Tascam M520 Story...

I can't recall if the M-512/M-520 has bottom panels that can be removed. Can you tip yours up and take a look or does anybody know off-hand? Its been years since I've had my hands on an M-500 console.

Basically at this point you're going to need to access the guts, either from underneath, or partially remove the 4-channel modules that have the poor functioning channels, and ideally use an oscilloscope to probe for test tone you have running through the channel, and use the Block Diagram and schematics to find a point where you should have tone and you don't and start tracing back until you have tone. That's the point at which you likely have a faulty connection or failed component. As I mentioned earlier you can also strategically and carefully manipulate connectors to see if you get lucky and find a failed connection that you can either, as needed, resolder or exercise and treat with contact cleaner. I'm sorry to say it, but you are into relatively high-level technical troubleshooting at this point, at least the kind that calls for a tone generator, an audio-grade multimeter, and an ability to read and follow schematics and trace out the problems...no silver bullet, no magic elixir.
 
From memory.... the bottom panel doesn’t come off in sections. The meter bridge hinges back and exposes connections
From the top it’s four channels per panel
 
No worries, happy to dig in and do the work. Just want to make sure I know what I'm getting myself into as to hurt myself or the board.
 
RFR said:
From memory.... the bottom panel doesn’t come off in sections. The meter bridge hinges back and exposes connections
From the top it’s four channels per panel
Click to expand...

Yeah I recall clearly the top panel access...could write step-by-step instructions on that from memory...I just couldn't recall the bottom side...I'm starting to picture it now though, unless I'm getting it confused with a couple other consoles I've torn apart...nope...just looked at the exploded view in the service manual. So if you tip the console up and look at the bottom you should see a series of panels on the bottom, each which fasten to the frame with four screws, two at each end...each section I believe exposes one 4-channel input module. So you can remove one panel to access the connections and the bottom edge of 4 input channels at a time. This *may* aide you in narrowing down your problem. If it was me I'd start at the channel fader...check to see if there is signal at the output of the fader. If no, check at the input of the fader. If no, just look at the schematics and start tracing your way upstream. The issue you will run into is you will not be able to get to everything you see on the schematics, so you have to puzzle out what you *can* access from the bottom. Ultimately, if there is a component failure or a bad solder joint you will most likely have to remove the module, which is a bit of a job, but at least they come out in 4-channel chunks, and then disassemble to get to the individual channel card. This is why I've come to really appreciate consoles with individual plug-in modules...if one is problematic, pop the one out in seconds, and in some cases with ribbon cable interconnection there is enough slack to access both sides of the channel card with it still fully connected and you can troubleshoot in seconds...if there is not enough slack or if the module utilizes edge connectors or euro connectors and a motherboard, then you get extender cards or cables, or make them, and you can have the module out of the console but still connected, again in seconds.

Again, if you tip the console up and remove the respective bottom panel you can *at least* manipulate connections (gently) while monitoring the output of the channel and see if anything you manipulate changes anything...crackles, intermittent signal, etc. That can quickly narrow down the problem without too much fuss, but it is shooting in the dark.
 
Aha! Well, it’s too damn heavy for me to flip it over to take a look at mine. :)
But if thats what the exploded view says.... it must be so.

Haven’t had a need to look at my manual in a while, but its good.
Really good. In fact, one of the better product manuals I have seen.
Practically takes you from basic recording, to using, to fixing your specific desk, as well as general info applicable to other gear.
 
It continues... I have discovered that buses 1 and 2 seem to be inop as well. No audio passing through stereo master or the individual pgm outs, and nothing registering on the VU meters. Ordered some deoxit that will get here over the weekend so I will get to work cleaning everything out over the next week or so.

I opened things up and noticed some pins are missing connectors, but I don't see any stray cables. Is it normal for some of the pins to be missing connectors? When I pulled out the 13-16 block, some channels would have certain connectors while one wouldn't have a connector in that spot.
 
