Help Troubleshooting Audio in One Channel Only + Hum

[SDup]

I was listening to a record on Friday when the audio decreased suddenly. I checked my setup (description below) and I noticed that the left channel was dead. When I use balance to isolate it I get a hum (loudness increasing with volume) and when I turn the volume up to at least 50% I can hear very faint music in background. Right channel is perfectly fine.

Here is what I tried to locate the problem (after looking at several AK posts):
- Different input (AUX, FM) = both channel work (so the problem is not with the speakers)
- Reverse the RCA cables = the dead channel (and hum) switch to the right (so the problem is not the phono stage but maybe the RCA cables?)
- Disconnect / reconnect the cartridge and clean the headshell pins with Q-Tip + alcohol = no luck.
- Remove and reinsert the stylus = no luck.

So I suspect the culprit to be the left channel RCA cable? Unfortunately the RCA cables are fixed on my turntable. I also doesn't have another cartridge to try out.

Should I have my turntable looked at by a profesionnal? Is there any other steps I can take?

Any help will be greatly appreciated, I saw so many problems get fixed on this forum, I hope this one can be one of them!

SETUP
- Mitsubishi DP-EC8 turntable
- Sansui 551 amplifier
- Ortofon SuperOm 20 cart

 

[revox-b77]

Do you have a digital multimeter? You can check the resistance of the cartridge pins L+ to L- and r+ to R-. You should get a few hundred ohms each. If it reads no continuity the cartridge is dead. You can also use the meter to check from the cartridge leads from head shell to RCA outs.
Figure out which one has no continuity.

 

[SDup]

Do you have a digital multimeter? You can check the resistance of the cartridge pins L+ to L- and r+ to R-. You should get a few hundred ohms each. If it reads no continuity the cartridge is dead. You can also use the meter to check from the cartridge leads from head shell to RCA outs.
Figure out which one has no continuity.

Resistance is good on both channels on my cartridge. I also checked RCA to the pins in my tonearm (RCA tip and RCA shield) and I get connectvity (beep) on all four. I have a Mitsibushi DP-EC8 with a straight tonearm, the pins are inside the tonearm not on the headshell unlike most turntables.

So I checked for resistance by touching the multimeter pins inside the holes in the headshell (this type https://www.turntableneedles.com/mitsubishi-model-dp-ec8-headshell-str8hs-mitsubishi-dp-ec8) and I get resistance on one channel only. I think this may be it so I ordered another headshell.

Will keep you posted!