Plz help me out: I got a Crown Power Base 2 amplifier for free and its not working. I'm trying to figure out what's wrong with it.
It appears that the previous owner connected the outputs to the inputs or something along those lines : (
So, basically I replaced/repaired a couple of blown small signal transistors(which have the same function for either channel), some pcb traces on the input ground of the amp, two or three blown resistors in the "voltage translator stage" and a couple more resistors on the output board near the output transistors along with some blown diodes.
I should have known better cause when I powered up the amp two of the resistors blew up again. I'm starting to think that some/all of the output resistors are shorted, but the strange thing is that its not blowing the fuses and apparently the protection circuit is not doing its job. What should I check for? Is it worth fixing?(They're about $250-$350 on ebay)
I called Crown and they say that the power transistors can only be bought from them since they are "screened" for specific characteristics, they are like $7 each (there's 16 of 'em $$). Furthermore I searched all over the internet for replacements and can't find any info on the output transistors. All I know is that they are Motorola and are C6492-0, and C4751-1, pnp and npn respectively.
BTW the schematic can be found at http://www.crownaudio.com/pdf/amps/PB 2 Schematic J0446-5_A.pdf
The parts which I found out to be bad from just looking at them
are:
Q101
Q201
R162
R240
R162
R180 and c147(maybe)
R01
D07
D08
D06 (along with pcb trace)
R09
R10
R08
C09 (maybe)
There are probably more bad parts, like the output transistors, and that's what I want to find out. I'm pretty sure someone who has worked a lot on power amps can tell whats wrong by looking at the schematic and the syptoms. BTW, how can I check the output transistors without a transistor checker? Can I use a diode checker?
Thanks in advance...
It appears that the previous owner connected the outputs to the inputs or something along those lines : (
So, basically I replaced/repaired a couple of blown small signal transistors(which have the same function for either channel), some pcb traces on the input ground of the amp, two or three blown resistors in the "voltage translator stage" and a couple more resistors on the output board near the output transistors along with some blown diodes.
I should have known better cause when I powered up the amp two of the resistors blew up again. I'm starting to think that some/all of the output resistors are shorted, but the strange thing is that its not blowing the fuses and apparently the protection circuit is not doing its job. What should I check for? Is it worth fixing?(They're about $250-$350 on ebay)
I called Crown and they say that the power transistors can only be bought from them since they are "screened" for specific characteristics, they are like $7 each (there's 16 of 'em $$). Furthermore I searched all over the internet for replacements and can't find any info on the output transistors. All I know is that they are Motorola and are C6492-0, and C4751-1, pnp and npn respectively.
BTW the schematic can be found at http://www.crownaudio.com/pdf/amps/PB 2 Schematic J0446-5_A.pdf
The parts which I found out to be bad from just looking at them
are:Q101
Q201
R162
R240
R162
R180 and c147(maybe)
R01
D07
D08
D06 (along with pcb trace)
R09
R10
R08
C09 (maybe)
There are probably more bad parts, like the output transistors, and that's what I want to find out. I'm pretty sure someone who has worked a lot on power amps can tell whats wrong by looking at the schematic and the syptoms. BTW, how can I check the output transistors without a transistor checker? Can I use a diode checker?
Thanks in advance...
Well, I'm not real experienced, but I've checked transistors. There are 3 pins on it, and the simplest way to check (not to test if it is working perfectly, though) is to use an ohmmeter or diode check (or transistor check if you have it). I initially check them in-cirucuit by the following method:
1. put red lead to left-most pin (from front), black on right lead.
2. keep red on left, put black on middle
3. move red to middle, black to right.
4. put black on left, red on right
5. keep black on left, right in middle
6. black on middle, red on right.
If you get almost 0 ohms (or diode check beeps) in one configuration, or usually more, then you should remove from the board and retest it. But, make sure the resistance or beep remains constant, as it may initially read short or beep if there's a capacitor between pins and will produce such results until it charges enough (usually less than a second to a few seconds). If you get the same results out-of-circuit, it's bad.
You should also test for consistancy between same model transistors (of course, the circuit may interfere and drastic differences should be confirmed by out-of-circuit testing).
Since transistors are like diodes, one polarity configuration between two pins should give some resistance (or foward voltage with diode check), but nothing in the opposite polarity (but can also be influenced by circuit).
In the end, I just want to say, you can do initial checking in-circuit and usually get an idea if a transistor is bad.... BUT! make sure you take it out of circuit and test it before you believe it's bad.
Good luck!
1. put red lead to left-most pin (from front), black on right lead.
2. keep red on left, put black on middle
3. move red to middle, black to right.
