Tascam M-___ Story...

Thanks for the confirmation. I just found on the evilbay, a paper user and service manual. I gave up on teac. They both should be here in week. I sure hope they are good and complete.
Cost about 35 bucks for both manuals.

But I digress, back to your thread. :D

Still trying to fathom the versatility of a 12 channel mixer. Wow, just wow.
 
It's like having amnesia...slowly flipping through pages and pages of handwritten notes, slowly retracing where I left off on this thing...

Bad idea: tackling multiple repairs and upgrades all at once and then stepping away for a year and a half mid-project. Life took another turn.

This is how the master section has looked since sometime in 2014:

image.jpeg

No joke, just like that sitting right there on the control surface all basket case like. :(

Trying to recall what all was going wrong, what I was working on and where I was at with it all. It's hard. I should have made some voice memos or something. I have some notes, and a good amount of emails with a friend about it, but nothing that lays it out or really captures where I was at with it all. So I'll have to just dig in and rediscover I think. I know the headphone amp was making popping, sputtering Sputnik sounds, and I replaced the LM386 opamps with brand new TI branded parts thinking that would fix it...I recall it didn't. hmmmm...4 D-cell batteries...right...I had to find out if the noise was upstream or coming from the headphone amp and in order to isolate the amp I had to power it separate from the rest of the board...the headphone amp will run on a 6V supply. Batteries. Okay so that was one thing. Then the other was this worsening popping sound when I'd switch control room sourcing...had advisement it may have to do with the analog JFET switch arrays used in this mixer for quiet switching. I was starting to try and draw out the circuit. Then I was also upgrading some opamps, but I seem to recall one that I wanted to use a 5532 in place of a 4556, but it didn't work and it was because I made an assumption...I didn't look at the circuit to ensure it would support the 5532. But I don't recall which amp section. And I was relocating an amp section for a ball of solder and resistors kludge to a vacant DIP-8 site on the board. I recall something didn't work right. I don't remember what. Or if I maybe fixed it.

Sigh

Lookit...a few pages of the many pages of notes I've taken as I learned the feature set of this mixer. I think I took these when I started the comprehensive function testing in 2014...as I was doing the testing I kept coming up with "oooo such-and-such function upstream or downstream from this-and-that function?" It's complicated because of all the different busses, muting and soloing functions...it's smart the way they set it up, like how the different functions are connected flow-wise is intuitive once you understand (or remember) just what that function *does*...it's the remembering part. The notes are helpful:

image.jpeg

And yes, at the bottom of the middle page is an incongruent "something isn't right" note when I first discovered an oscillation issue:

image.jpeg

THAT was a bugger...took parts of the mixer to a different state to have my friend help. We were unsuccessful, but after getting home and sleeping on it hit me what the problem was and the issue is resolved. Still have to swap out one of the 6 JRC TL072 opamps on the EQ boards with new TI TL072 parts. But at least I know what the problem is and remember where I am in the process. :D

And here is the sketch to remind me where the source switching popping was happening in the master section:

image.jpeg

Soooo...yeah...just staring at it.

image.jpeg
 
Maybe this was mentioned, but do you by chance have schematics, flow charts, and a service manual? Wouldn't that be helpful?

Anyway, I admire your tenacity . I doubt that in 2 years and multiple moves, that mixer would survive inact in my hands.
I'd probably have given up on it long ago. Lol.
 
This is a one-of-a-kind prototype mixer. Nothing exists as far as any documentation. I was never able to get Teac Japan to express any interest in it at all. Teac in California...I talked to Jimmy in analog support there before analog support went away. He verified (based on pictures) "oh yeah that's one of ours, but I'VE never seen it before, and at this point I've been here the longest of the current staff...that looks like around '81 or '82..." (which I verified based on the opamp date stamps) "yeah not sure what happened...something like that shouldn't be out in the world...it should have been destroyed."

Any barbaric technical docs on this thing are all by my hand.
 
One question answered: looks like I did all the selective opamp upgrades I had planned on doing, and the one site (that I tried haphazardly using a 5532) I see is a brand new 4556. So I'm taking that facet off the to do list.
 
Trying to (gently) remember how it goes back together... I should know...I've had it apart enough times...

