Tascam TSR-8 Takeup Problem

I wonder... The right tensioner has two opto-detectors. The one on the bottom is on-off, and the one on top is graduated (the bit of plastic or metal which blocks the beam is shaped such that it blocks more of the beam as the arm gets progressively higher). We've been presuming the tension mechanisms are all okay because the machine shuts down when the arm drops. What if the on-off detector is working, but the graduated one isn't? Would that produce this symptom?

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BTW - do you have an electronic copy of the schematics? That would be a groove...

That’s a good question, but I think if that were the case it wouldn’t work correctly in other modes such as FFWD, REW and EDIT.
 
The reason I’m going with “not a tension issue” is the takeup motor jumps. If it was a tension issue it wouldn’t move at all. If it won’t go when there is no load (the tape is slack), it certainly wouldn’t move at the beginning when it is overcoming static forces, tension arm load, etc.

Not necessarily. The _PLAY logic line does a number of things, one of which is to 'flash' the reel motors, sending a burst of 24v to start them up, before settling to 12v - and I think that bypasses the tension subsystem, so it's possible you'll get an initial kick even if the tension circuit has gone dead. This is just conjecture, of course - unlike the Studer or TASCAM 32 manuals there isn't really a "Theory of operation" section.

As for the rest of the _PLAY logic, I think it gets inverted by U15, goes through diode D11, with diode D12 possibly bringing in an input from _FF and _REW (inverted by U16). It then gets inverted again by U28, is attached to a 5v pullup resistor (R69). After that, the signal is split two ways, for the left and right reel.
One of them goes back into U28 to be inverted yet again, then through the R101 tension adjustment (4.7K by the way), through R41 (220 Ohm) and on to the reel motor drive op-amps and so forth.
The other signal does essentially the same, being inverted via U28 but then going though R102 and R42 respectively.

U28 is a 7-way inverter. Pins 1+16 are unique to the _PLAY logic, the other 6 inverters are used for each of the tension adjustments. Aside from the actual tension circuit itself (R101/R102, R41/42) the only unique component to the play/tension logic circuit I can see is U15, a DTA124ES, which I -believe- is being used as an inverter going by the schematic symbols and apparent behaviour, but frankly analysing this is hitting the limits of my knowledge. I can do digital logic, but my basic electronics are not really good enough.

I've been going by a print copy of the schematics I got off ebay, but since people are asking, I had a look and found this: TEAC TASCAM TSR-8 Service Manual download, schematics, eeprom, repair info for electronics experts
...which should sort you out for the service documentation and schematics.



EDIT:

Ooh! Something else to try... what happens if you put empty reels on the machine and put it into play? You'll need to hold the right tension arm to convince it to run. I'd be interested to see if the left reel spins at all, i.e. whether we have back-tension during play.
 
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with no reels at all, left spool spins backward, right spool continues its misbehavior.

Right, so we are getting tension on the left spool but not the right spool, only in Play mode.

Looking at the schematics again and comparing it to what I wrote the other night, it gets weirder and weirder. The _PLAY line from the U21 command decoder is fed into the R101 and R102 tension adjustments, but those aren't the ones for Play - they are for Edit. The link prior to D11 feeds the _PLAY logic level into U28 and R103 and R104 which is the correct pair.

It kind of makes sense if I'm wrong about U15 being an inverter - if it's somehow acting as a level shifter to force the logic high level to 5v (may be 3v prior), that means that when _PLAY is low, it will go once through the U28 inverter and come out around 5v, which is then fed into R103/R104. The level into R101/R102 should be 0v by virtue of being inverted twice.
When _PLAY is high (which should mean 'disabled') the reverse will occur and we'll get 5v into R101/102 and 0v into R103/104. This means that there isn't really a 'Stop' tension condition, it's either using the tension trimmers for Play, Edit/Dump or FF/REW. Which is a bit confusing. Someone who understands potential dividers better may be able to figure it out. I also note that there isn't an _EDIT logic line anywhere in the system - the CPU must be utilising some combination of _PLAY and _DUMP to achieve that, and/or the undocumented data lines.

Anyway. One thing I do notice is that TP5 and TP6 (by the trimmers) give us the output of the tension trimmer circuit. If you know exactly what you're doing, and have a multimeter or oscilloscope with insulated probes, try attaching positive to TP5 and ground to the GND pin at the top of the control board. Then put the machine into various modes, in particular FFWD, PLAY and EDIT, and note down the approximate voltages. Then repeat for TP6 (if you have a dual-channel 'scope, you can do both at once). If you haven't done this before, be extremely careful since a short may damage the machine for good.

If the tension trimmer system is somehow causing the problem, you should get broadly similar values for all the modes except PLAY, and the weird value should only be present on one of the test points. If it's not showing weirdness there, we're running out of places for the problem to be. I was wondering the the _DUMP line might be involved, because the go/no go for the reel motors seems to the the U43 switch, and that does have a tap off the _DUMP line. However, that should either affect both reel motors, or else knacker FF/REW as well. (And also that would imply the main CPU has gone bad, which wouldn't be fixable).
 
TP3 and TP4 are 4.8v with tension arms at rest, 2.something when they are lifted, so there's nothing wrong with then tension arm detector things.

I looked more closely at the tension trimmers, and it appears that R104 might be damaged as well as R106 (which is damaged, although apparently working).
At rest, TP5 and TP6 are 4.0v, and when the reels are supposed to turn for various reasons (other than takeup during play), they hang in around 4.2v.
But, in PLAY mode (with the tension arms up) TP6 goes to 14v. That seems... extreme.
 
The deck is a servo tension reel drive machine. They can go out of adjustment when people get into them as they move stuff around that they should not be touching. On the other hand in some servo controlled decks there is a flash voltage to start the reel and then it drops out and the hold voltage is left driving the reel. This is isolated by a diode that will open. When that diode opens you have no more hold voltage to the motor. That is indicated when it works for a few second and then stops. This is not servo tension but a part failure,
It has nothing to do with back tension as that is isolated from the TU by the capstan system. It is best not to guess as it then misleads the person trying to fix the deck. You MUST use a Tentelometer as this is exactly how servo tension machines get broken- too much torque adjusted by know-nothings and then the components overheat and fail. I have seen it many times already in other models.
The Diode on this model is called D2 on power supply B board. Also make sure the C1 6800uFd 25V cap is not leaking.
The 24 flash voltage at 24Vdc and then 12V comes through connector P2-5 and goes to the Joint P4 connector 3. I would first see if both voltages are there.
I am one who fixes decks all the time- I have 200 in shop now.
 
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Well, the result on TP6 is about what I would expect if R104 has failed. That said, I would definitely try SkyWaves suggestions first, since he fixes these for a living and I just fix software.
 
Hey K, I've got multiple tsr8's and kinda learning alot about working on them, if you think its r106 (rewind adjuster) you can swap control boards with your working machine, it's easier than it sounds, just make sure machine is off or better yet unplug it, all those colored plastic plug ins are colored differently and easy to pull out and plug back in, but I doubt that's the problem and swapping boards would at least eliminate that as the problem, do you know your way around a multi meter?
 
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