Tascam 122 MK3 Issues

Discussion in 'TASCAM Analog Forum' started by Thomas _Tascamuser, Jun 27, 2021.

  1. Thomas _Tascamuser

    Thomas _Tascamuser New Member

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    Hello guys!
    i´ve owned a tascam 122MK3 deck with the common faults (i´ve thought...). Yes gear C has been broken; the idler rubber has come off and the capstan motor has been more than very noisy. These probelems has been solved now, but i cannot get it back to work. Rew/FF and pause are ok. Play does not function, cause the idler drives the left reel (back) instead of the left. The rec button is out of function, no respond. No led will come on. The same issue has the middle group: the tube is working, reset, RTF and Control as well- but no other button. Has anyone an idea to fix it? Is there a wrong setting? And for what is the tact switch inside?
    I have made measurements at the processor: Play means: play out & rew signal to the driver IC.
    If the processor has gone: can i use the newer heads for my MK2?
    Thanks for any reply!
    Tom
  2. SkywaveTDR

    SkywaveTDR Well-Known Member

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    Hi Tom,
    The solution to the reverse take-up is to issue a play command from the remote socket from the remote connector in the rear. After that it will be fixed. I made a dB25 with a tact switch for my shop but a wire short between the ground and the play pin is all that is needed. The record issue might be the record detection switch in upper left- these can get out of position and can be adjusted back . The switch needs to close when the tape with tab is in the cassette holder. Tact switches can go bad but then the solder joints to the connectors on the control board also could be an issue- I have not had a Mk III with that problem myself yet. When working on the gear C it is important to clean off the feedback plate that has the contacts on it that have harden grease on it then I put a thin layer of Lubriplate 105 there.
    The reason the take up is wrong is the same IC is used for the 112R Mk II and that does have auto reverse so it can get stuck in that mode. I have seen it at least 7 times and it got fixed by my dB25 with play tact switch being pressed 1 time. Pin 1 and pin 24 is the closure as is on the diagram in the schematic P11. Make sure the two counter white connectors are on the right pins.
    They are the vertical ones down lower.
  3. SkywaveTDR

    SkywaveTDR Well-Known Member

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    The heads are not the newer one as they require circuit mod due to less output but the two heads are compatible from Mk II to Mk III. I have new heads to put in decks. They are not cheap. The Mk II is a better deck with more adjustments.
  4. Laszlo

    Laszlo New Member

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    Sam always amazes us with his sea of experience (especially re the Tascam 122 series decks..)!
  5. SkywaveTDR

    SkywaveTDR Well-Known Member

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    Well I work on a lot of them so I discover things. Ask me about a Nakamichi and I will refer you to Dan. Some big problem might be caused by the person working on a deck. Many things depend on how you do stuff and how gentle you are.
  6. Thomas _Tascamuser

    Thomas _Tascamuser New Member

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    Thanks for all these informations. These are my first tascam´s- normally i have the onkyo series (2070/2900). Yes, the MK2 is (in my eyes) more "service friendly" cause all drive issues can be measured faster. Now, i have shortend the pins as mentioned. And yes, it has reversed the rotation till.. shutting off. May be i have had luck, but i´ve tried out shortening like a morse code and: rotation ok, record function ok. But Loc/Memo and the OSC isn´t working anyway. And i have now a problem with the capstan; i think the switching transistor is bad, because i have a pulse on the 12V line now. 12V IC is glowing up and all lamps are flickering. I have tested the capstan drive with a regulated PSU and it is working well at 79mA.
    This deck makes me crazy with every minute....
    Do you know what the symbols means if i press the internal tact switch + power on? There are serveral possibilities for "on" and "off" - but what will be on?
    If anyone has the same issues with a bad osc and loc knobs please let me know.
  7. SkywaveTDR

    SkywaveTDR Well-Known Member

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    I wondered what that tact switch did and I pressed it many different ways- I do not know what it does and there is no mention of it in the service manual and I asked the two remaining service Technicians (Jim Finch from Monetbello Factory Service Manager) and Russ Bachmann and neither of them can tell you anything about that switch. I think you might have to ask Japan but the design people from those days are gone so I don't think they will know anything either.
  8. SkywaveTDR

    SkywaveTDR Well-Known Member

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    We have not had many of any power supply problems with these decks. I think I might have had to replace a 2 A bridge rectifier once but that is it. Now the soldering on the main audio board is not up to aerospace grade- I usually resolder many joints in deck as a standard practice- I find a lot of cracked joints on connectors and grey colored partially fractured joints where mine are shiny and have more lead on them- I call my joints bullet proof. Due to my age and not wanting to make mistakes I do my soldering with hood magnifiers on and good lighting using Kester 44 Lead containing solder. I used lead free solder as a radio station build and it took more heat and looked like slag when it cooled. I don't call that an improvement. I won't use it in my shop. Once on a 122 Mk II I did have the -15 Vdc supply at the connector wire but it never made it to the pin on the board. It was found that the loop contact had broken off and so I took one from another connector and attached it with shrink wrap to the connector on the deck and I was working again. These are very rare happenings.
  9. Thomas _Tascamuser

