Tascam M-___ Story...

You've made a lot of progress, but hit a few dead ends.

I don't see how the different 0V rails not tying together would be a problem,... but I'm not an engineer. EVM blows my mind with a lot of this analysis, too. Props to him, for sure.

At what point do you just plug 'er in, back up and give it the "smoke test"???

Nah,... you're being conservative and that's most proper. You don't want to turn your M___ystery board into a flaming pile of junk, rat turds and all!:eek:;)

You've got yourself a real one-of-a-kind! It would be a real achievement to give this board a second life!
 
Heyyyyyy...guys...0V rails tie in the power supply???

Okay...

So I asked that question in my last post, about the 0V rails maybe tying together in the power supply and not the mixer, about whether that was a possibility since I couldn't find any point in the mixer circuitry where that was happening.

I took another look at the schematic for the PS-520 power supply again last night with that perspective (looking to see if the 0V rails tie together) and boy howdy it seems pretty obvious to me, but I'd like somebody to confirm I'm seeing it right...

Here is a jpeg of the power supply schematic. Toward the top right of the diagram you see where the different rails leave the main PCB...they are labeled 1 ~ 14. Notice that terminals 2 (ground to mixer), 7 0V(D), 9 0V(C), and 11 (power supply chassis ground) are tied together just to the left...they all connect to one line! Notice further that terminal #'s 13 and 14 are not connected to the 20-pin umbilical connector, but they are tied in to the 0V rails! Is it possible that these are 0V(B) and 0V(A) respectively????


  1. Am I seeing that right, that all the GND and 0V rails are tied together in the power supply and I don't need to worry about them tying together in the mixer, and
  2. Am I also seeing it right that terminals 13 and 14 on the main PCB in the power supply are unused but available 0V rails and I could use one of those for my third 0V rail needed for the mixer???
 
Yep on both counts.

-Ethan

sweetbeats said:
Okay...

So I asked that question in my last post, about the 0V rails maybe tying together in the power supply and not the mixer, about whether that was a possibility since I couldn't find any point in the mixer circuitry where that was happening.

I took another look at the schematic for the PS-520 power supply again last night with that perspective (looking to see if the 0V rails tie together) and boy howdy it seems pretty obvious to me, but I'd like somebody to confirm I'm seeing it right...

Here is a jpeg of the power supply schematic. Toward the top right of the diagram you see where the different rails leave the main PCB...they are labeled 1 ~ 14. Notice that terminals 2 (ground to mixer), 7 0V(D), 9 0V(C), and 11 (power supply chassis ground) are tied together just to the left...they all connect to one line! Notice further that terminal #'s 13 and 14 are not connected to the 20-pin umbilical connector, but they are tied in to the 0V rails! Is it possible that these are 0V(B) and 0V(A) respectively????


  1. Am I seeing that right, that all the GND and 0V rails are tied together in the power supply and I don't need to worry about them tying together in the mixer, and
  2. Am I also seeing it right that terminals 13 and 14 on the main PCB in the power supply are unused but available 0V rails and I could use one of those for my third 0V rail needed for the mixer???
Click to expand...
 
yep that seems right... as you are finding out it's pretty unusuall to run multiple grnd planes... first time i ever saw it drove me crazy trying to figure it out... it was a guitar amp that had one problem when it was in the chasiss and a different one when you pulled it out ... serious drag... if you're feeling paranoid about firing it up make a little pigtail and fuse the lines you're worried about...

i guess this is a good time to also introduce you to one of my favorite tools...


The Idiot Light... go to the hardware store and get some cable(or a heavy short extension cord) an empty four outlet box a single outlet switch plate and a light plate that fits the rest of the box...

now wire it up so that the light is in SERIES with the single outlet and is turned on by the switch...

now when you're not sure about powering up something use this... as the light in series with the outlet will light heavily if the unit in question is shorted... this little jewel has saved many a repair atempt... it wont work for things that have a heavy inrush current though... so not real good for tube amps or pa amps over say 500wts/rms...
 
Ethan...wow...thanks...scary...

Everything is still all torn apart right now, but its coming pretty quickly.

I got the "Control Module" (noticed it labeled as such on the dress panel...not "Master Module" as I've been calling it...) frame de-rusted and primered, almost done cleaning up the dress panel. I plan on recapping the whole Control Module before plugging it in though and that may be a bit, so my plan is to get the frame put back together, make a temporary adapter for the power umbilical and power up just the mother board and make sure nothing blows and that all the voltages are as they should be...then I'll plug in just one channel module and see what happens...

if you're feeling paranoid about firing it up make a little pigtail and fuse the lines you're worried about...
Click to expand...

