Sony TA-4650 Death Diodes?

diesel1024

diesel1024

New Member
Hi guys. Long time lurker.

I just picked up this Sony TA-4650 from an estate sale and as I was reading up on it, I noticed multiple mentions of so called "Death Diodes" that need to be replaced. I have powered it on and it seems to work great, just concerned about the diodes at this point. I looked inside the unit and everything looks factory, but I noticed the heat shrink around the legs of the death diodes (D414. D352, D302) on my unit are black, from the photos I saw online, other's have been clear. Can anyone verify if this means these have been replaced? I looked on the back of the board as the solder joints and they look exactly the same as the rest. I'll likely end up going through everything and recapping it in the future, but I do not currently have the time or means. I'm not super sure on how photos work on here, but I attached an Imgur link with the pics!

Thanks all!

Jack


https://imgur.com/a/UHbKlXN
 
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Hmmmm… what is that white fuzzy stuff wrapped on the diodes. The replacements I saw in researching my TAN-5550 was a pair soldered in series. Perhaps that wrap is actually the body of the diode? They are quite small.
 
Lots of good VFET restoration info in this threads.

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Sony TA-5650 v-fet matching and 1N4148 diodes

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I just love the title "Death Diodes". I have no experience working on this unit. From the picture of the board it looks like a ->-> marking, correct? Also pictured is an original appearing blue dot diode. A VD1212? Is that the Death Diode here? I do know those are prone to fail. If it's in your bias chain the failure can be spectacular. If there is threads devoted to them, and referred to as Death Diodes, I think I would put it at the top of the list to have them replaced.
 
Warren-Oates said:
I just love the title "Death Diodes". I have no experience working on this unit. From the picture of the board it looks like a ->-> marking, correct? Also pictured is an original appearing blue dot diode. A VD1212? Is that the Death Diode here? I do know those are prone to fail. If it's in your bias chain the failure can be spectacular. If there is threads devoted to them, and referred to as Death Diodes, I think I would put it at the top of the list to have them replaced.
Click to expand...
I'd have to agree, I looked at a photo of a VD1212 and it looks like what is in there. I'm gonna pull one out to verify that it is indeed a VD1212. Just seemed odd with the black heat shrink. I have some 1N4148 diodes on hand that I should be able to substitute them with, easy enough. Not worth the risk regardless, speaking the Vfets are incredibly expensive and theres like what.. 6 of them and they all need to be matched? I'll probably just replace those and use it for a while until I have the time to go in and do all the service bulletin stuff and replace all of the nearly 50 year old capacitors. Also, nice to see a fellow Minnesotan!
 
diesel1024 said:
To the best of my knowledge it is some kind of thermal goop (almost like thermal paste) to keep both of those components at the same temp? For what reason, I have no idea.
Click to expand...

Yeah, that is the reason. Sometimes it's for keeping matched pairs operating as closely as possible together, sometimes for better bias tracking/compensation, etc.
 
Warren-Oates said:
I just love the title "Death Diodes". I have no experience working on this unit. From the picture of the board it looks like a ->-> marking, correct? Also pictured is an original appearing blue dot diode. A VD1212? Is that the Death Diode here? I do know those are prone to fail. If it's in your bias chain the failure can be spectacular. If there is threads devoted to them, and referred to as Death Diodes, I think I would put it at the top of the list to have them replaced.
Click to expand...
Why are they called that?
 
Man that's nasty. I found at leased three in the Sony TA-3200F amp I restored. Two on the amp oard, one on the power supply board. The two on the amp board introduced noise. I just used two 1N4148's in place of each one. I think they were VD1212's?, if I remember right.
 
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