Posted: May 9, 2018 1:37 pm
What you have more than likely is a set of, or at least one shorted output transistor. I am currently working on a 2220 for a customer, and ahve swapped out the left channel output transistors. When lloking at it on an Oscilloscope (Yes haveing one of these helps a lot, but you have to know what cut-off distortion looks like), The Upper voltage excursion gets cut off early in the Volume profile, even after following the alignment procedure in the downloaded for free Service manual. There are no Relays in this earlier model, but a feedbad current sensor design that keeps the system from expending excess current. I suspect one of the transistors in that circuit also being poor, or leaky, and will come back & tell you when I find it. The output of ALL amplifiers is AC, so incorrectly connecting the speakers doesn't cause an issue, other than a phase reversal of the sound, and bad bass response due to the low end being cancelled out. It is purely a listening problem, Not a hardware issue. If you have a leaky output cap, passing DC, instead of AC, it will show up on the scope as a DC offset when measuring the speaker outputs on a DC setting, or you can simply hook up a dc voltmeter and see if there;s a dc voltage at idle, with no input at moderate volume. Scopes are cheap. I bought a 20 MHz one for $50.00 at a thrift shop last saturday, and you can get a reasonably good Tektronix for around $100.00 on ebay from a few silicon Valey surplus houses. I suggest you get one if you are going to work on thois stuff, along with an Isolation transformer to connect the AC supply to whatever you are working on. Keeps things from going Kaboom!