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Sony Vfet 4650-NO SOUND HELP!


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I purchased the Sony Vfet amp from the US about 8 weeks ago. To make it more reliable, as precribed by many, changed the killer diodes and bias resistors. Have been playing amp for last month without a hicup. Turned the amp on yesterday no sound. Turned it off and on again and noticed that the relays are'nt  switching on either. Felt the heat sinks, which I image dissipate the heat from the VFets, they felt hot. Not sure how hot they should be? Then read the power supply and bias voltages. Power voltage reads correctly at 20 volts. The bias reading on right reads correctly at 45 volts but the bias reading on the left channel is down reading at 15 volts. No sign of burnt componets. Not sure if the above scenario helps with general diagnose. Hopefully have not blown Vfets?

Anyway because of my lack of techical knowledge will need someone  who can help. So I tryed connacting Dallas Clark in Melbourne  and Liquid Audio in Perth. Neither at this stage are interested in looking at it. So need   recommendations of an experanced  repair person preferable in Melbourne who would look at it. Would also consider paying knowable DIYer.

 

 

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I would but have 4 repairs on the go will all them being either extremely difficult and lengthy and/or intermittent making it hard to diagnose so the last thing I need right now is a finicky VFET 😁.

 

Don't even have the time to work on my own stuff (JBL active crossover) that needs some TLC.

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  • 10 months later...
On 27/08/2019 at 1:45 PM, IanB said:

I purchased the Sony Vfet amp from the US about 8 weeks ago. To make it more reliable, as precribed by many, changed the killer diodes and bias resistors. Have been playing amp for last month without a hicup. Turned the amp on yesterday no sound. Turned it off and on again and noticed that the relays are'nt  switching on either. Felt the heat sinks, which I image dissipate the heat from the VFets, they felt hot. Not sure how hot they should be? Then read the power supply and bias voltages. Power voltage reads correctly at 20 volts. The bias reading on right reads correctly at 45 volts but the bias reading on the left channel is down reading at 15 volts. No sign of burnt componets. Not sure if the above scenario helps with general diagnose. Hopefully have not blown Vfets?

Anyway because of my lack of techical knowledge will need someone  who can help. So I tryed connacting Dallas Clark in Melbourne  and Liquid Audio in Perth. Neither at this stage are interested in looking at it. So need   recommendations of an experanced  repair person preferable in Melbourne who would look at it. Would also consider paying knowable DIYer.

 

 

Did you get this sorted?

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Had it looked at. 1 vfet not working. But managed to swap the 3 remaining vfets for a matching set of  4 good vfets. Still sitting on the shelf. Might sell  to someone who knows how to fix it. I believe because I have 4 good vfets it is worth fixing. 

In the meantime  I brought a refurbished  Sony TA N7 vfet 100 watt power amp which I am very happy with

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