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#1
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Advice on repairing Halfer MOSFET amps
I have two Halfer P500's, a DH500, and a pair of P225's which I need to
reduce to at least a couple of working amplifiers. I have some technical experience, and have access to some test equipment (Tek 465B scope, HP 339A distortion analyzer, that sort of thing) but have never worked on this type of amplifer. One P225 blows the power fuse immediately, which appears to suggest the power supply itself is shorted - I haven't looked at it except to determine nothing (to my surprise) is smoked. The other P225 works with crackling from one channel, which to me suggests it's time to replace capacitors. I do have the Halfer P225/230, DH500, and P500 manuals; however, the only maintenance information regards setting the bias. I have a few spares (no MOSFETS). One question I have is how one tells a fried MOSFET from a good unit, without purchasing one of the Hafler rigs that shows up on eBay from time to time? Any suggestions? I did try Google, but nothing very useful turned up, other than the manuals which I'd already gotten from other sources. Mike Squires mikes at siralan.org |
#2
Posted to rec.audio.tech
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Advice on repairing Halfer MOSFET amps
"Michael L. Squires" wrote in message m... I have two Halfer P500's, a DH500, and a pair of P225's which I need to reduce to at least a couple of working amplifiers. I have some technical experience, and have access to some test equipment (Tek 465B scope, HP 339A distortion analyzer, that sort of thing) but have never worked on this type of amplifer. One P225 blows the power fuse immediately, which appears to suggest the power supply itself is shorted - I haven't looked at it except to determine nothing (to my surprise) is smoked. The other P225 works with crackling from one channel, which to me suggests it's time to replace capacitors. **Why? I'd suggest you look at the front end transistors, as they are a more likely cause of such a fault. I do have the Halfer P225/230, DH500, and P500 manuals; however, the only maintenance information regards setting the bias. I have a few spares (no MOSFETS). One question I have is how one tells a fried MOSFET from a good unit, without purchasing one of the Hafler rigs that shows up on eBay from time to time? Any suggestions? I did try Google, but nothing very useful turned up, other than the manuals which I'd already gotten from other sources. **I use one of these: http://www.peakelec.co.uk/acatalog/jz_dca55.html Very handy. However, testing MOSFETs with a multimeter is pretty easy. Set to the 'diode' position on your multimeter. Connect the leads to Source and Drain. Use a wet finger to Gate and watch the meter. Reverse the leads. You'll figure it out. -- Trevor Wilson www.rageaudio.com.au -- Posted via a free Usenet account from http://www.teranews.com |
#3
Posted to rec.audio.tech
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Advice on repairing Halfer MOSFET amps
In article ,
Trevor Wilson wrote: **Why? I'd suggest you look at the front end transistors, as they are a more likely cause of such a fault. Thanks for the hint. It's been a long time since I did this kind of thing; the last amp I worked on extensively was the Dyna MK III when Hafler had just stopped producing them. Mike Squires |
#4
Posted to rec.audio.tech
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Advice on repairing Halfer MOSFET amps
"Trevor Wilson" wrote in message .. . "Michael L. Squires" wrote in message m... I have two Halfer P500's, a DH500, and a pair of P225's which I need to reduce to at least a couple of working amplifiers. I have some technical experience, and have access to some test equipment (Tek 465B scope, HP 339A distortion analyzer, that sort of thing) but have never worked on this type of amplifer. One P225 blows the power fuse immediately, which appears to suggest the power supply itself is shorted - I haven't looked at it except to determine nothing (to my surprise) is smoked. The other P225 works with crackling from one channel, which to me suggests it's time to replace capacitors. **Why? I'd suggest you look at the front end transistors, as they are a more likely cause of such a fault. I do have the Halfer P225/230, DH500, and P500 manuals; however, the only maintenance information regards setting the bias. I have a few spares (no MOSFETS). One question I have is how one tells a fried MOSFET from a good unit, without purchasing one of the Hafler rigs that shows up on eBay from time to time? Any suggestions? I did try Google, but nothing very useful turned up, other than the manuals which I'd already gotten from other sources. **I use one of these: http://www.peakelec.co.uk/acatalog/jz_dca55.html Very handy. However, testing MOSFETs with a multimeter is pretty easy. Set to the 'diode' position on your multimeter. Connect the leads to Source and Drain. Use a wet finger to Gate and watch the meter. Reverse the leads. You'll figure it out. -- Trevor Wilson www.rageaudio.com.au -- Posted via a free Usenet account from http://www.teranews.com I would add to that that if it is blowing fuses at power up it tends to suggest an output device gone short circuit, very common - even with MOSFETs - if the loudspeaker terminals have been shorted. Remove the supply from one amp, insert a new fuse and switch on.... you know the rest. -- Woody harrogate3 at ntlworld dot com |
#5
Posted to rec.audio.tech
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Advice on repairing Halfer MOSFET amps
"harrogate3" I would add to that that if it is blowing fuses at power up it tends to suggest an output device gone short circuit, very common - even with MOSFETs ** However, Hitachi TO3 lateral mosfets, as used in most ( all?) Haffler amps, fail OPEN CIRCUIT !! The device's drain pins are connected to the chip's surface by easily fused aluminium wire links. The same is not true for other types of mosfet or flat pack mosfets. ........ Phil |
#6
Posted to rec.audio.tech
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Advice on repairing Halfer MOSFET amps
Phil Allison wrote: "harrogate3" I would add to that that if it is blowing fuses at power up it tends to suggest an output device gone short circuit, very common - even with MOSFETs ** However, Hitachi TO3 lateral mosfets, as used in most ( all?) Haffler amps, fail OPEN CIRCUIT !! The device's drain pins are connected to the chip's surface by easily fused aluminium wire links. The same is not true for other types of mosfet or flat pack mosfets. Repairing an amp using Hitachi MOSFET devices should indeed be pretty straighforward. Phil's entirely right. I've never seen one of their lateral 'audio' devices fail anything other than open. This means that you're unlikely to see any kind of cascade failure as you might in a bipolar amp. Graham |
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