Notice the different 4-channel modules have some different functionality. Like some have 2-track returns and yet another has instrument and phono inputs. That accounts for some of the variation in what connectors are used and what might be vacant. If you need anything more specific than that please post the connector number, what PCB assembly it is on, and the pin number(s).

Are you saying you can’t get signal to PGM 1&2 from *any* of the 20 input channels? Exercise the PGM 1&2 SEND/RCV jumpers. Connect audio to the PGM 1&2 SUB IN jacks and see if you can get signal to PGM 1&2 that way.
 
Well, I don't know what was going on when I tried before, but PGMs 1 and 2 work fine, seemingly. Both signal from the input channels and the sub in jacks pass through marvelously. I have no clue what was the problem before. (Probably user error, which is certainly not uncommon!)
 
Wanted to point that possibility out yesterday.....but figured it best to keep my mouth shut. ;)
As a longtime user of this desk, it seems like for new people, 50 percent of tech problems are simply user error.

I suggest downloading sweetbeats videos and store them in a “studio’ folder.

I have physical manuals for almost every piece of gear I have, but also have a folder on my computer. Comes in handy
 
Took another look under the hood today, and noticed that there's a resistor missing in both channel 14 and 15 in C-48. Every other functioning channel of mine has one. Still have to study the service manual a little bit to see what it most directly affects, but could this be my problem? Researching now to see if I can order one.
 
“C48” indicates a capacitor, not a resistor. Are you saying that those channels are missing a capacitor, or that all your other channels have a resistor where there should be a capacitor?

On channels 14 & 15 C48 is the input coupling cap for the TAPE IN input. It is connected to pin 5 of U2, the input buffer amp for the TAPE IN input. You want to have it there. Signal won’t pass from that input to the channel unless the cap was removed and a jumper put in its place, and even if that’s the case the coupling cap’s purpose is to block DC, so if it is not installed, depending on the source, there could be DC artifacts present which are not desirable.
 
How right you are. Dunno why I thought it was a resistor. Yes, the channels are missing a capacitor, there is nothing in that spot. That would likely explain my lack of signal flow, although I seem to remember it also happening with a mic input as well.
 
More problems. Signal flows into the console fine, but I can't get a damned thing to respond to the actual fader movement. Running it out of the PGM outs, stereo master out, I hear it just fine, but no volume adjustments work at all. Not on the fader itself, not on the monitor section, only on the bus faders and the master fader. I can run input into a channel, have the fader all the way down, and still hear it. How is this possible? I never had this happen before.

---------- Update ----------

It doesn't respond to EQ or trim, either, btw.
 
The output dies when I pull out the direct out on the channel but not when I pull the actual line input supplying the signal or the jumper. WTH is going on?
 
I'm having a difficult time following the limited detail of your posts...no offense, but to me the posts are somewhat cryptic. Can you take a video of your problem, put it up on YouTube or something and post a link here?
 
Okey-doke.

When you capture the video, try and be as pulled back as you can to see the control surface vs. focusing in on a control or two and moving all over...keep the video capture device pulled back and let your hands lead the viewer through your presentation of what is happening on the control surface. Share detail as far as what is hooked up to what, how the controls are set, etc.
 
Try hooking your motu up to the first channel. If the problem goes away it’s something with the appollo. To me, just on a quick watching of the video, it made no sense.
I’d dial it back and just test an analog signal into each channel of the board to make sure they’re working.
It seems like you’re dealing with multiple unknowns.
 
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I think you need to start by testing using a source that has nothing to do with your DAW interface hardware...connect a mic up to CH1. Test it. Have nothing else connected to the channel...just a mic cable and the jumper. Test for appropriate post-fader post-EQ functions to the PGM groups, and then check at the direct out jack for CH1.

Now test something at the LINE input...check for the same things with the routing to the PGM groups and then at the direct out jack.

Report back.
 
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