harman/kardon hk775 amplifier restoration

Discussion in 'DIY' started by z-adamson, May 7, 2017.

  1. z-adamson

    z-adamson Well-Known Member

    Messages:
    568
    Getting the ball rolling on this and to start I will order all the parts first rather than waiting till later.

    I have a complete parts list which helps. However, I want to order the right aluminum e-caps for the job rather than just blindly ordering audio grade caps of the right value. I would also like to order transistors. And replace the big filter caps.

    I hope to order this week, sooner is better.

    So, which caps do I order to replace which caps.
     

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  2. z-adamson

    z-adamson Well-Known Member

    Messages:
    568
    So, the filter caps are 15000uf, 71v. I dont want to use just any cap that fits those specs. What would you recommend?
     
  3. Blue Shadow

    Blue Shadow I gotta get me a new title

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    I pick caps by color. You can too.

    With such limited information if someone doesn't have a recap list, you need to make one.
    Figure out what is in the signal path and use good caps there
    Many use film caps to replace anything 4.7 µF or lower
    Measure the lead spacing of all caps and duplicate
    Measure size of the big caps and get ones that fit.
    Use same µF but you can go up in voltage (ConradH recommends 35V minimum for the small ones) unless you know what a change in capacitance will do in the circuit. There are some recap threads that discuss upping the capacitance and what it means. Those guys aren't cap swappers but technically trained knowledgeable repair/rebuilders.


    We'll be looking for your list and make comments.
     
  4. z-adamson

    z-adamson Well-Known Member

    Messages:
    568
    Historically I had gone to mouser and got nichicon caps, audio grade, same values. Results were good. However it was said that I should have used low leakage caps in certain spots, low esr in others.

    My goal is to select caps with the proper characteristics beyond uf and voltage ratings this time.

    I understand this amps runs hot so 105c spec caps will be used.
     
  5. jheu02

    jheu02 AK Subscriber Subscriber

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    What Blue was getting at (see I didn't use B.S. :D) is it will be helpful if you post a list. If the SM breaks it down by board, all the better. One thing to always do is check what's actually installed vs what's listed in the SM. That will sometimes give you clues as to what to use where...i.e. the orange caps you now know are low-leakage or special in some way like being bipolar.
     
    Last edited: Jun 10, 2017
  6. z-adamson

    z-adamson Well-Known Member

    Messages:
    568
    Here is the list.

    Let me state up front that all the caps are black unless specified otherwise.

    Power output and protection...4 caps @ 22uf, 100v....1 cap @ 47uf, 10v.....1 cap @ 33uf, 16v....2 caps @ 10uf, 16v - orange

    Power output and rectifier...2 caps @ 1000uf, 50v....2 caps @ 1000uf, 80v....1 cap @ 10uf, 16v - orange

    Driver.....1 cap @ 10uf, 16v - orange

    Power supply....2 caps @ 15000uf, 71v

    Pre-driver....2 caps @ 10uf, 16v

    Filter switches.....2 caps @ 100uf, 16v - orange......2 caps @ 1uf, 50v - orange

    Power level display driver....1 cap @ 1uf, 50v - orange
     
  7. jheu02

    jheu02 AK Subscriber Subscriber

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    My responses will be imbedded:

     
  8. z-adamson

    z-adamson Well-Known Member

    Messages:
    568
    Moving forward with this project, I have the amp apart and the filter caps are definitely soldered to the board. Does not have the appearance of a screw in or snap in, and perusing the mouser site, there are no offerings other than screw in and snap in. Kinda looks like the snap in version with the 45* bends broken off. Any idea what this could be?

    The manual for this amp really sucks. There are many components on the boards that are not listed. Hmmm.
     
