The KA-9100 restoration.

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

  1. SicMan

    SicMan Fire up those speakers Subscriber

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    Hey John:
    Good idea. I used some very thin weather stripping in a bind or similar to what you are using.

    John M
     
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  2. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Addressing the KA-9100 Service Bulletin

    There is a small 3-pin header on the top control board which is subject to strain from the connected cable and results in intermittents. Kenwood issued a service bulletin to deal with the issue which directs the tech to remove the header and connector and solder the wiring directly to the board. My suggestion instead would be to provide strain relief to the header with some adhesive or hot glue strengthening its bond to the board followed by a thorough redo of the three associated solder joints. The larger 6-pin headers don't seem to be as effected.

    [​IMG]

    [​IMG]

    [​IMG]
     
    Last edited: Sep 19, 2017
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  3. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    There were several wire wrapped connections which had broken. This occurred both as result of disassembly, and from continual board movement over the course of component installation. These wires were replaced with same gauge solid core wire. Each was wrapped onto the posts, mimicking the originals, and then soldered in place.

    Broken wire wraps are nearly inevitable to avoid when changing the number of components I've done on these boards. I attempted to make them appear as original as possible in my repair.
    [​IMG]

    Once the foam replacement, as documented, was completed on the two assemblies the VU meter wiring was reattached to its board. This board has a shield which was glued to it along the right edge (facing front) which had fallen off. Once remounted, I used a bit a hot glue to reattach the shield as it was meant to be.

    The control boards, small switch boards, diode boards, were all cleaned of flux and reassembled into the chassis.

    The amp was powered on with the dim bulb tester. After testing good, it was powered on in earnest checking for functionality and for a clean signal among all controls. In listening, there was a noticeable improvement in audio quality, primarily in the authority of low frequency reproduction.

    Problems with the volume pot start to exhibit themselves. With the pot turned turned to minimum the volume would jump wildy up in db and sometimes drop the right channel. The spray and pray method with F5 wasn't cutting it. Since only portions of the control can be reached with the board mounted it needs to be removed to expose the bottom of the control. After a flooding of CRC in the forward volume portion of the control some small debris was freed from the control which seemed to be the source of my issues. This was followed up with applications of F5 and G100L and the requisite 20-30 turns of the controls.

    Entry points for cleaner are exposed from the bottom of the combination balance/volume potentiometer once removed from it's PCB.
    [​IMG]


    Phase one of the restoration is completed.

    Up next, phase two of the restoration begins with the power supply.
     
    Last edited: Sep 29, 2017
  4. rjsalvi

    rjsalvi Active Member

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    As always, your attention to detail is enviable. PITA...the SicMan way.
     
  5. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    No matter how many times people have said it, I am just stunned at how hard the KA-9100/9150 is to wrestle around and work on and amazed at those of you who've done a great job of it already. I'm... wrestling my way to getting mine all back together after pulling everything out, recapping and upgrading. Man!

    IMG_5465_edited.jpg
     
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  6. rjsalvi

    rjsalvi Active Member

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    I see you have one of the rare 9100s with four transformers, Doug. :biggrin:

    The only advice I can give you is don't walk away from it! It's not like each board has four screws and they neatly bolt to the chassis, or that the components are easily accessible from the top and bottom side of the boards when the boards are mounted, or that all wiring has molex connectors. I'd love to see the instruction set given to the assemblers for exactly how they were instructed to pack those diode boards in there. :eek: Beyond that, it's cake. :)
     
    Last edited: Sep 21, 2017
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  7. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    Hah! Nice catch! I'd bought a spare set just in case these were toast. I'm 80% done with the restoration, so it was time to remove the tranny covers, sand blast them, and repaint before bolting them back down in the 9150. I pulled out the spare transformers so I could do all four covers at one time.

    No chance of turning back now. I bought this unit last year for myself, knowing how much acclaim the KA-9100 gets and how cool the Euro version looks. I was considering whether or not to dedicate this coming weekend to finishing it up when someone in BT posted "WTB KA-9100... recapped". That and a COBRA health insurance payment coming up made the decision easy.

