My first receiver restoration attempt: G-6700.

Discussion in 'Exclusively Sansui' started by ghazzer, Nov 12, 2012.

  1. DCinDC

    DCinDC I'm here to fix it

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    Just keep in mind that whatever voltage causes them to start conducting is, in the end, immaterial.

    Once in the circuit, you would adjust the bias pots to whatever it takes to get them to conduct the desired amount of current.

    Of course you know this already. I'm just trying to make the point that the adjustment is king, not any particular characteristic of the devices.
     
  2. ghazzer

    ghazzer Sansui addict Subscriber

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    Yes, but except for the length of the jumpers everything will be "in circuit". I am only remoting the OP TRs to make it easier to take the readings and change the transistors.
     
  3. vigman

    vigman SUBSCRIBER

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    Now THAT's a heatsink.... make sure the heatsinks are isolated from the circuit ( transistors ) electrically and you should be good to go.... for test
     
  4. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    +1 I think so too - good to go (PM sent).
     
  5. Grainger49

    Grainger49 Old Fart

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    I'm with the other guys. I see no problems. The heat sinks are enormous!

    Keeping the sinks electrically isolated would be am must for a complementary pair and it looks like you have done that.

    Good luck!
     
  6. ghazzer

    ghazzer Sansui addict Subscriber

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    Yeah. Once it dawned on me that the collectors are B+ & B- I made double damn sure that they are well isolated. I've already had too many sparks with this one.
     
  7. Grainger49

    Grainger49 Old Fart

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    Steve,

    If you get no smoke this afternoon, it is time for a little brown liquid on ice.

    You will deserve it.
     
  8. ghazzer

    ghazzer Sansui addict Subscriber

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    I don't think my Jack Black or Maker's Mark will compare to the liquid golden stuff that you shared with me. Guess I'll stick with my Chivas.

    Last nite was devoted to watching the Ole Miss football game, so I still have some work to do on the 6700.

    Wednesday I got it all wired up.

    Here is my 3058 bd with the OP TRs removed and jumpers attached to the pins leading back to the main amp bd.

    [​IMG]

    This shows the OP TRs installed on the heatsinks with the jumper harness leading back to the 3058 bd. I double checked the connections, and even labeled the leads to avoid confusion.

    [​IMG]

    When I laid out my DMMs I found the mini grabbers tips broken - again! This time I will go with a different style, as shown to the right of the grabbers I have been using. They have two arms that extend out and 'grab' onto a lead like a set of pinchers.

    [​IMG]
     
  9. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Can't wait till the 'Egg bowl' this year :D
    Care to wager a F-3058 board or two? lol
    Returning to regularly scheduled posting
    -Lee
     
  10. vigman

    vigman SUBSCRIBER

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  11. ghazzer

    ghazzer Sansui addict Subscriber

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    Today we are going down to Brookeville, MD, for re-enactments of when that small town was the Capital of the U.S. for a day. In 1814 the British were burning Washington and the White House. Everybody was getting the hell outa Dodge and most of them wound up here.

    I had some interesting times last night trying to put new mini grabbers (pinchers) on a set of leads. Also did some research on the mini grabbers, and now have a plan to modify them so that the tips don't crumble. Pics to follow later.
     
  12. ghazzer

    ghazzer Sansui addict Subscriber

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    Waiting for paint to dry ! ! !.....And it didn't.

    I guess that my tubes of JB Weld are just too old. I mixed up a batch to try my fix for the mini grabbers and it didn't set up. So I added more hardener and tried again, but this morning it was just a slumping mess.

    Time for another trip to the H/W store.
     
  13. ghazzer

    ghazzer Sansui addict Subscriber

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    I got sidetracked (as usual) but finally managed to get a working solution to my mini-grabber problem. You can see the photos and the solution here.

    Now, where was I before the well tank sprung a leak?????
     
  14. ghazzer

    ghazzer Sansui addict Subscriber

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    Finale

    Well, they say that no good deed goes unpunished, and I'm a believer.

