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Thread: Teac Tascam 80-8 Problems

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    Teac Tascam 80-8 Problems

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    Hi all, first post after years of lurking.

    I recently pulled a Teac Tascam 80-8 out of the corner where its been for 14 years. When I originally bought it all those years ago it worked fine except that channels 1&8 would not pass signal. I took it to a local tech who after a month tried his best and told me that the heads were finished and the machine wasn’t worth fixing. Younger me believed what the man said and took it home. I recorded with channels 2-7 for a little while before moving on to other machines and eventually forgetting about it until now!

    First thing I checked was Channel 1.
    I wanted to see if the heads were really as destroyed as I thought... Still didn’t work.
    I cleaned the heads and tape guides and got a good look at them. Not the greatest looking but actually not as band as I remembered. I threaded the tape and realized that whoever last adjusted the tape guides did and awful job. So awful that the tape was missing Channel 1 on both head stacks entirely. I realigned the tape guides and tested channel 1. IT WORKS.

    Checked channel 8.
    No signal still.
    Looked at the amplifier cards. Channel 8 had one blown resistor (R75).
    I Swapped channel 7’s card into channel 8’s slot.
    Test record/playback. Channel 8 PASSES SIGNAL.

    Now that I know the heads aren’t destroyed, I decide this machine is worth working on.
    One problem that seems to have developed since the last time I recorded with the 80-8 is that the capstan solenoid (actually part of the pinch roller) will not engage and lock. While testing channels 1&8, I had to manually “help” the solenoid into its full locked position, once it locked, the machine ran fairly smoothly.

    I decided to test the voltage at the capstan solenoid in play mode to see how much voltage it was receiving.
    It peaked at about 6v and dropped to a constant 3v when play engaged. It seems low to me but I don’t know what its supposed to be. (Anybody know?) I should note that it took me a while to realize that the solenoid was releasing from locked to free when I hit stop. That tells me the release function was at least getting enough voltage to operate. I also realized another issue.

    Earlier when I said the machine ran “fairly smoothly” I meant that it was just about up to speed but on occasion I would hear it lag and slow down. This was solved when I manually “helped” the brake solenoids for both reel motors.

    For a little while I had the machine running smoothly channels 1-8 for the first time!
    Then something bad happened.

    While I was probing and checking diodes on the power supply, something burned for about a second because I accidentally completed a circuit (naughty naughty me). I think it came from either C1 or C12 on the power supply. Since the mystery part burned, the poor 80-8 has even less voltage going to all three solenoids. None of them will lock into place even with help. (Bummer)

    I discharged the capacitors from C1 and C12 and removed them. I checked them out of circuit (like a good boy) with the help of a slow multimeter.

    C1 is a 25v 4700uF three pin capacitor.
    My multimeter read 4395 uF.

    C12 is a 50v 2200 uF three pin capacitor
    My multimeter read 1697 uF.

    I read on another post entitled “80-8 Total Solenoid Failure” and it led me to test the diodes leading to these capacitors. OP’s problem ended up being IC2.

    I have a gut feeling that the problem lies with one of these capacitors and when it burned, the solenoid problem became worse.
    Am I on the right track?

    Anybody got any ideas?
    Should I just replace the C1 and C12?

    Do you think I should replace the IC?

    What should I do?

    Thanks in advance.

    tldr: all three solenoids don’t engage in play mode and it seems to be a power issue. what should i do?
    Last edited by wildrecords; 01-22-2019 at 18:58. Reason: grammar

  2. #2
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    Repair of 80-8

    Ah yes, Another incompetent shop- that is what all local shops are in general.
    The Pinch roller mechanism may need cleaning and new grease- I use Lubriplate 105 type. The Caps on the power supply should be replaced. Age has taken it's toll and there is no reason to keep old caps in a machine. This model was in the racks when I started at the Teac facility and that was in 1982 so they can have some years on them. The tape needs to go across the heads in the proper way and even using magnification to get it perfect is sometimes required.
    The voltage on most Teac decks if I remember correctly was 33Vdc and then the hold was near 12Vdc. The meter reading you got of 6 and 3 are not good readings. The brakes and Pinch Roller get the same voltage so if it is decayed then none of them will work right. First rebuild the power supply with good caps. I get mine from Mouser. Three terminal caps are not needed as two of them are either the same or may be totally isolated. It is there to keep from wrong polarity.
    The 80-8 has a history of bad relays on the cards. These were often opened and burnished and then some grease applied to keep them from further decay. The slight amount of grease allowed the roughed up contact to stay in good condition as most of these machines were used in basements where high humidity could affect relays and heads. If the heads have unever wear and still have life in them they might have to be lapped at JRF to make the surface flat again. The wear of a head if for a long time can cause wear to take place in the wrong place thus leaving a step in the center of the head where one surface is higher than the next track wise. The tape to head contact needs to be a flat and consistent one.
    There were tantalum caps used in these decks. Then have a history of trouble by shorting due to voltage spikes that they do not like. We used to replace them with high grade Electrolytics that will work fine in those positions. It is true of the DX-8 dbx unit as well. I certainly spent a lot of time fixing those cards there.

    The 80-8 was a very good work horse for the typical musician with the right people giving technical support. We used to work on them all the time when I worked at Chicago Factory Service- they did not have too many major problems back then and we even fixed cards sent in- that is why we had a deck there to work on them. As time goes on there is the worry about the black card edge connectors cracking. It has happened in just about every deck including Sony that uses them. The Ampex ATR700 built by Teac had them too after all it was a A7300-2T with some dressed up front panel. I am still looking for these connectors.


