Tascam M-520 Monitor output right channel very weak

[Goldtonestudio]

Hi, it's my first post here, so I hope this is the correct spot to post. I use to post a long time ago on VSplanet. I am having a similar problem as onesong321 had in a post from 2009 except my right channel is very weak. I did all the tests that sweetbeats described in that post and I get both channels at the PGM outputs but not on any of the the monitor section. It seems like just the right side of the amp in that section is out or weak because I put in Van Halen one album and I can hear the left Eddie guitar track great but I have to push the fader up all the way on the right channel but I do hear the background vocals so the right channel is there but very weak. Please help!!

 

[Goldtonestudio]

Oh another thing too is that I did have a crack the Buss PCB by one of the screw holes but I put on a jumper wire. Also I completely resoldered the whole monitor board and checked for continuity on all the caps. I do have 2 extra channel cards that I could borrow a OP amp from if need be. I do not have the service manual but I do have the manual with a lot of diagrams and schematics but there are a couple pages missing.

 

[skywaveTDR]

First make sure it is not an interface problem by switching cables. If the right channel is bad it should stay on the right output. I tend to go after these problems with a scope and to use the block diagram and then if needed the individual circuits. Make sure the same signal is going into the monitor section and you might try another source into it. Usually when Op Amps fail they go all the way out or have some form of clipping. The scope will show you this as levels are increased. The Pot (VR- Potentiometer) might need cleaning. The unit could have a bad cap in it but in my experience with Tascam mixers the usually reason they fail is abuse to them. I have a M50 and M1516 and M520 here and have had few occasions to have to repair them but they are starting to age. Teac unlike some other companies used pretty good parts. I work on tape deck that still have working Electrolytics in them at 45 years of age. Still they should be changed out. It could be oxidation in a switch or something simple but that is eliminated as you work through it. I would place a 1KHz sine wave into the buss and trace the signal making sure the amplitude is not different before hitting the Monitor section. I work on all this stuff all the time here in Chicago area and as you need help you can feel free to E mail me directly. skywavebe@sbcglobal.net is what you need to know. We can work this out.