S.E.X. dead in left channel.

[hibuckhobby]

It was fine a couple days ago.  Turned it on today...tubes lit up, but no
left channel sound.  I've given it a close visual inspection, but since I didn't
build it and don't have a schematic...I don't even know where to start.  It
has the CS4 and impedance switches.  No sound at speaker terminals or
left channel on headphone.  Where to begin?
regards,
Hibuck...

 

[hibuckhobby]

OK...the "back" two led's are lit...the front two aren't?  Help?

 

[Doc B]

Give us voltages, that's always the place to start when LEDs won't light.

 

[hibuckhobby]

OK...given that I have no schematic I have looked up some voltages I should check.
Here is what I have so far:

0A=61.5  0B=0
T15=19.5  T25=19.4
A2=380  B2=0
A5=61.5  B5=0

With my limited knowledge...it seems that one side is testing OK and the other is not.
Where to start looking?
thanks,
Hibuck

 

[Paul Birkeland]

You have a loose power supply connection feeding the left channel, though it is really tough to tell where it might be since we can't be sure which SEX amp you have.

Can you post a photo of the underside of the chassis?

 

[fullheadofnothing]

It has to be a 2.1, Paul. Impedance kit can't go in a 2.0, and the 2.0 uses the little C4S boards, so no OA/OB...

 

[Paul Birkeland]

Ah, yes indeed.

In that case, I would be looking at the red wire that runs to terminal 20.

 

[hibuckhobby]

OK...I have over 360v both to 1A and 1B
ON 0A I have 61.5 v  on 0B I have nothing
and therefore nothing going to B5.
could it be the transistor for the left side on the CS4?
Either th TO22 case or the small round case?  BTW
I have 385v on one side of both LED's as well, but
w/o a schematic I'm lost as to the current flow.

Also...if I have voltage on one side of the LED's...
where are they grounded?  Is it through one
of the transistors or are they a part of the circuit and
possibly blown?

regards,
Hibuck...

 

[Grainger49]

You have a good side and a bad side.  Compare the components on them and verify the transistor leads are the same.

 

[hibuckhobby]

It just about has to be the 5731 transistor.  There is voltage on the emitter pin,
but not on the red wire.  I just redid the solder connection...no difference.
On the "A" Side, there is 370 in and 62 on the wire.
Is my reasoning OK?
HIbuck...

 

[Grainger49]

Can you measure to the trace that the 5731 transistor emitter is soldered to?  This will verify that the emitter is well bonded. 

If that is the last element before the output then the solder joint or wire at OA could be the problem.  (I don't have a manual or even a schematic so I'm at a loss for the circuit layout)

 

[Paul Birkeland]

It just about has to be the 5731 transistor.  There is voltage on the emitter pin,
but not on the red wire.  I just redid the solder connection...no difference.
On the "A" Side, there is 370 in and 62 on the wire.
Is my reasoning OK?
HIbuck...

Yes, resolder the center pin and you should be good to go.

 

[hibuckhobby]

Sadly, it made no difference.  My primary struggle is that since I
bought this from the person who built it...I have no schematics.
If there is anyone who would forward me a CS4 schematic...that would be
a great place for me to start.
regards,
Hibuck...

 

[Paul Joppa]

I don't suppose there's any chance you can get the manual from the person who built it? The manual has circuits and diagnostic information. If you can't, call or ping Eileen (Bottlehead - More - contact us - shipping status for her email, she's the Queen!) and ask about ordering one.

 

[hibuckhobby]

through the generosity of a person on another forum, I now have the construction manuals and schematics
for the CS4 and the S.E.X. amp.  I have parts coming and expect to be operational within the next couple
of days.
regards,
Hibuck....