The KA-9100 restoration.

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

  1. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    The same is true for the two GROUND screws. The backsides are soldered to the panel, but once you overcome that, turning the Phillips screw of the GROUND posts clockwise will back them out of the panel (if you need to eliminate rust spots under them or some such).
     
  2. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Adding a thryistor (triac) to the KA-9100 Part 1

    Among many models, the power switch is a Kenwood weak point. It's important to protect and one of the best ways to do that is to add a Triac inline with it. The Triac suppresses inrush current which otherwise causes arching. The arching damages the contacts which eventually destroys the conductivity of the rocker interrupting electron flow. This renders the switch inoperable and power to the amplifier is lost. When power to the amplifier is lost, it no worky. I make a point to describe this with exactness in jest having had this subject be a previous point of contention. A contemporary was being "nit-picky" about my use of semantics in describing the cause of switch failure. This time, I hope to have left no room for interpretation.

    When it comes to wiring the triac I've come to use the annotation provided by Glenn McDonald. For the KA-9100 I'll be using the part number Q6040J7TP along with a safety rated X2 0.1uf film cap and a couple of 100ohm 1/2W metal film resistors. (Thanks and credit to Glenn for the diagram photo below)
    [​IMG]

    The first thing to do is to identify which of the wires leading to the switch is coming directly from the 120V AC source this will be the "Hot" as noted in the diagram. In my unit the white wire is the "Hot". This white wire is connected at a terminal of the unswitched convenience outlet to the incoming brown power cord. The yellow wire connects to a red wire from the transformer(s) or "Load" in the diagram.
    [​IMG]

    Next, I want to document what the switch appears like in stock form. In my unit the hot wire (white) is on the toggle side and the load (yellow) is at the middle position. There is a .01uf safety cap across the switch that will be discarded. There is a second set of contacts that is unused on the other side of the switch which will be implemented later in the install.
    [​IMG]

    The wires and safety cap are snipped from the switch. All of the remaining wire and solder is cleared from the tabs of the switch in preparation for the new wiring.
    [​IMG]

    The switch is then disassembled for cleaning. Notice the damage arching has caused to the upper right contact and also one side of the top rocker. This is what we are trying to avoid from happening further. The below photo is prior to any cleaning which should be done with D100L followed by an application of G100L. When reassembling I turn the damaged rocker 180 degrees toward the undamaged contact.
    [​IMG]

    Once the switch is reassembled it is wired with the "hot" to the top toggle side, the gate to middle tab, and the right and left sides bridged together as shown below. Wiring both sides will divide the current, though it's not entirely necessary with the Triac in place. The Triac will dramatically lower the current that the switch sees, though in practice, bridging here is still a positive thing for the life of the switch.
    [​IMG]
     
    Last edited: Sep 25, 2017
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  3. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Adding a thryistor (triac) to the KA-9100 Part 2


    The pinout for the Q6040J7TP part is MT1, MT2, G left to right as shown below.
    [​IMG]

    The gate is given a 100 ohm 0.5W resistor. I recommend using a longer length of wire between the gate and resistor legs then what is shown here. It needs to be flexible so use stranded wire for this connection.
    [​IMG]

    A 100ohm resistor is added to a leg of the .1uf safety cap to create a snubber. This will go across MT1 and MT2.
    [​IMG]

    Heat shrink tubing of adequate diameter needs to be put in place prior to soldering in the snubber.
    [​IMG]

    The white wire from the switch is put through the heat shrink tubing and soldered at the same time as the resistor side of the snubber to MT2. You have to be careful not to shrink the tubing too much with the heat of the iron while you solder here. You only get one shot at this or you'll be undoing some things, don't screw up. No pressure....we're all counting on you!
    [​IMG]

    Some thin black Insulation is placed on the capacitor lead (hidden below, but can be seen above). The yellow wire from the transformer is placed through the heat shrink tubing and soldered in place at the same time as the capacitor side of the snubber to MT1. Again, you get one shot to not shrink the tubing too much so it can be put in place. (Rob Schenider voice form Waterboy) "You can do it!"
    [​IMG]

    Success!, no early shrinkage. The tubing is put over the leg of MT1 and insulated.
    [​IMG]

