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The KA-2002A restoration

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by hopjohn, Oct 13, 2018.

  1. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,104
    Location:
    Dallas, TX
    Here is the Kenwood KA-2002A integrated introduced in 1973. It is rated around 12 to 13W/channel into 8 ohms both channels driven. The fascia shares cosmetic similarities with the U.S available units KA-4004, KA-6004, and KA-8004. It is another of Kenwood's entry level amplifiers based on the earlier design of the KA-2002. The most notable difference between the 2002, other than the appearance, is that the 2002A lacks the pre-out / main in jacks of its predecessor. The 2002A did add a few minor improvements. Firstly, the inclusion of a two amp fuse in the lamp circuit. The 2002A dropped the notoriously noisy 2SC458 for the well-regarded 2SC1416 low noise differentials in both stages of the phono amp. Unfortunately, the 2SC458 still remained in the tone amp and power amp, definite areas to improve upon during restoration. The TO-220 2SC1060 outputs (two per channel) are the same devices used in the 2002, and are coupled by a 1000uf 25V axial electrolytic at each output.

    [​IMG]
    Front view. The plastic surround around the power switch is loose and causing it to stick. Add it to the restoration to-do list.

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    Rear view. The jacks badly coated in gunk typical of units that have lived near the coast.

    [​IMG]
    Top view. This is a look after most of the dust has been removed. The board is loaded with low leak style Elna brand caps. The main cap is Matsushita ( Panasonic's mother company ). Kenwood used quality parts.

    [​IMG]
    Main Board. A closer look. The metal cased 2SC1416 are well regarded.

    [​IMG]
    Before, Single 2200uf 50V power filter capacitor and the 10DC-1 three pin rectifier

    [​IMG]
    The Hitachi 2SC1060 output devices are collector insulated, mounted to a L-shaped heatsink

    [​IMG]
    Output coupling caps. These axial style caps are a pain to find quality replacements for, but I have an idea on how to deal with them.

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    Bottom view. The removable bottom panel is a nice touch. Thanks Kenwood.

    Coming up...the "after" photos and more.....stay tuned.
     
    Last edited: Oct 13, 2018
    dlucy likes this.

     

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  2. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,104
    Location:
    Dallas, TX
    [​IMG]
    The KA-2002A Schematic

    [​IMG]
    Top view with new components installed.

    [​IMG]
    The rear panel RCA jacks, speaker terminals, and hardware are cleaned of the gunk and grime.

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    A close look at the main board with all new electrolytic capacitors. Matched pairs of 2SC1845F replace the 2SC458 outhouses in the tone and power amp.

    [​IMG]
    The main filter capacitor was replaced with a high quality Kemet 3300uf 100V with screw terminals. The 10DC-1 rectifier is replaced with two 1N5393 1.5A 200V rectifier diodes. The axial caps at the terminal strip are replaced with .01uf 630WV film types.

    [​IMG]
    The wiring at the output coupling capacitor terminals was altered to allow for quality Panasonic FM 1000uf 50V radial capacitors to be implemented in place of the original axial types.

    X09-0013-00

    Ce1/Ce2 3.3uf 6.3V LL white 4mm Input > MKS2 3.3uf 50V
    Ce7/Ce8 10uf 25V LL 6mm > MKS2 10uf 50V
    Ce9/Ce10 10uf 25V LL 6mm > 10uf 50V RFS 8mm (Negative to long side of board)
    Ce11/Ce12 100uf 6.3V GP 8mm > 100uf 25V FG 8mm
    Ce15/Ce16 10uf 25V LL 5mm > 10uf 50V RFS 8mm
    Ce21/Ce22 > film .01uf
    Ce23/Ce24 > film 2700pf
    Ce25/Ce26 1uf 25V LL white 4mm > 1uf 50V MKS2
    Ce27/Ce28 10uf 25V LL 6mm > 10uf 50V RFS 8mm
    Ce45/Ce46 1uf 50V GP 5mm > 1uf 50V ECQ
    Ce47/Ce48 470uf 6.3V LL 10mm > 470uf 35V FC 10mm
    Ce49/Ce50 10uf 25V LL 5mm > 10uf 50V RFS 8mm
    Ce51/Ce52 10uf 50V GP 8mm > 10uf 50V RFS 8mm
    Ce55/Ce56 47uf 6.3V GP 5mm > 47uf 35V PW 5mm
    Ce57/Ce58 47uf 50V LL 10mm > 47uf 50V RFS 10mm
    Ce61 47uf 50V LL 10mm > 47uf 50V RFS 10mm
    Ce62 47uf 6.3V GP 5mm > 47uf 35V PW 5mm
    Ce63 100uf 25V LL 10mm > 100uf 50V KL 10mm
    Ce64 220uf 50V LL 16mm > 470uf 100V PW 16mm
    Ce65 220uf 35V LL 12.5mm > 470uf 63V 16mm
    Ce66 100uf 25V LL 10mm > 100uf 50V KL 10mm
    Ce67/Ce68 47uf 6.3V GP 5mm > 47uf 35V KL 6mm
    Ce69/Ce70 10uf 50V GP 8mm > 10uf 50V RFS 8mm
    Ce151/Ce251 1000uf 25V Axial 16x40mm Output > Alter wiring to allow for radial caps to be used > Panasonic FM 1000uf 50V (Use audio caps)
    Ce301 2200uf 50V 35x50mm Main Filter > 3300uf 100V 36x52mm Kemet ALS70A332DA100
    Ce302/Ce303 .01uf 630WV > .01uf 630WV Kemet PHE426MK5100JR05
    Qe5/Qe6 2SC458 > KSC1845F ~430 hFE
    Qe9/Qe10 2SC458 > KSC1845F ~430 hFE
    VRe1/VRe2 500 ohm Bias trimmer > top vertical, in line pins. Bourns 3296
    DC10-1 3 pin Rectifier > 1N5393 x2 (1.5A 200V)

    Kenwood KA-2002A Bias adjustment :
    Measure bias across pins 41 (incorrectly screened as pin 44 on the odd #'d side of board) and 45 left channel and pins 42 and 46 right channel. Adjust each channel for 9.4mV after a 20 minute warm-up. (20mA x 0.47uf = 9.4mV)
     
    Last edited: Oct 14, 2018
    Dandy, rickl, dlucy and 2 others like this.
  3. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,104
    Location:
    Dallas, TX
    Restoration complete
    [​IMG]
     
  4. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Messages:
    2,057
    Location:
    Philadelphia, PA
    Beautiful photos, as always!
     

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