4. put black on left, red on right
5. keep black on left, right in middle
6. black on middle, red on right.
If you get almost 0 ohms (or diode check beeps) in one configuration, or usually more, then you should remove from the board and retest it. But, make sure the resistance or beep remains constant, as it may initially read short or beep if there's a capacitor between pins and will produce such results until it charges enough (usually less than a second to a few seconds). If you get the same results out-of-circuit, it's bad.
You should also test for consistancy between same model transistors (of course, the circuit may interfere and drastic differences should be confirmed by out-of-circuit testing).
Since transistors are like diodes, one polarity configuration between two pins should give some resistance (or foward voltage with diode check), but nothing in the opposite polarity (but can also be influenced by circuit).
In the end, I just want to say, you can do initial checking in-circuit and usually get an idea if a transistor is bad.... BUT! make sure you take it out of circuit and test it before you believe it's bad.
Good luck!
If you expect that amp to work you will need to replace all 16 outputs, 4 drivers, and 4 predrivers, emitter resistors, the bias diodes and the bias transistor as a MINIMUM.
Check the current limiter transistors, they are probably bad.
Check the last voltage amp (high side), it is probably
OK. If bad, replace the whole front end.
The protection circuit only works in a properly working amplifier.
During testing use a 100W lightbulb in series with the line cord, play for 3 or 4 hours before going direct.
Outputs
MJ15022/23
Drivers
MJE15030/31
Predrivers
MPSA42/92
Keep in mind a couple of things:
You can buy a new POS 500W amp for $300, but how long will it last?
The Crown circuit board and heatsink is drilled for another set of outputs (used in the PB3, MA2400, etc), add them to the PB2 and it will handle low impedance loads much better (change all the emitter resistors to 0R27).
Check the current limiter transistors, they are probably bad.
Check the last voltage amp (high side), it is probably
OK. If bad, replace the whole front end.
The protection circuit only works in a properly working amplifier.
During testing use a 100W lightbulb in series with the line cord, play for 3 or 4 hours before going direct.
Outputs
MJ15022/23
Drivers
MJE15030/31
Predrivers
MPSA42/92
Keep in mind a couple of things:
You can buy a new POS 500W amp for $300, but how long will it last?
The Crown circuit board and heatsink is drilled for another set of outputs (used in the PB3, MA2400, etc), add them to the PB2 and it will handle low impedance loads much better (change all the emitter resistors to 0R27).
Hi BlackUnikorn,
djk is right. I have repaired these before too. These are not pretty when blown. Be aware that this is not a "normal" amplifier to repair. I'd feel better about you repairing this one if you had experience and better test equipment. If you do proceed, keep your eyes open and use common sense. If you can get someone who knows these to help, do it.
Use new mica insulators and proper heatsink grease. Do not overtighten the transistors. Please clean all the old grease off, it will cause you grief if you don't.
-Chris
djk is right. I have repaired these before too. These are not pretty when blown. Be aware that this is not a "normal" amplifier to repair. I'd feel better about you repairing this one if you had experience and better test equipment. If you do proceed, keep your eyes open and use common sense. If you can get someone who knows these to help, do it.
Use new mica insulators and proper heatsink grease. Do not overtighten the transistors. Please clean all the old grease off, it will cause you grief if you don't.
-Chris
Those are great little amps and I completely understand wanting to fix it yourself, but sending it back to crown might not be as devastating on the pocket book as you might think. I've had many crown's repaired and the most expensive was an old mt600 with both channels blown up by a rental. It was $181 +shipping to bring it back to factory specs. (your results may vary of course) Cheaper than buying another amp though.
"sending it back to crown might not be as devastating on the pocket book as you might think"
Crown has BOHICA pricing on repairs.
A friend returned a working MA600 that had the fan air flow reversed. Crown replaced the fan (rather than reversing the blade), replaced every non-Crown part with CPN (keep in mind the amplifier worked when returned), and sent it back with a bill for over $300.
If your pockets are that deep, just buy a new amp.
"Use new mica insulators "
On what?
There are none on the outputs or drivers, the heatsinks have voltage on them and are isolated from the chassis.
Crown has BOHICA pricing on repairs.
A friend returned a working MA600 that had the fan air flow reversed. Crown replaced the fan (rather than reversing the blade), replaced every non-Crown part with CPN (keep in mind the amplifier worked when returned), and sent it back with a bill for over $300.
If your pockets are that deep, just buy a new amp.
"Use new mica insulators "
On what?
There are none on the outputs or drivers, the heatsinks have voltage on them and are isolated from the chassis.
