Sansui solid state 7000 repair, recap, and restore

Discussion in 'Exclusively Sansui' started by dlucy, Jan 28, 2018.

  1. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    Apparently I've missed the temp-tracking bias-setting function of the transistor at TR804, so the below photos will have to be retaken after I move that transistor to connect with the heatsink. More to come on this.
    View attachment 1116908
    View attachment 1116909
     
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  2. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    The majority of the components have been pulled from the time board. This would not be fun without a desoldering gun.

    IMG_7808.JPG
     
  3. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    What doesn't make a lot of sense to me is why, on the tone board, a 2WATT resistor, a 1WATT zener and multiple 200VDC caps are needed.

    What exactly is going on on this board that needs any significant amount of current or voltage higher than 25V?

    Am I just too much of a newbie to get it? Or is this heavy duty a line of components seem odd for a tone board?


    IMG_7821.JPG
     
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  4. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    For anyone opening up one of these, here's the naked silkscreen PCB for the tone board. I've confirmed all the transistor pinouts and cap polarities are correct in the silkscreen printing.

    Tone-board---02-naked.jpg
     
    Last edited: Mar 9, 2018
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  5. Hipocrates

    Hipocrates Anti-Muppet

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    :lurk:
     
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  6. gslikker

    gslikker Super Member

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    It looks like one resistor is missing in the pile. Did it fall on the floor? ;)

    Anyway nobody can say it will not be totally restored when you are done :thumbsup:
     

     

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  7. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Quite often transformer secondary voltages didn't seem to be chosen that well, or higher voltage windings were used for more than one internal supply, requiring 'dropper resistors' to compensate, sometimes generating a lot of heat. The higher voltage had to be got rid of somehow - enter the 2W resistors. Use of a 1W zener would be proportional to the amount of current needed by the 'zener-ed' supply, a little unusual for a tone board, but not unduly so. Use of 200V capacitors? - I assume these are film capacitors? - also wouldn't be out of the ordinary, used for their increased stability when used at significantly lower voltages than they are rated for.
     
    Last edited: Mar 9, 2018
  8. ghazzer

    ghazzer Sansui addict Subscriber

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    Sometimes it is hard to believe that those masterful designers and engineers of yesteryear did not have unlimited budgets and carte blanche on parts selection. I guess we have to be grateful for what has survived.
     
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  9. stereoguy70

    stereoguy70 AK Subscriber Subscriber

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    So basically you are creating a heck of a lot more work for yourself than is really required to get the thing working correctly again by doing this.:crazy:

    I am in the camp of replace every electrolytic capacitor in the receiver once it gets past a certain age. If one is out of spec or failed, the others aren't too far behind. I try to use the same specs as original for capacitance, sometimes staying the same voltage rating, sometimes upping the voltage rating if I am trying to replace a specific physical size to fit a bracket or something to that effect. Other than that, I don't usually do blanket/shotgun repairs. Resistors, I only replace carbon composition ones that have drifted far out of spec. I replace them with carbon film as they are more stable than carbon comp. Tantaliums, film, and ceramic caps I leave be. Unless they are burnt up, they are fine. As far as semiconductors go, I only replace them if they have failed. If they haven't failed before the recap, chances are they aren't going to fail after for quite some time after the recap was done. If they are working as intended, I leave them be.

    I've owned two pieces of vintage electronics that I have had to do ZERO work to, and that includes capacitor replacement, and they work like the day they were made. One is an all original Sansui 4000 made in 1970, which I believe the original owner used regularly since the day he got it new, and the other was a Zenith tube tabletop radio from 1941 with everything original to it including the caps and tubes. It worked fine as well. So if you go on the theory of replace everything because it MAY fail, you are giving yourself a lot of work for nothing. That 1941 Zenith had to have been used on a regular basis since new, as there would be no other explanation as to how 77 year old capacitors could still test and work fine oh so many years past when they should have failed.

    You can do what you like as its your gear, and clearly you have the time, but by shotgunning everything like that not only do you make extra work for yourself, but you also have the potential for mistakes to creep in which could cause other problems/damage to the unit in question.

    :lurk:
     
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  10. Hipocrates

    Hipocrates Anti-Muppet

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    Are you saying that the amount of work required is dictated by your standards otherwise is madness?
    Man...thank God you haven't seen my HK330, 9090,AU999, and Pioneer SA-7500 they will give you nightmares.
    Doug's write ups are documented like no one does and are very nice readings. Specially on times that more and more people just post asking for BOMs, asking for help, fighting in A vs B threads, ranting for some reason and fewer posts of restoring gear.
    I have tested the metal films 1% like Doug use them and can honestly say is not for nothing.
    Even when I can see your point, is just your way of doing things.
    @dlucy keep up the good work man, can't wait to see the outcome.
     
