Tascam 122MkII Capstan Speed

[scan80269]

A colleague's Tascam 122MkII suddenly developed a problem today where the capstan spins at nearly 1/2 normal speed. There is also a rather loud rattling noise coming from the capstan motor whenever it spins. The speed, while still adjustable with the front knob, is nowhere near correct.

I suspect some component on the capstan DD motor circuit board went bad.

Has anyone experienced this?

[Pacific Stereo]

I've never had to work on the drive section of one of these, but there are some commonalities amongst all direct-drive motor schemes. On the drive motor board, you are likely to see three identical electrolytic capacitors (one for each motor coil) near the drive IC. In some cases, you will see two sets of three, each set being the same value.

Change those. If in doubt, there won't be many electrolytics on the board- you can just change them all.

[Skywavebe]

Hello Scan,
I have come across a number of units that had wrong speeds associated with the poor components (surface mount) that were used on the Capstan DD motors. I was told by other well known technicians that they twist off these caps and replace them with good through hole type caps of the FC type from DigiKey or Mouser and your problems will go away. This may not be the job for the not too technically experienced but this is what we have to deal with. I don't know if PS was eluding to this as it did not state but if it was he is right- in fact PS that I have seen here put a whole different light than the people I met here in Illinois while that company was open here.
I guess it was therefore not good to generalize in the negative about the Pacific Stereo company based just on the experiences I had here in the Midwest.

[scan80269]

Thanks for the pointers, PS and skywavebe!

I'm happy to report that my colleague purchased a replacement DD motor assembly from Tascam, and his 122MkII is now working fine.

The original DD motor assembly was beyond repair. Replacing the SMT caps on the PCB did not help.

[Skywavebe]

I am back with a similar issue.
The DD motor of a Mk III cassette deck seems to stop at a dead spot in the motor- I did not know there were dead spots on a DD motor but this one seems to prove it is true. I have changed all the caps on the board and have tried the freeze spray method with the three IC's that are visible. I know this can be fixed but to what extent will I have to go? I was wondering if any other seasoned Technicians have investigated into the circuit further that I at this point or will I have to do it? I have a spare machine with worn heads on the shelf that the motor works well in. I am resistive to just changing it out. I am of the opinion that far too many parts get thrown out because of the lack of investigative initiative to find the real problem. This one has me at a stand still at this point but I may move on. The caps were not the problem in this case. The motor will turn on speed but it has a point that it will not start up with the insertion of a cassette and the activation of the upper RH switch.

[fyzygy]

I have the same problem - noisy mechanism, tape playing back way too slow on this 122 mkII, even with pitch control & internal trimpot maxed out. This is after I replaced the caps on the capstan DC motor PCB (previously, mechanism had been even louder, and running away too fast). Any help fixing this new speed problem would be appreciated.

[A.N.T.]

Here is the schematics for the DD motor PCB from the Tascam 122mkIII I've traced from the pcb - may be of some help. I think that the 122mkII uses exactly the same motor.

Cheers

Alex


http://www.ant-audio.co.uk/Tape_Recording/Service/Tascam_122mkIII_DD_schematics_small.gif

[Tinman]

I am back with a similar issue.
The DD motor of a Mk III cassette deck seems to stop at a dead spot in the motor- I did not know there were dead spots on a DD motor but this one seems to prove it is true. I have changed all the caps on the board and have tried the freeze spray method with the three IC's that are visible. I know this can be fixed but to what extent will I have to go? I was wondering if any other seasoned Technicians have investigated into the circuit further that I at this point or will I have to do it? I have a spare machine with worn heads on the shelf that the motor works well in. I am resistive to just changing it out. I am of the opinion that far too many parts get thrown out because of the lack of investigative initiative to find the real problem. This one has me at a stand still at this point but I may move on. The caps were not the problem in this case. The motor will turn on speed but it has a point that it will not start up with the insertion of a cassette and the activation of the upper RH switch.

Sam, this sounds like an open driver transistor/IC. It's also possible one of the hall sensors is bad. I run across this on occasion. You'll have to scope the outputs to see.
It CAN be a coil as well, but usually that's a bad solder connection.

That's when I break out the microscope and very small iron. You can also try re-soldering the ic's first before you get too deep into it.

