Thank You Miklos. Here are my latest readings after letter the amp
settle down. At #61 connection pin 1(all of these pins are counting
from the bottom) is -49, pin 2 reads -77 pin 4 reads +72 and pin 5 reads
+49. Big 10,000uf caps read -49, +49. Emitter of Q403 is 20volts, Emitter of Q401 is 97. Voltage without v-fets installed at the source pin of 2SJ-18
is +49.1 and 2SK-60 -49.1 all the way down the line for each appropiate
one. The pin #4 reading of +72 I know is a little low. You think that it's
safe to install fets with these readings? These Sonys sure seem a little
temper mental to me. Scary.
The Yamaha B-2 and B-1 seem a little better built to me and not so spastic. Just my humble opinion. Thanks for link to obtaining some v-fets. You are so kind. Do you own any of the
Yamaha V-fet amps as well? Cheers,
Klipschorn dude
Except the B2 voltages (+-76V) all voltages seems to be in range.
Try to disconnect the B2 wires coming from the PS board and load the supply with a 6.8k 5W resistor in between the +76 and -76V outputs, and measure the + - voltages to the ground. They should be symmetrical. In any case before you plug in the VFet's, some current limiting in a form of two resistors (100 ohms) in the +-B1 line would be a good thing, just to give you an indication if something is drastically wrong and measure the voltage drop on them which should be equal. Start with only one channel and only with one pair (sk/sj) transistors. This way you could go through all other pairs to. Unfortunately one need some patience to check everything and not to blow one of the VFet's, they only can take 5 Amps and those large PS capacitors able to deliver high currents. Good luck
Try to disconnect the B2 wires coming from the PS board and load the supply with a 6.8k 5W resistor in between the +76 and -76V outputs, and measure the + - voltages to the ground. They should be symmetrical. In any case before you plug in the VFet's, some current limiting in a form of two resistors (100 ohms) in the +-B1 line would be a good thing, just to give you an indication if something is drastically wrong and measure the voltage drop on them which should be equal. Start with only one channel and only with one pair (sk/sj) transistors. This way you could go through all other pairs to. Unfortunately one need some patience to check everything and not to blow one of the VFet's, they only can take 5 Amps and those large PS capacitors able to deliver high currents. Good luck
Thanks again miklos. I'm in no hurry to ruin the v-fets, so I will trackExcept the B2 voltages (+-76V) all voltages seems to be in range.
Try to disconnect the B2 wires coming from the PS board and load the supply with a 6.8k 5W resistor in between the +76 and -76V outputs, and measure the + - voltages to the ground. They should be symmetrical. In any case before you plug in the VFet's, some current limiting in a form of two resistors (100 ohms) in the +-B1 line would be a good thing, just to give you an indication if something is drastically wrong and measure the voltage drop on them which should be equal. Start with only one channel and only with one pair (sk/sj) transistors. This way you could go through all other pairs to. Unfortunately one need some patience to check everything and not to blow one of the VFet's, they only can take 5 Amps and those large PS capacitors able to deliver high currents. Good luck
down the problem piece by piece if I have to. Will do as you suggest
and let you know how she does. Cheers,
Klipschorn dude
Hello Elwood. I'm happy that you own a B-2. Wow, what an amp. I'm
trying to get some Sony V-fets going. Do you own a B-1 or any Sony
amps as well? It seems like the Yamaha amps are built better than the
Sonys are IMHO. Do you have a SM for the B-2? Good Luck,
Klipschorn dude
Hello Miklos. The only Service Manual I have is downloaded from TheExcept the B2 voltages (+-76V) all voltages seems to be in range.
