Tascam 122 MKII do not move heads

[wavebourn]

Hi gurus!

I bought on epay a nice tape deck but it does not move heads. A motor that moves them does not work. What is most common cause: dead motor, or potentiometer, or something else?

I searched Google for "+tascam +MKII +potentiometer +motor", but got a lot of links about potentiometers, motors, and decks for sale, but no technical information at all. It looks like search engines are not useful anymore, they are totally commerciolized...

[KL7OF]

Tolly,  Great to see you are still around!......You are right the commercialization (sp) is rampant on the search engines.....so....Buy google stock!....I can't help with the problem you are having but I will keep a lookout for info for you....Good Luck.... Steve KL7OF

[WA3VJB]

Not sure what you mean by "do not move heads."

The 122 is a fixed head, 1/4 track hissette deck, that requires you to flip the cassette if you want to record on the other side. It has an erase, record, and playback head, and since R/P are separate you can immediately hear what the record head just laid down on tape. This is known as confidence monitoring (making sure the tape's taking signal).

Consumer grade hissette decks with an "auto-reverse" feature, including most car stereos, move a head stack up and down to play the opposite set of tracks. Maybe that's what you're thinking of ?

[w3jn]

Tolly, good to see you on the board again!  Long time no see.

Are you talking about the transport mechanism (ie the motor that drives the spindle that engages the tape, and moves the tape across the heads)?  There is generally a servo circuit to keep the speed constant.  On high end decks there's sometimes a tachometer output from the motor, this feeds a small amplifier, with a potentiometer to adjust the speed, and this in turn drives a transistor that drives the motor.

Could be the motor is seized, or the pot is dirty, or anything else in the servo mechanism.  99% of the time, though, the drive belt has broken, but I'll bet you've already checked this.

If all else fails go to google groups -->  sci.electronics.repair newsgroup is a network of experienced technicians on consumer electronics that can probably help.

Good luck, bud!

73 John

[wavebourn]

Thank you guys, I'll continue investigations.

Both tape drive motors work well. The third motor moving heads and pressing them to a tape does not work. It rotates a gear which rotates a cam and other gear put on an axis of a potentiometer. The potentiometer looks like an ordinary pot, however wirewound one would serve longer, so I suspect it may be worn out.


http://wavebourn.net/images/tascam/tascam06.jpg

http://wavebourn.net/images/tascam/tascam07.jpg

[W1RKW]

Tolly,
Are you getting any DC to the servo motor when you try to engage the deck?
Try removing the servo belt and see if the motor spins up at all.  And while the belt is off see if the motor spins freely.  Some consumer electronic motors are notorious for seizing.

[flintstone mop]

That's an intersting problem!! Lemme check my Tascam deck and try to figure out the mechanics involved moving the heads to the tape in the
play position.
In the mean time did you contact the seller about your problem?? Or was this bought "as-is", "the panel lights are on and I hear motor sounds inside.......I know nothing about tape decks and because of the age of the unit I'm selling it as-is"....typical legaleez from an e-Pay deal.
The Tascam unit you have is supposed to be a good rugged deck, but it still hissses.
G'day
Fred

[wavebourn]

That's an intersting problem!! Lemme check my Tascam deck and try to figure out the mechanics involved moving the heads to the tape in the
play position.
In the mean time did you contact the seller about your problem?? Or was this bought "as-is", "the panel lights are on and I hear motor sounds inside.......I know nothing about tape decks and because of the age of the unit I'm selling it as-is"....typical legaleez from an e-Pay deal.
The Tascam unit you have is supposed to be a good rugged deck, but it still hissses.
G'day
Fred

The answer was,
"we would need a cassette
no one here would have one.
click the policies link in the auction"

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=7381430564

The next time I should understand what means: "Powers on, unable to test further".

It means "test failed".

[wavebourn]

Tolly,
Are you getting any DC to the servo motor when you try to engage the deck?
Try removing the servo belt and see if the motor spins up at all.  And while the belt is off see if the motor spins freely.  Some consumer electronic motors are notorious for seizing.

Thank you Bob, I did not check yet.

By the way, I searched newsgroups as John suggested and got a lot of messages with questions "What tape recorded to buy" and religious wars about which one to buy. 

