My poor old Nak 681ZX is on it's way to PerryinVA for repair.

Discussion in 'Tape' started by Bigerik, Mar 18, 2012.

  1. Bigerik

    Bigerik AK Subscriber Subscriber

    Messages:
    19,831
    Location:
    I've Been Everywhere
    My poor old Nak 681ZX is on it's way down to Nak tech PerryinVA to get sorted out. Hopefully, the after 3 years, Perry will be able to get this sorted out. Will update how things go. Likely will take a while, as Perry is pretty busy. I don't expect to hear much for a month or so anyway.
     
  2. Bigerik

    Bigerik AK Subscriber Subscriber

    Messages:
    19,831
    Location:
    I've Been Everywhere
    Actually, Perry, could you give everyone an overview of what is involved in the overhaul process?
     
  3. perryinva

    perryinva IS it vintage????

    Messages:
    2,172
    Location:
    Richmond, VA
    Missed this when you posted it, Bigerik. Sorry.

    I'm sure every tech has a different approach, but mine is to first clean the tape path, as I've NEVER ever gotten a deck for repair that had a clean path, where I would put any of my cal tapes in it. I have a set of trashed tapes that I use for evaluation, so I use them to get an "as found" evaluation of what ever the problems are. Depending on the condition and operation of the deck, I run it through it's paces and get a base line, until I am confident I can proceed with a normal overhaul.

    I unfortunately had to learn this the very hard way, when I was working on a deck that didn't seem to play any sounds, though all seemed OK. It turns out the erase head was in full erase mode when ever the deck was running, whether the record protect tabs were in or not :-(.....so I was rewarded with nice, 30 second to 2 minute gaps of silence in 3 different calibration tapes, two of them very expensive Nakamichi tapes.

    Since your deck has had very little use since you got it, always had issues and had been previously "serviced" by persons unknown to me, I was extra careful. You told me you hadn't done any DIY service to it, and were unsure of what might have been done to it before you got it. Besides ESL and a very few others, I've been underwhelmed by the methods used by most DIYers and service places. I get way too many decks where the description starts with "I sent this deck to so and so, and was told "it works fine now/couldn't find the problem/all it needed was a belt/a little deoxit fixed it/it's fixed", but it still does the same thing", or "now it's worse than ever". Yours appears to be from the same category.

    Your deck arrived fantasically packed. Wrapped in a towel, and firmly encased in a cocoon of rigid styrofoam, with at least 2.5 inches in every direction. Well done. Your deck basically worked, but had obvious, very common, standard transport issues. The start/stop squeal was there, the FF/REW rumble, play noise, and other typical issues all consistent with old belts and tires, old lube. Autocal did not function, always flashing "not completed". Opening up the deck, I found contact cleaner lube spray (deoxit?) pretty much everywhere. Every connector, every pot and switch, dripping with the stuff. Running between components. On the plus side, the pressure roller arms both rotated easily, the capstans cleaned up very shiny, and the heads looked to be low hours, as did the counter bulb, with no blackening. The original well light is working, another sign the deck was not used too much. There was a missing cover on one of the rocker switches, and 2 others slide right off with no effort. I glued the 2 back on, and have to search the box in case the other is in there. The cam belt and XAAC belts appear to have been replaced. W&F was a poor .08%avg and highly erratic, hitting .12% at times, speed very slow, off by more than 5%. HF response was poor, down 20+dB at 20kHz. The right channel did not appear to work. There were no feet on the deck. There was a service card taped to the side with "Does not calibrate" written on it. Regardless of whether a service place over used the spray or a PO, that any "service place" would return the deck to you like this is such a case of shoddy work, its just plain sad. How hard is it to use some paper towels and alchohol to clean up? The tape well was fairly groddy with hair, and even some roach body parts. The supply roller, turned with fair effort, as it was bound with oil soaked hair, as if it had been lubed to try to free it up. There is NO way any meaningful evaluation of the decks performance to correct the obvious symptoms could be performed in it's condition. The transport needed to be restored before I went any further.
     
  4. BMWCCA

    BMWCCA AK Subscriber Subscriber

    Messages:
    5,287
    Location:
    Virginia
    Thanks for that description. Not too far off-topic but while you're here:

    I'm the original owner of a Nak Dragon Cassette recorder. Never had any problem with it other than a few Sony tapes that wouldn't calibrate which seemed to be the batch, not the deck. Never moved from the cabinet where it still sits, never serviced, only de-magnetized with the Nak wand and heads cleaned with original swabs. So, after decades of limited use and while it's still working apparently just fine, is there some preventive service that should be done before a problem crops up? It's main function was to transfer vinyl to cassette for use in the car and remaster live recordings from my Nak 550 and tri-mic system (which I also still own).

