TEAC A-1250 7.5 IPS playback slow

Discussion in 'Tape' started by Radioham, Aug 5, 2018.

  1. Radioham

    Radioham New Member

    Messages:
    26
    I have a TEAC A-1250 that plays a bit slow on 7.5 IPS. I can tell by playing a commercially recorded Beatles tape from Capitol. I know what the Beatles are supposed to sound like and this is slow. Not really slow, just a little. Playback on another deck is fine.
    I have checked the 50 / 60 Hertz switch and belt position, they are fine. I lubricated the capstan and reel motors using those little tubes and sewing machine oil.
    Interestingly enough the 3 3/4 IPS seems OK. I played another commercially recorded tape and that sounds OK. Not sure where to go next. Didn't want to play with pinch roller tension, (yet). Everything else seems to work fine. Motor start / run cap?
    Let me know your thoughts.
     

     

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  2. JH Magnecord

    JH Magnecord Member

    Messages:
    91
    The motor-run cap would seem to be the most likely problem...if you don't hear any hint of excessive "grinding" or see the shaft of the motor -particularly in reverse mode- having a wobble to it (which, otherwise, would indicate worse things: like broken windings from overheating or a grooved armature seat from no lubrication).
     
  3. Radioham

    Radioham New Member

    Messages:
    26
    No grinding. Lubricated the capstan motor, pinch roller, flywheel bearing etc. No help. I guess I'm not convinced that the cap would cause a consistently slow problem.
     
  4. audiojones

    audiojones Jonesin' for audio Subscriber

    Messages:
    7,108
    Location:
    Central NJ
    Try pushing the pinch roller linkage tighter against the capstan by hand while it’s playing, see if it speeds up. I’ve run into this problem on old 4010 and 1500W models due to lack of pinch roller pressure and hardening of the pinch roller itself. A few times I have found the pinch roller to look just fine with no glazing but the rubber had hardened up enough that it wasn’t gripping properly. I kind of doubt it’s the run capacitor since it’s working properly on lower speed, it really sounds more like a mechanical slipping issue.

    Regarding lubrication, don’t forget that motor has probably never been oiled in its life, so you may have to open it up to really soak the felt oiling wicks in there, a few drops in the tubes probably won’t get it.

    Make sure the belt is good too, hold the flywheel still with one hand and try turning the cooling fan on the motor with the other. If the motor turns without a fight while the flywheel is being held back then the belt is slipping.
     
  5. Radioham

    Radioham New Member

    Messages:
    26
    I tried pushing the pinch roller closer, it slowed it down more. I pulled it away a bit and it sped up but I think that was just the take up reel pulling it. I tried a different known good run cap of the same value, no change. I actually removed and disassembled the capstan motor and lubed the shaft directly. The wicks were already wet. No change.

    I did try holding the flywheel and turning the motor just now and it does slip on the motor pulley. I'll order a new belt. If it was slipping would the speed be so constant though?
     
  6. audiojones

    audiojones Jonesin' for audio Subscriber

    Messages:
    7,108
    Location:
    Central NJ
    If you pushed the pinch roller in a little tighter and it slowed down then I would suspect a slipping capstan belt. The speed is fairly consistent due to the inertia of the flywheel and the steady pressure of the pinch roller, same thing happens on a turntable when the belt starts to slip. I find that very often with these "A" series machines the capstan motor speed isn't exactly on the money but it should be close enough that it's not really noticeable. See what happens with the new belt.
     

     

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  7. Radioham

    Radioham New Member

    Messages:
    26
    Just for kicks I moved the belt to the larger side of the capstan motor pulley and it plays perfect. I'm not real sure what goin on there but I think thats the side for 50 Hz not 60 Hz. Confused. But it plays PERFECT. I compared it to another machine and an online digital version and its dead on. Not sure if I should leave it that way or get another belt.
     
  8. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,355
    Location:
    uk.. the middle bit
    large pulley for 50hz .. what is your line frequency ? if 60hz is the back tension set correctly ?
     
  9. Radioham

    Radioham New Member

    Messages:
    26
    Yes its 60 Hz. I didn't see a way to set the back tension in the service manual. Maybe the belt is just stretched out.
     
  10. audiojones

    audiojones Jonesin' for audio Subscriber

    Messages:
    7,108
    Location:
    Central NJ
    Please do not fool around with the back tension adjustment, this is not an adjustment to be casually tinkered with and it is not likely to be the cause of your problem. Altering that adjustment can get you lost in the weeds very quickly and cause damage / wear to the heads and tape path if it’s not set properly. Just try a belt and see what happens, sounds like a simple stretched belt issue.
     