    Thomas _Tascamuser New Member

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    Now, something from the research company.. :) We have here two friends working together.. one HD74HC138P which will share a divided square wave signal to Y0-Y6; starting with 1K/500H/250H.... this will go out to different switches (as LOC1, LOC2...) and we have a nice processor which will receive this signal - means P140-P143. The received pulse at one line will tell the processor what to do. If they are incorrect, there is no switching possible. P140 to P142 has a needle impulse over a diode. P143 has a bad square wave signal- not a needle type. So, i guess. that will be (one) of my problems. Next of this issues has been the switching transistor (negative) for the capstan motor; driven by the processor. If there are any signal errors, this transistor will not switch to ground- he is pulsing. You will always restart the capstan- and with this glowing up the 7812. If i have additional time, i will check all outgoing and incoming signals; i think the resetting over the play socket will not reset the processor completely. U3 has a eeprom function....
  10. SkywaveTDR

    SkywaveTDR Well-Known Member

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    These decks do not go into this state from no reason. There has to be something plugged in backwards or could be a stuck switch. Even noisy switches can confuse a processor polling process as they have a longer response and the wave are random like noise. I replaced tact switches in a deck one that I press pause and it did fast wind. New switches fixed the problem.
    If the A,B, C is output from processor correctly then the 3-8 decoder will put out a signal to a single line as selected- some are diodes like LED and others are switch contact that are sending the signal on to go back to the polling controller. There are switches in the deck that are like cassette in switch that grounds the motor- that is all it does. It is the upper right switch. the motor should run if 12 Vdc is applied to the positive lead and the other black wire is grounded. The motor is a self starting device and can run outside of the deck with 12 Vdc applied as long as a resistor is substituted for the pitch control and I use 56K to 82K resistors there. just bend the resistor in a U and plug in the orange wire. The three pin wire is for HX Pro LED. The Pitch controls are so cheap that they break all the time from age or from looking at them. I am surprised they used such a low grade part. This is the penny pinchers doing this. I put a $5.00 plastic conductor 1 million rotation pot in that position but the shaft length needs lengthening and the correct orientation of the D shaft added to allow for knob position. So motor transistor- there are not many or any transistor there it is a BA6911 driver IC that if it works outside the deck then it should also work inside the deck. IF a skeleton switch as they are sometimes called is bent then it could send signal all the time- how did it get bent? easy to check. They are all along the top of transport- this is where tape type detection is, cassette in is and record enable. Check all power supply parts for correct voltage and I usually do a lot of resoldering down there. the cover comes off the bottom to get to this and also while you are in there I usually add the diode 1N4148 to base of mute transistor as Alex Nikitin has suggested to reduce distortion on higher level signals.
    The vertical white connectors of the switch board under the counter can cause issue if plugged in one over or pins bent or other issues like them reversed- people have found this to be their issue when they are not as experienced as myself. Unplug these and see if these are causing the problem. The function may not work but the deck will still run normal without them- they are just not there at this time. Other problems can be cause by things I do not even consider- that is why the guy who works on this has to observe and detect things I can not guess at.
  11. Thomas _Tascamuser

    Thomas _Tascamuser New Member

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    Hmm, next time i will give my screws names ;) All switches of the drive are cleaned now. I have checked every cable in and out. I have reworked the capstan drive too. My ideas have run out now. All is working with the exception of the two rows. I can see the signal going in at P143. Without having tact sheets for the functions you can only guess... and this takes much time. If i find a solution i will let you know.
  12. SkywaveTDR

    SkywaveTDR Well-Known Member

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    The schematic diagrams should tell you what switches go where and what lines should be returning a signal. What function are not working as you mention two rows.
  13. Thomas _Tascamuser

    Thomas _Tascamuser New Member

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    The first row is Adjust, RTZ and Reset = working. All other buttons not. I have checked the lines out from HC138. They are ok. And i have checked the ports P141 to P143. There are clear signals too. I have checked the data lines; for the working button i get a signal. For all others... not. I think that the processor cannot handle these datas. May be a communication error. Now, i have to replace the processor or the board (or forget it and use my MK2).
    The schematics tell me only the direction of the signals. A function/wave description would help me to control if the signals on to off are as wanted. And they are working with an overlay... you have a square signal from the cassette switch always on P143. If you press one button like Memo in, you will get a combination.
  14. SkywaveTDR

    SkywaveTDR Well-Known Member

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    First find out why P143 has a signal all the time. Next find out why signals for the two rows that do not work are not getting through. Comments like the processor can not handle it or changing boards tells me you are not experienced enough to work on these. If you are going to work on decks like this you have to deal with all of it. Not all of them are easy to fix. Most the time these kinds of issue do not happen. Did the unit do these things before you worked on it? Keyboard polling as it is called or multiplexing is just a matter of sending out signals in sequence and then detecting when they get back and through this they are then interpreted as to what button was pressed. If a Processor is bad then it would not work at all. I think you have a defective interfacing cable or broken solder joints that stop the signals from getting through. All the tact switches do is complete a circuit- with a scope if a square wave signal appears at the one pin and you press the button then it should appear at the other pin then trace that signal to connector and then to other boards where they are detected. If they do not pass then a defective tact switch so change it. People get intimidated because a processor is involved but they are not hard to work with. To date I have never had a 122 mk III that did not work after I repaired it. Keep looking- it is the guys who do not give up that will complete the repairs. Dean in Canada was getting ready to send me a V900X and it is just as complicated as yours. he tried one last time and he figured it out. You can not be easily defeated.
    Sam,