Hello. Unfortunately, in Sony STR-DB 940, 840 receivers the system responsible for switching sources often breaks down. It is located on a vertical board next to the tuner board. I had two such receivers on my desk, one of which I was able to repair only because I managed to buy a functional selector board. The system itself is missing and is designated TC9273F-012. Measure the voltages supplying this system, pins 1 and 28 (first and the latter) relative to the ground. They should be -15 and +15V, if they are lower, then the system is 99% damaged (be careful not to short-circuit, because if the system is operational, then it would be a shame to destroy it). You can take measurements on one of the op amps on this board (pins 4 and 8) since they are powered by the same voltage. Perhaps on the entire +15 and -15 V rail going to this board.

@Oklawolf

6 ай бұрын

Very likely that's the problem with this unit. I can't see all three op-amps failing simultaneously, and both voltages were there.

@alexanderguzeev

6 ай бұрын

I think you're right. There are 4 common faults with these amplifiers. 1. Poor soldering in the area of the output transistors and DC protection relays. 2. Failure of TC9273F-012 (There is no sound from the 5.1 input but there should be when connected Optical. 3. Failure of IC1503 Converter AK4527 (The sound will be distorted). 4. Failure of IC1201 System controller MB90573PFV-G-296 -BND (As happened with my copy of the receiver. Symptoms are strong heating, no sound, the menu works with strong delays.) Signal to DVD/LD in Optical, I think there will be sound.

@Oklawolf

Ай бұрын

4 months later and I now have a working MD unit with optical out to try with this receiver. It does pass sound using the optical inputs but it's still very quiet. So the TC9273F has definitely failed. I think IC1503 may have also failed.