    If you all see any posts from me in the next few days saying "help! where the heck does the pink wire go?" please be kind to me. This isn't my first restoration, not even my first Kenwood, but it is certainly the trickiest. I've got a pair of KR-6160's and a KT-140X's opened up where I stopped and said "whoa, THAT is gonna take serious attention and time." The 9100/9150 is denser in design and WAY harder to physically wrestle around the bench.
     
  8. SicMan

    SicMan Fire up those speakers Subscriber

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    dlucy---->> Just start another thread on your restore. Gets confusing to others that follow along.
    Thanks
    John M
     
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  9. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    Good point. Will do.
     
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  10. fernarias

    fernarias AK Subscriber Subscriber

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    It wasn't as hard as everyone said. One board at a time: power supply first, then amp, then preamp, then main cap board. I have a hakko 808 so maybe that helped. Made a mistake and was able to find it (broken wire). I didn't have to take the whole chassis apart, like in your pic Good luck.
     
  11. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    The KA-9100 power supply in stock form. (X00-1870-11) This is the K version of the power supply for North America. Foreign or multi-voltage supplies may differ.
    [​IMG]

    Changes made to the KA-9100 power supply board (X00-1870-11) have been completed.

    After the changes were made a DBT power on was performed. After a glow and dim on the DBT a full power up was performed. The amp took a full 20 seconds or more to come out of protection and the VU meters were reading 10W. Shiite Muslim! What's going on here? Rather than panic I applied the KISS method. I know it worked fine before working on this board so it has to be something wrong with the supply. After a thorough recheck of every component changed I was confident nothing was replaced incorrectly. I turned my attention to the bottom edge of the board to see if there were any broken wires and again found nothing wrong. As I was moving the board looking things over I spotted pin 25, the -B supply, had a cracked solder joint. Bingo. I re-flowed all the pin joints just as precaution and then powered up again. After 3 or 4 seconds, PING! relay engaged.

    The KA-9100 power supply with new components installed.
    [​IMG]

    Rk11 1K 2W was replaced with a 3W metal film and given strain relief. The two stock 470ohm at Rk2 and Rk4 were replaced with 1W KOA Speer SPR Carbon Film replacements ( I believe the originals may be flameproof type so I went with the SPR which have flameproof coating ) and their leads given strain relief. All the other resistors were replaced with the 1% .5W metal film. I made point to raise the 820 ohm Rk1 and Rk3 off the board a bit for better heat shedding. All the W06B diodes at Dk1-5 were replaced with 1N4007G rectifiers, raised a little off the board. The YZ-140 at DZk1 was swapped for a 1N5244B Zener.

    There are ten electrolytics here.

    Ck11 4.7uf 35v (25v actual) > MKS2 4.7uf 50v
    Ck14 47uf 16v 8mm > 47uf 25V RFS 8mm
    Ck8 47uf 35v 10mm > 47uf 35V RFS 10mm
    Ck6 47uf 50 10mm > 47uf 50V KZ 10mm
    Ck10 10uf 25v > 10uf 50v FC
    Ck5 100uf 50v 12.5mm >100uf 63V PM 12.5mm
    Ck12/13 220uf 35v 12.5mm > 220uf 50V FC 12.5mm
    Ck3/4 470uf 50v 16x35mm > 560uf 63V HE 16x30mm

    The four transistors were replaced as follows

    2SC1983 > MJE15032G
    2SA755 > MJE15033G
    2SA673 > KSA1220A
    2SC945 > KSC945CGTA

    There are some points of interest to working on this power supply. It should be noted that Ck16, a 47 picofarad ceramic cap, is on the rear of the board. It is soldered across the collector and base of Qk4 2SA673. If you replace Qk4 you'll need to remember to put this cap back in place. My board had glue over the solder joints so you may need to remove that first.

    [​IMG]

    Ck16 47pf

    [​IMG]

    Also of note, the regulators at Qk1 and Qk2 are mounted to heatsinks which mount to the bottom of the PCB. During removal it was obvious that all of these screws were very loose and might have easily come unscrewed given time. Whether you replace these transistors or not I would suggest tightening them up and adding some thread lock to prevent any of them from falling out. These same transistors also did not have any thermal compound on them. I would suggest adding a thin layer for better heat dissipation.