  9. jheu02

    jheu02 AK Subscriber Subscriber

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    When you get one desoldered we'll know for sure. They'll either be snap in or solder lug (straight prongs sort of like a thin screwdriver blade). Take good "before" pics to aid in reassmbly (polarity, etc). Since the manual is poor, I would definitely make a list of the capacitor values and positions and plan on desoldering/installing one part at a time vs a mass desoldering and then parts installation. Any problems with it before you started opening it up? i.e. was it functioning properly or do we need to fix it first before recapping?
     
  10. z-adamson

    z-adamson Well-Known Member

    Messages:
    568
    It was seemingly functional before opening up. I only listened to it for a short time with the hk725 which was a long ways from full health however. I would like to restore to like new condition.

    They are definitely solder lug...ie flat head screw driver blade, still no pic, but that is what it is. What is the term for this on mouser? I could have missed it, but I didn't see solder lug on there.
     
    Last edited: Jun 6, 2017
  11. z-adamson

    z-adamson Well-Known Member

    Messages:
    568
    I am contemplating replacement of the output transistors.

    They are 2SA1094 and 2SC2564...toshiba. Four each per amp, so 8 each total.

    Neither Mouser nor their main competitors have them. A few ebay guys have them, but they want big money for them. Is there a good replacement that is economical and readily available through mouser?
     
  12. redk9258

    redk9258 Super Member

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  13. z-adamson

    z-adamson Well-Known Member

    Messages:
    568
  14. z-adamson

    z-adamson Well-Known Member

    Messages:
    568
    I don't follow.
     
  15. jheu02

    jheu02 AK Subscriber Subscriber

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    The insulator between the transistor and the heat sink.
     
  16. jheu02

    jheu02 AK Subscriber Subscriber

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    What are the dimensions of the large cap?
     
  17. z-adamson

    z-adamson Well-Known Member

    Messages:
    568
    Filter cap pics...

    52mm diameter, 80mm length, 22mm center to center in the terminals
     

    Attached Files:

  18. jheu02

    jheu02 AK Subscriber Subscriber

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    These are a little long (100mm) and unfortunately only one in stock currently, but would be a good choice when in.

    http://www.mouser.com/ProductDetail/Nichicon/LKG1K153MKZ/?qs=sGAEpiMZZMvwFf0viD3Y3TGBqvvFdz90Rzy/6Nc/jdMl79%2bkbKRswQ==

    These are screw terminal, but pretty perfect. Just get a thin piece of flat copper, drill a hole for the screw, and make your own tabs. With the way they're mounted, you actually have lots of options.

    http://www.mouser.com/ProductDetail/United-Chemi-Con/E36D750MLN183TC79M/?qs=sGAEpiMZZMvwFf0viD3Y3ZyaTCbqW/DTN9TU0mrie7w=

    EDIT: Perhaps even using 10 or 12 guage solid copper wire soldered to a ring terminal with silver solder for it's higher melting temp. Then pound flat the end not soldered to make your tab. No drilling required.
     
    Last edited: Jun 7, 2017
  19. z-adamson

    z-adamson Well-Known Member

    Messages:
    568
    Some other items I am trying to replace but not sure what to use.

    -Variable resistor.....VR402....part#.....5101 1517475.....150ohms
    -Variable resistor.....VR401....part#......5101 1027875.....1kohms

    I would like as many turns as I can get to aid in adjustment.

    -Cement resistor...R446,447,448,449,450,451,452,453...part# 5723 R33672.....0.33ohms, 3watt x 2 special dual (2 leads on one end, 1 on the other).
     
  20. jheu02

    jheu02 AK Subscriber Subscriber

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    If you can get a nice picture of how the trimmers are oriented it will help in selection. It's hard to tell from the SM whether you'll need side adjust or top adjust, hence the photos. I'm not having much luck finding 150ohm...you may need to go to 200, again, depends on orientation. VR402 for setting Bias would be better served by a single turn or it will take forever. DC Offset will benefit from multiturn. Haven't yet lookd for the dual resistors. Do you know if they're bad? Most times they're fine.
     

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