Is it a lab power supply?
This topology looks like the typical voltage reference + opamp setup. The core of a lot of supplies.
Also: the electrolytes seem to be Philips. They should be toast by now, as you realized.
Seems to be 2 components missing from beginning, but there was sound anyway
have you removed this one?
These two were missing from the start, my first thought that it might be the same as the other one you marked, but the other one in middle i do not know.
These two were missing from the start, my first thought that it might be the same as the other one you marked, but the other one in middle i do not know.
the other one in middle i do not know
If the two holes are connected to the opamp pos and neg supply, I expect it's for a decoupling capacitor
looking at the photo of the solder side, looks like there wasn't ever something mounted there. The pads look unused.
Not unusual on TUAC amp modules for resistors to be omitted or even cut off
There is a name for that. It's "munching" (edit - Muntzing) or something. Named after a USA electronics company owner that would walk down the production line and randomly cut out components.
If the device still passed the QA, the component was removed from the BOM.
They all still work ok. TUAC were always changing their circuit designs. I've got 5 TD150 amp modules that are all different, ranging from a few resistors to number of transistors
I have a TD300 amp which is just a TD500 with a pair of output transistors omitted