My Behringer A500 is just 2 years old and hardly been used . I turned it on two weeks ago and use it on my sub. Worked well and didn't heat up at all as I played it as reasonable levels.
This morning as was listening to it it suddenly died. Apparently blew the main line fuse ( on the power extension box). It tried it on another extension box and it blew that fuse also. It did come on but suddenly after about 5 seconds the fuse blew and the power light faded away. No noise from the sub. There's copper all over the inside of the glass fuse , so it went of with a 'bang' ! can't imagine what happened.
However when I opened it and looked at it, nothing was burnt and there was no heated or burnt smell at all. I noticed that the power transistors didn't seem to have any insulators on them ! Just bolted directly to the heat sink. Any form of insulator would be visible around the edges of the transistors but there is nothing on either channel . Do they just depend on the insulation of the anodising on the aluminum ? Is this safe? The fuse on the power amp board is also intact !
Anyone had a similar problem ?
This morning as was listening to it it suddenly died. Apparently blew the main line fuse ( on the power extension box). It tried it on another extension box and it blew that fuse also. It did come on but suddenly after about 5 seconds the fuse blew and the power light faded away. No noise from the sub. There's copper all over the inside of the glass fuse , so it went of with a 'bang' ! can't imagine what happened.
However when I opened it and looked at it, nothing was burnt and there was no heated or burnt smell at all. I noticed that the power transistors didn't seem to have any insulators on them ! Just bolted directly to the heat sink. Any form of insulator would be visible around the edges of the transistors but there is nothing on either channel . Do they just depend on the insulation of the anodising on the aluminum ? Is this safe? The fuse on the power amp board is also intact !
Anyone had a similar problem ?
They definitely wont depend on oxidation for insulation. Either the heatsink will be at the same potential as the transistors or the circuit configuration (devices used) allows the metal case of the transistor to be grounded or the transistors are plastic backed.
There are 4 power transistors per channel. The heat sink is physically connected to the chassis and so it's at ground potential. Unlikely they are with plastic insulation like the chip power amps.
I just found one circuit diagram. The collectors ARE at ground potential. So nothing is missing ! Right, now I'll have to find out what's wrong. 🙁
Thanks for suggesting the possibilities.
I just found one circuit diagram. The collectors ARE at ground potential. So nothing is missing ! Right, now I'll have to find out what's wrong. 🙁
Thanks for suggesting the possibilities.
Disconnected the power cable to the two power amp boards. Fuse still blows !
Now only the transformer and low signal circuits are connected. I think it must be the transformer ! Could it just be the input surge current ? Do they have an inrush protection ?
Will need to check it out. I AM happy it isn't the power amp board. Fiddly to dismantle it fully and didn't look forward to that.But power up still lights up the blue power LED which fades away slowly. Of course the power line fuse would have blown ! The fuse on the amp power line is intact !
The amp was working well earlier without any problem. Any 110V rated protection parts on the primary of the transformer ? I am using the 220 V tap on the transformer with 215 V mains.
Anyone ?
Now only the transformer and low signal circuits are connected. I think it must be the transformer ! Could it just be the input surge current ? Do they have an inrush protection ?
Will need to check it out. I AM happy it isn't the power amp board. Fiddly to dismantle it fully and didn't look forward to that.But power up still lights up the blue power LED which fades away slowly. Of course the power line fuse would have blown ! The fuse on the amp power line is intact !
The amp was working well earlier without any problem. Any 110V rated protection parts on the primary of the transformer ? I am using the 220 V tap on the transformer with 215 V mains.
Anyone ?
I'd be surprised if the tranny were faulty. Only if it blows the fuse with all secondary's disconnected would it be suspect. Much more likely would be a bridge rectifier or something directly related to same.
This was a 110V unit. I connected the dummied tap which did appear to be for 230 V.
But there is something on the power switch all wrapped up in insulation tape. Need to open it and see what it is. Could be a 120 V rated cap across it !🙂
Would have gone dead by now. I need to open that and check it out before going to sleep. I agree that it does look unlikely that the transformer is broken. It was stone cold when the problem occurred the first time. Will first check that then remove the only other cable coming from the transformer.
But there is something on the power switch all wrapped up in insulation tape. Need to open it and see what it is. Could be a 120 V rated cap across it !🙂
Would have gone dead by now. I need to open that and check it out before going to sleep. I agree that it does look unlikely that the transformer is broken. It was stone cold when the problem occurred the first time. Will first check that then remove the only other cable coming from the transformer.
As I mentioned the mains fuse on the power strip blows on power up. Everything disconnected from the secondary and it still blows.
Pulled out the second good amp that I have ( luckily) and compared the two. On the bad one the thermistor limiting the inrush current was 1 ohm at room temp. On the good amp it was just over 3 ohms at room current.
