Tascam M520 Story...

sweetbeats

Reel deep thoughts...
So you probably did this, but I can’t quite tell from your last post…you had the SOLO and PFL switches depressed at different times right? Like, you didn’t do the test with both pressed down at the same time? The intention was to test each separately.

Question: is the EQ section on or off when you’re doing these tests? Make sure it is off.

Lastly, did you try the AUX buss tests? Monitor your input signal using the AUX buss in both PRE mode and POST mode? I’m guessing signal will be good in PRE and bad in POST.

And that’s a great idea to do these tests on a separate channel to compare. Good job with that.
 

bleachboy

New member
Hey,

Yeah maybe that wasn't clear but I did indeed test the SOLO/PFL switches separately. The EQ section is OFF.

As for the AUX BUSS tests : I have a fairly good signal in PRE mode on channel 3, and no signal at all on POST mode. However, when testing the same settings with channel 2, the signal level is much higher (PRE) than on channel 3 (PRE).
 

sweetbeats

Reel deep thoughts...
Okay. So first of all I want to say thanks for the detail you are providing as to what you’ve tried, and how you’ve implemented my suggestions, and what the results are. It really does help me help you.

Secondly, we’re getting deeper into this now, so here comes the disclaimer: am not a professional, and am not liable if you injure yourself or your equipment in carrying out any attempts to repair or service your equipment whether related to my suggestions or not. Also, milliamps can kill. Please be careful if you are working on electronics. Take the proper precautions, and if you don’t know what those are, then maybe you should consider not working on your equipment. I’m not saying this because I’m liable, but simply because I value other human life and welfare.

Can you remind me if the signal is bad at the D. OUT (direct out) jack?

Any change if you turn the EQ section on?
 

bleachboy

New member
Hi,

Well it's you that I have to thank for all that help ! English isn't my native language so explaining and troubleshooting technical issues can be very difficult to explain clearly, I'm glad you understand me well !!

Yeah the signal is still bad (pretty much non-existent) at the D.OUT jack. No change at all when engaging the EQ section.
 

sweetbeats

Reel deep thoughts...
Hi,

Well it's you that I have to thank for all that help ! English isn't my native language so explaining and troubleshooting technical issues can be very difficult to explain clearly, I'm glad you understand me well !!

Yeah the signal is still bad (pretty much non-existent) at the D.OUT jack. No change at all when engaging the EQ section.
Have you ever traced out a circuit using test tone and an oscilloscope or level meter?
 

Acequia

New member
Does anyone have that link to preserve your control settings on your M 520 Mixes ? I think its a virtual app or something. I would be fine with a simple drawing of each channel strip too.
 

Acequia

New member
---> can be the capacitors, i'm no expert as well :-)

yes the bulbs are expensive here too!
5 euros over here!

check this out i have found a virtual m-520 on the net that allows you to move al knobs and faders. so you can "remember" EQ and fader settings on your projects. so you have all your settings saved. at the end of a session, i just make a screenshot and save it in word....
maybe this is old news for y'all:

http://multimedia.utsa.edu/technology/3153/tascam520/large.html

http://multimedia.utsa.edu/technology/3153/tascam520/medium.html
This is the post. A virtual m-520 board. I just finished mixing and want to remember all my settings on my board. Does this exist anymore. It's brilliant.
 

sweetbeats

Reel deep thoughts...
Does anyone have that link to preserve your control settings on your M 520 Mixes ? I think its a virtual app or something. I would be fine with a simple drawing of each channel strip too.
I don’t have a link to any 3rd party hosted site anymore for the Virtual M-520, but it looks like I had the foresight years ago to snipe the .swf file itself.

So here’s the deal…the .swf file format is the legacy Adobe Shockwave Flash file type. It’s not a currently supported file type, but a quick Google search revealed a work-around…you can download the Flash Player projector content debugger from the Adobe Flash Player Support Center here:

https://fpdownload.macromedia.com/pub/flashplayer/updaters/32/flashplayer_32_sa_debug.exe

And then I copied the .swf file to my web directory. It is here:

https://torridheatstudios.com/Documents/Tascam/Virtual Tascam M-520.swf

So first download the .swf file, and then download and open the content debugger, and in the content debugger app go to file > open and then browse to where you saved the .swf file. It should work. I’ve not tried this on a Mac, only a Windows-based PC.
 