Think I've got it...I found some bad solder joints...gonna put it back together and run through a function test and see what does.

image.jpeg
 
Well, I am working on some music for the wedding, and working on some vocal removal...the freeware VST plugs suck, so I decided to do it old school on an analog mixer. Great reason to finally reunite the M-__'s power supply, plug the master module back in and see if anything smokes, and to actually plug up some cables and see if it still works. This was refreshing. And good news the thugs wrong with the master section are still wrong (as opposed to new problems), and being exposed to the problems again is helping refresh my memory as to what I was going to do to resolve them.

But anyway, it was fun actually using it, and powering up my old DAW laptop I haven't used in years...I have to say every time I use the M-__ I am reminded how smooth and full the sound is. The low end has this nice effortless presence that is very musical across the low band. It's really a nice sounding mixer.

image.jpeg
 
Considering my own current adventure with the Trident...I find this thread very inspiring to say the least! :)

I flipped back through the thread pages, and all I can say is WOW!...you really had a project on your hands.
That's way more than I would want to dive into!

Shit...I just spent the whole day chasing a single channel issue on one of my group modules on the Trident. There's a pair of channels per strip, one above the other (odd above even)...and the lower/even channel doesn't pass signal. Checked and rechecked everything I could think of...so it's got to be a component issue...cap...IC...?
I probably won't use the group modules much in my typical SOP...but since everything else appears to be working OK, it's like an itch I can't scratch.
At some point I'll be re-capping and re-chipping the group channels...so it may sort itself at that time...but I give up for now.

Anyway...compared to your project M____...my single group channel issue is like a small pimple on my ass. :p


Hey check your PMs....
 
This is what it looks like when you cobble two flashlights together to make a 6V power supply so you can isolate and test your headphone amp...trying to resolve the noise issues with the headphone amp.

image.jpeg
 
So I'm working at tackling the noise issue in the control module (master section)...there has always been some random sputtering fuzzy noise in the headphones...thought I had it fixed last night, but...nope...and to make matters worse it turns out it's in the STEREO and MONI busses too. I just never cranked things up enough to hear it. So it's time to build an extender cable in order to be able to power the control module while its out of the frame. I was going to do this a couple years ago and then life kept happening.

I hope to have this thing 100% by the time I've had it a decade. :eek:
 
Not my prettiest work...a bit kludgey...but I can't find the EDAC connector in 14-pin, and had to use what I had on hand for the card-edge end...12 positions...cut out of an old Ampex card of some sort. It gets the job done.

image.jpeg

image.jpeg
 
So, 1kHz tone recorded on my Tascam 238 has an audible "warble" in it when reproduced. Like pretty bad.

My prime suspect is the pinch roller...I cleaned it and it looks and feels nice, but upon closer inspection it looks like there might be a slight wobble to it.

What does this have to do with the M-__? I was going to record some more tone while watching the pinch roller closely to see if the rhythm of the warble corresponds visually to the pinch roller wobble. My handiest oscillator is part of the M-__. Of course the master section is all pulled apart right now trying to chase down the sputtering and popping in the master section...waiting for a new set of probes for my oscilloscope to arrive because my old 10X probes aren't proving sensitive enough for the HF noise I'm trying to see on the scope, so I can start tracing and hunting down the source. Anyway, it looks like this right now:

image.jpeg


Anyway, as I'm carefully positioning the guts to make sure nothing is going to make fire when I power up the mixer to use the oscillator I notice a problem with my master fader...can you see it?

image.jpeg


It appears the yellow wire has decided it doesn't like the fader anymore. I've had to deal with a healthy number of fragile wire joints on the M-__...didn't notice this one, until now of course.

So, okay, time to repair and improve. The joints should be reinforced by some heat shrink, and it's always bugged me one wire was yellow...it should be brown to go along with the standard color/number scheme; brown is 1, red is 2. Yellow is 4. Brown and red often represent left and right in audio gear guts too.

So I dig out spare connectors and wiring and find a good equivalent AWG donor set of wires of proper colors, desolder the old wires, remove the sockets from the plug housings, and prep for the replacements to be installed:

image.jpeg


And...better.

image.jpeg


And with that I believe the matter is repaired and improved, and I'm about 25 minutes closer to the afterlife.

Somebody please get me a job doing this stuff.

