Sony TA-4650 odd channel drops

[bobdod]

Curious if anyone has any thoughts on possible trouble shooting or causes on a strange issue I am having with my Sony TA-4650. Every once in a while, the right channel just drops out and won't come back no matter what I do with the controls. Hitting the power button for a quick power off and back on again brings the missing channel back and it'll play fine for another half hour or so. The amp also has a "pop" on power off (even with volume fully attenuated). Not sure if this is a related symptom. Any ideas? The amp was recently restored (all electrolytics replaced, safety mods done, etc). The amp plays and sounds awesome otherwise.

 

[Vint Age]

Hitting the power button for a quick power off and back on again brings the missing channel back and it'll play fine for another half hour or so.

Did you change out the protection relay yet?

 

[bobdod]

Did you change out the protection relay yet?

Yes, I did.

 

[avionic]

Might try cleaning the pre-out and main-in jumpers.

 

[bobdod]

Might try cleaning the pre-out and main-in jumpers.

I cleaned everything thoroughly during the restoration, but I'll give them another cleaning. How would dirty jumpers cause a dropout that is resolved by cycling the power?

Also, this unit is powered on and off via a power strip. I don't use the on/off button.

 

[Vint Age]

How would dirty jumpers cause a dropout that is resolved by cycling the power?

Generally speaking, since they're plugin type jumpers the mating contacts can oxidize over time just like most switch contacts do. Cycling the power off and on breaks and makes the current that the contacts are carrying, momentarily refreshing them, especially if they carry enough current but it's usually short lived.

 

[bobdod]

Cleaning has not helped unfortunately and the issue persists. I'll put this together with another amp and see if the issue comes from the amp board or something else...

 

[bobdod]

Well, I can confirm that the issue still occurs when I use the main in jacks, so it's something with the power board. Today, the time between powering on and the issue occurring has also dropped some, so it seems as though whatever it is, it's getting worse. I've removed the amp from service. The board has new electrolytics, double diodes replaced, etc. I've really been enjoying this amp and this is really a bummer. List of parts replaced:

 

[avionic]

Did you deox-it the speaker selector wafer switch ?

 

[bobdod]

Did you deox-it the speaker selector wafer switch ?

The switch was disassembled and cleaned during the restoration. Binding posts were also installed (original terminals were screw posts). I've not tried connecting the speakers to the "B" terminals, so can give that a try if perhaps there is a contact issue with the posts or switch, but it's worked fine for a month before this issue appeared.

 

[002]

Hi @bobdod - did you ever get to the bottom of this issue? I have a 4650 that is doing the same thing.

EDIT: Never mind! I figured it out...and I'll post it here for posterity. The issue in my case was a flaky connection on connector 17 which is right at the top of the amp board and very easy to access. If I very gently jostled this connector while the amp was running the sound would cut out on the right channel. Actually, all the connectors in this amp are a bit crap honestly. Nice idea by Sony but poorly executed, and frankly, a bit scary given the sensitive nature of VFETs. It's probably a good idea to secure longevity by implementing sturdier connections - big job tho.

 

[bobdod]

Hi @bobdod - did you ever get to the bottom of this issue? I have a 4650 that is doing the same thing.

EDIT: Never mind! I figured it out...and I'll post it here for posterity. The issue in my case was a flaky connection on connector 17 which is right at the top of the amp board and very easy to access. If I very gently jostled this connector while the amp was running the sound would cut out on the right channel. Actually, all the connectors in this amp are a bit crap honestly. Nice idea by Sony but poorly executed, and frankly, a bit scary given the sensitive nature of VFETs. It's probably a good idea to secure longevity by implementing sturdier connections - big job tho.

I did manage to solve the issue, and it was different from yours. Turned out to be a bad solder joint on one of the resistors I replaced on the amp board.