaced all the failed regulator components, connect a meter across pins 4 and 11 of the 14 pin op-amp. Set the meter to DC volts and power up the amp. If the voltage goes over ~35 volts, immediately remove power from the amp. It should be ~30 volts.
are all of those small transistors next to the rectifiers part of the regulator circuit?Or just the one with its emitter connected to the capacitor?Is it possible for that transistor to be faulty even if it isn't shorted or even if it isn't giving off any funny readings?It seems like it measures exactly the same as the one in the other channel that isn't blowing caps.
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