Technics SA-203 with DC offset

[klamsoss]

A friend of mine brought me the above mentioned receiver hoping I could fix it up for an office system for him. It's a compact little unit with decent specs and some trick looking panel functions for the tuner section.
The original issue was that it wouldn't turn on. I figured it might be a dead switch, which would be easy enough to remedy. Turns out it was even easier than that! The fuse was missing!
With a suitable test fuse in place and some test loads, everything came on as it should and the tuner seems to lock on stations pretty well.

BUT

There is DC offset, and not a little. I'm getting 50mV on one side and a whopping 0.3 V on the other. There are no trimmers for offset adjustment. The amp section is an all-in-one module. I have perused the threads on here and see that I could tweak the resistors driving the amplifier module, but that fix seems only to have been applied with relatively limited offset correction in mind.

I'm thinking there is probably something going on that is more significant than can be fixed with a few swapped resistors. I figured I would inquire here to see if anyone had some easy input for how I might resolve the issue without resorting to the shotgun method of replacing tons of stuff and hoping for the best. That's a poor method for problem solving to begin with, and I don't want to sink a lot of time and parts into this unit without some reasonable idea that it'll work. Even in good shape, this thing is worth no more than a hundred bucks or so.

If I can't find a solution, I'll probably throw it on BT for the cost of shipping. Seems a waste for a unit like this to go in the bin when so much of it appears to be working just fine.

 

[spark1]

Pehaps the differential pairs?

 

[SVI2004A]

Iirc this is STK2028 ot STK2038 but DC balance is controlled by 2x AN7060 - can try swapping them over and see if dc swaps channel

 

[spark1]

Iirc this is STK2028 ot STK2038 but DC balance is controlled by 2x AN7060 - can try swapping them over and see if dc swaps channel

Ahh, good info. Those are hard to find (as are the STKs). Swapping is good way to see if it is the problem.

 

[klamsoss]

Iirc this is STK2028 ot STK2038 but DC balance is controlled by 2x AN7060 - can try swapping them over and see if dc swaps channel

Yeah, it has the STK2028 module in it.

So, swapping them, if the dc offset migrates with the AN7060 then I know the faulty component.
These appear to be out of production. The bay has some chinese parts for $14 but as we know, those can be a roll of the dice. Appear to be some in the UK but at $40+ with shipping, that doesn't make a lot of sense.

I will poke around some more and see what I find out. The pain part is that accessing the bottom of the board on this thing means taking apart the tuner string, I think. I have a poor track record of getting them back on the right way... I always end up getting there but it's usually a major headache.