sweetbeats

Reel deep thoughts...
@bleachboy So see my question above about your experience with and available equipment to trace out a faulty signal path, but here’s the quick answer…if you don’t have experience with that or the equipment to do it, my hunch is you have a zorched ACCESS RCV input buffer amp. That’s “U5” on the Input PCB. It’s a TL072…readily available and affordable part…I recommend getting a genuine Texas Instruments branded part from a reputable vendor…if I didn’t want to take the time to suss out the circuit or didn’t know how I would just replace U5 on channel 3 and see what happens. There is almost nothing in between the RCV jack and U5, and U5 feeds everything downstream with which you are having trouble on that channel. But since you’ll have to remove your channel 1~4 block anyway, exercise the connector that connects the RCV jack on the jack module with the input PCB…it’s pin 3 of a red 3-pin connector on the jack module…you could even swap that connector with another jack module to see if you still have the same problem and if so that would indicate it’s not the RCV jack, bad solder joint on the jack PCB or the wiring in between. And then beyond that you can also visually inspect the solder joints where the cabling is soldered to the input PCB, and then inspect the traces that go from the RCV jack wire to U5. There is one cap in between the RCV jack wire and U5, the input coupling cap C25, a 10uF 16V part…I *suppose* that could be bad? But your problem doesn’t strike me as a bad signal path capacitor. Capacitors block DC voltage but allow AC voltage to pass. Audio signal is AC. You don’t want DC in your audio, which is why coupling caps are strategically placed along the signal path. Some DC offset is a common artifact of most opamp-based amplifier designs, and this DC offset or DC voltage component is mitigated by these coupling capacitors that block the DC. DC components in your signal path manifest as excessive pops and clicks as you engage switching functions, or increased “skritchies” as you adjust potentiometer controls (levels, pans, etc.). In extreme cases signal won’t pass at all if the cap has totally failed, but I just don’t run into that very often and it’s usually more the case the cap is dried up, is off-spec with its capacitance value and isn’t doing a good job blocking DC components. None of this sounds like your problem. But anyway you could also shotgun C25 if you want.

If you’re curious, and I’ve wanted to do this for awhile, I uploaded a new YouTube video demonstrating how I use the Block Diagram and any relevant schematics to diagnose signal path issues and narrow in on the likely culprit or culprits. I used your issue as the example for the video:

 
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Acequia

New member
I don’t have a link to any 3rd party hosted site anymore for the Virtual M-520, but it looks like I had the foresight years ago to snipe the .swf file itself.

So here’s the deal…the .swf file format is the legacy Adobe Shockwave Flash file type. It’s not a currently supported file type, but a quick Google search revealed a work-around…you can download the Flash Player projector content debugger from the Adobe Flash Player Support Center here:

https://fpdownload.macromedia.com/pub/flashplayer/updaters/32/flashplayer_32_sa_debug.exe

And then I copied the .swf file to my web directory. It is here:
https://torridheatstudios.com/Documents/Tascam/Virtual Tascam M-520.swf

So first download the .swf file, and then download and open the content debugger, and in the content debugger app go to file > open and then browse to where you saved the .swf file. It should work. I’ve not tried this on a Mac, only a Windows-based PC.
Thank u!
 

sweetbeats

Reel deep thoughts...
You’re welcome. Also, as alternatives for creating a cue sheet, you could photocopy and blow up the relevant section of page 6 or page 7 from the manual which has a black and white line drawing of the entire control surface of the M-512 or M-520, and I also attached a .jpg screenshot of the Virtual Tascam M-520 control surface to this post you can download and print and markup (would probably print nicely on 8.5” x 14” or 11” x 17” paper if you have that capability), -OR- if you have a tablet PC with digital inking capability you could digital ink right on the image and save as many different markups as storage will allow.

EEF373B8-3EA3-45B9-B66E-6D78B92D4690.jpeg
 

bleachboy

New member
Hi !! Sorry for getting back to you so late. Thanks you so much for that goldmine of information and help. To answer your previous question no I don't have any experience with signal generators, oscillators and testing equipment unfortunately. But your video is extremely helpful, and if I can manage to open the console rack to access the individual channel strips, I'm fairly confident that I'll at least be able to find that part you're talking about, removing it and replacing it, but that's the extent of my tech abilities I'm afraid. BTW if you have any tips on how to remove the channels from the console to access that part, that'd be great. I have opened and worked successfully on a couple Tascam reel to reel machines, but I have never opened a mixing console...