Wow, thanks for the help guys. I got around testing the output transistors and most of them were bad. I figure its best to replace them all with new ones, but both output transistors and drivers are almost $100 !!, plus I'm missing the top and bottom panels(necessary to make the chassis pressurized/cooling). I see these on ebay for around 300 every once in a while so I guess its better to buy a new/used amp.
Is this a decent sounding amplifier for HIFI? What other amps would you recommend? I'm looking at least 250-300 watts/ch of clean power. BTW, my speakers are around 8 ohms and very inneficient (82 dB).
Is this a decent sounding amplifier for HIFI? What other amps would you recommend? I'm looking at least 250-300 watts/ch of clean power. BTW, my speakers are around 8 ohms and very inneficient (82 dB).
Wow, I guess I've been lucky guys. I did have a techron DO2000 repaired once come to think of it, that was very expensive as I recall.
The panels are pretty critical for proper cooling on these amps. Especially if it's got a fan (don't remember if the pb2 does). These are really great amplifiers though, any of the amps with the construction of the ma/mt series, which the pb2 has, are rock solid as long as their not abused- as with any good amp. Their specs are pretty good and not "fudged" at all and right up there with the rest of the tour worthy amps of its time. Crown even gives you the specs of YOUR amp when you buy one new. The main drawback is the limited output impedance range of the pb series, but if you're gonna do 4 or 8 ohms, it's no problem.
The panels are pretty critical for proper cooling on these amps. Especially if it's got a fan (don't remember if the pb2 does). These are really great amplifiers though, any of the amps with the construction of the ma/mt series, which the pb2 has, are rock solid as long as their not abused- as with any good amp. Their specs are pretty good and not "fudged" at all and right up there with the rest of the tour worthy amps of its time. Crown even gives you the specs of YOUR amp when you buy one new. The main drawback is the limited output impedance range of the pb series, but if you're gonna do 4 or 8 ohms, it's no problem.
Oops!
Hi djk,
"Use new mica insulators " On what?
-Yup, brain fart, just general advice. And you are right, this amp doesn't use 'em.
I was just thinking of how many amps for service that just came from other shops I've seen. Many with the old grease, insulators and new blown outputs. Kinda makes you sad, don't you think?
Thanks for pointing that out.
-Chris
Hi djk,
"Use new mica insulators " On what?
-Yup, brain fart, just general advice. And you are right, this amp doesn't use 'em.
I was just thinking of how many amps for service that just came from other shops I've seen. Many with the old grease, insulators and new blown outputs. Kinda makes you sad, don't you think?
Thanks for pointing that out.
-Chris
Depends on how much power you need. Adding transistors probably won't give you enough power to make a difference, just enable it to drive lower impedence loads. If 200w/8ohm 240w/4ohm is enough, then it should be a good amp.
If you need more power, choose another amp.
They get a bad rep sometimes because it's pretty much bare bones, but as long as it's operated within it's limits, it's a good amp.
If you need more power, choose another amp.
They get a bad rep sometimes because it's pretty much bare bones, but as long as it's operated within it's limits, it's a good amp.
"i know this is an old subject, but is this true of the PB1 as well? i might be able to get one for a decent price, would be good for stereo subs."
If you double up on the outputs on a PB1 it will do 500W in mono bridge at 8 ohms, or 250W at 4 ohms in stereo. Same as stock, it just won't blow up.
djk []
diyAudio Member
Online
Registered: Feb 2001
Location:
Post #99
"and it will actually work with just a pair of transistors (one per rail) in the output, "
Of course he actually means four outputs per channel, two NPN and two PNP.
One heatsink per side is at + potential, the other at - potential. There are two NPNs on the + heatsink, the two PNPs are on the - heatsink.
There are several Crown amps in the series that use the same basic chassis/heatsink/board layout. For reference I will call them 1,2,3. The 1 uses one pair of outputs per half of the bridge (two per sink), the 2 uses two pair, the 3 uses three pair. The circuit boards are the same, they just stuff the extra parts on the bigger models, and use more transformer.
The 1 blows up driving less than 8 ohms. It's really quite simple. The outputs are only rated at 15A continuous and the Beta is only rated at 5 at 10A DC, and of course is lower at AC. With the amp driving a short duration peak at 4 ohms, it is trying to drive 160V peak-to-peak, or 20A. Of course it will never get that high, the Beta drops like a rock and the driver transistors blow up, and then the whole channel lets the smoke out.
The MacroTech 600 hangs together at 4 ohms because they doubled up on the outputs (like the 2).
If you want to drive bass, I suggest that you stuff up at least the same number of outputs (four pair per channel).
I will sell sets of four pair from the same date code batch for $20, or eight pair (two channels worth) for $32.
