Tascam m312 tracks 11 & 12 cutting out

[simonschole]

Hi there,

I have a Tascam m312 and tracks 11 & 12 are cutting out when panned to the right hand side. If panned to the left hand side, there is no cutting out at all for these two channels.

It seems it's the connections to the PCB board. Have attached a few photos below and also a video of the issue.

Anyone had a similar issue with a Tascam mixer?

 

[SkywaveTDR]

I had worked on a mixer just recently and found that the buss board that has connector on it were having some broken joints. Remember that these products were made with wave solder type construction and this kind of stuff would never make it to aerospace grade products. I resolder a lot of joints in these units as well as many open reel decks I work on- not only Teac or Tascam but Sony, Technics, and others. Use a good solder like Kester 44 and go over each joint adding some to make a good shiny solder joint. Make sure the component- connector lead is accepting the bond to the solder- if it does not then some solder flux might be needed on some particular ones. Usually when I get done with a unit it is bullet proof with regard to bad solder joints. At this point the board or the component needs to fail as it will NOT be the solder joint as it could be before hand. The connectors can also be treated to Deoxit contact cleaner as it would be purchased at a place like MCM Electronics. With these practices you will likely come out with a board that works like brand new. Keep in mind the pan pot may have a dead spot at the end which is most likely accumulated dust and dirt that can be sprayed out with Deoxit or better Fader Lub. I have been working on this stuff since the late 70's. I get the impression I am pretty good at it.

 

[simonschole]

thanks very much for the response. It seems it might be a dodgy solder joints on the pan pots. I've sprayed both of them out but it hasn't made much difference. Will take on your board your advice re: resoldering the board, type of solder, contact cleaner etc. Once again, thanks for the thorough explanation and advice.

 

[SkywaveTDR]

I had one channel of a board not work because the bad solder joint was up at the top of the card. I took the channel strip out and found it. Of course you need to take the channel strip out with all knobs off and whatever is required. I see people place item on top of the pots of their boards and the pressure that goes into these pots does cause damage in first breaking solder joints and then the destruction of the control. Never is it a good idea to place or drop things on a boards control surface. Some studios that did not cover their boards nightly with a plastic cover also experienced additional cost of repair as switches and pot that had to be sprayed out due to the additional dust that got into them. Smoking is also something that should be eliminated from electronics. It does get into everything and especially state switches of DAT and VCR equipment.

 

[simonschole]

thanks for that Skywave, yes is fair enough, have got the mixer nicely covered when not in use. It does seem like quite a task to get the channel strip out, fair bit of un-soldering then re-soldering etc, will serve as good practice as a first time project.

 

[SkywaveTDR]

I would not unsolder anything unless there is no other way. Most of this stuff has connectors on the cables one side or the other. The channel once the Buss PCB is pulled up and out of the way usually can be removed and laid on the other strips for you to repair the card. If the board is on it's face I would support it with wood blocks from the sides. The card does not have to be taken entirely out of the mixer but just that access to the board is had. I use a magnifier head set to find bad solder joints. You are looking for broken solder joints all over.
The problem can be the buss board- having a scope around can help you trace signals as well.
At least these are repairable unlike the Mackie product.

 

[simonschole]

no worries, thanks Skywave, yes I did not want to unsolder so I appreciate the advice. Will see how I can get to the pan pot without too many hassles.

 

[SkywaveTDR]

I don't remember this board specifically but they most of the time take some pot nuts off and then a couple or few screws and out they come. Then with it out you can use an DVM to sweep the pot to see if it has any discontinuous sections. If you do find it that way I would opt to put in the same size and knurled knob type pot but try for Cermet or Plastic conductor type.
Once the card is out you can use Fader lub on all pots that are accessed. In my 40 some years the pots I have had to change were only due to severe damage from the outside not any other failure. Despite the cheapness of these ALP parts they hold up pretty well.

 

[simonschole]

great thanks Skywave, yes it seems those two pan pots on 11 & 12 have been cranked to the right, damaging the solder.