Few things here:
1) Do not remove the output MOSFET's before doing bias and DC offset adjustments. That said, I do recommend removing them (one at a time, if you want to be really careful) to clean off the old thermal grease and add fresh). These run warm, and it's better that the whole heat sink get hot than just the hard-to-find Hitachi parts themselves, if they aren't transferring heat well across the old dry grease barrier.
2) You can use any standard red LED. I made a jig by soldering the two together anode to cathode and vice-versa, then also attaching a 2-wire harness with connector at the end - there are places you can plug that in on some Tandberg amps.
3) That said, they did not provide the same 2-pin connectors on the 3012/3012A but if you put a small spring-loaded and insulated wire grip fitting (like test leads come with) on the ends of the two wires coming off the LED fixture, it will facilitate clamping them to the two differential pair transistors the manual calls out (Q415/Q417 for the left channel, and Q416/Q418 for the right channel). You need to do that with the power off and rail voltages down to minimal values, and make VERY sure you are connecting to the collectors of the two transistors.
4) The reason for this jig is you get a very quick visual reading for DC offset and it's easier to zero in on the balance point where both LED's go out. I use that jig together with a voltmeter on one of the two speaker outputs so I can get as close to zero as possible after reaching relative balance between +/- sides via watching the LED's.
5) The DC will tend to lope up and down a bit so give it time to settle after you stop adjusting, then check the speaker terminals for offset and tweak again very delicately, as needed.
6) IIRC, getting to R615 and R616 to clamp on to them for doing the bias adjustment is no picnic and I've typically stabbed a sharp meter lead into the two suitable solder pads instead, but you need to be ultra careful not to let either tip slip off the pad while adjusting. And yes, quiescent current = bias. Follow the instructions on that including the 30 minute pre-heating part and keeping the covers in place or otherwise covering it to get up to operating temp.
7) I'd definitely check the RIAA DC offset along with the tone control amp as there's a good likelihood there's enough DC offset to cause popping when you change source or other issues (distortion etc.) if you don't. You'll have to make a couple of RCA dummy plugs with resistors to match the loading requirements for the different RIAA section adjustments. Be careful with clipping onto component legs in that circuit too, easy to short something out by mistake if you get in a hurry.
John
