Case # 769877 . 03.27.2026 . Adcom GFA555 ii amplifier. Missing left channel.
Interesting case. Fuse – ok, right channel is ok. 82 volt DC on the left channel speakers plugs. Speaker start smoking. Powerful amp for someone who loves power.
Most Adcom amplifiers don’t have a protection circuit in the schematics, so the results are standard. If something happens, speakers take a direct hit from the amp’s output section. This case is interesting because even after issues like that, all output transistors are still alive, meaning good-quality components were used. Found a bad driver transistor 2SA1210 on the input/driver board. We changed all input and driver transistors and plus 8 pin Opamp IC . Channel starts working, but DC OFFSET is more than 2 volts, and it is not good. Bias not in range also. All new parts we used were purchased online. Finally , after couple more hours of troubleshooting we found that the new IC LT1006 we purchased online is bad. Next time, we’d better use new old stock parts, we trust them more than new production. Bad IC,S on the last image.