    And, if you can answer here, what would that service entail in work as well as cost? Belts? Updates? I'd love to plan and budget for this and I count myself fortunate that I'm within driving distance of your expertise because I'd hate to think of my Dragon at the mercy of UPS.

    Thanks from up in Jefferson's country.
     
  5. perryinva

    perryinva IS it vintage????

    Messages:
    2,172
    Location:
    Richmond, VA
    Honestly, if it is still silent when if operates, the NAAC functions fine, still cals tapes, etc, unless you want to do an alignment & calibration check and a "quick" capstan lube, I wouldn't do anything to it. It really depends on how much you use it. Normally, when I get a deck, there is a problem, and it is shipped, and it becomes a "well, since there is shipping both ways, do everything that would need to be done so I know it will be good for years to come" kind of thing. But if you just want peace of mind that everything is as it should be, like just a capstan outer bearing lube (where it needs it the most), and a PB & Rec head alignment, and calibration, it's well under $100, and in fact, I drive down 64 often to Harrisonburg and West Virginia, so I could even pick it up and drop it off, though not for the next few months. Or if you brought it by, I could do it while you were here if the timing was right. Once you need to replace the idler tire, then thats when the transport comes out, and you may as well do everything, and the price goes way up.

    On a Dragon, I typically:

    remove the transport and label each connector. This is very time consuming.

    I replace the idler tire.

    I replace the counter belt, cam belt, and NAAC belt. The NAAC belt is a PITA to do, but a bit easier if the transport is out.

    I lube the mechanism, and oil the shafts: Idler tire, reel, cam, and motor pulley. I lube the outboard motor bearings and both capstan bearings with Isoflex PDP-65, and clean off the old grease on the thrust bearing and set to factory spec and regrease.

    I replace both common failure prone counter bulbs with white LEDS and a new dropping resistor, which should last forever. The deck will not operate if either bulb burns out in that direction and they are on all the time the deck is powered, in either direction.

    I replace the 10V 470uF cap on the motor control board, with a new 16V one, as this is a common failure.

    I replace the 2 soldered in, 4066 cmos switches, with high quality sockets, and perform Alex's level translation circuit. This is on the non-audio side, and allows the use of either his $50/ea chip, the original chip, or one I've found, that while not quite as good as his, reduces the THD from the original switch from .4% to .02%, and has a much lower linear "on" resistance of around 20 ohm vs the original non linear 145 ohm, IIRC.

    I align the erase, record, & playback head with the Nak gauges and tapes exactly as described in the Service Manuals, which covers stroke, tilt, height, azimuth, reverse skew, and guide path, as well as supply and take up torque in both directions.

    I calibrate all levels per the SM, as well as a NAAC alignment and calibration.

    Depending on the serial number, there are a number of updates that I may perform, and other cap replacements.
     
    Last edited: May 8, 2012
    'cisco and alexanderino like this.
  6. Bigerik

    Bigerik AK Subscriber Subscriber

    Messages:
    19,831
    Location:
    I've Been Everywhere
    Gentlemen, there is so much good information in this thread already, I think we need to make a sticky of it.
     
  7. shelby1420

    shelby1420 Enjoying the music.....

    Messages:
    4,295
    Location:
    St. Catharines, ON-Canada
    Hey Perry, glad she got there in one piece!! Hoping my wife 's not reading and figures out I used one of her good towels for this............................ I have the feet, most times if I can during packaging I remove the feet for a good snug fit!!!! Can't wait to hear this beast ( most likely making a stop at club Martin before it makes its way back to Erik..............
     
  8. SPL db

    SPL db It's all about the music! Subscriber

    Messages:
    17,337
    Location:
    Omaha, NE
    While we're talking Nak decks, anything to look out for with a ZX7?

    I picked one up a couple of years ago, no known issues save a few of my
    tapes squeal when played in this deck (haven't tried them in other decks yet).

    The tapes seem to move fine, just squeal a little bit.

    Could there be too much tension keeping the tape too tight where some tapes
    are affected by it and not others?

    Or it could be I just have a few bad tapes... guess it's time to break out another
    deck to test them.
     
  9. junkaudio

    junkaudio Super Member

    got a 670 zx runs great only the playbuttom lamp needs repair so far
    but belts need soon service
     
  10. perryinva

    perryinva IS it vintage????