[W1RKW]

Tolly,
One thing you can try that's easy is to squirt a little contact cleaner into the servo motor.  I think if you look at that motor you will see that it is open in the back exposing the brushes and commutator.  It is possible that that motor is not working because of oxidized brushes and a commutator. I've seen this happen with these types of motors.  It's common for CD player motors to exhibit this and contact cleaner is a sure fire method of verifying a motor problem.  All you need is a small squirt and manually rotate the motor to get it started if its the problem.

The other thing to look at is the servo motor amplifier.  Sometimes the transistor(s) or op-amp that drive the motor may be a cold or broken solder joint.

I'd suspect the motor before anything though.

[wavebourn]

Bob, you were right.
Indeed, the motor had dirty or worn out brushes.
I replaced it with one taken from a CD changer, but it spins endlessly; 9V on it all the way.
Going to check electronic parts...

By ther way, do you have schematics of that part? I took the nmechanism apart and tried to move potentiometer's axis, it has no impact on the motor.

[W1RKW]

Tolly,
Sorry, I don't have a schematic for that though the mechanism looks and my operate similarly to the Dragon and LX series Nakamichi machines.  Who knows the microprocessors maybe the same too for all I know.

In any event, if there are similarities between the Tascam and Nakamichi I'd look for any leaf or micro switches on the mechanism that is used for position sensing and check them for proper operation.  I know on the Nakamichi machines they used a couple of position sensing switches in addition to a potentiometer for sensing head position and other mechanism functions. It's possible that there is a switch that's not doing its job.  The Nakamichi machines used cheap leaf switches that crapped up easily and would make the machine to do weird things.

One thing you also need to determine by tracing from the motor backwards is the motor servo amp.  Typically they use a complementary pair like an output stage in a typical audio amp.  One of those transistors could be shorted causing the rail supply to turn the motor and no matter what you do with the position sensing potentiometer the motor will just keep on turning in the same direction.

Keep me posted.
Bob

[wavebourn]

Bob. it has a potentiometer for sensing and analog control circuit. I've found a service manual on epay, hope it has needed schematics: I am toooo lazy to fix without schematics now...

Thank you a lot for the moral support! 

[W1RKW]

Excellent on finding the manual.  Keep me posted on what you find.  You have me curious.  I used to service audio gear many years ago so that's why I'm curious.

[wavebourn]

Excellent on finding the manual.  Keep me posted on what you find.  You have me curious.  I used to service audio gear many years ago so that's why I'm curious.

Oops...
I was outbid tonite, no manual yet...

[flintstone mop]

Tolly
If your replacement motor spins all the time then it sounds like the logic circuits or the chip that controls that motor might be defective. I'm thinking there must be limit switches....tiny microswitches in there to tell the logic circuits where the heads are located for a particular function. Fast Forward, Rewind, Eject, or scanning the tape looking for the next selection of music. "Music Search"
Good luck
I don't have patience for that small stuff any more. The older Tascams were work horses in Churches and radio stations, believe it or not. The newer decks are so clunky and noisy. I have one of the newer ones. The older ones are still commanding a high price on e-pay.
Fred

[wavebourn]

No Fred, it don't have switches, it uses a potentiometer.
I bought one more cheap, with capstan motor dead, the rest should be fine as it "wow"s as described. Waiting for the donor now...

[flintstone mop]

OK Tolly,
Glad that you have a 'donor unit' on the way. I worked in a real sleezy TV repair shop that took parts from a pile of VCR's that were on the floor and they would charge outrageous prices. Change just the rubber tire on an idler and charge the customer for an entire idler assembly. $.25 vs $14.00
And their TV techs were parts changers. Keep changing out parts until it works. They were baffled with the new Horizontal high voltage transformer that produces every operating voltage known to man.
I should talk, after the so-called portable tube 19 inch TV's,those switching power supplies and HV transformers were a mystery to me too.
Good luck
Fred

[wavebourn]

One manager promised a huge premium for fixing automated production line. One technitian took a hummer and knocked couple of times something, after that the line started working fine. Manager asked him to write a report, what kind of work should cost so much money.
The report was:
1. $1.00 for knocking
2. $9999.00 for knowing where to knock.

So replacing a rubber on an idler may give as good results as replacing the entire idler.