    Yesterday I was taking some voltage readings from the pins of the HAI2002 chip to help a fellow AKer troubleshoot his G-7700. As much as I preach about being careful, I let the probe slip off of pin 5 while glancing at the DMM and drew an arc and a POW. Looks like I bridged between the junction of C31 & R49, over to the track between R43 & R44, which is B+.

    The SO relay remained engaged after the arc. I cycled power and everything seemed to come up OK (still on a 135W DBT). Pin 3 on the chip had changed from 4.0mv to 105mv??

    I cut power to double check where the arc was and what damage it may have done. The next time I applied power the SO relay would not engage. Both sides of ZD601 read ~40VDC and are slowly discharging with the DMM attached: about one volt every 20 seconds.

    I let the voltage at ZD601 discharge until it bottomed out at 14mv. When I tried it again the SO relay still will not engage and ZD601 reads ~40V again. The main caps are quickly discharging down to less than 6vdc and dropping. I don't know where this voltage is coming from.

    EchoWars answered some questions about bias, enough to make me realize that I have been chasing wild geese, again. So, I don't have to use my remoted heatsink rig to find the conduction point of the replacement OPTRs. Assuming I can fix the SO problem, I will still use that rig to check out some additional pairs of OP TRs. The tracks on my homemade F-3058 boards cannot take much more soldering, so I want to get them all checked out and select the replacements before one final install to the 3058 bd.

    This will be the finale of this thread. Thanks to your support, answers, directions, etc I was able to get this G-6700 operational again, and I have learned Sooooo much. I will start a new thread to try and resolve the SO problem, and eventually try to figure out why the signal through one channel is weaker than the other.

    I sincerely hope that others can find some useful information in this thread.

    Thanks - - -
     
  15. Grainger49

    Grainger49 Old Fart

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    I did the same thing poking around in the power supply of a DVD/CD player. POP! And the thing was dead. I have some parts to try to resurrect it.
     
    ghazzer likes this.
  16. Robert.garb

    Robert.garb New Member

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    Hello Ghazzer. I just finished reading this entire thread. Way to go. I am starting a 6700 restoration. It's in rough shape but I feel still doable. Left channel outputs were shorted and all the wire jumpers were removed prior to me getting the amp. I read every page of this but still can't make sense of the wiring diagram. Can I wire the 3058 boards to the print or are there big mistakes. I read throughout this thread that there are mistakes and was hoping you had an updated print or some suggestions. I would be very grateful.
     
  17. ghazzer

    ghazzer Sansui addict Subscriber

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    Hi Robert, and welcome to AudioKarma!

    Remember that the 3058 boards are identical, but the components are installed as mirror images.

    The traces on the 3058 boards are OLD and brittle. They cannot take a lot of R&R of parts. That is why I wound up making my own PCBs as replacements.

    This is the latest revision of my drawing of the driver circuits. The colors of the jumper wires are correct for my G-6700, but YMMV. Note that the bias trimmers have been corrected to the "as built" configuration.
    (updated 1/17/17)


    [​IMG]


    I bought some 2SA1101 & 2SC2344 replacements for the 2SA968 and 2SC2238 drivers but have not tried them yet.

    Good Luck - - -
     
    Last edited: Jan 17, 2017
  18. Robert.garb

    Robert.garb New Member

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    Hello and thanks Ghazzer. I got some work done to it this weekend. I had 2SD381/2SB536 as drivers and replaced with KSC2073/KSA940. I would be very excited to hear how the other drivers you mentioned turned out. Thanks again for your advice and time.
     
  19. princever

    princever AK Subscriber Subscriber

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    Steve what software did you use to draw that schematic 2 posts above?
     
  20. ghazzer

    ghazzer Sansui addict Subscriber

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    Princever: TurboCAD. Call me if you are interested.

    Robert: I just sent you a Private Conversation. Scroll to the top right of this screen and click on "Inbox".
     

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