Sony TA-E86B Fault

[Chrisr3521]

I've come across a fault with my Ta-e86b where as at low volumes the right channel looses all low frequency and the channel goes out of phase with the left channel, pic of the scope traces attached, when the volume is turned up say 5db it corrects itself in volume and almost in phase, the fault? comes into play at volume control out.

 

[llwhtt]

C356, 57, 60, and 61 might have something to do with it. Compare the signal going in and coming out of those capacitors.

 

[Chrisr3521]

I've replaced those capacitors with one 10uf in each channel and taken out c308/358, I'll check I've installed correctly

 

[llwhtt]

The series connection, + to +, is a way to make a Bipolar capacitor. Did you use Bipolar capacitors? The Series/Parallel connection makes for a 10uF Bipolar cap. So the caps were replaced and the problem is still there?

The output relays can cause amplitude problems but not phase problems I wouldn't think.

What is the style of 2SC458? Outhouse looking? Those are on the "shoot on sight" list.

 

[Chrisr3521]

I just used 1 x wima mks2 cap to replace all four and bridged the connection where the capacitor in series would have gone, I've just checked all connections and they are correct. Yes the fault is still there.

 

[Chrisr3521]

The 2sc458's are the to-92 style case as far as I can tell there not on the bad transistor radar?

 

[llwhtt]

You say if you turn up the volume the problem corrects itself, what happens when you turn the volume back down?

 

[llwhtt]

What type of capacitor is C351?

 

[Chrisr3521]

I'll verify properly tomorrow but the fault only seems to happen on a small portion of volume control say between 10db marked on the volume control scale. Set underneath this is OK, above almost ok

 

[Chrisr3521]

What type of capacitor is C351?

It's original, I'm assuming a ceramic, is this part of the feedback loop?

 

[llwhtt]

C351 IS part of the feedback loop, increases feedback at higher frequencies, which in turn reduces the gain at whatever that frequency may be.

 

[Chrisr3521]

C351 IS part of the feedback loop, increases feedback at higher frequencies, which in turn reduces the gain at whatever that frequency may be.

Thanks, anywhere else I should be looking or is all the flat amp suspect?

 

[llwhtt]

IF the signal is good going to and from the volume pot the flat amp has to be the problem, Do the BASS BOOST outputs act the same way?

 

[Chrisr3521]

IF the signal is good going to and from the volume pot the flat amp has to be the problem, Do the BASS BOOST outputs act the same way?

Fault is on both outputs, also discovered a new fault which makes sence with the scope pin in post one, the left channel is outputting 10vdc at the output jack

 

[llwhtt]

Start comparing DCV from the schematic to see where the problem is.

 

[Chrisr3521]

Ok, so measuring dc voltage and relating to the schematic in the flat amp it all seems to be correct apart from the collector of Q302 which is 25v not 12.5 which I'm sure is an error. The -10v that is on output one NOT output 2 on the left channel is only evident on the R401 side of the new film capacitor that has been installed. The voltage seems to be coming from the relay side of R506 probing around this area seemed to correct this back down to essentially 0v dc, strange, could the reed relay be intermittently conducting? I don't see how this voltage can appear on the output?

 

[jean-paul]

Is the 2SK42 still OK? If it is leaky/defective you'll need 2 of them. No precise knowledge in JFETs but I happen to have 2SK30 in various versions new/unused.

 

[Chrisr3521]

It seems to be ok? The gate when the channels faulty is 10vdc, when not its essentially 0vdv, drain is 29vdc and source is ~0.48v, apart from the 10vdc fault this is the same in both channels I take it this is ok?

Q402 collector is ~0.3vdc and Q403 emitter is ~0.2vdc this is the same in both channels, not sure what to make of this?

 

[jean-paul]

You mentioned voltage on R401 to be off. Well when output 1 is used things float in the air at that side so it must be at the input.

Maybe I misunderstood so I am out of the thread. Good luck!

 

[totally analogue]

Sony loved those 2SC458 transistors which are known to fail. The odd thing is they measure fine on a DC test but stop passing audio. You can tell them as the legs go black. I recently refurbished a Sony reel to reel, low level one channel nothing on the other. Replacing the 458s brought it back to spec.