VA50

Repair Tech recommendations for a sony vfet

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VA50   

Is anyone or does anyone know of a Technician experienced with working on v-fets that could take a look at my TA-5650 for me? Unfortunately i have to admit defeat on this thing, i got the one out of everyone that had none of the common TA-5650 issues and a million problems no one else has encountered. Without going into much detail it wasn't in good health when i got it and is 90% back to life now. I've restored a number of amplifiers but none this rare and troublesome. No expenses have been spared on this one but i still can't get it to work, It's going into oscillation with the treble control turned to max and I've done all i know/ have the equipment to test to try and find the cause and with the rarity of v-fets i am going to stop here and quit while i'm ahead. I am 100% confident in the work i have done up till now to not have added any extra problems for the tech to work out and this is the final problem that was existing in the unit when i got it.  I'm located in Tas so local obviously would be preferred but i am willing to post if need be.  

IMAG0138.jpg

Edited by VA50

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Simonon   

look up tonym on stereonet. He had one fixed last year

Sent from my SM-G925I using Tapatalk

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Grizzly   
17 hours ago, VA50 said:

Is anyone or does anyone know of a Technician experienced with working on v-fets that could take a look at my TA-5650 for me? Unfortunately i have to admit defeat on this thing, i got the one out of everyone that had none of the common TA-5650 issues and a million problems no one else has encountered. Without going into much detail it wasn't in good health when i got it and is 90% back to life now. I've restored a number of amplifiers but none this rare and troublesome. No expenses have been spared on this one but i still can't get it to work, It's going into oscillation with the treble control turned to max and I've done all i know/ have the equipment to test to try and find the cause and with the rarity of v-fets i am going to stop here and quit while i'm ahead. I am 100% confident in the work i have done up till now to not have added any extra problems for the tech to work out and this is the final problem that was existing in the unit when i got it.  I'm located in Tas so local obviously would be preferred but i am willing to post if need be.  

IMAG0138.jpg

 

Theres a chap who calls himself @hififormusic who, by all accounts, knows his way around a VFET every which way. I think he's based in Qld.

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VA50   

Unfortunately it doesn't look like hes been active on here since late last year so i don't know how much luck i'll have contacting him. I think it might be tough to find a tech willing to touch this thing though, one wrong move could kill all those v-fets and i doubt anyone would want that on their hands. Thats why I've called it quits for my efforts on it, to much risk from here onwards.

Edited by VA50

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Grizzly   
24 minutes ago, VA50 said:

Unfortunately it doesn't look like hes been active on here since late last year so i don't know how much luck i'll have contacting him. I think it might be tough to find a tech willing to touch this thing though, one wrong move could kill all those v-fets and i doubt anyone would want that on their hands. Thats why I've called it quits for my efforts on it, to much risk from here onwards.

 

Hes also on Facebook- www.facebook.com/hififormusic/

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VA50   

I've sent him a message and will see what happens. Open to any other suggestions, @vintagejapan you've had a lot to do with these perhaps you know of someone? 

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16 hours ago, VA50 said:

I've sent him a message and will see what happens. Open to any other suggestions, @vintagejapan you've had a lot to do with these perhaps you know of someone? 

@VA50 sorry don't know anyone who can repair these. You can do most of the checks without the V-fets installed. I would look into the equaliser and preamp board and make sure all the transistors are ok. I think there is modern replacements for most of them. Check out audiokarma also. Lots of threats there about 5650 issues. 

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VA50   

I've noticed there is a lot of fets on both the pre amp and equalizer board that might be harder to find replacements for. With the v-fets removed it sounds great though headphones although i can detect a very faint whistle varying in pitch in the background that sounds like oscillation. Only thing that steers me away from the pre amp being the culprit is the thing plays up with the inputs shorted to ground however this only happens with the vfets removed, once they are installed it doesn't phase them. Unfortunately this machine has all the guys over at both ak and diy audio stumped as well. I think i'm going to have to bite the bullet and purchase a scope, I've been meaning to for ages now. 

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Check the input jfets on the preamp and equalizer board (modern equivalent N and P-channel drop-in's can be used as long as the parameters are similar or higher rated, ensure IDSS grade and value is within the same range as original). Have you changed out any coupling, smoothing and snubber film capacitors? If so, check that you have replaced with the right type, the incorrect type of film capacitor in the power supply for example will cause oscillation problems with the power supply to the boards. If not, check and measure all film capacitors, don't skip and skimp on them.