Note that the amp was rated 110 volts. It was changed to 230 V as it had a 230 V dummied tap on it. So possibly the thermistor for the inrush current should have been different. About 6 ohms at room temp ?
The current thermistor has no markings on it. It is about 3mm thick and about 20mm dia and green in colour ! Plus of course 3.0 ohms at room temp ( 27 deg C) on the good one.
Would anyone have any idea what it could be replaced by. The so called good one will also probably die eventually. I haven't used that one much.
I'm guessing I should look for a 6 ohm/ 8 A rating ?
Thanks
Pulled out the second good amp that I have ( luckily) and compared the two. On the bad one the thermistor limiting the inrush current was 1 ohm at room temp. On the good amp it was just over 3 ohms at room current.
Note that the amp was rated 110 volts. It was changed to 230 V as it had a 230 V dummied tap on it. So possibly the thermistor for the inrush current should have been different. About 6 ohms at room temp ?
The current thermistor has no markings on it. It is about 3mm thick and about 20mm dia and green in colour ! Plus of course 3.0 ohms at room temp ( 27 deg C) on the good one.
Would anyone have any idea what it could be replaced by. The so called good one will also probably die eventually. I haven't used that one much.
I'm guessing I should look for a 6 ohm/ 8 A rating ?
Thanks
As said, try it with a light bulb. If the bulb lights you have a fused primary (or secondary) on the transformer and will need rewinding or replacement.
Unlikely it is caused by the thermistor failing to limit the inrush, then you would not have a 5 second delay ever. If you use a light bulb in series, you may try to omit the thermistor. A lit bulb will indicate transformer failure.
Unlikely it is caused by the thermistor failing to limit the inrush, then you would not have a 5 second delay ever. If you use a light bulb in series, you may try to omit the thermistor. A lit bulb will indicate transformer failure.
I did think of doing this except that I didn't have a regular lamp and socket etc. Then Max reminded me of this and now again by you. I will get it and try it out. I doubt the transformer is shorted out as the capacitors still charge up. Could be a flaky one . Rare but I have seen it happen.
I did determine that the thermistors are OK. They are rated 1 ohm ( at 25 deg C) and 13 Amps. Might need a larger resistance for 230 V I think. Possibly 2 ohms 6 amps. This is in the primary circuit.
It appears that the supply to the power amp is 80 V ac and the one to the board on the front panel is 20/0/20 volts ac. Can someone confirm this ?
Getting ready in case I need to get a new transformer. 🙂
I did determine that the thermistors are OK. They are rated 1 ohm ( at 25 deg C) and 13 Amps. Might need a larger resistance for 230 V I think. Possibly 2 ohms 6 amps. This is in the primary circuit.
It appears that the supply to the power amp is 80 V ac and the one to the board on the front panel is 20/0/20 volts ac. Can someone confirm this ?
Getting ready in case I need to get a new transformer. 🙂
Sometimes you will get insulation punch through on the primary in case of lightning strikes or line surges etc. We've seen cases where a part of the primary goes open or shorted to another winding. And no, not restricted to cheap equipment, this was a Cambridge Audio CD player. Kept blowing fuses and had to replace transformer.
Your voltage estimations seem fine, but I would check the service manual. You could also use the QSC manual for the A400 (?) that Berry simply lifted it out of. That ran off 54V per polarity (with the CT connected to the output). Not sure about the opamp at the front, but 20V input into a set of regulators sounds about right. The 4580 runs off +/-18V max.
Your voltage estimations seem fine, but I would check the service manual. You could also use the QSC manual for the A400 (?) that Berry simply lifted it out of. That ran off 54V per polarity (with the CT connected to the output). Not sure about the opamp at the front, but 20V input into a set of regulators sounds about right. The 4580 runs off +/-18V max.
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Hi Sangram,
This is a new amp. Not exposed to anything so far. BUT it did have a very rough trip before delivery. I was concerned that the toroid bottom might have been affected. No way to check that out easily.
I am also aware of the output stage with collectors going to ground. However I have never had an amp with that kind of circuitry before the A500. I'm not too sad about the situation. I might just trash the insides and put in my own supply and boards one day !
Too many interesting things happening right now.
Thanks for your post.
This is a new amp. Not exposed to anything so far. BUT it did have a very rough trip before delivery. I was concerned that the toroid bottom might have been affected. No way to check that out easily.
I am also aware of the output stage with collectors going to ground. However I have never had an amp with that kind of circuitry before the A500. I'm not too sad about the situation. I might just trash the insides and put in my own supply and boards one day !
Too many interesting things happening right now.
Thanks for your post.
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