The KA-9100 restoration.

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by hopjohn, Aug 16, 2017.

  1. gort69

    gort69 AK Subscriber Subscriber

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    That looks fabulous. Do you use one of those lead bender contraptions or do you have a bionic eye? - those things are perfectly centered.
     
  2. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Thanks. I have fond memories of Lee Majors and even fonder of Lindsay Wagner.

    I have a set of those plastic, red, triangular shaped lead benders I think you're speaking about. For small components I find them useless as I can never get them to work as well as I'd like....too much slop. What I use are bent nose pliers. Just some cheapies I got from Harbor Freight many moons ago. They were part of a set. Looks like they still have a set or you can get these individually. Anyway, I just eyeball them. Once you get a handle on the lead spacing just memorize where the bend needs to be. No bionics required, though I will make the sound effect while I bend these from now on thanks to you.
     
  3. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Back at it again after taking care of some priorities. The remaining metal film resistors were installed as well as all of the new electrolytics.

    The 10uf 25V back to back capacitor pairs at Ci119/121 and Ci120/122 were each replaced with a single 4.7uf Wima stacked poly and a jumper. The small ceramic 100pf caps Ci101/102 were traded for C0G type MLCC ceramics of the same value. The .033uf Mylar caps at Ci115/116 were upgraded to Wima polypropylene. Ci103/104 47uf 16V got low leak 47uf 35V Nichicon KL. The four 100uf 35V local filter caps at Ci123-126 were bumped to 220uf 35V Nichicon PM. Ci107/108 and Ci117/118 220uf 10V were replaced with 220uf 25V Nichicon FG.

    [​IMG]
     
    Last edited: Sep 8, 2017
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  4. ghamilton

    ghamilton Super Member

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    LOOKING GOOD! :lurk:
     
  5. SicMan

    SicMan Fire up those speakers Subscriber

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    Just curious, are you changing the transistors?
    John M
     
  6. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Elsewhere absolutely, but not on these two boards, EQ and Tone amp.
    Here are the transistors on these boards:
    (10) 2SK68 JFETs
    (2) 2SC1328 (2SC1345 in others)
    (4) 2SA847
    (4) 2SA640
    (2) 2SA850 (2SA777 in others)
    (2) 2SC1904
    (2) 2SA899

    I could maybe see replacing the 640 differentials with KSA992 or ZTX795A, but meh. 640s are in nearly every Kenwood I work on, and they don't cause trouble. Everything else I'd prefer to leave alone.

    I may however replace the diodes Di1-4 1S0276 with 1N4148, haven't decided yet.
     
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  7. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    All the main filter caps have been desoldered and pulled so access to the two diode boards has been obtained. Many of the components on these board are getting replaced.

    Here is a look at the first of the two diode boards. It houses rectifiers for one of the two supplies and likely the most unreliable part of the amp, the relay driver 2SC1212A.

    [​IMG]
     
  8. rjsalvi

    rjsalvi Active Member

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    Fwiw, since modern parts tend to take up less real estate, I upped the wattage of all the power resistors, i.e., 1w to 2w, 2w to 3w, 3w to 5w. In fact, with the exception of the 1/4w resistors, IIRC, I over-spec'd all other parts for higher voltage ratings. Price difference was negligible so WT ... heck. :)
     
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  9. gort69

    gort69 AK Subscriber Subscriber

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    That was the most difficult board in the amp for me - the access,all the stuff crammed at one end, figuring out what's what on the solder side, reinstalling the board w/o mashing a resistor or something, etc.

     
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  10. rjsalvi

    rjsalvi Active Member

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    LMAO! Classic. You know how many movies we'd enjoyed that if they were pitched to studios today, they'd be thrown out the door because of political correctness? Blazing Saddles, as well as this one, comes to mind...
     
  11. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    It's definitely not the most enjoyable board to work on. There's quite a few wires on the rear of the board to be waded through in order reach everything. Bringing the iron to the work and taking it out has to be done with precision. Most of the components leads are bent flat to the board which always makes it more of a challenge to remove them. Patience is key.

