Right Channel Power Amp (X07-1440-00)
Every transistor on the right channel power amp board, with the exception of the Dual FET, was evaluated. None of them test shorted. All of the resistors were checked for value in circuit and only a couple of them weren't close to the rated value. Those two were pulled and they checked out fine.
I suspect either one of the the two 2SA810 (Qe3,Qe4) or the 2SC1452 (Qe6) were going bad though, as these are known to fail. They were replaced with KSA1381 and KSC3503 respectively. I also replaced 2SA673A (Qe7, Qe10) with KSA733C and 2SC1213A (Qe8,Qe9) with KSC945C. The heat sink mounted Qe11,Qe12 were given fresh compound.
Though they tested fine, I figured I'd replace the zener diodes while I was in there. For De1 EQA01-24 24V 500mA, I used a 1N5252B. For De2 YZ-140 14V 500mA, replaced with a 1N5244B.
R14 looked pretty shabby (see the before photo), so it was replaced with Vishay/Dale 1K metal film. Having looked at photos of other Model500/600 amp boards and also the parts list in the service manual, my board is the only one one I've seen use a 1K resistor in that position. The others all had a 100Ohm part. I verified that the left channel had a 1K installed also.
An orange low leak Elna CERB 10uf 25v capacitor is checked. Notice the ESR measures pretty poorly when compared with say a Nichicon PW of the same size and value which likely has an ESR half that. This is not an anomaly, all of the 10uf orange Elna low leak caps measure this way and seems to indicate the leakage current was of more importance to the engineers than the ESR.
One of the special features of the Model 500/600 Supreme amplfier is this Sony 2SK58 dual FET which is enclosed in this small, shielded metal case due its temperature sensitivity.
Here is the finished right power amp. I've squeezed three Wima 10uf 50v polyester caps in place of the 10uf 25v Elna CEBR caps at Ce5-8 and an Elna Silmic II 10uf 50 at Ce5. Each of the Vr trimmers were replaced with 3386H Bourns single turn. Vr1 and Vr2 got 500ohm, and Vr3 a 50K. Vr1 is the coarse adjust and Vr3 the fine adjust for the offset metered at pin 13 and set as close to 0mV as possible. Vr2 is the bias adjust set to 25mV while metered across pins 5 and 6.
Edit : July 30, 2018 : There is an error in the service manual that identifies VRe1 as the fine trimmer, and VRe3 as the coarse trimmer.
VRe1 is the COARSE trimmer (faced down on the amp board), VRe3 (faced up on the amp board) is the FINE trimmer. Read this
thread for further information on the adjustments for the model 500/600/650.
After a partial reassembly and the 4 Sanken outputs reinstalled I fired the 500 back up under full power. I set the offset and bias per the service manual and then shut down long enough to hook up a CD source to Aux 1 and have a listen through the headphones. The right channel distortion is GONE, just a nice clean signal now. As I said before, I can only speculate that I had a failing transistor at Qe3,Qe4 or Qe6 as all parts tested okay. A bit anti-climatic in finding the guilty part, but you can't complain with the end result.
With the repair completed it's time to move on to the restoration.