V-fet Repair of a WEGA V4810 solid state heaven

[Mooly]

Originally Posted by miklos

"Or does that defeat the whole object of owning one of these"
Yes.
They would become Hitachi amplifiers from the seventies.

Fair enough

[Klipschorn dude]

Originally Posted by miklos

The VFet's are now only available from littlediode in England. Here's the ebay ad:
2SK60 Transistor x 1 pieces - - eBay (item 380175321852 end time Mar-06-10 11:00:13 PST)

2SJ18 Transistor x 1 pieces | - eBay (item 400074931993 end time Feb-20-10 01:45:47 PST)

They're pretty expensive and they are made by Hitachi, not Sony. On the ebay ad is no picture.

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

[miklos]

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

[Klipschorn dude]

Originally Posted by miklos

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

Thanks again miklos. I'm in no hurry to ruin the v-fets, so I will track
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

[eyoung]

I own a B2 the rails run 58V +/- pretty solid amp as I have beat it up pretty bad and it still works, If I could get the meter board to work...

Regards, Elwood

[Klipschorn dude]

Originally Posted by eyoung

I own a B2 the rails run 58V +/- pretty solid amp as I have beat it up pretty bad and it still works, If I could get the meter board to work...

Regards, Elwood

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

[Klipschorn dude]

Originally Posted by miklos

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

Hello Miklos. The only Service Manual I have is downloaded from The
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

[miklos]

I think if it worked before with those values it should work now to.
Is the PS B2 voltages are symetrical if you load it with the resistor only?

[Klipschorn dude]

Originally Posted by miklos

I think if it worked before with those values it should work now to.
Is the PS B2 voltages are symetrical if you load it with the resistor only?

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

[miklos]

Hello K dude,
Yes, with all the VFet's out disconnect the B2 +- lines from the PS board and hook up the resistor with a piece of wire there. This way you would be one step further to isolate the problem being on the PS or the PA board. The diodes seems to be OK.