Try to disconnect the B2 wires coming from the PS board and load the supply with a 6.8k 5W resistor in between the +76 and -76V outputs, and measure the + - voltages to the ground. They should be symmetrical. In any case before you plug in the VFet's, some current limiting in a form of two resistors (100 ohms) in the +-B1 line would be a good thing, just to give you an indication if something is drastically wrong and measure the voltage drop on them which should be equal. Start with only one channel and only with one pair (sk/sj) transistors. This way you could go through all other pairs to. Unfortunately one need some patience to check everything and not to blow one of the VFet's, they only can take 5 Amps and those large PS capacitors able to deliver high currents. Good luck
HIFI Engine. It is very good and legible. I have discovered that what
the manual calls for on the PS board on some resistors and what is
actually on the boards are different. I'm not talking about what was
changed per the Sony Service Manual. R413 in the manual is 10k, but
is actually 150k on the PS board. R410 calls for 470 in the manual, but
is actually 5.6K on the PS board. and R424 calls for 470 in the manual
but is actually 400 on the PS board. This situation is the same on two
different PS boards from two different amps. Maybe Sony did some
in house changing of the boards and did not change the manual.
Could this be the reason I cannot get the + - 76 voltage right?
Thanks,
Klipschorn dude
Hello miklos. I'm not even close to being the technician that you are.
I don't know how to load the power supply with a resistor. Does the power
board have to be completely disconnected from the PS board to obtain
the - + 76 reading? I have changed out all the caps on the PS board and
the readings of the diodes are: D407.666, D405.631, D404.674. When I
first power up the amp, the voltage is +94 at pin #4 at the #61 connection
but drifts all the way down to +61 volts. All the resistors show to be the
correct values. I read them on the board with power off when I checked
them. Is that the correct way? I already changed the dreaded 1221 diodes
on the power board. I appreciate you having patience with me.
Klipschorn dude
Hi Helmuth,
Was is your experience with the changes proposed in the Belgian Service Paper. Did they give you any problems? What is your opinion on the fact thes were advised for safety purposes.
The lower bias values are not new to me.
I own quite a few v-fet amps and when this changes make sense I have to go through them once more.
And Yes great job and very entertaining and educational. And thanks for extra potential weak points you point to. Makes sense.
Was is your experience with the changes proposed in the Belgian Service Paper. Did they give you any problems? What is your opinion on the fact thes were advised for safety purposes.
The lower bias values are not new to me.
I own quite a few v-fet amps and when this changes make sense I have to go through them once more.
And Yes great job and very entertaining and educational. And thanks for extra potential weak points you point to. Makes sense.
The repaired end stage blew a year after the repair I did turn up the bias higher then the belgium paper.
I think this is the cause of the failure. I would advise to follow the advise.
Also the chinese nos Vfet could be the cause I have al ready a new set that I have to install.
2SK60 rank 55
I'm going to repair a Wega VFET amp I just bought and I already ordered two 2SK60 rank 55.
I do not have the amp yet so I don't know if I even need to replace the VFETs.
Doesn't hurt to have a few spare ones though
I did some testing with 32V between D and S.
To get the current down to 30mA I needed to apply 12V between G and S on one VFET and 17V on the other.
This cannot be right or what do you think?
They should probably be within a few hundred mV if they are the same rank.
Paralleling these must be impossible!?
Same ebay seller offers rank 33 2SJ18...I would like to measure one
I'm going to repair a Wega VFET amp I just bought and I already ordered two 2SK60 rank 55.
I do not have the amp yet so I don't know if I even need to replace the VFETs.
Doesn't hurt to have a few spare ones though
I did some testing with 32V between D and S.
To get the current down to 30mA I needed to apply 12V between G and S on one VFET and 17V on the other.
This cannot be right or what do you think?
They should probably be within a few hundred mV if they are the same rank.
Paralleling these must be impossible!?
Same ebay seller offers rank 33 2SJ18...I would like to measure one
Got a pair of 2SJ18 from Jims and same thing.
One is perfect and the other has a Vgs of like 23V.
Jims was anyway helpful and promised to replace it for me.
The chinese seller I got the K60 from had to get negative feedback.
He was useless
Wonder what the rank 33 devices are??? Many chinese sellers have them.