    Messages:
    2,172
    Location:
    Richmond, VA
    I have a lot more to post, just need some more time. Also, there is really very little difference between the 681zx and 682zx, as far as a tech is concerned, besides the dolby board and transfer switch. Most everything else is the same.

    Some pics:

    Level pots, saturated with lube.

    ALCU, note oil on base. This was abit loose on the PCB

    Autocal board, with replaced opamp and power transistors

    Good tape guide alignment

    Good erase head alignment

    Good Stroke, both PB and Record
     

    Attached Files:

  11. Bigerik

    Bigerik AK Subscriber Subscriber

    Messages:
    19,831
    Location:
    I've Been Everywhere
    I deleted all the off topic threads. If anyone wants to discuss it more, please shoot me a PM.
     
  12. Bigerik

    Bigerik AK Subscriber Subscriber

    Messages:
    19,831
    Location:
    I've Been Everywhere
    Perry, I was told they had replaced a bunch of caps when trying to get the auto cal working. Any evidence of that?

    Interesting pics you posted. I guess just having a can of deoxit doesn't make you a repair tech, huh?
     
  13. perryinva

    perryinva IS it vintage????

    Messages:
    2,172
    Location:
    Richmond, VA
    Really? That is sadder still. Not a single cap has been replaced on the auto cal board, dolby board, or level board. I haven't look carefully enough at the logic or main board to verify. Unless they put in old caps from another deck (Shoeis) and dulled the solder afterwards, I really doubt it. Only evidence of work, besides the Deoxit everywhere,is the cam belt, and both NAAC belts have been replaced. The 2nd counter belt was so floppy thin, any drag at all stopped the counter. If you had told me the deck stopped playing periodically, I would have bet it was that belt. I hope to finish it this weekend.

    There have not been a lot of play hours on this deck. The counter bulbs blacken with use (just being on, not even in play) and yours was clear, but I upgraded to a white led and dropping resistor anyway, and there is usually a lot of reel hub rubber "brake dust" under the reels when you crack the transport open, if there was appreciable ff & rew, and there was none to speak of on yours.

    While the 682zx & 681zx appear dauntingly complex when you remove the cover, in reality, they are extremely service friendly, with easy transport removal, fairly open access to boards and components. The Dragon, ZX-9 and even 680zx are worse to work on.
     
  14. perryinva

    perryinva IS it vintage????

    Messages:
    2,172
    Location:
    Richmond, VA
    The ZX-7 is a very under rated deck, IMHO, based on the prices they go for. ZX-9s typically go for double what a 7 will go for, and that is unjustified for simply better W&F, I think. It was the TOTL chronologically (not including the Dragon) after the 682zx.

    Some tapes may squeal more in a dual capstan deck than a single, but that is not a Nak thing. It has to do with the tension to the reels and the isolation of the intra capstan tension. Prerecorded tapes tend to do it more often, than quality shelled tapes. Also, if the reel shafts are dry on a Nak, they can squeal, but not really loud, like a shell/tape squeal.

    Otherwise, it just requires the same maintenance as other Naks of that era.
     
  15. Bigerik

    Bigerik AK Subscriber Subscriber

    Messages:
    19,831
    Location:
    I've Been Everywhere
    That's really disappointing, Perry. I kept getting updates on all the work they were doing. I can't imagine why they were doing sloppy work otherwise, but then worked do hard to hide the caps they switched.
     
  16. perryinva

    perryinva IS it vintage????

    Messages:
    2,172
    Location:
    Richmond, VA
    Like I said, perhaps on the logic board, where the power supply is, though nothing stood out, and I tend to notice stuff like that. The main board is the amplifier and oscillator board, and it has all original caps, too. If you want, I will include the removed parts to you, but in reality, that means little. I have bags of removed parts, and it is pretty easy to see new caps, as all the Nak ones are powder blue or orange. I use Nichicon audio electrolytic caps, or wima or panasonic for polypropylene. I replaced the trouble prone oscillator caps, as a preventative.
     
  17. perryinva

    perryinva IS it vintage????

    Messages:
    2,172
    Location:
    Richmond, VA
    Since Erik is curious about how I work on a deck, for this thread, I'll show a few pics on the bench in my mancave, in action!

    My bench setup, with a recently finished, LX5.

