Marantz 2275 Receiver - No Sound Left Channel

[AudioScout]

Receiver: Marantz 2275
Problem: No sound, left channel. (Both Speaker and Headphone)

What I've done so far:
Connected the main out and in via RCA and swapped the cables. Left Channel still out.
Swapped P700 Output board positions. left Channel still out.
Swapped Output capacitor positions. Left Channel still out.
Sprayed with Deoxit and thoroughly cleaned. Left Channel still out

Initial problem
Protection relay was kicking in after receiver warmed-up. Both channels were working at the time.
I replaced some caps, transistors and the relay on the board and the protection issue was solved.
Some time after, the left channel went out.

I am assuming the problem still lies on the protection board.
I've swapped out a couple of transistors and capacitors again to see if my components were bad with no change.

Thoughts on how to further diagnose?

 

[dankik]

What I've done so far:
Connected the main out and in via RCA and swapped the cables. Left Channel still out. (L channel of Main Amp issue)
Swapped P700 Output board positions. left Channel still out. (Both L & R channel P700 boards functional)
Swapped Output capacitor positions. Left Channel still out. (Not the output caps)
Sprayed with Deoxit and thoroughly cleaned. Left Channel still out (???)

I replaced some caps, transistors and the relay on the board and the protection issue was solved. (Probably not the relay, but we can test later?)

The audio signal path (red dotted line) from the L channel relay output to the L speaker is entirely passive so we can check continuity by measuring resistance from the relay output at J807 to the speaker binding posts for Left channel, Main & Remote.

• Set your DMM to measure Ohms. Make sure 2275 is powered off and unplugged.
• Connect one probe to J807 and the other to L Main or L Remote speaker terminals. Make sure to push in both Main & Remote speaker switches.
• You should have continuity. If not the issue is the speaker switch.
• The other thing to check is whether the L channel headphones work OK. (The headphone outputs do not go through the speaker switches.)

The other issue could be that you are not getting power to the Left Channel P700 board.

• With power on, check the voltages at P700 J709.
• Set your DMM to read DCV and clip the black lead to chassis ground, then measure the voltages on J709.
• You should get +48VDC and -48VDC on two terminals (the other 2 terminals are GND and audio out)
• Also, check continuity from the L Main In RCA jack center conductor to J710 on P700.