I used to replace a few drive IC's on a capstan or 10. Dead spot is usually the first clue. Happens on Revox decks a lot, but it's a re-solder of the drivers on those.

Marc

[Skywavebe]

Thanks Marc,
I do not have access to the deck that I once had to support in Radio and it is now their problem. If I know their history, they will probably just throw all the decks into the dumpster and at the same time lay people off because of no money. I do have one motor at home that I was going to get into deeper but that takes time that I am now using to get units out the door. I do find your advice always helpful and do recommend you as a repair person in LA depending on if you want to work on those units or not.

[GeoPT]

I also have the same problem. Someone could tell me what kind of component are H1 and H2. Thank you.

[A.N.T.]

I also have the same problem. Someone could tell me what kind of component are H1 and H2. Thank you.

These are Hall effect sensors.

Cheers

Alex

[GeoPT]

In my case, the motor slows down for about a minute, then back to normal, remaining so. I made the change of the capacitors, but not solved. Would have any suggestions of what can be? Do not believe that the ICs, but it will be my next attempt. Thank you.

[zzpuh]

Does anyone know where is it possible to purchase Tascam 122mk2 capstan motor, part number: 5370007501 ?

Full Compass used to have it but now I don't see it in there catalogue? Discontinued?

Any ideas please.

[rotovator]

A.N.T

Thanks for the schematics. It's being of great help to me.

[rotovator]

Hello.
I'm trying to fix my 122MK II

From what I've observed in the motor pcb, there are some differences between the schematics above and my observations.

C3 is C13 in my deck 10u 16V
C4 is C15 in my deck 10u 16V

Also C6 seems to be 100nF (it's not marked in the schematics)

I've still have a question C1 and C2, which have 3u3 have a electrolytic shape, but there's nothing that indicates the polarity (only a "V"). Are they polarized electrolytic or non-polarized??

Also, to ease the soldering I'm using short cables soldered to the capacitors and to the board from the other side. I will later glue the capacitors and they will have a 2cm wire to the soldering point. They seem to be stabilizing capacitors (all but one). Is it a problem? Should I solder them right to the board?

[A.N.T.]

I've still have a question C1 and C2, which have 3u3 have a electrolytic shape, but there's nothing that indicates the polarity (only a "V"). Are they polarized electrolytic or non-polarized??

Also, to ease the soldering I'm using short cables soldered to the capacitors and to the board from the other side. I will later glue the capacitors and they will have a 2cm wire to the soldering point. They seem to be stabilizing capacitors (all but one). Is it a problem? Should I solder them right to the board?

C1 and C2 are non-polarized. I don't think that 2cm of wire would be a problem on the supply filtering caps, however on the coupling cap C5 it may be a bit of a problem.

Cheers

Alex

[rotovator]

Thanks ANT.

You are _fast_

Those are bad new, as I don't have cannibalized non-polarized electrolytic. I will have to search for them from my electronic shop.

Anyway, I guess that the current to the coils is altern current, and not direct (don't remember the electric motor principles right now). Can you tell what would the symptoms be if these capacitors were bad? Or what is their function in the circuitery?

Thanks again

[A.N.T.]

Anyway, I guess that the current to the coils is altern current, and not direct (don't remember the electric motor principles right now). Can you tell what would the symptoms be if these capacitors were bad? Or what is their function in the circuitery?

Thanks again

The current will be AC and these caps do some smoothing, filtering HF - I don't know what exactly would happen if these caps go bad, but it is unlikely to do any good for sure.

Cheers

Alex

[rotovator]

Yesssssss!!!!!!!

My MK II FIXED
I did it. Capstan replacement of all electrolytics except the non-polarized 3.3uf ones.

The Deck started to play slow but not as before the replacement. i turned the speed pot next to the pitch control on the panel and adjusted speed by ear. A 1000 hz test tape will do the fine job .

I couldn't do more tests, as I was doing the fix and initial test at about 12 degrees celsius, and my hands started to disobey me, my feet sole were unsensitive and my nose was driping. But I can affirm that this unit had the capacitors dried, and the replacement has brought it to life.

[rotovator]

YEsss!! AGAIN

MK III fixed

here's some video I did about this motor
http://www.youtube.com/watch?v=16OOtIjUc2w


ANT: ANother modification to the circuit I found:

c7 is 4.7 uF 35Volts