    Some of my Cal and test tapes, and Nak gauges

    More Cal tapes, including my Nak ones

    This is the connection from the output points. I can monitor what the play head is putting out as it would go to the output of the deck in Play mode, while in Record

    Here I am recording 400 Hz,at 0dB (Dolby level), from a T-100, where I can see the matched outputs on my dual channel Leader VTVM, and see the inputs and waveform on the Leader Audio Analyzer. I just move the leads from the VTVM to the ANalyzer, and I can do a direct comaprison of the input waveform to the output wave form. At this level, on a Nak, and any decent deck, they are identical. This setup is necessary to calibrate the auto level part of the 681zx.

    Same as above, but at 15kHz, -20dB, from the T-100. Note that the right channel meter on the 681zx is one segment low. This is not uncommon, and not really important compared to making sure that when in enhanced mode, where -20dB is 0dB indicated for a 1dB resolution, everything is correct. It wasn't on his deck originally, but it is correct now! Very important to note, that when you record the internal built in 15kHz level, I have calibrated it, so it is exactly -20dB. The 681zx meters, when recording the internal 15kHz tone, goes into enhanced mode and displays the PLAYBACK of the tape, so you can adjust the bias very accurately, within 0.5dB, for each channel. This was Naks way of allowing very accurate calibration, without a Tape/Source switch. Very cool. So as far as setting up and calibrating a tape, it is exactly as accurate as the 682zx. During normal playback, you would see that one segment disparity as illustrated.
     

    Attached Files:

    Last edited: Jun 1, 2012
  18. junkaudio

    junkaudio Super Member

    serious tech working there :thmbsp:
     
  19. perryinva

    perryinva IS it vintage????

    Messages:
    2,172
    Location:
    Richmond, VA
    The transport on this deck required a total restoration. In this case, where W&F is unacceptably high and the transport is noisy, it was obvious. I take apart the whole transport, clean out the old grease in the reel stacks, the transport, capstan thrust bearing and mechanism (exactly like the 505 transport restore in the sticky), relube, install a new capstan belt, idler tire, new counter belts, and replace the counter sense bulb with an LED and dropping resistor. I reset the head and guides alignments (stroke, height, tilt, azimuth, & skew for all 3 heads), reset the supply torque, and check for proper operation. At some time, someone had flipped the original belt, so the direction arrow was underneath, a poor attempt to get a few more hours of operation from the belt. The restored W&F, JIS, is a very nice low 0.025% now, and a DIN of just over 0.04%. Really excellent for a deck this age.

    Autocal now works properly, after locating a faulty op amp and bad driver transistor, which caused the NAAC unit to only move in one direction. I always replace the driver transistors in matched pairs. After that, I checked the playback frequency response. Using the Nak PBFR tapes, I found the 20kHz PB at around -10dB below 20dB, and 10 kHz at -3dB below 20dB. No adjustment of azimuth or height improved the numbers, and the 23kHz filter was set correctly. On other decks, it is usually enough to adjust the eq, via the shorting pads, but this has little effect at 10kHz, so I suspected other culprits in the eq circuit. In general, if a Nak head is badly worn it would act this way, and the waveform would be distorted, but this one was not at all, and it actually appeared to have very few hours on it in general. If a Nak head is bad, it is usually bad at all frequencies, or just one channel. The eq circuit has 4 low noise caps directly from the heads to the amps, so I pulled them and found them to be barely in spec, which is actually unusual for the orange Shoeis, I installed 2 matched pairs of Nichicon audio caps in their place, FG for the direct coupled, and KT for the indirect. This gained about 1.5 dB at 10kHz, and perhaps 5dB at 20kHz. I then shorted the high frequency eq resistor pads, and the rest fell nicely in to place.

    After calibrating the record head height and azimuth to match the playback, I then calibrate the automatic azimuth (phase) adjust and level adjusts, using a number of different test tapes, to ensure compaitibility. On older decks such as these, bias adjust will affect level adjusts, so in order to get the best calibration, you must run autocal, then adjust for best bias on the front panel, then autocal again, to compensate for any gain change. Normally when you check bias after the second autocal, all is well, but on some tapes, where you are extremely off to begin with, a 3rd iteration is required. On all these era decks, it is prudent to replace the trouble prone caps in tha bias oscillator circuit, as shown, and readjust for 105kHz.
     

    Attached Files:

    Last edited: Jun 2, 2012
  20. perryinva

    perryinva IS it vintage????

    Messages:
    2,172
    Location:
    Richmond, VA
    Some more pics of work in progress.

    The oscillator, the right tool for the job, lube the front capstan bearing felts with the right lubricant, new idler and belt
     

    Attached Files:

Share This Page