I got some J28 K82 today, they might work too.
Anyway I got my amp and it was working, but one channel was very weak.
Turned out the weak channel had shorted VFETS, all of them.
I did the diode change (loosely matched) and a total recap of the PA board.
The PS board is not yet totally recapped and some caps are SAMXON.
I hate Samwha and samxon and all other crappy caps, will replace all with Panasonic FC when I get them.
The ones in the signal path I may try to replace with something even better
Anyway I have the same drive voltage issue as many others here.
No blown trace on cap board.
I will check connections, but I think those are wrapped in mine too and not with a connector.
Interesting is that the amp was working, so PSU section cannot be totally faulty
One is perfect and the other has a Vgs of like 23V.
Jims was anyway helpful and promised to replace it for me.
The chinese seller I got the K60 from had to get negative feedback.
He was useless
Wonder what the rank 33 devices are??? Many chinese sellers have them.
I got some J28 K82 today, they might work too.
Anyway I got my amp and it was working, but one channel was very weak.
Turned out the weak channel had shorted VFETS, all of them.
I did the diode change (loosely matched) and a total recap of the PA board.
The PS board is not yet totally recapped and some caps are SAMXON.
I hate Samwha and samxon and all other crappy caps, will replace all with Panasonic FC when I get them.
The ones in the signal path I may try to replace with something even better
Anyway I have the same drive voltage issue as many others here.
No blown trace on cap board.
I will check connections, but I think those are wrapped in mine too and not with a connector.
Interesting is that the amp was working, so PSU section cannot be totally faulty
I'm going to repair a Wega VFET amp I just bought and I already ordered two 2SK60 rank 55.
I do not have the amp yet so I don't know if I even need to replace the VFETs.
Doesn't hurt to have a few spare ones though
I did some testing with 32V between D and S.
To get the current down to 30mA I needed to apply 12V between G and S on one VFET and 17V on the other.
This cannot be right or what do you think?
They should probably be within a few hundred mV if they are the same rank.
Paralleling these must be impossible!?
Same ebay seller offers rank 33 2SJ18...I would like to measure one
As per other members JUMA, ILIMZN and Nmos57 and even Mr. Pass, V-fets should be matched, see some discussion here http://www.diyaudio.com/forums/solid-state/241272-what-do-sony-v-fets-15.html
How did you measure your VFets , do you have a schematics and can you share it with me. I want to do it since I also have 2SK60 rank 54 and J18 ranks 57.. i want to try the designs posted in that thead and matched the devices for parallel mode.
Thanks
Thanks for the link to the other thread.
I did not see that one before. It sure has lots of useful info!
I have a 2x32V Thurlby Thandar powersupply (very good PSU, can recommend)
I set the two outputs in series and the one over drain and source to 32V 500mA
Then I measured voltage drop at VGS=0 (usually around half a volt)
Then the IDS=0 voltage, usually around 10V for good devices, 20V for chinese ones
Then IDS 40mA (just a value I thought about using for some reason) This was usually like a volt lower than the previous value.
From the TA-5650 schematic it was easy to figure out how the voltages should be connected.
Which schematic do you need?
The amp schematic can be found at hifiengine and other schematics I do not have.
I will sure send the one I have if you like?
I did not see that one before. It sure has lots of useful info!
I have a 2x32V Thurlby Thandar powersupply (very good PSU, can recommend)
I set the two outputs in series and the one over drain and source to 32V 500mA
Then I measured voltage drop at VGS=0 (usually around half a volt)
Then the IDS=0 voltage, usually around 10V for good devices, 20V for chinese ones
Then IDS 40mA (just a value I thought about using for some reason) This was usually like a volt lower than the previous value.
From the TA-5650 schematic it was easy to figure out how the voltages should be connected.
Which schematic do you need?
The amp schematic can be found at hifiengine and other schematics I do not have.
I will sure send the one I have if you like?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.