OK, thanks Stereoguy. Just spent some time running tests and have a lot of great info here.
I tested every pin on both ICs, IC601 and IC602. I am using the values on the schematic here to validate. At least with the online schematic I can enlarge it, but I still can't really make out all the numbers.
http://akdatabase.org/AKview/albums/userpics/10006/Technics SA-200_200K SM.pdf
From the schematic, it looks like the values should be
0 = 1.36v??? (can't read it)
1 = -1.2v???? (can't read it)
2 = -31.4v
3 = 0v
5 = ??? marked but no value
8 = 0v
9 = 31.4v
I did note that pins 4,6, and 7 are not soldered to anything. So I would expect 0v for all those and that explains why they are not marked. And that was the case when I measured both ICs, so I will omit here.
When I measured IC602 (right channel):
0 = between 1v and 2v
1 = about -.1v
2 = -31v
3 = 0v
5 = 31v
8 = 0v
9 = 31v
When I measured IC601 (left channel):
0 = 11v
1 = 7.5v
2 = -31v
3 = 18v
5 = -30v
8 = 18v
9 = 31v
So it looks like IC602 is pretty much on the mark. I can't confirm pin #5 is correct because I don't know what is the expectation, but given the rest are ok, and the DC offset is not completely 'whack' on the right channel, I think that IC is ok.
The left one, IC601, is clearly whack. And that channel is the one that now has a standing DC offset of 20V when on (and, interestingly, 5V when off). So it looks for certain that I fried it.
I ordered a new one from this seller on ebay. Hope this one is legit.
http://www.ebay.com/itm/STK0029-Hea...385881?hash=item1c56cd6619:g:aMwAAOSwa-dWs1KR
If anyone has any better places to go to get good electronic parts, please let me know. I assume Radio Shack is useless at this point.
I know I need to continue following the signal path to see if anything else might be fried, but I'm not real sure how to test each component. If anyone has a reference to point me to, please do.
...And then since I was getting more comfortable with the probe, I decided to try to see if I could get the DC Offset on the right channel, which was still the original 80mv, back to zero.
So I experimented with a bunch of different resistors shunted to R614 (again, following Ecluser's advice at the beginning of the thread).
Here's what I found:
No shunt (orig) ==> 80mv dc offset
51ohm shunt ==> -.22 mv dc offset
150ohm ==> -13 mv
200ohm ==> -.11 mv
300ohm ==> .-07
430ohm ==> .-035mv
560ohm ==> -.015mv
620ohm ==> .005mv
680ohm ==> 0 mv
750ohm ==> +1mv
The R614 was a 471ohm resistor to begin with. So does this imply that I can either add a 680ohm in parallel, or if this equation is correct: 1/R = 1/R1+1/R2, then I could replace the 471ohm resistor with a 280ohm one to get the offset pretty darn close to zero? Or could there be a different reason / root cause for the 80mv DC offset (which sounds really good right now compared to the 20V on the left channel).
While I've created my own problems today, I've learned a lot, and I am eager to learn more here. I tend to get obsessive about new hobbies, and I am looking to soak up knowledge from other members and would appreciate good references to learn as well. I was an engineering student in the day, and still have my Electrical Engineering text book from 30 years ago on my bookshelf 2 feet away from where I type (of course I think it's been sitting there untouched for the last 20 years). I believe I have the background and capacity to learn and certainly have the interest.
That being said, I would certainly appreciate any guidance related to my issues above and/or explanation for why things happen.