 

One way of troubleshooting these sort of things is work in blocks and isolate each stage of the amplifier as you're working on you think the problem is related to i.e. Amp blows fuse on power up? Check the output transistors and PS rectifier for shorts, no power supply voltage on the rails? Check the PS stage and raw transformer winding AC voltage, no input? Check the input or interstage, Problems with output and driver stage? Check the current source and output devices etc etc.

 

Cheers,

Edited by willio747

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djb   

Always amazes me the tech knowledge available on this site

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VA50   
20 hours ago, willio747 said:

Check the input jfets on the preamp and equalizer board (modern equivalent N and P-channel drop-in's can be used as long as the parameters are similar or higher rated, ensure IDSS grade and value is within the same range as original). Have you changed out any coupling, smoothing and snubber film capacitors? If so, check that you have replaced with the right type, the incorrect type of film capacitor in the power supply for example will cause oscillation problems with the power supply to the boards. If not, check and measure all film capacitors, don't skip and skimp on them.

 

One way of troubleshooting these sort of things is work in blocks and isolate each stage of the amplifier as you're working on you think the problem is related to i.e. Amp blows fuse on power up? Check the output transistors and PS rectifier for shorts, no power supply voltage on the rails? Check the PS stage and raw transformer winding AC voltage, no input? Check the input or interstage, Problems with output and driver stage? Check the current source and output devices etc etc.

 

Cheers,

Thanks, i haven't touched any of the film caps in the pre amp and eq sections yet, that was actually going to be my next step. I did replace all the mylar film caps on the main amp board with wima polypropylene caps. At this point i know this issue was present in the amplifier prior to me touching it, it had a bunch of other problems also that are now sorted. I might do all the film caps throughout the amp anyway, despite being a reliable device I've seen enough fail in amps now to see them as being something worth replacing in a restoration. I've also found original replacements for the jfets throughout the amp if needed. Powering the amp from an external preamp it appears to remain stable and through headphones a slight varying whistle can be heard so the preamp/ eq board is next to look at. 

Edited by VA50

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Tony M   

Well, I sent my very dead Sony TAN 8550 to @hififormusic late last year for repairs and it arrived home a few months ago, fit and well and sounding very sweet indeed.  He's a genuine bloke and definitely knows his way around a V-fet amp, which he's quite passionate about.  Yes, it might take a while as I think he is very busy in his main profession as a piano tuner, but he is easy to contact and happy to give progress reports as well as providing many options for restoration/configuration.  Costs were very reasonable, too - in fact genuine bargain territory given the limited number of available techs you could trust a V-fet amp to.

 

Definitely recommended as one of the good guys when it comes to understanding and sourcing parts for v-fet amps, which is a is part of the battle in keeping these beauties alive. His first-hand experience in repairing them and his attention to detail is pretty important, too. :thumb:     

 

 

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VA50   
On 18/07/2017 at 9:12 PM, Tony M said:

Well, I sent my very dead Sony TAN 8550 to @hififormusic late last year for repairs and it arrived home a few months ago, fit and well and sounding very sweet indeed.  He's a genuine bloke and definitely knows his way around a V-fet amp, which he's quite passionate about.  Yes, it might take a while as I think he is very busy in his main profession as a piano tuner, but he is easy to contact and happy to give progress reports as well as providing many options for restoration/configuration.  Costs were very reasonable, too - in fact genuine bargain territory given the limited number of available techs you could trust a V-fet amp to.

 

Definitely recommended as one of the good guys when it comes to understanding and sourcing parts for v-fet amps, which is a is part of the battle in keeping these beauties alive. His first-hand experience in repairing them and his attention to detail is pretty important, too. :thumb:     

 

 

 

I've just been in touch with hififormusic via facebook and he confirmed he is indeed very busy at the moment and has another TA-5650 on his bench waiting to be fixed but that he'd have a think about it and get back to me. Since the actual bulk of the restoration of the amp has already been done and all the necessary upgrades and mods performed the majority of the labor will be in finding the problem as there's not much i haven't already covered to replace so hopefully it isn't to difficult of a job for someone that has a little more knowledge on these things then me. If i don't hear back from him in a few days though i will start digging around the pre amp and eq circuits next.

Edited by VA50

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