Nawww...not worried a bit... :rolleyes:

More like TERRIFIED!!

How do I know what fuses to put in there?

I'm probably most concerned about the +/-15 and +/-18 rails...

i guess this is a good time to also introduce you to one of my favorite tools...


The Idiot Light... go to the hardware store and get some cable(or a heavy short extension cord) an empty four outlet box a single outlet switch plate and a light plate that fits the rest of the box...

now wire it up so that the light is in SERIES with the single outlet and is turned on by the switch...

now when you're not sure about powering up something use this... as the light in series with the outlet will light heavily if the unit in question is shorted... this little jewel has saved many a repair atempt... it wont work for things that have a heavy inrush current though... so not real good for tube amps or pa amps over say 500wts/rms...
Click to expand...

So, wait...the idiot light box is plugged into a wall receptacle, and then I'd do something like wire hot to one terminal of the boxed outlet, neutral to...wait...shoot...can somebody explain the wiring in there to me?? I'm probably making it harder in my mind than need be...I'm so much more comfortable with series and parallel circuits in DC...

60W bulb will do right?

So demented...does the idiot light work because you've got a finger on the switch and if the bulb is bright you can shut it down quick and hopefully minimize the damage? Like a kill switch with a 'kill me now' indicator?
 
sweetbeats said:
So demented...does the idiot light work because you've got a finger on the switch and if the bulb is bright you can shut it down quick and hopefully minimize the damage? Like a kill switch with a 'kill me now' indicator?
Click to expand...


amazingly simple idea... system analysis tells you that any complex circuit can be reduced to just a resistence relative to the other circuits... iow... the test piece is one resistence when compared to the light... if the test piece is working it's seen as a high resistence... if shorted it's seen as a low resistence... make sense so far??? so we know that the overall voltage is devided in a series circuit proportional to the resistences right??? so when the test is shorted the light getsmost/all of the voltage so the light comes on... and the test doesn't drop any voltage to speak of so ya dont blow something else... conversely when the test is good it's higher resistence than the light so it gets all/most of the voltage and works without the light coming on... make sense???

the wattage of the bulb is irrelevent for us...

wiring... hot outta the wall to one of the lights terminals... out the other terminal to the hot of the recepticle... cold of the recepticle to the switch... out the switch to the wall cold...
 
demented...

Got it...that's cool.

I gotta go to the hardware store again today to pick up some paint...its to touch up the meter bridge housing. They mixed some up for me but it totally doesn't match so I took it back and this time brought the whole housing and left it there to work on the match-up...:eek::( Don't like leaving one-of-a-kind parts at the hardware store...

Anyway, I will indeed pick up parts to make the kill switch...that is a simple but really effective neat idea. The series wiring makes sense now...no different than a DC circuit really as far as wiring (like the classic example of a battery and multiple bulbs)...I was making it more complicated in my mind...and I think I do understand how/why it works now because the bulb is the first thing the current sees...that's cool. :cool:

Thanks!
 
Just a smattering of updates on cosmetic stuff...

Got the new "feet" from Tascam today along with some new black nickel screws...also picked up new screws to mount the new feet. Only two of the original feet were intact and badly damaged, and all the screws were pretty much toast.

Got the old armrest upholstery removed and got the armrest de-glueified...probably get the new material adhered in the next few days.

SO...a little more cleanup of a few parts and I can get the main frame sections reassembled and get the motherboard assembly reinstalled.

Can't remember if I mentioned this earlier or not, but Mouser has the mating plug for the power supply connector...$0.77.

Here is a picture of the future trim panels...english walnut. Taking the log(s) to the mill in a week or two and then It'll probably be a couple months after sawing, drying and planing before I have stock to fab the panels.
 

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sweetbeats said:
Here is a picture of the future trim panels...english walnut. Taking the log(s) to the mill in a week or two and then It'll probably be a couple months after sawing, drying and planing before I have stock to fab the panels.
Click to expand...
Nice chunk of firewood you've got there. ;)
 
Yeah...we had to drop that tree this last Summer...it finally died and the branches were starting to drop from high up...it was over 100 years old. The stuff that was starting to decay I'm bucking and splitting for firewood, but there are about 5 logs I've got up on craigslist right now...they could make some pretty nice hardwood...not very many burls, but a decent amount of fiddleback, and just plain pretty wood...even the raw wood has a shimmer to it. :eek: Log #6 is the base...we are keeping that one. Its about 3' in diameter...maybe more...9' long with a crotch...crazy hard and dense. Took a large backhoe lugging down to topple it and that was after it had been cut all the way round except for a radius band about 2-3" tall where the saw cut didn't match up...hard.
 

