| spooney |
| 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? |
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| Perry Babin |
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. |
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| spooney |
| 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? |
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| Perry Babin |
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? |
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| spooney |
| 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 |
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| Perry Babin |
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. |
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| spooney |
| 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? |
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| spooney |
| somethings else I just noticed that I'm not sure of is that the power on LED is dimly lit when power and ground are applied.When remote turn on power is applied it gets real bright as it should.Don't know if that helps or not |
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| Perry Babin |
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. |
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| spooney |
| just got a look at the solder side of the circuit board and holy ****. 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 |
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| Perry Babin |
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. |
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| spooney |
| 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? |
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| Perry Babin |
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. |
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| spooney |
| 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. |
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| Perry Babin |
| It sounds like the regulator transistor is shorted or the zener diode is open. Either would allow rail voltage to pass to the 16v cap and cause it to blow. |
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| spooney |
| is the zener the little diode right underneath that capacitor? |
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| Perry Babin |
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. |
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| spooney |
| 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. |
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| Perry Babin |
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. |
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| spooney |
| 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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| Perry Babin |
This amp has 3 caps per reg.
One cap is in parallel with the zener. If it were faulty, it could only make the regulator output voltage low or noisy.
The second and third caps are connected between the regulator's output terminal (the transistor's emitter) and ground. If they were faulty, they could also make the output of the regulator low or noisy (because they weren't stabilizing the voltage as they should). If they were pulling the output down, the transistor would be damaged due to excessive current flow.
Pull the regulator transistor and check it out of the board. Check it to make sure it's not open, shorted or leaking (electrically). If you're not sure how to check it, let me know.
Check the zener while the transistor is out of the board. If the zener is open, the regulator output would be higher than normal.
The attached photo shows a basic discrete regulator without the capacitors. |
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| spooney |
| would I check the regulator transistor the same as I would test any npn or pnp transistor?I believe the transistor is pnp. The number on it is a1220a and I'm thinkin it is the same as a KSA1220A.I can't remember which meter lead goes on the first and second legs but I do remember that when they are oriented correctly the transistor should only read resistance in one direction if it is working properly.If its different than this please let me know Perry and thanks for the help you give whenever I have a question. |
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| Perry Babin |
The PNP transistor is a KSA1220A.
The transistor is a standard BJT type transistor and you check it just as you would any other BJT. The pin configuration is reversed (ECB) compared to the higher power to-220 case transistors (BCE).
With the black lead on the base, the meter should read ~0.65v (with the meter set to 'diode check') when you touch the red lead to the other two leads. It should read open when you have the red lead on the base and touch the black lead to the other two leads. There should be no continuity/leakage (it should read as open) between the emitter and collector. For a more thorough test, switch to resistance when checking for leakage between the collector and the emitter.
You can check it on resistance. Instead of reading near 0.65v, it's going to read near 2 mega-ohms.
This must be done with the transistor removed from the board. |
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| spooney |
| the regulator transistor checks out fine.Theres no leakage from the collector to the emitter and it reads exactly as you described with the meter set to diode check.The small diode underneath the capacitor that keeps dying is open.Does the regulator transistor need to be replaced as well?Or should it be ok as long as I replace the capacitor and the diode?I'm not exactly sure how to read this diode.Its very tiny and has only a few numbers on it.With the black stripe pointing downward it reads 91- .pointed the other way it reads - 16 .I'm assuming that a 1N goes in front of one of those. |
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| Perry Babin |
If the transistor is OK, it doesn't need to be replaced.
The diode is a 16v Zener. The alpine part number is HZS161L. Any 1/2w 16v Zener will work. |
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| spooney |
| so after I replace that part ,if the amp makes it four hours do you think its out of the woods as far as the op amps are concerned? |
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| Perry Babin |
That should be plenty of time to determine if you have any bad op-amps. Remember to check them in all possible crossover/phase/input modes.
