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Thread: Tascam 312B Project

  1. #61
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    Yeah. I’m trying to figure out the meter problem. Let me know specifics when you replicate what you did last night, because in looking at the circuit, the only way the switch could source the opposite of the other buss PCBs is if the wires from the TAPE IN jacks (they go to terminals 4 & 6 on the BUSS PCB) were swapped. TAPE IN 4 should go to terminal 4, and TAPE IN jack 8 should go to terminal 6. The meter source switch just taps into the signal paths of the respective TAPE IN jacks.

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    channel 5 line in----> assign buttons 1,2,3,4 latched------> meter function switch 1/5,2/6,3/7 latched- meter function switch 4/8 unlatched -----> all meters function

    channel 5 line in----> assign buttons 1,2,3,4 latched------> meter function switch 1,2,3,4 latched -----> meters 1/5,2/6,3/7 function. Meter 4/8 does not function
    Brad Bachelor
    "Marrying an old bachelor is like buying second-hand furniture." - Helen Rowland

  3. #63
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    Back up.

    For the two tests above, what is the position of the 8 TAPE RTN switches in the monitor mixer, and what is plugged into the TAPE IN jacks?

    [EDIT]

    And what is plugged into LINE IN 1-4 and 6-8?

    To narrow down this issue, because the TAPE IN jacks are normalled to LINE IN jacks 1-8, and because the meter select switches are post TAPE RTN switches, you need to take all that stuff out of the picture to test your meter select switches.

    Do this:

    1. Use channel 12 LINE IN for the test, not 5.
    2. Make sure nothing is plugged into LINE IN jacks 1-8.
    3. Make sure nothing is plugged into TAPE IN jacks 1-8.
    4. Make sure all 8 TAPE RTN switches are in the up or unlatched position.
    5. Now route your channel 12 LINE IN source to all 4 mix busses, PAN center, channel fader at unity (shaded area), PGM faders 1-4 at unity.
    6. Check the meter activity. You should have the same thing on all 4 PGM meters regardless of the meter select switches’ positions.
    7. If you don’t, verify you have good signal at all 4 PGM output jacks.
    Last edited by sweetbeats; 1 Week Ago at 18:39.

  4. #64
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    The Meter issue is resolved. As you probably figured out, it was user error. TAPE RTN 8 was latched. As soon as I unlatched that the meter worked as its supposed to.

    It is interesting to me though looking at the block diagram, it looks like latching TAPE RTN 1,2,3, and 4 should have the same effect as latching TAPE RTN 5,6,7,and 8 but it doesn't.

    using your setup:
    1. Use channel 12 LINE IN for the test, not 5.
    2. Make sure nothing is plugged into LINE IN jacks 1-8.
    3. Make sure nothing is plugged into TAPE IN jacks 1-8.
    4. Make sure all 8 TAPE RTN switches are in the up or unlatched position.
    5. Now route your channel 12 LINE IN source to all 4 mix busses, PAN center, channel fader at unity (shaded area), PGM faders 1-4 at unity.
    If I do latch Tape returns 1,2,3, and 4 with the meter function switches 1/5, 2/6, 3/7, and 4/8 latched, the four meters function. if I latch TAPE RTN 5,6,7, and 8 and the meter function switches 1/5, 2/6, 3/7, and 4/8 latched. The meters don't function


    AHHHHAAAAA!!!!! ----Because I am only sending the signal to program busses 1-4!!! (....I was typing out all this when it occured to me....)

    I'm sorry to waste your time on this meter thing Cory, but believe it or not this is a mental milestone for me...
    Brad Bachelor
    "Marrying an old bachelor is like buying second-hand furniture." - Helen Rowland

  5. #65
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    No time waste, Brad...glad you got it.

    I’ve always struggled keeping my head around functions that follow or are dependent on other functions. And you have got a couple layers here because of the LINE IN jack normalling. It’s one of the neat features of the M-300 series butnit does add complexity.

    I think of it this way...the meters aren’t PGM GROUP meters or TAPE IN meters per se...they are the pre-level control *monitor mixer meters*. Each of those meters sources whatever is being sent to the respective monitor mixer level control. For instance for meter 1/5 when the meter source switch is latched, it is sourcing whatever is at the monitor mixer channel 1 level control...pre level not post level. If the TAPE RTN 1 switch is unlatched, then the meter is sourcing the PGM GROUP 1 post group fader sum. Latch the TAPE RTN 1 switch and now the source is the TAPE 1 jack. Same goes for when the meter 1/5 source switch is latched...still PGM GROUP 1 post group fader sum if the TAPE RTN 5 switch is unlatched, but match TAPE RTN 5 switch and the meter source is TAPE IN 5.

    So consider thinking of it that way...the meter source select switch isn’t a shift switch for the TAPE IN jacks, it switches which monitor mixer channel the meter is sourcing (and remember it’s at the point just before the monitor mixer channel LEVEL control), unlatched or “up” it’s the upper row of monitor mixer channels...latched or “down” and it’s the lower row of monitor mixer channels.

    The default source for each pair of monitor mixer channels is the PGM GROUP they line up with. But you can independently source a pair of TAPE IN jacks on each vertical pair of monitor mixer channels. On the M-312 and M-320 you also have those additional AUX busses, one on each monitor mixer channel row. And they are switchable PRE/POST monitor mixer channel LEVEL control. This is pretty powerful!

    Another thing to note that I was maybe a little confused about earlier and hopefully didn’t add to any confusion is the TAPE IN jacks *always* connect to their associated TAPE RTN source switches in the monitor mixer...it doesn’t matter what’s plugged into LINE IN jacks 1-8. The LINE IN jack 1-8 normalling is a convenience so you can plug your tape outs to the mixer tape ins and have them automatically connected to BOTH your monitor mixer and the input strips for mixdown time or cue feeds during overdubs (using the AUX 1 LINE source switch, yah?), but be able to plug in outside line sources to the LINE IN jacks without having to unplug anything from the tape deck outs.

