picked up a 5550 vfet with matching preamp. Preamp works fine, no output though from the amp. Innards look like they’re caked with nicotine and I noticed d602 diode looks to be bad or at least disconnected. Is she a boat anchor? Sell for parts? Replace the diodes?
Sony TAN-5550 no output
- Thread starter betamax
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Check out this thread - it references "death diodes" so I think you just need to do some restoring and troubleshooting to get it going again: http://audiokarma.org/forums/index.php?threads/sony-tan-5550-build.726468/
The above. Depending on the circuit, no idea which one is right but I'm sure it went full bias or no bias with the diode gone. Hopefully the latter. That VD can be replaced with 2 1N4148's in series.
Vinylcafe
Linvin' the Dream
If one or more of those diodes is gone, you will be lucky if the VFETs for that channel surrvived.
No bias voltage kills them.
They come in matching sets - multiple sets per channel depending on amp.
One channel might still be good.
Finding another set(s) near impossible.
The multiple transistors in each channel should be identical ranking, though IIRC
Sony did allow for a one rank difference if need be.
Also you can have different rankings for each channel, as long as they are identical within that channel.
If this is the case, a different resistor will need to be added in the second channel to hit the proper voltage for the new ranking.
Here is the service bulletin that shows you how to check them.
All you need is a multimeter.
No bias voltage kills them.
They come in matching sets - multiple sets per channel depending on amp.
One channel might still be good.
Finding another set(s) near impossible.
The multiple transistors in each channel should be identical ranking, though IIRC
Sony did allow for a one rank difference if need be.
Also you can have different rankings for each channel, as long as they are identical within that channel.
If this is the case, a different resistor will need to be added in the second channel to hit the proper voltage for the new ranking.
Here is the service bulletin that shows you how to check them.
All you need is a multimeter.
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restorer-john
Addicted Member
When that service bulletin was written, most multi meters were analog and the ohms scale (x1) would swing a decent voltage (around 3v or so) across the probe tips. Transistors and diodes would indicate about 1/3 scale in one direction and infinite in the other. We got used to being able to tell a diode or transistor junction virtually instantly by the ballistics of the meter pointer, before it even stabilized. Ah, the good old analog days.
These days, practically every DMM has a diode range scale. Use that, it will give you a close voltage drop of around 0.5-0.6V on a good junction in one direction and open in the other.
These days, practically every DMM has a diode range scale. Use that, it will give you a close voltage drop of around 0.5-0.6V on a good junction in one direction and open in the other.
Well, I replaced the double diodes, reseated the vfets with new thermal paste, fired her up, and she works!!! At first I thought I had a bad right channel, but it turned out that the preamp (TAE-5450) isn't putting anything out on the right channel. It was before I cleaned it. I did notice that since I didn't put the wood sides back on but did put the cover on, the screws go farther in, allowing one to touch a board. I'm hoping that it just shorted out and with the screw no longer touching it'll work again, we'll see. But I'm very happy that the 5550 amp lives again!
Vinylcafe
Linvin' the Dream
Way to go!!
Not all stories of dead VD1221 diodes have a happy ending.
Good sounding amps.
Just be sure your bias voltage is dialed in right, as per service manual.
I need to learn how to do that. I did use thermal paste for the vfets, but the manufacturer states it has negligible electric conductivity. I figured that was ok, since you don’t want conductivity on your cpu processors either.
Can all the bias settings be done with a multimeter? I feel very fortunate that replacing the diodes brought it back to life.
Can all the bias settings be done with a multimeter? I feel very fortunate that replacing the diodes brought it back to life.
no, it is not OK to have ANY electrical conductivity.
if you want something betther than the average white goop, you could use some of the modern stuff, given that its dielectric perfomance is specifficly spelled out such as these:
https://www.newegg.com/Product/Product.aspx?Item=N82E16835186056&ignorebbr=1&nm_mc=KNC-GoogleAdwords-PC&cm_mmc=KNC-GoogleAdwords-PC-_-pla-_-CPU+Thermal+Paste+/+Grease-_-N82E16835186056&gclid=Cj0KCQjwgMnYBRDRARIsANC2dflYEEA_QqqN1XMnYuLqvjOPXDtMeccY6Oi6tbMdwPPlT0TJOtQ9AdIaAhShEALw_wcB&gclsrc=aw.ds
https://www.newegg.com/Product/Prod...lectrically_conductive-_-35-856-011-_-Product
Vinylcafe
Linvin' the Dream
What he said ^^^^^^^^
And yes, download the service manual, and set the bias per instructions.
There are test points and a pot for each channel of the main output board.
Let the unit warm up for 5 munitues or so.
Multi meter and small screwdriver is all you need.
Also, looks like Sony changed the bias voltage for your amp after releasing the service manual.
See this thread:
http://audiokarma.org/forums/index.php?threads/must-be-read-for-v-fet-5650-5550-4650-owners.74078/
Do some further research, but it looks legit.
I have the 8550, and have not worked on a 5550.
And yes, download the service manual, and set the bias per instructions.
There are test points and a pot for each channel of the main output board.
Let the unit warm up for 5 munitues or so.
Multi meter and small screwdriver is all you need.
Also, looks like Sony changed the bias voltage for your amp after releasing the service manual.
See this thread:
http://audiokarma.org/forums/index.php?threads/must-be-read-for-v-fet-5650-5550-4650-owners.74078/
Do some further research, but it looks legit.
I have the 8550, and have not worked on a 5550.
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do you have a color service manual for the 8550?
Here’s what I got at the local computer store:
https://m.newegg.com/products/N82E16835230014
I will go fully through it now that’s she’s show some life, I actually ran it with my ps-x75 and a Steely Dans greatest hits, sounded really nice.
So do I need to change thermal paste? It stayed remarkably cool while running for over an hour.
https://m.newegg.com/products/N82E16835230014
I will go fully through it now that’s she’s show some life, I actually ran it with my ps-x75 and a Steely Dans greatest hits, sounded really nice.
So do I need to change thermal paste? It stayed remarkably cool while running for over an hour.
Vinylcafe
Linvin' the Dream
Cool is good.
Assume that is why Sony lowered the bias voltage on the service bulletin, to cool those V-FETs.
By-the-way, they also ordered a resistor upgrade ... from 1/4 to 1/2 watt.
I would do that.
Likely a critical resistor that kills bias voltage if it fails (though have not looked at schematic).
As for the thermal paste ...
Users only rate it 3/5 to start ...
Then there is the issue of "negligible electrical conductivity" - what does than mean??!!
If it were me, I'd use these:
https://www.mouser.ca/ProductDetail/951-SPK10-006-00-05
They are single use pads. Do not over torque, or you will break through the material.
When Echowars was around here (resident VFET expert), these are what he always recommended.
I have used them in multiple rebuilds,any time I had TO-3 output devices.
They are also very neat, no messy paste all over the place. No clean-up.
If you have a meter, be sure to check the bias voltage, one way or another.
If you chose to lower it, up to you.
But lower voltage means cooler, means longer lasting.
What it does for signal quality, you will have to decide.
Vinylcafe
Linvin' the Dream
I have the original service manual, but alas no scanner.
Hifiengine has them for free download.
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