Also, check the temperature of the op-amps. If one is running significantly hotter than the rest, it could be defective. |
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| spooney |
| well I finally got the parts in and got around to working on this amp again. I replaced that zener and capacitor and so far so good.The first time I replaced that capacitor it blew within 5 minutes.Its lasted a good 20 or 30 so far.I'm just waiting now to see if the op amps give out on me. |
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| luvtheoldschool |
| Hello, I'm jacking this old thread instead of starting a new one. I've got a mrv1000 that needs help. I got it with the right channel out. I know enough now to get myself in trouble, but I'm trying to learn as I go. I see the IRFZ44's had been replaced before so I took them out and found them to be bad. I replaced them with some IRF540's I had around. Hooked it up and it worked! Then, not sure if coincidence or not, but I was fiddling with the RCA's and poof! So I Replaced the RCA Jacks, Read some posts, Checked the Gate Resistors, All 4 were in spec of 100 ohms. I replaced the IRFZ44's with new IRFZ44's. I didn't see anything else that looked suspicious. I hooked it up and the amp ran good for about 10-15 minutes then the 1st leg on the second fet got red hot and was smoking! I pulled power and obviously found the fets to be bad again. I'm now at a what next situation and would like some help. Maybe some things to check, other threads to read, anything really. Thanks. |
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| luvtheoldschool |
| Also have a question about another part. It's a dual emitter resistor I believe. there are 4 of them, 2 per channel. It has HMR MPR 5w 0.1ohm JX2 on the side of it. Is there a special way to check these or just go leg to leg? Thanks. |
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| spooney |
| go from the center leg of the dual emitter resistors to each individual outer leg. You'll have to make sure you get good contact and stay stable with your meter leads for a few moments to get accurate readings on them. I would check your output transistors to see if one is shorted or leaky as well. |
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| jol50 |
Should just start a new thread but, the resistors for the outputs? They don't go bad often and are hard to read with meter because ohms are so low. Some run an output into each end and sum in the center pin that would go to speaker terminal, or have two inputs one end and out the single pin on other end. You have some other problem with the alpine. The resistors could still be off enough to cause a problem according to what people say, there might also be pull down resistors upstream of the gate resistors you should check. Was it drawing a lot of current? What do you have at the outputs when you run it? Should start them with a 10A fuse or so. I just did one put all PS fets in one side, all resistors, seemed to work fine but have not used it yet. The one I have each channel is its own amp pretty much.
Test the larger outputs, none should have low resistance between any legs. Most of the time they short but not always. |
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| luvtheoldschool |
| Thanks for the replies. I pulled the dual emitters off both sides to do comparisons. I didn't have my good meter at home so I'll have to check them today. The reason I ask about them is because I remembered that the first time I ran it with the temporary fets and wiggled the rca's, I saw a flash in one of them, I thought. Anyways, I will check the other resistors down the bad side and see if any are bad or leaking. Yes this amp is also like 2 amps in one. One amp per side basically. Kinda nice, because I can compare alot of things from the good side to the bad side. I have to wait till my irfz44's get here to run it again, but I have things to check out till then. Thanks again. |
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| jol50 |
| You might play around and check some other obvious stuff, like for shorted rail caps and bad diodes shorting to ground. You know the PS is blowing so could be it is being asked to make too much power (short/etc after PS/bad outputs/caps), or PS is not working right like driver has issue/gate resistors/etc. If you limit power to it when you fire it up, and only run short time then check for heat, you may be able to find where power is going and what is hot/etc. Get a big 2 ohm resistor and use a small fuse before amp like 10A. |
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| luvtheoldschool |
| Thanks Jol, I got good readings on the dual emitters, all were .1 if I sat still. The gate resistors checked ok. I will be going down the line tonight and checking the other transistors and diodes. My fets should be here in a couple days so if I don't find anything between now and then, I'll install them and hook up a resistor and small fuse on the power side and see what gets hot. Been looking for places to get parts incase I need them. The one source I have doesn't carry some of the resistors I see on the board. Maybe they won't be bad. Thanks for the input. Have a good day. |
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| luvtheoldschool |
| Well I checked everything and came up with a PWM IC for that channel that was out of spec. Replaced it and the amp seems to be running good. Will put it through some real trials here and see. Thanks for everyone's help. |
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| spooney |
| Its really a nice amp when its up and running. surprising for 400 watts. |
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| luvtheoldschool |
| It does seem to be pretty tight and clean on the bass end. I've been running my 2 12's with it. I think it might be underrated a bit. Thanks again. |
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| spooney |
| I think dynamic power is rated at 600 watts.Either way it does do a nice job of running a pair or single 12 inch sub. |
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| jol50 |
| I bought two for a friend of mine, and I have a 1002 that is nearly the same thing inside but have not tried it yet. I have to repair the power terminals first, had to put a new PS in one side to get it going. There is only 420w on my four 12s right now and they bump, so 600 ought to do something. Think they are 600 x1 at the newer 14v ratings. Thinking of using it on midbass actually and a MRD-500 on subs....but its larger in size and watts than the class d 500...? lol, oh well. |
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