Thank you so much for making a video about my problem, this is going to help me a lot.
 

sweetbeats

Reel deep thoughts...
I think I’ve posted these instructions elsewhere in this thread…but to get the 4-channel groups of input channels out of the frame you:

1. Remove the screws that run along the front of the meter bridge from left to right…the ones below the meters and right above the input strips and master section. With these removed you can tip the meter bridge back exposing the top of the sub-chassis for the input channels and the master section, as well as the wiring that connects the input channels to the backplane.

2. Now remove trim strip that runs in between the wrist rest and the input channel and master section modules…the one that has the channel numbers on it. You’ll see there are some screws that fasten that trim strip to the frame. With that removed you’ll see the bottom of the sub-chassis for the input channels and master section are now exposed.

3. For the input channel module you want to remove from the frame, remove the four screws that fasten the module sub-chassis to the console frame, two at the top and two at the bottom of the sub-chassis. You’ll see them. These are the two pairs of screws that were exposed when you tipped the meter bridge back and removed the trim strip. The module is now unmounted, but before you can remove it from the chassis you have to…

4. Unplug everything. This includes all the plugs for the module you are removing that connect it to the backplane and IIRC there are also two larger plugs that connect the module to the adjacent module. It’s been too long since I’ve done this on an M-500 console so I can’t remember the detail, and my spare M-500 input and master section modules (I have enough to make an M-512…I don’t know why I have these anymore…) are semi-buried in the attic somewhere, and it’s faster to type this than go on an archeological-like dig to get to the spares. What I really wanted to do was exhume those spares and do another video sort of demonstrating this process, but without the console frame. Anyway, I *think* if you unplug everything at the backplane, you can then tip the module up at the rear and access the connections that join the module to any adjacent modules. Once those connections are unplugged you can remove the module completely from the frame. It’s possible I’m missing a step. But hopefully that’s enough info to carry you through. The plugs, a mini Molex type connector, have a little retaining tab…just look at them…you’ll see what I mean. Often you can gently rock the plug away from the side of the connection with the retaining tab and then unplug the plug with a gentle rocking motion while pulling. Again, be gentle. It’s not like eggshell fragile, but you don’t want to be a gorilla about it either. The concern here is the solder joints of the jack to which the plug is connected on those backplane jack PCBs. So just take some reasonable care not to be a muscle head about it. If you need to you may be able to, in most cases, slip the tip of a small flat-blade screwdriver or better yet a small plastic spudger in between the plug housing and the retaining tab, effectively separating the two and making it easier to unplug the plug…or you may even be able to lift the tab away from the plug housing with the finger or thumbnail of one hand while grasping and gently rocking/pulling a plug with the other hand. I usually use a mix of all of these techniques when disassembling a bunch of these connections. IIRC they are all color coded and have varying pin counts, so it’s relatively easy to put the connections back together correctly, just make note the connections are in rows that correspond to the channel and it’s jacks, and there is nothing wrong with taking lots of pictures and labeling connections with blue masking tape and a sharpie or whatever.

5. Now you have to disassemble the module to get the one channel PCB out that needs serviced. The first step to this is getting the beige dress label free of the sub-chassis. Remove all the knobs, remove the two screws that fasten each of the four faders to the module (8 screws total)…the faders will fall free of the module chassis, hanging by their wires. You can unplug them from their respective channel PCBs…you should be able to get to those 3-pin connectors. No need to label…the faders are all identical and can be reconnected to any channel PCB in any order. Be aware each fader has two screws and likely a small toothed washer on the underside, between the fader body and the sub-chassis. As you remove the faders these may fall free or they may be stuck to the rubber dust shield. But they’ll be there somewhere and you want to be aware of this so you don’t loose them, because they need to be there when you put the faders back in.

6. Now that the faders our removed and the knobs are all removed, there are two more small screws that fasten the dress panel to the sub-chassis, you’ll see them along the center line of the panel, one down toward the faders and the other up toward the input TRIM pots. Remove those two screws and you should be able to lift the dress panel free of the sub-chassis.

