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Post by dobrykamil on Oct 26, 2016 11:07:33 GMT -5
Hi. I'm looking for the service manual or amplifier schematics. Main fuse keep blowing. I think, from some reason one of the power mosfets has no DC on its gate. Amplifier board is quite small and with all the smd components its hard to follow the traces. Photo of the amplifier attached. Thanks in advance.  |
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Post by mastertech on Oct 26, 2016 11:58:38 GMT -5
What fuse is blowing? F1 on the PS board?
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Post by dobrykamil on Oct 26, 2016 13:27:55 GMT -5
What fuse is blowing? F1 on the PS board? The one in the mains 230V socket. The sub supposed to be faulty according to the ebay seller. But it wasn't. I've been testing if for couple of days and worked fine. But one day, I turned the volume up to the max and bang! Both mosfets, IFR540N were shorted. I've replaced them, switched it on and the fuse was blown after 3-4 seconds. Few weeks ago, I was working on a Mordaunt Short 309 sub. Power amp is a class d amp, also build on mosfets. I'm more then sure that both power transistors have had dc (+/- 50V) on their gates. Here, only one mosfets gets dc on the gate. |
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Post by mastertech on Oct 26, 2016 17:22:12 GMT -5
See if this is your power supply.  |
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Post by dobrykamil on Oct 27, 2016 4:58:39 GMT -5
Hi.Unfortunately it's not. Mine is a bit more complex (photo attached)  |
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Post by mastertech on Oct 28, 2016 14:44:43 GMT -5
Where is the fuse located that keeps blowing?
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Post by dobrykamil on Oct 29, 2016 1:14:17 GMT -5
Where is the fuse located that keeps blowing? Power supply is ok. I can switch it on without mosfets.  |
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Post by leeboy22001 on Jul 29, 2017 10:31:15 GMT -5
See if this is your power supply. I have a problem with my boston sub, the output supply +-33v is there when supply is not connected to amp module, but drops to about 3v when connected !.. there doesn't appear to be any shorts in the mosfet outputs (pair of IFR540). Did anyone find by schematics ? Also the schematic you posted is the first sage of the amp power supply. |
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Post by leeboy22001 on Jul 30, 2017 10:44:30 GMT -5
I've been trying to repair mine, tested voltage across zd3, and is 10v. I replaced zd3 with 18v zener, and still 10v. I removed zd3 and still 10v, so something else is clamping the supply to the half bridge mosfet driver (ir23531s). The driver output (high side) is pulsing on/off, so can only assume the 10v supply (minimum working voltage) isn't enough, and the low side isn't working at all. In my wise wisdom I shorted the high and low side gates and blew both fets! Eek
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Post by leeboy22001 on Jul 30, 2017 11:19:22 GMT -5
I have ordered two new mosfets, 11n40c to replace the blown ones, plus a new half bridge driver, my guess is that the driver has an internal clamping 15.6v zener diode, if that has failed it could be clamping the voltage to 10v !? If I can get that voltage back up to working voltage, the dual bridge driver will operate correctly, and both high and low side will work as expected, and result in the correct output voltage to the amp +- 33v not +- 18v I was getting
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Post by dobrykamil on Jul 30, 2017 11:50:06 GMT -5
Hi.I think I have a psu schematic somewhere.
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Post by dobrykamil on Jul 30, 2017 11:52:10 GMT -5
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Post by leeboy22001 on Jul 30, 2017 13:48:38 GMT -5
Thank you very much, perfect  |
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Post by leeboy22001 on Jul 30, 2017 16:52:46 GMT -5
Looking at schematics, the 15v zener used for the voltage follower cct to supply the half bridge driver may have failed, I've removed the output fets ready to be replaced, so will check voltage at base of transistor
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Post by dobrykamil on Jul 30, 2017 17:05:08 GMT -5
I've seen this before.I've purchased this sub off ebay and I think, the light on the back would turn from red to green but could not hear speaker relay.Was able to fix it by replacing zener diode and IR2153 IC.
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