    The final connection is made from the black wire coming from the switch to the 100ohm resistor that connects to the Triac's gate. Additional insulation is provided on each side of this resistor. Zip ties provide strain relief to the rather fragile leads of the resistor. The Triac is mounted with a split washer with one of the existing self tapping screws (albeit a little longer one ) that mounts the left side amp heatsink to the main chassis. Some thermal compound can be applied to the back of the triac body before mounting it to help keep things cooler. I recommend some thread lock to the back side of the screw to keep it in place, but not until after work on the amp boards has been completed.
    [​IMG]
     
    Last edited: Sep 24, 2017
  4. SicMan

    SicMan Fire up those speakers Subscriber

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    Looking good John, I'm sure people will bookmark this thread. Very good reference.
    I take it you are going to keep this one.
     
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  5. rjsalvi

    rjsalvi Active Member

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    I agree, John. I don't know if it's possible, but it might be cool to have a "sticky" section for threads with best practices/most informative for each model. And similar to the Marantz group, maybe a sticky for schematic errors? Again, I do agree, this thread is a keeper! Nice work, Mr. Hopjohn!
     
  6. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Thanks John, I appreciate it. This one is filling a gaping hole in my personal collection.

    I think a sticky makes sense, but it should be a comprehensive new thread that lists and links all the best restorations for each Kenwood/Trio/ Accuphase model. If anyone is up for it, give it a go. I've got my hands full at the moment.

    HUMOR AHEAD, I TEASE...dlucy is busy right now cleaning rust off his 9150 and hijacking a thread. Sicman is microwaving his Stoufer entree for a parts tray and tripping over his 9100 and 9600s. gort69 is at work polishing his Camaro and deleting my nutty memes before anyone else sees them. I'm taking another photo for this ridiculous thread (think how useless this thing will be if/when the images go offline.) I nominate rjsalvi. Robert's white-out 5700 hasn't sold so he's just twiddling his thumbs waiting for a payday.

    Totally kidding with all of you! I'm no comedian, but I hope you laughed a little. And seriously if anyone wants to make that resto link thread, that'd be awesome.
     
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  7. dlucy

    dlucy dlucy67 (Doug) Subscriber

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  8. rjsalvi

    rjsalvi Active Member

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    LOL! PM sent so I don't hijack this thread.
     
  9. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    The left and right amp boards are up next. (X07-1500-11 A/2 and B/2) or (X07-1500-00 A/2 and B/2)

    Access to the amp boards require removal of the large heatsinks. This is a pretty straight forward procedure that involves taking out around a dozen screws. With the heastsink out, all of the thermal paste from both the heatsink and the amp module is removed to prevent making a massive mess on the bench. The amount of paste Kenwood used seems way too much. Perhaps that was the recommendation back in the 70's with the type they had available, but using today's modern thermal compounds, the recommendation is instead for a very thin coat.

    The heatsink freshly removed from the amp module. The stock application of the compound is curiously thick.
    [​IMG]

    The left amp board in stock form. (X07-1500-00(A/2)

    [​IMG]

    Planned changes:

    Ce3/4 100uf 35v 10mm > 100uf 35V PX 10mm
    Ce13/14/15/16 47uf 16v 8mm > 47uf 35v KL 8mm

    De1/2 EQA01-24R Zener > 1N5252B 24V 0.5W Zener

    Qe5/6/7/8 2SA912(R) or (S) > KSA1220AY (TO-126 package)
    Qe9/10 2SC1400(U) or (E) > KSC1845F
    Qe11/12 2SC1885(R) or (S) > KSC2690AY (TO-126 package)

    All resistors to metal film 1% 0.5W, except Re13/14 3.3K 1W > 3.3K 2W metal film

    Vre1/2 470ohm > 500ohm Multi-turn
     
  10. rjsalvi

    rjsalvi Active Member

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    Qe1-4? 2SC1775 >>> 2690, or 1845?
     
  11. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    The 2SC1775 is a low noise, low current amplifier so the low noise, low current amplifier KSC1845 would be a better match than the not-specifically-for-low-noise, higher current KSC2690A, right?
     
  12. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    The left amp board is completed with the components as planned in my previous post. It should be noted that the value of R23/24 may or may not match what is shown in the service manual, but should be kept as it is found on the board. In my case the stock mounted part was 100ohm, the S/M has it listed as 1K. I replaced it with the 100ohm (seen dead center of the board) value that was there.