    So for your setup as far as the meter sourcing, you’ve got the best of both worlds since you are using a 4-track...if you have your tape outs connected to TAPE IN jacks 1-4, then if it was me I’d always latch the TAPE RTN 1-4 switches, and now my meter source select switches when up monitor tape returns, and when down or latched monitor the PGM group’s post fade.

    If you don’t have any line sources connected to the mixer channel 1-4 LINE IN jacks, you have *two* ways to send cue feeds...using the AUX 1 LINE source switches on mixer channels 1-4, *and* using the AUX 3 buss on monitor mixer channels 1-4...with TAPE RTN 1-4 switches latched, your TAPE IN jacks 1-4 are the source for AUX 3.

    The M-312 is a very capable mixer for an 8-track machine. It has even more capability when meter to a 4-track. It’s got lots of breathing room for you and your current setup; room to grow if needed.

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    I am looking forward to getting this mixer setup....and that's where I think I am having some problems is not getting myself familiar with it yet. That will come, but it is so much more complicated (I think this is where you would insert the word "capable".... ) than the M-106. I appreciate your help on all of this!!
    Brad Bachelor
    "Marrying an old bachelor is like buying second-hand furniture." - Helen Rowland

  7. #67
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    You bet! Happy to help along the way. Keep the questions coming. Still planning on looking closer at the monitor buss issue too.

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    Channel 9 Input Strip

    I was looking today at my Channel 9 input as it has a diminished input signal vs the other channels. The shortest path I can find is putting the signal through the LINE IN and monitoring it through the insert which is what I did. The signal was as strong comparatively to the other channels until I latched the eq button. Then the sound was extremely diminished. When fiddling with the knobs, there was a weird noise in the 200-4k gain knob.

    Here is the test:

    Test Signal 1000Hz



    Is this an amplifier problem? (I only say that because I wanted to sound smart and be in the club...... I have no earthly idea what kind of problem this is.......)

    Brad
    Brad Bachelor
    "Marrying an old bachelor is like buying second-hand furniture." - Helen Rowland

  9. #69
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    So the way to troubleshoot this is powering the board outside the mixer (otherwise it’s hard to access the traces or solder lands you need to probe) inject the 1K tone and start tracing with a scope along the signal path. With the scope you can see the waveform to confirm it’s 1K as you probe along (confirm you are seeing your test tone) and also see the amplitude to see where it dies or diminishes. If you don’t have a scope you *can* use a multimeter set to AC volts, - probe on the signal ground and + probe touching your test points along the signal path.

    But that’s the kind of thing you need to do to determine what’s not working at this point.

    Get out the INPUT PCB schematic. The EQ section is in the lower left quadrant. The input to the section is on the left. Look at the drawing as you read through the next paragraph.

    We can be reasonably certain the problem is in the EQ section because when the EQ is out of the signal path the channel performs alright. The symptoms remind me of experiences I’ve had with bad electrolytics in EQ sections. I’d start with probing at the + leg of the input coupling cap C117. That’s the output side of that cap...feeds the first amp stage, the 10K filter. If the signal is already diminished there then replace that and see if that fixes the problem. If signal is normal there then test at the + leg of output coupling cap C126. That’s the input of that cap. That’s the last component in the EQ section. If the signal is diminished there then the problem is somewhere in the EQ guts and further tracing will be needed. If the signal strength is good there then check at the - leg of output coupling cap C126. That’s the output of the whole EQ section. If the signal is diminished there then replace that cap and see if that fixes the problem.

    C117 and C126 are the only electrolytic caps in the whole EQ section. So you could just shotgun those with new parts and see if that fixes it if you want.

    It could be lots of other problems, including a problem with an amp. Normally a good step is to make sure each opamp is getting good power from both power rails, but because you can make that thing squak, I think the amps are getting power. It will be one of the things to check if checking signal at the input and output coupling caps and changing for new parts as indicated by the tests doesn’t fix the problem.

    So there’s some stuff to chew on.

    Questions? Your turn.

  10. #70
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    Powering and diagnosing the board outside the mixer may be a problem. . I don't have a power supply,or a oscilloscope (although those may end up on a Christmas list......)

    I started thinking last night about shotgunning some parts and had some general questions about that:

    1. Looking through some threads last night, I noticed you use TI op amps and not less expensive ones (.....honest..... I'm not stalking you Cory..... you just happen to mention 5532 op amps more than others.... ). Is there a spec you follow or is this just a brand (or parts house ) preference?

    2. Should I socket all op amps?

    3. Who is the best small quantity vendor to buy electrical components from in terms of customer service.? The reason I ask this is I noticed some of the amps on my 312b are obsolete (like in the monitor section). If I need some of those I would like to talk to someone about replacements.

    I'm getting my shopping list around some caps and some op amps and sockets for now.

    One other thing.......

    I was looking at putting my replacement input card in and was looking at the mods that were done. Here's the replacement card:

    file-nov-14-2-36-15-pm-jpeg

    and here's the one I took out of my 312

    file-nov-14-2-30-23-pm-jpeg

    I looked in the schematics and couldn't find those resistors (?) anywhere. I assume, I'll need to replace those blue ones with ones like were originally like the mixers right?

    As always...... Thanks,

    Brad
    Attached Thumbnails Attached Thumbnails file-nov-14-2-29-08-pm-jpeg  
    Brad Bachelor
    "Marrying an old bachelor is like buying second-hand furniture." - Helen Rowland

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