    Quote Originally Posted by wildrecords View Post
    Hi all, first post after years of lurking.

    I recently pulled a Teac Tascam 80-8 out of the corner where its been for 14 years. When I originally bought it all those years ago it worked fine except that channels 1&8 would not pass signal. I took it to a local tech who after a month tried his best and told me that the heads were finished and the machine wasn’t worth fixing. Younger me believed what the man said and took it home. I recorded with channels 2-7 for a little while before moving on to other machines and eventually forgetting about it until now!

    First thing I checked was Channel 1.
    I wanted to see if the heads were really as destroyed as I thought... Still didn’t work.
    I cleaned the heads and tape guides and got a good look at them. Not the greatest looking but actually not as band as I remembered. I threaded the tape and realized that whoever last adjusted the tape guides did and awful job. So awful that the tape was missing Channel 1 on both head stacks entirely. I realigned the tape guides and tested channel 1. IT WORKS.

    Checked channel 8.
    No signal still.
    Looked at the amplifier cards. Channel 8 had one blown resistor (R75).
    I Swapped channel 7’s card into channel 8’s slot.
    Test record/playback. Channel 8 PASSES SIGNAL.

    Now that I know the heads aren’t destroyed, I decide this machine is worth working on.
    One problem that seems to have developed since the last time I recorded with the 80-8 is that the capstan solenoid (actually part of the pinch roller) will not engage and lock. While testing channels 1&8, I had to manually “help” the solenoid into its full locked position, once it locked, the machine ran fairly smoothly.

    I decided to test the voltage at the capstan solenoid in play mode to see how much voltage it was receiving.
    It peaked at about 6v and dropped to a constant 3v when play engaged. It seems low to me but I don’t know what its supposed to be. (Anybody know?) I should note that it took me a while to realize that the solenoid was releasing from locked to free when I hit stop. That tells me the release function was at least getting enough voltage to operate. I also realized another issue.

    Earlier when I said the machine ran “fairly smoothly” I meant that it was just about up to speed but on occasion I would hear it lag and slow down. This was solved when I manually “helped” the brake solenoids for both reel motors.

    For a little while I had the machine running smoothly channels 1-8 for the first time!
    Then something bad happened.

    While I was probing and checking diodes on the power supply, something burned for about a second because I accidentally completed a circuit (naughty naughty me). I think it came from either C1 or C12 on the power supply. Since the mystery part burned, the poor 80-8 has even less voltage going to all three solenoids. None of them will lock into place even with help. (Bummer)

    I discharged the capacitors from C1 and C12 and removed them. I checked them out of circuit (like a good boy) with the help of a slow multimeter.

    C1 is a 25v 4700uF three pin capacitor.
    My multimeter read 4395 uF.

    C12 is a 50v 2200 uF three pin capacitor
    My multimeter read 1697 uF.

    I read on another post entitled “80-8 Total Solenoid Failure” and it led me to test the diodes leading to these capacitors. OP’s problem ended up being IC2.

    I have a gut feeling that the problem lies with one of these capacitors and when it burned, the solenoid problem became worse.
    Am I on the right track?

    Anybody got any ideas?
    Should I just replace the C1 and C12?

    Do you think I should replace the IC?

    What should I do?

    Thanks in advance.

    tldr: all three solenoids don’t engage in play mode and it seems to be a power issue. what should i do?
    Best regards,
    Skywave Tape Deck Repair, Chicago area

  3. #3
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    Thanks for your response!

    I went ahead and ordered new supply caps and will swap them out when they get here in a couple days.

    The heads are not in beautiful shape by any means and like you said it seems there is some wear across them due to bad alignment,
    BUT... for the first time with this machine in over a decade I've passed signal in two of the channels that didn't work. Once I get this solenoid issue figured out I plan on using the machine with the heads as is unless I come across any sound issues I can't live with. I've sent the rec head from my 388 to JRF twice now and I'd love to rescue this machine from the graveyard and use it to lessen the wear and tear on the 388.

    I'll check back in again once I swap out these caps and let you know if it works.

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    The new capacitors arrived earlier than expected.
    The 63V C5 cap has the wrong spaced threads so I haven't swapped it, but I went ahead and replaced The 25V C1 cap and the 50v C12.

    The C12 is completely unresponsive, D9-D12 are also virtually 0.

    I'm assuming at this point I have 4 bad diodes because everything in the whole circuit is dead (R16-R20, Q3, Q4, D19, C9, C11, C13, C15).

    I'm already browsing the internet to replace these diodes but I'm not sure what to look for.
    Teac's part number is GI 601 but I can't seem to locate that code anywhere to even find a value. Any help?

    Thanks

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    I replaced D9-D12 after the rectifiers from mouser finally arrived.
    I also found a blown F5 fuse (I wonder if that has been my problem the whole time.)

    My C12 is drawing 41V now. F1 and R16 are also at 41V.
    C14 and R17 are at 7.8V

    I'm seeing that voltage is virtually nil at Q4. Two of the pins are at .3V and the other is 0.

    R18-20, and D19 are all 0V.

    Q3 is 41V on the C pin and the B & E pins are .3V

    I'm guessing the Q3 transistor is my problem.

    Could this be why the solenoids aren't engaging?
    I'm just about out of ideas for now, any input would be greatly appreciated!
    Last edited by wildrecords; 02-05-2019 at 20:03.

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