    [​IMG]

    The TA-100WA gets a fresh coat of thermal paste before reinstalling the heatsink.
    [​IMG]


    The Qe1-4 2SC1775 aren't problematic so I don't intend to change them, but if you were going to the KSC1845F is what to use.

    Edit: FWIW Qe5 and Qe7 on the left amp board had visibly stressed solder joints, so I'd say replacing those, at minimum, is a healthy idea.
     
    Last edited: Oct 5, 2017
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  13. SicMan

    SicMan Fire up those speakers Subscriber

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    Hey John:
    You don't need much thermal paste, that's just to fill in the unevenness of metal to metal contact.
    I've found many with hardly any grease or way too much. That pic you showed looked quite excessive.
    More is not better here.
    If redoing the amp boards I would put all new components, why leave an old one or two that may fail. :dunno:

    Nice work on that Triac fix too.

    John
     
  14. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Here is a view of the solder side of the right amp board highlighting evidence of stressed joints at Qe6 and Qe8. These are the corresponding transistors to Qe5 and Qe7 that I mentioned had poor joints on left amp board. One of these joints is holding on by a thread, nearly desoldering itself from the board. The others all show thinning and ringing from thermal cycling. When mounting the replacements, be sure to leave some breathing room between the transistor body and the PCB.

    [​IMG]
     
    Last edited: Oct 7, 2017
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  15. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    I learn something new every single day on AK. Awesome.
     
  16. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Replacing the "center voltage" trimmers on the KA-9100.

    Bias is fixed on the 9100 so there is no adjustment required for it. The trimmers on these amp boards are stated to adjust the "center voltage" in the service manual, but are really nothing more than an offset adjustment. By measuring at the speaker terminals, this should be set as close as possible to 0V.

    The offset was checked and set for each channel before any work on this amplifier took place. That's standard procedure anytime I receive a new item. The OEM trimmers VRe1 and VRe2 are Alps 470 Ohm single turn common in late 70's amps, receivers, tuners, etc. These are replaced for increased reliability and precision by sealed 500ohm multi-turn trimmers. (Replacement 470ohm trimmers are typically only available as single turn parts.)

    Photographing or marking the position of the original trimmer once set is helpful in keeping the setting during the removal process. This is important because the setting will be duplicated by the replacement part to help keep the offset close to an ideal setting. This is even more critical when a bias trimmer is being replaced in models where that is relevant.
    [​IMG]

    The center pin of the trimmer should be identified.
    [​IMG]

    Using a multi-meter the resistance should be measured across the center pin and either the left or right pin and the value recorded.
    [​IMG]

    The replacement trimmer should then be adjusted to match the resistance of the original trimmer measuring across the same pins as before.
    [​IMG]

    The pins of the new trimmer need to be formed for proper fit.
    [​IMG]

    An alligator clip is helpful for holding the trimmer in place for soldering.
    [​IMG]

    With the new trimmers installed, and the amps / heatsinks reinstalled the mini grabber leads of the mult-imeter should be placed across the speaker terminals of the appropriate channel (It's easiest to do this from the interior). Volume should be set to minimum, with no speakers connected, the tone controls defeated, and the proper speaker selection set. After powering on, a plastic adjustment tool should be used to set the trimmer for an offset of 0 mV in each channel.
     
    Last edited: Oct 5, 2017
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  17. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Unlike the left amp board, there is a metal, u-shaped wire channel beneath the right amp board that should be uninstalled prior to working on this board. It then needs reinstalled prior to putting the heatsink back in place once the soldering work is done. It's also a good idea to keep the two amp board mounting screws loose (shown below) until the TA-100W module is tightly secured to the heatsink. Just don't forget to tighten them up once the module is mounted.

    The completed right channel amp board and heatsink reinstalled. This board is a mirror of the left amp board with an added jumper wire.
    [​IMG]
     
    Last edited: Oct 5, 2017
  18. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    I just received some photos from the fabricator / powdercoaters. Here's a little sneak peek of things to come.

    [​IMG]

    [​IMG]
     
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  19. cwh

    cwh AK Subscriber Subscriber

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    How's that new Fluke hanging in there during all this?

    Thanks for the thorough posting, can't wait to my 9100 up and running.
     
  20. rjsalvi

    rjsalvi Active Member

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    Teaser. :biggrin:
     

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