Technics SU-G50 Amplifier

[hillbilly]

Hey,

I'm new to electronics, so go easy on me.

I'm trying to fix this Amplifier, I get perfect sound from the right channel and very faint sound from the left channel.
So far I've fixed a couple of dry joints, and cleaned the speaker switches with electrical cleaner, but still no sound from the left channel.

I'm thinking it probably a capacitor on the amp section, but I can't find a schematic and I have no idea what I'm looking for to be honest.

here's an image of the board if that helps.

[bob_m_54]

Did you also clean the pots? volume, balance etc?

[GT250]

Besides cleaning the pots as BM54 says, I'd suspect that if you have found some dj's there might be more...

You could try a freezer spray on an area that might think is at fault. And visa/versa a hair dryer as well.

Sorry for the 'basic' level, but you never know...

[Uncle Fester]

From my experience with these things it is often the STK block (the big black thing, may start with SAK or similar but usually STK ) in the power amp section.
Without any means of signal tracing (oscilloscope, signal generator or at least a test amplifier) it will be difficult to track this down.
Sometimes when you probe with a metallic tool you might hear it clicking or humming out of the attached speaker but you shouldn't touch it with you bare hands unless you are 100% sure what you are doing. The power supply could be 100V (+/-50V) or more. You could use a resistor 100k as a probe.
The two caps left of the words 'power amp' look like the input and you could touch probe on those without touching anything else!

I would re-solder EVERY joint in the power amp section and surrounding area. It looks like it may have suffered from heat.
The electro Caps in the power amp section could be also damaged from heat. If you don't have an ESR meter you will have to start replacing them one by one or better all. Watch the polarity, voltage and heat rating!
I believe this may be a Class A amplifier and it always gets hot.

A fault with the fan or it's control circuit could also be the cause of overheating and damage to the STK.
It will run only when things get hot but with a hot air source, maybe hair dryer over the heat sink you might be able to test it's function.

[BCNZ]

Agree with Nomeat. I have repaired plenty of Technics amps (I specialise in vintage audio and Technics is a favourite of mine) and these amps with the audio output ICs were not one of Technics' greatest designs.
The ICs can give all sorts of problems from no sound out at all, to sound on one channel only, low sound (as in your case), rail voltage on one or both outputs (relay won't pull in) and anything in between. The ICs are obsolete now, although they can still be obtained from a few places online although I'd doubt their reliability.
Many a nice amp has been laid to rest simply due to a faulty output IC.
It's still worth checking other components and for dry joints etc anyway, as it's not a given that it's the IC in EVERY case.
Take extra care however if you are tinkering around with the power applied.
The output IC is VERY susceptible to being damaged if you accidentally short any of its pins together.
The number on the IC will probably start with 'SVI' - it's the Technics prefix for the STK series of power output ICs.