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Such a family resemblance to the Model 15 mixers...

Wow...

I was looking at some pictures of some Model 15 modules on eBay tonight...the pictures were small...couldn' see much. I've asked the seller if he/she would be willing to email me some more detailed pics, but no response.

Anyway, the terminal connections of the PCB's look so similar, and I'm betting that the mother PCB assembly looks similar to the M-___...

Is there anybody that has access to a service manual for a Model 15??? I'd love to have a look...even at certain sections like the PCB layouts and exploded views...Anybody? Upload scans maybe huh?
 
The family resemblance tightens...

I had the good fortune of some assistance in getting access to an operations manual and parts list for the Model 15 mixer. I haven't looked really closely yet, and there are no schematics, but the blade-type modules, their design and structure on the M-___ are clearly derived from the Model 15...jack layout, inline topology and plug-in style PCB's. Even the finger-hole that is at the top of each module for the purpose of lifting up and disconnecting each module is the same on the M-___ as on the Model 15.

So it continues to be my opinion, based on my observations and the assistance of some of your posts, that this mixer is kind of a missing link in between the Model 15 and the M-500 series mixers. Obviously the screening, color-scheme and trim (knob caps and trim panels and such) are pure M-500, and the 8 PGM groups with individual assign, the AUX buss features are all very M-500, but inside it is much like the Model 15 though the opamp choices are all much akin to the M-500 as are the transformerless mic pre's. So interesting (to me anyway... :)). Oh to be a fly on the wall when decisions were made that brought the evolution of the M-50 and then M-500 mixers...so many bells and whistles of the M-___ were left off...But of course there are some cool features on the M-500 mixers not present on the M-___, and the M-___ would have clearly been more expensive to produce and hence would have been in a somewhat different price bracket, at least out of reach of the market that grabbed ahold of and popularized the Tascam family of products.

I mentioned way back in shoulderpain's original thread on this mixer that the eq section is very similar to the PE-40 parametric eq...I just got a service manual for my PE-40's and I'm going to be studying it and comparing it to the eq PCB on the M-___...I already see a number of similarities though...maybe the eq section on the M-___ seemed like overkill for the M-500 series but the design had found a home in the PE-40...as I mentioned earlier, the bottom knob of the stacked pots is the same on the M-___ as the MX-80, and I noticed that it is also the same as the PE-40, so timeline-wise there is arguably a link chronologically between the PE-40 and the M-___.

Great idea for the side panels. I bet they will look fantastic.
Click to expand...

Like most of my ideas/applied information, I got it from somebody else. Check out evm1024's work on his M-312 mixer.:eek:

https://homerecording.com/bbs/showthread.php?t=241555
 
Thanks for the plug

That mixer with the side panels is for sale.... I also have another set of M300 series side panels too.

I'd talk an alesis micron for the mixer....

I'm not trying too hard to sell it - yet.

--Ethan
 
Yer welcome!

I wondered if that had sold...

By the time I make up trim panel stock for the M-520 and the M-___ you and I will have enough material to go into business and live like KINGS!!!


:rolleyes::rolleyes::rolleyes::rolleyes::rolleyes:

um...considering how well your extra set of panels for the M-300 have moved...mayyyyybe I'm getting a little too excited...
 
Very cool...

Winz, thanks for putting that up. I studied the pics and schematics and read the guy's story.

I sent him an email too just to try and connect.

Yeah...There is definite Model 15 hereitage in the M-___...the motherboard design and such. I also see some of those same polystyrene caps in the Model 15 as are in the M-___, but absent from the M-500 series.

What was really interesting to me was the carry-over of the monitoring section of the Model 15 to the M-500 mixers...granted the Model 15 is obviously in single-channel modules, but if you look at the 8 monitor/buss master modules on the Model 15 you can see the same basics as the M-500 mixers with 16 monitor channels (stacked 8 x 2) that can be sourced to the buss masters or the tape jacks, and then the 8 buss master faders at the bottom.
 
sorry for going off topic, but i know some tascam heads will read this
did anyone work with a model 15?
comparison to M520?
and wheres the difference to model 15 B ?
 
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