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Sony TA-E77ESD odd symptoms...

Z

zxryder93

New Member
Hello-
I picked up a TA-77ESD preamp, was supposedly in "great condition". Not so much, tested it and was going to to pass but got it for a reasonable "needs repair" price. So just thought to ask the expertise here for a starting point on areas to check.
  • It powers up, checked several inputs and they pass sound. Took off the cover, very clean inside.
  • The volume control passes sound at a constant low level for the first third of travel, no change as it moves, doesn't get lower all the way down. At about the 1/3 point, sound gets louder as I turn up but almost seems to be an increase in base rather than volume. (Same with output or the headphone jack, same in source direct or not.)
  • The balance control is odd also, loudest in the center then both channels drop some when moving either left or right (again, almost seems like a change in base tone rather than volume. In source direct balance does nothing.)
  • Tone controls do nothing.
  • I get a loud pop when switching inputs or changing to source direct.
So just looking for ideas on a starting point for figuring this out. Thanks in advance for any help!
 
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At the first, every single switch and potentiometer requires cleaning, the next repair cold joints, measure power supply voltages
 
I owned one of these preamps for 20yrs or so. I did always get a pop when switching inputs. I took it back to the store right after I bought it, but it didn't do it there, so I'm not sure if it's dependent upon how clean the power is, etc, but I lived with that issue and it never really bothered me, but it was also never loud enough for me to worry about any possible damage to my speakers.

I agree with above post on cleaning switches and pots and looking for cold solder joints. I would also look for any visible signs of bad caps - I read somewhere that the type of caps used in that unit can go bad in a fairly destructive way, but I don't remember the details.
 
Inputs are switched via relays as i remember, there should not be any pops when switching unless you are missing grounding connections somewhere, 100% there are cold joints on RCA sockets
 
Thanks for all the responses! I went through all the switches and pots with non-residue contact cleaner, no change. Opened up the bottom, looked for corrosion on solder joints, all looks very clean, no corrosion anywhere. Gave a good look at all components and didn't see anything unusual. Haven't checked any voltages and not sure about working on re-soldering yet since all looks good.

I connected to a Sony TA-N330ES power amp with a CD player, all inputs work and sounds great when I tweak the volume carefully. Listening more carefully, the volume control seems to be working the treble. Sound gets louder but seems to be only mids and highs going up with bass staying the same. Even seems like I hear a little reverb effect when I turn it way up. Balance control seems to just decrease treble when turning left or right. Mute button works normally on left channel, minimally on the right.

I'm thinking this involves shorts between volume, tone, and balance. I will look at schematics but wouldn't a bad volume pot be a good possibility? I'm thinking to start by testing it, it's an ALPS 120K with motor control.
 
zxryder93 said:
Thanks for all the responses! I went through all the switches and pots with non-residue contact cleaner, no change. Opened up the bottom, looked for corrosion on solder joints, all looks very clean, no corrosion anywhere. Gave a good look at all components and didn't see anything unusual. Haven't checked any voltages and not sure about working on re-soldering yet since all looks good.

I connected to a Sony TA-N330ES power amp with a CD player, all inputs work and sounds great when I tweak the volume carefully. Listening more carefully, the volume control seems to be working the treble. Sound gets louder but seems to be only mids and highs going up with bass staying the same. Even seems like I hear a little reverb effect when I turn it way up. Balance control seems to just decrease treble when turning left or right. Mute button works normally on left channel, minimally on the right.

I'm thinking this involves shorts between volume, tone, and balance. I will look at schematics but wouldn't a bad volume pot be a good possibility? I'm thinking to start by testing it, it's an ALPS 120K with motor control.
Click to expand...
Do you ever resolve this issue? I just purchased one of these units and there's absolutely no mid-range volume. Vocals are almost completely muted (at all volumes).
 
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