Portastudio 424 mk II - Unable to play, rec or rewind after a while

Discussion in 'TASCAM DIY Repairs and Mods' started by Ari Manninen, Nov 23, 2020.

  1. Ari Manninen

    Ari Manninen New Member

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    Hello

    Just got this recorder. It will not play, record, rewind or f.fwd for no longer than 2 seconds and during that 2 seconds the counter doesn't move. It doesn't do this all the time, because I just managed to record 3 minute worth of drumming into it, but after that it started again and it just won't work.

    If I put in cleaning mode, everything is working as supposed. Everything is rolling as intended and the operation feels smooth.

    If I don't use cassette, but use my finger instead to press the "switch" in the top right corner it does the same thing. Plays for 2 seconds and then quits.

    If I let it cool down for a while, I can do all the things, like record, playback and rewind, but it doesn't take long after the problem occurs again.

    So, something to do with warming up? Because cleaning mode seems to be working perfectly, it shouldn't be motors or belts? Some detector?
  2. Ari Manninen

    Ari Manninen New Member

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    And I got another hint. Before it stops working, you can see it from the counter. The counter is not keeping up when rewinding.

    If the tape starts at 0000 and let's say I play it until 500 mark, and after that I will rewind back to the beginning, the counter is going rather slow backwards while rewinding and the tape gets rewinded to the beginning but there will be still like 300 left in the counter. So it seems like the component that is counting the tape might be shot (?)

    All comes back to normal after I leave it to cool down for a few minutes.
  3. SkywaveTDR

    SkywaveTDR Well-Known Member

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    Reporting all the strange things with it is not going to fix it. There are hall effect sensors in some of these and if not positioned right they can cause error in the counting. These are not SMPTE stripped tape decks like pro equipment so some error of reel rotation will be present. Not 300 counts. In one deck I service there is a magnet wheel that can have hardened lubrication and the magnet actually comes lose from the nylon part it is attached to- I use latex glue to fix it. If that magnet is turning rather then staying where it is suppose to be creating mag signals then that could be the reason for inaccurate counting also IR bounce sensors can get dust on them and this might be what is in the 424. Why does it get so hot? There is nothing in there that should be creating a lot of heat. A hot motor would mean it is time for a new one.
  4. Ari Manninen

    Ari Manninen New Member

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    Hi and thanks for your reply!

    After writing here I managed to (somewhat) clean the IR sensor and it seems to solve the issue, because after that I was able to play and record for a much longer time and didn't experience any problems. I will continue testing tonight and hopefully the problem was that.

    It doesn't exactly get "hot". At least I don't feel anything getting hot. I was just thinking that somehow the warming up is causing the problem to arise. Maybe the sensor with that dust/dirt on it was able to barely work when cool, but after warming the situation changes.

    I will keep you updated.
  5. SkywaveTDR

    SkywaveTDR Well-Known Member

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    That is good at least you made some progress. Most decks stop for other reason due to the fast wind or reel drive system and often times there is the need to lubricate reel tables or gears that with the wrong lub in them have frozen up. I had one Porta Studio that had a reel drive gear that I could not turn by hand- I cleaned and lubricated it with a grease I use and then everything worked normal- this gear was deep inside the mechanism which you could not see from the outside. It is amazing that they used this kind of looks like damping grease in a lot of products with no idea if it was any good. At least I have never had a failure when using Lubriplate 105 through the years- that is what I use to replace the bad stuff they used.
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  6. Ari Manninen

    Ari Manninen New Member

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    Just an update.

    I went inside the machine again and tried to better clean the surfaces that matter, but it's in a pretty tight spot if I'm not gonna tear it all apart. After this cleaning operation I can get almost 3 hours of continuous usage before the problem starts, so we are advancing here.

    Next stop could be to throw new lubricants inside as well, because I have no idea if this machine has been serviced ever before. I'm gonna take your tip about that Lubriplate to my heart, thanks!
  7. dylnet_industries

    dylnet_industries New Member

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    Keep us posted on your progress. I don’t know if it’s the same issue but my 424 MK II won’t play, the playhead doesn’t engage when I hit the button. FF and RW work. I took out the transport and the belts and motor look good. What exactly is cleaning mode?
  8. Ari Manninen

    Ari Manninen New Member

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    Hi, that could be a different kind of a problem in case your FF and RW still works.

    The cleaning mode is the mode you turn on when you want to clean the tape heads, pinch roller and capstan shaft. To activate it, follow the pages 47 to 49 of the manual.
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  9. dylnet_industries

    dylnet_industries New Member

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    Thanks! I figured out the issue. Somehow one of the 1/4" input jack locks became loose and lodged itself in the transport, jamming the spring/arm mechanism that engages the tape heads.