    Here's the current state of the first diode board. The rectifiers and caps have all been removed. Nearly all the resistors have been replaced. All diodes and transistors have been changed. The only remaining stock parts are the ceramic disc capacitors, the mylar cap, and the inductor.

    [​IMG]
     
  12. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    The first diode board is complete aside from the main filter caps. The glue was removed from the board at Cz4 and Cz9. All the 0.25W resistors were replaced with 1% 0.5W metal film. The three stock 1W resistors at Rz5, Rz10,and Rz17 were upped to 2W to match the original size. The large 4.7 ohm 3W resistor was upped to 5W. The two 2SC945 transistors at Qz1 and Qz3 were exchanged for KSC945CYTA (center collector like the original part). The relay driver Qz2 2SC1212A was swapped with a KSC2690AYS. Cz8 10uf 50v, was replaced with a Elna Silmic II 10uf 50v (modern, low esr parts in this value are mostly 5mm in diameter, thus a larger 8mm diameter audio cap was chosen here). C4 is a stock 100uf 16V Bi-polar replaced with a 100uf 25V Nichicon ES. C9 is a stock 100uf 25V low leak cap replaced with a 100uf 35V Nichicon KL. The original rectifiers U05C 2.5A 200V were replaced with UF5404 3A 400V.

    This board is challenging. First of course there is the main caps needing desoldered just to gain access. Then there's several small pads that would love nothing more than to lift when you try to remove the components with bent over leads on them. Then add to that a minefield of terminal posts and wires obstructing access to the solder pads and tempting a melting of insulation with a small slip of the soldering iron. Not the very worst board I've seen possibly (a full recap of a Pioneer SX-727 tuner board comes to mind), but also not one a novice has any business touching. I'm now convinced there's a reason the KA-9100 has the PITA reputation it has.

    [​IMG]
     
    Last edited: Nov 10, 2017
  13. SicMan

    SicMan Fire up those speakers Subscriber

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    AHH ! PITA ... "Patience In This Application" is it.
    I've done a ton of these, seems the the relay driver goes bad alot.

    John
     
  14. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    The second diode board contains four U05C rectifiers for the second supply along with five resistors that I'll be replacing. With the exception of the filter caps of course, there are no electrolytic capacitors present on this board.

    [​IMG]


    Shown is a very handy lead forming tool at work making lead bends for strain relief. All the 1W and larger resistors and each of the rectifiers receive this treatment.

    [​IMG]


    The second diode board shown completed below. As before, the four U05C 2.5A 200V rectifiers were replaced with UF5404 3A 400V. All the resistors are replaced with metal film types of similar size. The 4.7 ohm 3W resistor is upped in wattage to 5W. The 1W 10ohm resistor goes to 2W, and the two 56 ohm 2W go to 3W. There's just one 0.25W resistor here and that is replaced with a 1% 0.5W.

    [​IMG]
     
    Last edited: Sep 12, 2017
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  15. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    The meter board has two general purpose 47uf 10v electrolytic caps that were replaced with a couple of Panasonic FC 47uf 25V. The eight carbon film 0.25W resistors are replaced with 1% 0.5W metal films. As mentioned earlier pins three and four are vacant due to the removal (for protection) of the meters.

    [​IMG]

    [​IMG]
     
  16. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    The four main filter caps of the KA-9100 are solder tab type. It seems the only drop in replacements are Nichicon Gold Tune which cost $25 apiece and are not available through the large suppliers like Mouser and Digikey. Not wanting to spend $100 for four filter caps I took to finding an alternative. When Mouser had some nice Kemet 15,000uf 63V caps with solder tabs I thought I had lucked into a nice find so I quickly ordered some, but when I received them the differences from the originals were soon realized. I knew that the tabs would not be offset like the stock caps, but the spacing difference was quite a surprise. Having already invested in these caps I turned to an idea that I'd been mulling over in previous builds.