    Thread lock is added to the transistor mounting screw. Some should also be applied to the board mounting screw.
    [​IMG]

    A thin layer of thermal compound is applied between the regulator and heatsink prior to mounting.

    [​IMG]
     
    Last edited: Sep 29, 2017
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  12. gort69

    gort69 AK Subscriber Subscriber

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    Good work John, and good catch on the cracked solder joint. I was going to mention the possibility, but thought 'nahhh'..... I had the same thing happen on mine and only noticed it when I saw and heard the arcing. I forget which pin, but I think #1. I also reflowed all of them.

    Interesting note on Ck16 - I didn't remember seeing that. Looked at the photo I took and found it mounted on the top side. Must have been a board change at some point or due to mine having switchable voltage, who knows.

    P1011024.jpg
     
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  13. ghamilton

    ghamilton Super Member

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    LOOKING GOOD!
     
  14. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    I should point out that the brackets on either side of the power supply board, as can be seen in the photo of post #63, are shown mounted incorrectly. This is how it came to me, but the metal tabs where the plastic rivet goes through should be at the back of the board, not the front. When positioned correctly the board will be perfectly vertical with the brackets screwed to the chassis.

    Thanks for the information. I hadn't considered they'd make a change to the board for one additional cap. Replacement of Qk4 on these type boards should be hassle free.

    Thanks!, much appreciated.
     
  15. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Some basic housekeeping is in order before moving away from the back panel. There's probably nothing here anyone restoring hasn't done a hundred times, but I always find it interesting nonetheless just to see what methods people use. I'm hoping that some of you do too.


    First, I need to get to the normal/separated switch. It resides behind a shield on the back panel. With the shield off, it's just a matter of removing the two screws from the panel to free it. The sides of the switch allow access to the sliders and contacts for a good cleaning with D5 or D100.
    [​IMG]


    Since the rear panel is still opened up, now is also a good time to clean the speaker selector rotary switch. A good spray down of CRC followed by some D100 or D5 will do nicely here. The contacts are on either side of both wafers. I follow the cleaning with a lube of the selector mechanism where the two steel balls are.
    [​IMG]


    The RCA jacks on the vintage stuff always need a good cleaning up. I used DeOxit Gold G100L applied with a Q-Tip. In the photo you can see the before and after difference where the AUX, TUNER, and Tape B jacks have been cleaned and the rest have not.
    [​IMG]


    For the insides of the jacks a mascara brush is useful for getting out all the dust and cleaning up any oxidation with some D100L or G100L applied.
    [​IMG]


    The speaker terminals are always dusty and have nasty dead skin in their grooves. A soapy tooth brush does wonders at getting rid of the gunk. I carefully follow the grooves with the bristles of the brush while slowly turning them.
    [​IMG]

    The mascara brush is also useful for getting into and cleaning the wire slots of the terminals.
    [​IMG]
     
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  16. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    Ok, here's a great learning opportunity for me: you're saying DeOxit Gold is good for non-gold standard RCA jacks? I'd bought a tube thinking it would be useful, but thought it's directions said "for gold contacts only".
     
  17. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Ideally you should use some D series on the jacks to remove any oxidation first (I did a bit of no-no) and then use the G series to preserve what you've cleaned. These jacks weren't too badly oxidized, more dirty than anything. The G series works fine on base or plated metals. The gold thing is more of a way of distinguishing it's not a cleaner it's a preserver.
     
    Last edited: Sep 23, 2017
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  18. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    Is there any downsides to disconnecting the rec/play DIN connector on the back?
     
  19. SicMan

    SicMan Fire up those speakers Subscriber

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    the thread is drifting in the wrong direction
     
  20. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    An additional note about cleaning the speaker terminals. After receiving a reminder from gort69 that the terminal screws can be removed on the 9100 (they are reverse threaded type), I took advantage of this and cleaned the insides of the posts and all the thread throughs on the terminal block with D100L. I followed that up with some G100L for preservation. Thanks gort69 for the timely PM.

    [​IMG]

    Just functionality of the jack and potential shorts if the wires aren't managed. I don't like disabling things personally.

    We're back on track Johnny boy. Up next is the Triac install. :thumbsup:
     
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