From my tech: The diodes, 2 per channel, are designated H720, H721. If they are a small black diode, they should be replaced with 1N4148 diodes. Be very careful of the polarity. Also, look for any glue on the top or bottom of the boards. If there is, it has probably turned black and is possibly conductive. Carefully scrape it off. After the repair, set the D.C. offset adjustment R741 for 0 volts D.C. at the speaker outputs. The other adjustment is for bias and is a trickier adjustment. You should not need to adjust this unless the amp tends to run hot with no signal after being on for 10 to 15 mins. The 1N4148 diodes should be available at any electronics shop. Rich