    Thanks for the tip on cleaning mode. Any luck with your issue?
  10. SkywaveTDR

    SkywaveTDR Well-Known Member

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    As was found out in the last post, these are not that hard to figure out as complex as they are. The fact that the fast wind works never has any bearing on the play function as the play function involves a lot more of the mechanism than just a reel motor. Often times the reel drive system may work when nothing else does but it does no good to state that it works as what you need to find out is why the head base will not operate. The Lubricant they used evaporate and get hard. In many cases if one was to take the mechanism apart sufficient to clean these out and put Lubriplate 105 in then the deck will not fail again at least not for the lack of good grease. I don't remember the model but the one gear that transfers rotation to the reel table was frozen solid. I use Denatured alcohol and I freed up the gear and then removed it and put Lubriplate in that section cleaning out all the old garbage they used- the deck left working perfectly from my shop.
  11. Ari Manninen

    Ari Manninen New Member

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    Great to hear! The issue of my machine is not bothering me at the moment, because I'm using it for short times only. After getting my on going recording project finished I might have it serviced.
  12. Ari Manninen

    Ari Manninen New Member

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    Hi, it's been a while since I last messed around with my 424 mk II.

    Long story short. I had my portastudio serviced by an audio repair shop. Even though I hinted them that I believe the sensor or the wheel to be the culprit, they thought the problem was old belts and they replaced them all. Nuff said, back home I found out that the problem persists.

    Fast forward a year and now I managed to gather enough motivation to go deeper into the machine. Still I couldn't get easy access to the sensor, but I found out that the wheel the sensor is facing was looking unhealthy, please see the video below:



    In the video you can see green in part of the wheel. I guessed the condition of that wheel might cause the problem when it gets warmer, so I tried to clean it the best I could. The green came off almost completely, just a light tint remained and the whole wheel was looking "shinier" after cleaning.

    Now when I tested the machine, I had a sense it worked longer than usual but eventually it came to a halt, so the problem still persists.

    Do you guys have any idea how that wheel is "supposed" to look like when in good condition and do you think the Hall sensor could be crapping out when it gets warmer?
  13. SkywaveTDR

    SkywaveTDR Well-Known Member

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    Local shops are a waste of time because they have the lowest grade of technicians if they are technicians at all. Why don't you approach the problem like a real technician would and put a scope on the first stage of amplification off the hall sensor to see if it has the proper output. I did not look at the schematic for this unit yet and perhaps it is assumed a bad hall sensor is there when it is something entirely different. I don't recall a green substance in the decks I have worked on perhaps it is glue to a ring magnet that has fallen off the part that has the green. Usually hall or even reed switches work off ring magnets that have in other models fallen off and then the deck did not know the mechanism was rolling. I use Latex glue to put the magnet back on which was found in the unit. If the magnet is missing then that part will need to be found. The Tascam 112B I worked on last night has a ring magnet and hall sensors in it as does the 122 Mk II. These have shafts that had the wrong grease on them as well as reel tables. I take them off clean with denatured and apply either Lubriplate 105 to bottom bearing area and AMSoil to the shafts- when the breaks are off my reel tables now spin like a top and do not make that noise died out shafts make.
  14. Ari Manninen

    Ari Manninen New Member

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    Well, I don't have access to a scope unfortunately and I can't find schematics for 424 mk II. Service manuals seem to be available only for mk I and mk III.

    Yesterday I cleaned the mechanism entirely and put new grease in it. I also scraped off some "stuff" that was on the hall sensor. I was sure that was the problem, but no. Once I put the machine back together it worked normally for like 7 minutes before it stopped.

    But then I performed a test with the hood removed. I could use the machine all evening, without a hitch. Played like 300 minutes of tape, rewinded it back many times, counter was always as precise as it should (off just by a few counts).

    So there are zero problems when the hood is off. At some point I also used the machine with an external fan moving air through the machine and it also helped drastically.

    So in my opinion, it has to be some electric component that starts to crap out when the temperature gets a little bit too much and it affects the counter circuit.
  15. SkywaveTDR

    SkywaveTDR Well-Known Member

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    With that said I would suspect a thermal brake in a solder joint and the power supply would be extracted and resoldered entirely. If not thermal brakes are observed then you will need to monitor the power supply to find out which supply is failing due to heat- the part that is failing might be getting hot under the hood. Run for a time until failure and take cover off and go looking for abnormal heat issues. I think I remember one deck has a bad bridge rectifier in it but it was only 1 or 2 in my 47 year history. These kinds of percent of failures are going to be expected with all the units out there and then not having used Military grade parts. Bridge rectifier is those small square or round items that have 4 diodes in them that convert the AC from transformer to DC that then gets filtered by the filter caps. After this time you might not be wrong to change filter caps but I just have not seen any that needed it in large numbers so far.
  16. SkywaveTDR

    SkywaveTDR Well-Known Member

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    The only place to get a complete manual of the Mk II was on Stereomanuals.com which is paper but since Rick died last year it is unclear to me if they are still operating the business at this point.
  17. SkywaveTDR

    SkywaveTDR Well-Known Member

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