Boss REV3000D blown amp. Repair Suggestions? - diyAudio
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Old 19th April 2004, 04:28 AM   #1
KyferEz is offline KyferEz  United States
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Location: Wilmington, NC
Question Boss REV3000D blown amp. Repair Suggestions?

Ok, this amp has had a hard life. It is a Boss REV3000D ClassD mono block amp. It is 1-ohm stable.

The first time the amp was ever hooked up, the polarity of the power was wrong. It instantly blew the fuses. (Sorry, it was a dumb moment and late at night with almost no lighting.)

I replaced the fuses and it worked fine, however was nowhere near as loud as I expected it to be.

I used it for a while, then put it away. I drug it out again and hooked it up to a sub. It played for a while, but was even quieter than before. Eventually, it stopped playing and all I got out of it was hiss.

I cracked open the amp and noticed very quickly that the leads of one of the output fets was broken. There were no burn marks, so I assumed it was ok and soldered it back on.

There was another problem: one of the big torrodal inductors had some wires burned at the solder joint. I removed it, and managed to resolder it in place by pulling some slack out of the coil to make it reach.

I hooked up the amp again. It played again, however it was quiet just like before. I just left it again. (Note: The reason I kept leaving it was because it didn't bother me too much cause this amp was hooked to the 3rd 12" sub. The other two still were palying strong off different amps.) Well, after leaving it playing quitely for about 1 week, it stoped playing and began to smoke. I have taken the amp apart again and found that the IRFZ44N fets are literally melted. The IRF2807 FETs are not burnt at all.

My questions are:
1) What would cause the irfz44n fets to burn up like that? (There are 10 of them.)

2) I believe the irfz44n fets are on the voltage stepup section, and the irf2807 fets are the audio output stage. Correct me if I am wrong.

3) What else should I be looking for?

4) Why would the amp not play loud? Others who use this amp always say how powerful it is (even if the output isn't all that clean). It just drove a 12" pioneer wired for 2ohm operation with the gain/level turned all the way up and the volume all the way up when it was new (granted I had screwed the power polarity before I ever used it so I don't know if it was louder before that).

5) Any other suggestions?

Please no flamers - save your breath for someone who cares.

Thanks,
KyferEz
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Old 19th April 2004, 12:38 PM   #2
Immo_G is offline Immo_G  Australia
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Have you tried measuring the rail voltages, they might be sitting low for some reason. If say 1 set of the switching mosfets had dropped out, i presume the rail voltages would be 1/2'd (had an amp do this). This would mean you had a lot less power.

If you want to find which mosfets are doing what, i guess just trace where they are connecting to, one set should all go to the speaker out eventually (maybe via large white ceramic resistors).
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Old 20th April 2004, 04:51 AM   #3
KyferEz is offline KyferEz  United States
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Hi Immo_G, and thx 4 responding.

No I haven't tested anything that requires power to be connected yet. I am trying to figure out what I can / should do with all those irfz44n fets blown. My biggest concern is that if I should spend the money to replace them ($11 + s/h) the problem that caused them to burn up might/will still exist. I really need help figuring out what caused them to smoke.

I did just grab my dmm and tested some things. The IRF2807 fets are the audio output stage. Many of them also read 0 ohms between all 3 pins so they are obviously fried as well.

BTW, I am an electronic engineer, I just have little experience with analog circuits and none with power amplifiers. I am a digital/embedded systems person. So point me in the right direction, tell me what I should be testing for, and I will be good. I have an oscilloscope, dmm, power supplies, freq generators, etc. so I can really do serious testing if I know what I'm looking for.

Also, could someone else answer the other questions from my previous post, as here are a few new ones:

1) Can fried fets on the audio output cause the voltage stepup fets to burn up?

2) Would some of the output fets being burned up cause the power output to decrease (versus causing the amp to shutdown or burn up the rest of the fets)?

3) How do I test the amp with all these blown fets/what do I look for? I don't want to buy and burn up a bunch (18) fets because I hook up the amp and there is some problem that caused all of this to happen that hasn't been corrected.

Thanks for all the help,
KyferEz
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Old 4th May 2004, 07:36 AM   #4
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Hi KyferEz

Q 1 that power supply driver is faulty ,that it no oscilling and drian DC high current ,so your fet & coil is burn.
Q 2 ??
Q 3 trial looking some driver (ic tl494/sg3525/sg3524....) to drive
irfz44 & some transistor
Q 4 that maybe cause by static to burn out your fet & ic.
Q 5 ?????????.....
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Old 6th May 2004, 12:30 AM   #5
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KyferEz,

Do you have access to a current monitored bench supply? If so, do this...

You have to start with the power supply - get it working and all that. To do this easily (not properly) with a sorta cheap amp like the Boss is this:

1. Remove the rectifier diodes. There are probably two or four per rail (depending on dual or single diode config). Just take all of them out.

2. Install three IRFZ44N's per "side" so you can get a switching waveform going. The current limited supply will keep you from blowing all your FETs and other stuff.

3. Connect your oscilloscope leads to each winding of the secondary of the transformer (it is center tapped, and each winding leads off to the aforementioned recitifer diodes...maybe a choke, too... Dual trace scope is needed here.

4. Power 'er up, making note of the current draw. It should be less than 1/2 amp and you should see an OK square wave output on the scope. It is probably ringing a bit because it's unloaded, but it should be symmetrical.

5. If you get a spike followed by a slow rising of current, your transformer is saturating. For whatever reason, the transformer is either being driven asymmetrically or the PWM IC (usually a TL494) is bad. Typically it's the latter.

6. If you get an instant massive current draw, there are several points to check.

a) The FETs you installed are new...are not static damaged and are not shorted.

b) The PWM IC is shorted (open collector outputs)

c) The driver transistors (speed-up circuit) are shorted - they are usually anti-parallel connected NPN/PNP pairs that help the driver IC overcome the high gate capacitance of the paralleled FETs. They are connected between the gate resistors of the FET bank and the ouput of the PWM IC These almost always short C-E if you find burnt FET gate resistors.

Let's get this part first, report back and we'll move ahead.
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