Now back to my 238 warble problem.
 
Packing this up to take to the doctor tomorrow eve...the "Control Module", aka the master module.

image.jpeg

Been continuing to struggle trying to figure out the source of the sputtering/popping/fitzing in the headphone circuit...it's simply over my head. I've been able to determine, with reasonable assurance, it is upstream of the headphone level pot, but isolated to the PCB upon which the level control is mounted. That leaves very few possible suspects because the signal path upstream of the level control on that PCB includes only the headphone source select switch, and some direct traces to the connectors that interface with one of the buss PCBs that connect the two possible sources of the headphone circuit to the PCB with the level control...so what I'm saying is there are no components either active or passive on that PCB upstream of the level control...just the switch...and something is throwing noise.

Ideas: if you go back early in this story, you will find a vignette about a pile of mouse poo and pee...the mouse poo and pee was primarily on the PCB with the headphone level control. I fastidiously cleaned all the boards in the Control Module, and replaced any components that had any signs of corrosion on them...and I have also replaced all the opamps on that PCB as well as a number of the opamps on the other boards. BUT, these are phenolic resin boards as opposed to glass fiber. It is possible the base material of the PCB is contaminated due to the historical piss, and there is current leaking through the board itself and that is the cause of the noise...OR, maybe it is a problem with the power rail itself; the rail that powers the headphone amp also provides the signal ground, and ALSO powers the LED indicators on the module...it's a bit of a strange design in my limited experience, but there could be extended opportunities for weirdness there, though there are only 5 LED indicators on the module...but it's a possibility.

This issue is the last complicated and stubborn jank on this one-of-a-kind console, and I'm at the point of saying "uncle"...reached out to an old friend evm1024 and he's graciously willing to assist. Headed over to his place tomorrow eve to pick up a Tascam 58 parts machine and extender card that I sold to him many years ago, and bringing the M-__ Control Module and console power supply with to put on his bench and see if we can figure it out.

I'd love to traverse this hurdle and be that much closer to calling this project 100% done.
 
Good luck with this. Hopefully this is the last hurdle and you can get this puppy back together and run some sounds through it.
 
I have read all the posts here. It's better than a mystery novel!! Here's hoping you get the girl in the end.....
 
Just like to wish you luck Sweets. You give so much of yourself in helping others on this forum, it would be good to see some of that karma returned. Here's sending you and the problem some good vibes.
Al
 
This is good, very good. This has been a long project. It will be quite a victory having the mixer fully up and running.
 
Thanks for all the encouragement, everybody. It means a lot to me.

Unfortunately this evening was not the success I was hoping for.

For some strange reason now the peak LEDs on the control module for the stereo master buss are constantly lit, we couldn't get the noise to sound in order to start tracing it (and I wish I could be excited about it being absent, but it's been a moving target and I'm sure it's not magically fixed), and we discovered the -15V power rail is throwing about 4V of half rectified AC. So I've got three problems now instead of one.

But it was really good to visit with Ethan...to talk about life, cars and boats as well as electronics...to see a real live Ampex ATR-100 1/2" mastering deck and see just how good a tape pack can be on a really nice machine...and he gave me lots of good nuts-and-bolts steps to start addressing the issues, as well as some good ideas to try next for the headphone noise issue. He's a down-to-earth guy who's steady and unflappable, which is helpful at a time like this when I might get pretty discouraged.

And I did take a Tascam 58 parts machine and extender card off his hands as well as a full set of new relays for a 58, and a full set of Tascam M-512 I/O modules and the master module for a VERY fair price, especially considering I got a healthy chunk of tech time and advice from him...and a good beer.

So, thank you Ethan. :thumbs up:

Stay tuned, folks. The first issue to tackle is what? Power supply...always power supply first. It is surely possible that bad -15V rail has been that way for a long while and that can cause noise issues. So that will be the next step and Ethan explained how to isolate the culprit.
 
Im sure discovering more problems, while not being pleasant, puts you closer on the road to salvation.

Isn't knowing whats wrong half the battle?

Just curious, what ya gonna do with the 512 modules? Aren't they the same as the 520?
Do you have a 512?

I'm not scoping. With two 520s, I'm set, its just my curiosity talking.
:)
 
You must log in or register to reply here.
Back
Top