388 Headphone and Monitor hiss right side only. Solved!!

[Halloween3]

Hi glad to have joined the group! I picked up a Tascam 388 in non functioning condition and have quickly made it functioning at least as a mixer. I even used this site to help me stop crackling noises from the monitor pcb board so thanks! I am now tracing back a loud hiss that is like an over exaggerated “noise floor” sound from only the right headphones and or right monitor. The stereo outs sound perfect no issue over there and the hiss can only be made worse or better with the headphones/ monitor volume knob. Should I be thinking about replacing something on the heaphones amp pcb? Thanks- Brian

 

[Halloween3]

Update: I reflowed the solder joints to the pcb and connections to the “microphone amp board” checked the volume pot for resistance and when I plugged it back in and powered it up there was a pop and the hiss got louder (right sided) as if whatever was going bad finally went, unfortunately the headphones signal and monitor signal was lost completely.

Some adjustment of the main connector buss board (was loose at channel six where I had my drum machine for testing) it quickly brought back the left stereo signal clearly again in the phones and monitor but the right side signal was still a wall of noise.

On the headphones board I shotgunned the U101 and U102 chips and things were maybe more stable but no major change. Then also replaced U103 op amp and this got rid of the nasty hiss but never brought back my right side signal. Any idea where I can trace back the lost right sided signal?

I’m thinking maybe another op amp on the monitor pcb board. I was trying to get voltage readings but my meter doesn’t seem to read millivolts in ac only dc which does give me some readings coming off the monitor pcb and I know I’m at least getting a decent left side signal. Everything is great coming out of the stereo outs they aren’t affected.

 

[Halloween3]

Problem solved! So the trace from the volume knob heading to the right monitor had what looked like a scratch across it but after running a pin over it was actually cracked and fully separated. I cleaned the area and soldered across it neatly and was back in action. I must have been too rough with removing the volume pot to check it for resistance. So again since this will probably help someone in the future the main problem was monitor and headphones hiss and was fixed by replacing the bad op amp on the microphone amp board. The secondary problem caused by me was a broken volume pot trace fixed with a quick solder touch up.