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Akia GX 635D

Discussion in 'Tape' started by pjf610, Nov 24, 2018.

  1. pjf610

    pjf610 Active Member

    Messages:
    207
    Hi all, Well I am looking to start work on a 635 that was given to me, I just finished restoring a couple of pioneer and marantz receivers. I would like to know what are the most common problems i can expect. I noticed first that the right VU meter does not move and the sound is crappy, so the first thing is to DEOXIT all switches and controls. Any help would be greatly appreciated.

    Thanks Pat
     

     

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  2. Grbluen

    Grbluen AK Subscriber Subscriber

    Messages:
    2,344
    Did you clean the heads?
     
  3. hertzdonut

    hertzdonut Press Play and Stand Back Subscriber

    Messages:
    833
    Location:
    Claremont, NH
    Here's a thread referencing the 14 transistors that need replacing. http://www.audiokarma.org/forums/index.php?threads/scored-an-akai-635d.454856/

    One of them is tricky to get to, you can either install it from the reverse side of the board, or work your way through a couple components for access. I've been meaning to post these pics for a while, kind of a photo help guide for this particular transistor.

    Good luck!

    - Jeff

    Access-to-transistors-01.jpg

    Access-to-transistors-02.jpg

    Access-to-transistors-03.jpg

    Access-to-transistors-04.jpg

    Access-to-transistors-05.jpg

    Access-to-transistors-06.jpg

    Access-to-transistors-07.jpg

    Access-to-transistors-08.jpg
     
  4. pjf610

    pjf610 Active Member

    Messages:
    207
    Yes the heads was the first order of business, and thanks Jeff this really helps

    Pat
     
  5. hertzdonut

    hertzdonut Press Play and Stand Back Subscriber

    Messages:
    833
    Location:
    Claremont, NH
    You’re welcome, Pat!

    Some might wonder why go through all that (meaning the photos above) just for one transistor. I guess it started out for me as more of a “hey, can I do it this way?” And it turned into “Heck yeah!” ;)
     
  6. pjf610

    pjf610 Active Member

    Messages:
    207
    After digging into this a little the right channel id dead, so my question would be are these semi's the culprit???

    Pat
     

     

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  7. tapehead

    tapehead Active Member

    Messages:
    145
    Location:
    Tejas
    Great pix from Jeff. Note in his picture the black slide switch and the slotted arm connected to a solenoid that should move the switch back and forth. I believe these switches make and break connections between forward and reverse play heads. These switches can become oxidized and prevent play. Check these switches and use some deoxit - may correct your right channel problem.
    Mike
     
  8. pjf610

    pjf610 Active Member

    Messages:
    207
    Hi Guys, Question since I have the unit open what is the conciseness of while you can get to all the Cap's and Transistors should they be replaced since you can get to them?? I did the Deoxit treatment but NO right channel so I plan on replacing all the Cap's and Transistors Mistake or not??

    Pat
     
  9. pjf610

    pjf610 Active Member

    Messages:
    207
    Hi Jeff, did you replace the 2SC2130?? If so what did you use??
    Pat
     
  10. hertzdonut

    hertzdonut Press Play and Stand Back Subscriber

    Messages:
    833
    Location:
    Claremont, NH
    Pat, the general consensus is shotgunning is a poor substitute for troubleshooting. It's entirely possible to introduce additional problems without solving the root cause. I completely understand where you're at, though. It's tempting to think that the problem will be fixed with recapping. And re-transistoring. Hell, that thought has crossed my mind more than once when faced with an issue. But, I always step back, get help when I need it, and track down the issue first.

    By the way, just to confirm, when you Deoxit'd, did you work the switches/pots 100 times? (Yeah, I'm not kidding!)

    - Jeff
     
  11. hertzdonut

    hertzdonut Press Play and Stand Back Subscriber

    Messages:
    833
    Location:
    Claremont, NH
    I only replaced the 458's.
     

     

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  12. pjf610

    pjf610 Active Member

    Messages:
    207
    Sure did still DEAD right channel, that is what I am thinking,only the 458's
     
  13. phantomrebel

    phantomrebel Serial Tapist Subscriber


    I agree. One of the big ones to address first is the long switch assembly that sits on the bottom PCB (Tapehead referred to this as well). It is in the perfect location to collect dust and causes all kinds of problems when the switches under there are dirty. Some folks clean the pots along the faceplate and ignore this troublemaker located within several Akai models. Here it is shown at the 5:00 mark in a GX636 for reference:
     
    Last edited: Nov 26, 2018
    Audiotfoot likes this.
  14. pjf610

    pjf610 Active Member

    Messages:
    207
    Thanks for the tip, I will start on the right channel and see as we go.
    Thanks Pat
     
  15. pjf610

    pjf610 Active Member

    Messages:
    207
    Well I started to change out the 458"s their were 20 of them and I only had 19 on hand I have another 100 on order should be here in a day or to, there were NO 945"s in their only the 458's so now I am wondering should I look on the main amp board to see if there are any there. Your thought's.

    Pat
    .
     
  16. hertzdonut

    hertzdonut Press Play and Stand Back Subscriber

    Messages:
    833
    Location:
    Claremont, NH
    My thought would be, once you get #20 in place, is to put enough of it back together for testing. You need to make sure there’s no changes (for the worse!) after completing that board before you move onto the next one.
     

     

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  17. pjf610

    pjf610 Active Member

    Messages:
    207
    Hi Jeff, one question did you pull the pc board out?? I found it easier to take the board out to change all transistors, also i checked all the transistors and the range for the HFE 1 was at 74 the rest between 120 and 333 does that tell you something???

    Pat
     
  18. hertzdonut

    hertzdonut Press Play and Stand Back Subscriber

    Messages:
    833
    Location:
    Claremont, NH
    Pat, I don't believe I pulled the board out, but I could be wrong. It was a couple of years ago when I did the work on mine. But you're right, it's always easier to work on a board when you've got good access.

    Regarding the numbers, (I'm assuming you were testing the old transistors, yes?) I don't think the HFE numbers (gain) have any bearing on your issue. They can all vary from each other, and usually do. But I'm no electrical engineer, so if I'm passing on incorrect information, I trust someone will correct me.
     
  19. pjf610

    pjf610 Active Member

    Messages:
    207
    Yes those were the old ones, did you do your own calibration on your deck???
     
  20. hertzdonut

    hertzdonut Press Play and Stand Back Subscriber

    Messages:
    833
    Location:
    Claremont, NH
    No, I never messed with the heads, and I have a bunch of Maxell UD XL and XLI big reels that I record to. I set the bias and eq based on the owners manual, and it sounds fantastic!

    My understanding is if you mess with the heads, calibration is mandatory. Merely recapping a unit doesn't necessarily mean it has to be calibrated. If I was a tech with all the gear, then yeah, I probably would go that extra step. But I'm not a tech, and I don't have a cal tape or o-scope.

    I realize there are tape guys who dial their machines in specific to one and only one tape, and that's probably the utmost in accuracy. But if my decks pump out awesome sound, I'm not going to go after that last 10%. (5%? 1%? )
     

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