    What I'd planned to do was to take a lid from a Powerade bottle and epoxy it atop the cap as a spacer. This basically serves three purposes. It enhances the height of the cap about 10mm, provides a stable base for them to rest, and most importantly allows for the tab spacing to be dealt with via flexible wiring.

    Using 22 AWG wire, I wound it once and fitted it into the small hole of each tab in the new Kemet cap. Once through the hole, I wound the wire again to provide a nice 1.5" to 2" lead and soldered them on. Using some large pliers I flattened the leads to allow them to more easily fit through the slots in the PCB where they mount. After drilling two small holes spaced for the tabs in the Powerade lid I roughed it's surface along the top outer edge with an emory board. I also carefully roughed the top edge of the heatshrink on the capacitor. The purpose of this is to eliminate smooth surfaces for better epoxy adhesion. With the lids attached and the epoxy cured, I put a small piece of red heat shrink on the positive lead of each capacitor as an identifier. As a final prep for installation I took one of the original caps and used it as a guide to bend the leads of the new caps into ideal position and spacing for installation.


    A comparison of the original cap on the left, and it's replacement, right.
    [​IMG]

    Powerade cap atop the capacitor to act as a spacer. 22 AWG wire wound around the solder tab serving as a through hole lead.
    [​IMG]

    Two capacitors almost ready for installation. The leads soldered on, flattened, and formed to the proper spacing.
    [​IMG]

    Edit Additional thoughts on the mounting of the filter capacitors.

    The mounting of diode boards is solely reliant on the filter capacitor brackets. This is important because the position of those boards have only about a 1/8" sweet spot for them to avoid shorting grounding pins and components to the chassis, potentially disastrous. Therefore it is critical that the main filter capacitors be FIRMLY clamped in the brackets.

    The Kemet capacitors I used, and pretty much any other modern 40mm diameter replacements that you may want to use, will undoubtedly be about 1-2mm smaller in diameter to the originals. In order to ensure a snug fit I would strongly recommend wrapping the caps with a material based tape a few times around where the bracket tightens around, hiding it from showing. A tape such as this will serve to grip rather than slide. Gaffers and athletic tape are some common examples.

    This image shows the proper mounting height. The boards' pins are clear of the chassis by about 1/8" . I marked the filter capacitor polarities on the chassis prior to installation since there are none silkscreened anywhere on the boards.
    [​IMG]
     
    Last edited: Nov 10, 2017
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  17. rjsalvi

    rjsalvi Active Member

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    Interesting mod. I used the Kemets as well and Dremel'd the board slots for the smaller lead spacing, then bent the cap's lugs on an angle facing each other before dropping them in. As you know -- and as you'd just remedied with the plastic spacers -- without the asymmetrical positioning of the lugs on the caps, these caps don't like to fit next to each other when mounted. Fortunately, bending the lugs inward gave me barely enough space to get them positioned, soldered and clamped, but your mod greatly increases installation flexibility. Nice job!
     
  18. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    In my best southern draw :
    It ain't purdy, but I rectum it'll get the job done. Duct tape, bailing wire, and a rock fer a hammer 'bout all you need to fix all you need...ceptin your seeg-neefa-gunt utter.
     
  19. rjsalvi

    rjsalvi Active Member

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  20. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    The foam used in these 70's Kenwood's is always starting to dry rot. I make a point to remove it because if you don't it begins to disintegrate into particles that crumble into switches and pots and start resulting in issues. I've been using adhesive backed craft foam to replace the old stuff. It comes in some nice 9" x 6" inch rectangles in various colors which I trim to size.

    Old foam from the meter assembly mostly removed
    [​IMG]


    The meter assembly cleaned of all the old foam, old adhesive, some crumbling debris still remains.
    [​IMG]

    Preparing a piece of craft foam to be trimmed.
    [​IMG]

    The strip of craft foam applied in the same manner as the original.
    [​IMG]

    The light assembly has a foam strip on it as well so the same approach was taken.
    [​IMG]

    A nice clean piece of foam is applied. No more crumbling foam.
    [​IMG]

     
    Last edited: Sep 20, 2017

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