  11. KentTeffeteller

    KentTeffeteller Gimpus Stereophilus!

    Messages:
    25,680
    Location:
    Athens, TN
    Replace the capstan belt with a new one. A drop or two in the oil hole for the motors, you should be good.
     

     

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  12. Radioham

    Radioham New Member

    Messages:
    26
    Put on a new belt, using the correct pulley location and it still played slow. I put the old belt back on again using the 50 Hz pulley location and it was back up to speed. But I did notice that in that orientation it plays WAY too fast on 3 3/4. Remember I said way back in the beginning that the 3 3/4 IPS played fine but the 7 1/2 was slow? Well that is a definite fact. Then I smelled smoke!!!! The 400v 0.1 Mfd cap on the speed switch melted! It is the one going to the red capstan motor wire which according to the schematic is for the high speed. So something is wrong between the two speeds. Now I have to find and replace that 400v 0.1 cap before I can proceed. Not sure if that cap was the problem or something else is wrong but there is a difference between the two speeds.
     
  13. dhnash

    dhnash Active Member

    Messages:
    491
    Location:
    Wildwood, MO
    The "cap" that melted is actually a spark killer (aka arrestor, suppressor or snubber) which consists of a 0.1uF capacitor in series with a 120 ohm resistor. These are known to fail unexpectedly. There are four of these connected across the contacts of the tape speed switch which are intended to protect them from arcing damage. There are also additional ones in other sections of the unit. It would be wise to replace all of these. Replacements are available from sources like this one:

    http://www.newark.com/roxburgh/xe1201/arc-suppression-snubber-network/dp/01M9475
     
    Last edited: Aug 13, 2018
    KentTeffeteller and rojoknox like this.
  14. KentTeffeteller

    KentTeffeteller Gimpus Stereophilus!

    Messages:
    25,680
    Location:
    Athens, TN
    Yes, replace that 400 V/0.1 uf capacitor and the 120 ohm resistor in series, on the speed switch, and also don't ignore the others in other sections of this machine, those are past their prime.
     
  15. Radioham

    Radioham New Member

    Messages:
    26
    Would that have caused my speed problem?
     
  16. dhnash

    dhnash Active Member

    Messages:
    491
    Location:
    Wildwood, MO
    Are you able to tell us if the spark killer that failed is one of the two that are connected across the tape speed switch contacts that are closed when the 3.75 IPS speed is selected? If so, leakage through the spark killer might have affected the current flow through the capstan motor windings which in turn could affect the motor speed when the 7.5 IPS speed was selected. One way to check this is to temporarily remove the spark killers from the tape speed selector switch, keep the switch in the 7.5 IPS position and check the tape speed to see if it is normal. If you do this it is important that you do not change the position of the tape speed switch while power is supplied to the capstan motor.
     
    Last edited: Aug 13, 2018

     

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  17. Radioham

    Radioham New Member

    Messages:
    26
    Two things:
    One, I believe that the spark killer that failed is across the contacts that are closed for the 7.5 IPS
    Two: I did notice earlier that I did see sparks on the contacts when the speed switch is turned with power supplied.
     
  18. dhnash

    dhnash Active Member

    Messages:
    491
    Location:
    Wildwood, MO
    It is quite possible that the deterioration of the spark killer(s) created a situation where they were no longer protecting the tape speed switch contacts. This may have caused damage to the switch contacts which resulted in an increase in contact resistance. This could affect the operation of the capstan motor.
     
  19. Radioham

    Radioham New Member

    Messages:
    26
    OK, someone wanted real numbers so I did calculations and came up with a 7.5 IPS tape speed of 2625. The 3.75 IPS tape speed is 3000, (or VERY close).
    When I put on a new belt there is no change.

    When I put the belt, (new or old) on the 50 Hz pully, (just for kicks - simulating a larger pulley size), the 7.5 IPS tape speed goes up to about 3090 but the 3.75 IPS also goes up the same about the same amount to 3465. Based on those findings a new custom oversized pully is not the answer.

    So I am back to the same old question: Why is there a difference between the two speeds? 3.75 IPS is correct, (around 3000) but 7.5 is slow, (around 2625). There is no drag, everything has been cleaned, lubricated and lubricated again as well as trying a new belt and start / run cap. I also used jumper leads to jumper across the speed switch contacts in a troubleshooting measure to eliminate them. There was no change.
     
  20. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,355
    Location:
    uk.. the middle bit
    is the frequency selector switch in the correct position ?
    also the line voltage selector needs to also be set correctly . as according to the manual if set wrong will mess with back tensions .
    section 6-6 in the manual
     
    Last edited: Aug 14, 2018

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