Tascam MS-16 Transport Not Working....

ethyrvalve

Norman Nanoweber
Hi all,
I'm in a bit of a panic because I'm dealing with a deadline and my MS-16 very suddenly stopped moving tape.
None of the transport buttons are lighting up or functioning. Not even 'Edit'.
To summarize...
-the capstan *is* spinning
-the speed readout lights up
-the track arming panel lights up and behaves normally
-the minute/second readout is working (well it's stuck at 0:00 because none of the transport modes work).
-All the fuses are OK
Any thoughts? Experience with this issue?
It seems to be the identical issue posted by this guy: Tascam MS-16 Power Problem (sadly there was no posted followup).
 
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Inside the transport, on the Motor Control PCB, there are 3 heat sink mounted transistors which are susceptible to heat failure from age. They are listed as Q-10,11 & 12. I would replace all three of those and that should fix your dead transport issue. I've read other stories of this specific issue with the MS-16 and ATR-60 transports and that seems to be the most common fix. That board slides out through the rear of the transport casing but requires a fair bit of disassembly to get to so this is not a job for the timid or the inexperienced DIY'er. Page 8-28 of the manual will give you the specific part numbers. Pages 8-26 and 8-27 will show you the board layout and where those parts are located on the pcb.

Good luck!
 
Fair point about the ratings!

Hmm, the transistor junctions seem to test ok. Could they still be bad but test ok in a multimeter?

The person on groupdiy told me his issue ended up being the 5v regulator on the PSU pcb (mine is ok; all voltages seem to be ok).

I'm a bit stumped as to where to look next.
 
If the transistors were tested properly and (out of circuit to avoid any false readings), I guess the next thing to look at is to do with the power supply and testing whether or not the motor board is receiving all of the voltages it needs from the power supply. If all that checks out OK then I too am stumped as to where to look after all that is confirmed, beyond looking for visual signs of burnt components such as caps or resistors that show discolorment, (browning).
 
Thank Gle, they tested fine using the diode mode but I just verified again with the method used in the video.
I just noticed that the IC mounted on the heatsink is another 7815a 15v fixed regulator. I'm thinking this needs further investigation too.
 
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After having a surprisingly hard time finding an appropriate source voltage, I found the 7815A on the Motor Control board is ok too. I'm truly stumped now.
 
I re-soldered and reassembled the motor control board.
Another clue: I can now get into dump edit mode by clicking Edit+Play. And once in this mode. Stop will work. And the supply tension arm can be manipulated to vary the supply motor.
I wonder if there could be something wrong with the takeup tension circuitry? It's weird that all this happened so suddenly in the midst of tracking with no warning...
 
I'm of no help here. But i will say you are finding out what is NOT kaput. For example the transistors.
I'm sure through your process of elimination you'll discover and remedy the problem

Good luck.

I mainly chimed in to bump your thread, and let you know I checked out your blog. Cool stuff.
:thumbs up:
 
I re-soldered and reassembled the motor control board.
Another clue: I can now get into dump edit mode by clicking Edit+Play. And once in this mode. Stop will work. And the supply tension arm can be manipulated to vary the supply motor.
I wonder if there could be something wrong with the takeup tension circuitry? It's weird that all this happened so suddenly in the midst of tracking with no warning...
If there are other transistors or diodes in that part of the motor control PCB, try testing those as well.

Not sure of what else to offer at the moment. :(
 
Thanks guys.
I just checked my keyboard panel (with the transport buttons) installed on a friend's MS16. It worked fine. Using his machine I discovered that the takeup tension roller needs to be engaged for the play and fast wind modes. So maybe that's something to investigate...
 
Dont have a MS-16, but, do these have a tape sense switch? If so check it. If it doesnt have a switch, and instead relies on the right tension arm to "know" whether tape is loaded, that where I'd snoop a bit. Sounds like you were headed their on your own. Good job!
 
I have definitely seen regulator & motor drive transistors in many things that measured "good" but were weak in use. For instance I had an MS16 in for service recently where the capstan motor maintained speed but lost torque and slowed down after a few minutes... The tip-off, when compared to a new transistor of the same type, was that (for example) the difference between Vbe and Vbc when checked (out of circuit) on my DMM was much greater than the usual few mV. (This obviously doesn't apply to Darlingtons/FETs etc)

Agreed with mdainsd - I would check the "end sensor" PCB on the right-hand tension arm - also the tach board the signal passes through on the way to the control board - I think these might be FR-2 and prone to cold solder joints. Check the end sensor input at J2 pin 4 on the control PCB. Maybe you're looking at something as simple as a bad crimp or a cold joint on that Molex. The signal then passes through IC12 (4001 nor gate) and 14 (4049 inverter) before the CPU sees it, I'd check the inputs and outputs of those - you have an oscilloscope handy? I can take measurements off my working unit if you need to know what anything's supposed to look like in there. It sounds like the mask ROM CPU is OK if you can get dump edit to work.
 
I don't see anywhere in your comments that you verified the correct voltages coming from the power supply PCB...
 
I can't get at the machine today because of some construction going on in my building but I'll pore over the relevant sections of the manual. That's lots to chew on. Thanks!!!
I did check the voltages. They were all quite good. I think one of the rails was maybe one volt high. I'll recheck and write down the exact voltages when I can.

As an aside, Goreski put up a nice scan of the maintenance manual in case any MS-16 owners need it: Free TASCAM Semi-Pro Tape recorder Schematics and Manuals - from AnalogRules.com and AudioSchematics.com
It's a fair bit easier to read than the one that I remember being shared on here a few years ago.
 
I would check the "end sensor" PCB on the right-hand tension arm - also the tach board the signal passes through on the way to the control board - I think these might be FR-2 and prone to cold solder joints.

That was it! Thanks so much!! One of the end sensor wires was disconnected from the speed sensor board (still can't figure out how it came loose... vibration?). Of course hours of head-scratching and pouring over the control board preceded this discovery...
This is a huge relief. Three bands had tracks that needed mixing very soon.
 
Very glad to read that you got your machine up and running again. :)

Sorry that I sent you on a wild goose chase. :(
 
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