7. Look at the underside of the module. You’ll see each PCB is connected to its adjacent PCB by at least a couple (can’t recall exactly how many) larger connectors and cabling, just like what you had to disconnect from the adjacent modules when removing the module from the frame. Identify the specific PCB you want to remove from the module and disconnect any connectors from it and/or the adjacent PCB so there are no connections terminated that will prevent the PCB from being removed from the module assembly.

8. Turn the module back over so you are looking at the control surface again. With the dress panel removed, you will now see all the pot shafts and pot nuts. Remove all the pot nuts for the PCB you want to service. I think there may also be a screw or two to remove, like up by the source select, phase and pad switches, and maybe a couple other places? You’ll see them. Once those screws are removed and the pot nuts are removed, the PCB should be free of the module.

Do the steps in reverse to reassemble.

This should apply to the M-520, M-512 and M-50.

This is all from memory so forgive me if I missed a step or two.

Yes, it’s a little bit of a PITA, but it’s not too terrible. But recounting these steps makes me appreciate my Studer console…each channel is an individual module, connected to a motherboard via high quality PCB-mounted “eurocard” connectors with gold-plated pins. Loosen the two captive screws that fasten the module to the console frame, slip the two module pullers under each screw, gently rock and pull upward, the module pops out, disconnect the ground wire plug and the module is out for service; both sides of the PCB are fully exposed. I can get a module out in about 15 seconds. Reinstalling takes even less time.

But hopefully you don’t have to do this very often, and I appreciate the tilt-back meter bridge concept on the M-500 series consoles…makes it super easy to get to the jack PCBs and backplane connections. I think with all the tools handy one, with practice, can get an individual PCB out of an input channel module of an M-500 series console in about 15 minutes.
 
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bleachboy

New member
Thank you so much for your invaluable help...I'm in the middle of mixing a couple of albums and I'm using the working channels for summing so I won't try to open the mixer right now, but as soon as I have a little more time to do that I will let you know how it goes. I'll try to source the part you mentioned in Europe, or better still in France.
 

Lourykem

New member
First of all, hello to everybody. I m new here and I ve read the threads in this forum for quite a long time (special thanx to Sweetbeats) I m the happy owner of a M 520 that works great and I m actually mixing my album (in french, I live in Paris France) with it. I own a tsr 8 but don t use it at the moment. (I use an old computer as a recorder with minimum copy/paste) everything has been done with
Juno 60
JX 8P
RX 11
SPX 90
...
The M 520 is a great desk in spite of what I ve read on the forums. Warm, efficient and so cute with its 80s look.

Have a nice day everybody.

Hervé
 

sweetbeats

Reel deep thoughts...
Hi Sweetbeats ! Could you tell me which TL072 to buy exactly ? I see several on that website : https://www.mouser.fr/c/semiconductors/amplifier-ics/operational-amplifiers-op-amps/?m=Texas Instruments&series=TL072

Thanks !
Are you in France? Hopefully I did this right…you need the through-hole PDIP-8 type case, and it needs to be in stock, so that leaves this one:

https://www.mouser.fr/ProductDetail/Texas-Instruments/TL072IP?qs=5BZzbFV4k2v7IBrcArRPQw==

I think.

Let me know.
 

bleachboy

New member
Well, I don't really know where to start except by saying THANK YOU SO MUCH Sweetbeats.
I have spent the whole day carefully going through your instructions on how to disassemble the module, access and replace the U5 op amp that was indeed faulty, exactly as you thought it would be. The faulty IC op amp was a TL072CP, and the one that I purchased and installed is a TL072IP, I hope it does not make a big difference.
I have to say I was really scared of doing that because the hardest technical thing I've ever did on an electronic musical device is changing a capstan belt of a Tascam Reel To Reel...But thanks to your very concise and precise instructions I've managed to make my M-512 mixer fully functional again ! At first I was afraid that since I'm not a native english speaker I might not understand your instructions but the operation went without any issues.

Thank you again for taking the time to explain all this to me. That's very generous of you !

Now let's record some drums !
 

sweetbeats

Reel deep thoughts...
That’s amazing! Nice work!

And your English is really very, very good. It was easy to help you and I’m so glad it worked!

Essentially no difference between the TL072CP and TL072IP. Sometimes those differences only have to do with how the part is packaged, or maybe it was a run of the part ordered by a large company and they certain parameters and so the part was given a specific part number. But the CP and IP are pretty much the same thing.

Again, good job to you…enjoy!
 
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