If you double up on the outputs on a PB1 it will do 500W in mono bridge at 8 ohms, or 250W at 4 ohms in stereo. Same as stock, it just won't blow up.
djk []
diyAudio Member
Online
Registered: Feb 2001
Location:
Post #99
"and it will actually work with just a pair of transistors (one per rail) in the output, "
Of course he actually means four outputs per channel, two NPN and two PNP.
One heatsink per side is at + potential, the other at - potential. There are two NPNs on the + heatsink, the two PNPs are on the - heatsink.
There are several Crown amps in the series that use the same basic chassis/heatsink/board layout. For reference I will call them 1,2,3. The 1 uses one pair of outputs per half of the bridge (two per sink), the 2 uses two pair, the 3 uses three pair. The circuit boards are the same, they just stuff the extra parts on the bigger models, and use more transformer.
The 1 blows up driving less than 8 ohms. It's really quite simple. The outputs are only rated at 15A continuous and the Beta is only rated at 5 at 10A DC, and of course is lower at AC. With the amp driving a short duration peak at 4 ohms, it is trying to drive 160V peak-to-peak, or 20A. Of course it will never get that high, the Beta drops like a rock and the driver transistors blow up, and then the whole channel lets the smoke out.
The MacroTech 600 hangs together at 4 ohms because they doubled up on the outputs (like the 2).
If you want to drive bass, I suggest that you stuff up at least the same number of outputs (four pair per channel).
I will sell sets of four pair from the same date code batch for $20, or eight pair (two channels worth) for $32.
I wouldn't touch a PB with a very long pole. The most unreliable amp I have ever seen. Certainly in the UK, it's common to go to a rental company that used these and see them sitting rusting gently, (the one thing they do well), in a corner. They are just not economic to repair, and don't last when you do. Avoid.
edit: Actually, they do have a use. The ali heatsink plates are very good as a jig for marking out new heatsinks.
edit: Actually, they do have a use. The ali heatsink plates are very good as a jig for marking out new heatsinks.
"I wouldn't touch a PB with a very long pole. "
Not to use as-is. As I explained, the Macrotech 600 uses twice the number of outputs on exactly the same board. They hold up.
With double the number of outputs you have 2.88KW worth of SOA in the output stage, for a 500W (bridged) amp. You can replace all the outputs, and double up at the same time for $32 (that's $3 a pair plus postage).
If you can find these being used as a door-stop at some hire place for a few quid (working), it is probably worth the trouble. Otherwise, probably not.
I have a blow one laying around, I don't think they are really worth fixing. If I had a working one, I would double up and replace all the outputs and drivers before it blew. Once they go they are a PITA to fix.
Not to use as-is. As I explained, the Macrotech 600 uses twice the number of outputs on exactly the same board. They hold up.
With double the number of outputs you have 2.88KW worth of SOA in the output stage, for a 500W (bridged) amp. You can replace all the outputs, and double up at the same time for $32 (that's $3 a pair plus postage).
If you can find these being used as a door-stop at some hire place for a few quid (working), it is probably worth the trouble. Otherwise, probably not.
I have a blow one laying around, I don't think they are really worth fixing. If I had a working one, I would double up and replace all the outputs and drivers before it blew. Once they go they are a PITA to fix.
Hey,
Wow, old thread. Just got a Crown PB2 this morning for $50. One channel working, the other not. I figured I could use the somewhat clean chassis and tranny for a P101 I was thinking of building.
Opened it up and cleaned it out...gunk everywhere...put it all back together and still one channel out. I opened it back up and took a better look at the output boards and saw two 5.6 ohm resistors toasted (R21 and R02 on the P10397 board). I went to frys and purchased a couple 1/2 watt 5.6 ohm flameproof resistors and replaced them... she fired right up. Lotsa power on my B&W 220s and sounds quite nice...just can't get past that fan....
This is the fourth time I bought a broken amp for the parts and ended up fixing the amps...now what do I do with it??
Wow, old thread. Just got a Crown PB2 this morning for $50. One channel working, the other not. I figured I could use the somewhat clean chassis and tranny for a P101 I was thinking of building.
Opened it up and cleaned it out...gunk everywhere...put it all back together and still one channel out. I opened it back up and took a better look at the output boards and saw two 5.6 ohm resistors toasted (R21 and R02 on the P10397 board). I went to frys and purchased a couple 1/2 watt 5.6 ohm flameproof resistors and replaced them... she fired right up. Lotsa power on my B&W 220s and sounds quite nice...just can't get past that fan....
This is the fourth time I bought a broken amp for the parts and ended up fixing the amps...now what do I do with it??
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