Pioneer Class AB Integrated Amplifier A-2050

Overall, there are noticeable scratches and dirt.
In particular, there is a chip in the heat sink (image 11) and a chip in the power connector (image 8).

The operational checks were as follows:
The power turned on normally.
The SPEAKERS A/B switch functioned, and sound was confirmed from both.
BASS and TREBLE also functioned.
The TONE switch seems to have faulty contacts; switching it caused the sound to disappear from one channel, or sound would come and go with just a slight touch without fully switching the switch.
SUBSONIC 15Hz was not clearly understood, perhaps because there are no speakers to demonstrate the effect.
BALANCE confirmed changes in the output of the left and right speakers.
The VOLUME knob initially had crackling, but it disappeared with use.
LOUDNESS confirmed a change in the sound output.
I'm not quite sure how to use TAPE MONITOR, but when switched, the volume became extremely loud and distorted.
FUNCTION switched between the three inputs normally.
Therefore, PHONO, TUNER, and AUX inputs on the back all worked. Also, the volume levels were different.
TAPE was unchecked due to lack of environment.
The LR of SPEAKERS A and B were both normal.
All three AC OUTLETS were confirmed to be functioning normally.
The top two were linked to the amplifier's power switch.
The POWER and TAPE MONITOR lamps on the front panel also lit up.