  11. gpounce32768

    gpounce32768 Active Member

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    Its cheaper to use another of a part already stocked then to set up stocking for an entirely new one. Or the use of the higher spec part let them avoid stocking the lower spec also. Or they had lots of excess inventory parts and this was a harmless place to use them up. Lots of reasons...
     

     

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  12. stereoguy70

    stereoguy70 AK Subscriber Subscriber

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    The "madness" as you put it is because he is replacing ALL the carbon metal film resistors with new carbon metal film resistors for no reason other than he potentially sees a problem down the road.....which may or may not be there. This is like rebuilding a car engine that has very low miles and runs perfectly fine, but we're gonna rebuild it anyway because we were there replacing a leaky gasket.......:rolleyes::dunno::crazy:
     
  13. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    Thanks for all the perspectives everyone. I appreciate the input and will take it into consideration.

    The rest of this thread will be a documentation of my process to create a reference disassembly, pinout verification, and nearly complete BOM for the purposes of recapping, repair and restoration.

    If you have some facts or pointers on the specific unit or with a specific replacement, please share it here. If you have a "hey, there is a operational problem with how you're doing X", like me missing the need to keep TR804 thermally connected to the driver board heatsink, please share it here or in a PM.

    For all the "you're crazy" comments: you're right, I am crazy, perhaps even more so in some ways than the typical AK'er, and I'm ok with that. What I'm doing and the learning I'm sharing is aimed at being helpful as a reference to other crazy people.
     
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  14. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Actually, as I understand it, and to clarify what is being done, Doug is replacing the original Carbon Film resistors with new Metal Film 1% resistors - that is a big difference in terms of noise reduction, stability and value accuracy, however maybe just a resistor type 'typo' on your part.

    I have just completed changing around 190 resistors as above in one of my amplifiers, I can tell you that the difference is very marked, and despite that it was a very arduous task, well worth it and something I would consider doing again. - so I'm crazy too.
     
    Last edited: Mar 14, 2018
  15. Overundr1

    Overundr1 AK Subscriber Subscriber

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    As a full on collector of Sansui goodness there are two pieces that I wish I had the time to do a full component restoration on, one being my CA3000, the other my AU-919. The benefit of changing to metal films has already been discussed, ditto the replacement of functional transistors with modern low noise tarnish free variants. Sansui green chicklet caps have to go, those old cog caps also have better modern examples, frames need new powder coating, utrasonic cleaner use on switches etc etc. What I do not have now is the time. Go Doug go, we do have time to Watch and enjoy :)
    -Lee
     
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  16. Hipocrates

    Hipocrates Anti-Muppet

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    Not exactly, he's grabbing an old stock car and installing some high performance parts, the concept may be called ''resto-mod''? He's not servicing it.
    Plus is very helpful to clean boards.:naughty:
    So enjoy the thread, I can see that 7000 cutting corners on the track like a nice Lotus Evora:p
     
    Last edited: Mar 12, 2018
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  17. americannigh

    americannigh Active Member

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    Watching this thread. Very nice work Doug and informative. Thank you for posting the TO-66 to TO-220 example as I will be doing this later this week. I am also interested to see how you solve the thermal coupling of transistor TR804. In my project I have a diode that is thermocoupled to the TO-66 so haven't figured out yet how to make that work. Your thread may provide me some ideas. Thanks!
     
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  18. Bahamayellow

    Bahamayellow Well-Known Member

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    I have a Sansui 7000 also that I really like but lost a channel. I am going to have it restored on day. Can’t wait to see this one done.
     
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  19. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    The switch board needed a lot of cleaning and had three sets of caps, each a different kind.

    Switch board 01 before IMG_7867.JPG
    Switch board 02 after IMG_7880.JPG
     
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  20. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    On the rear panel, underneath the manufacturer's label, there is a box that covers over the voltage selector... plugs. It looks like you could very carefully select the AC mains voltage going into the unit.

    Voltage selector 01 IMG_7945.JPG

    Voltage selector 02 IMG_7946.JPG

    Voltage selector 03 IMG_7947.JPG

    Voltage selector 04 IMG_7949.JPG

    I think I've got 120 VAC here and I don't want to push the circuitry over its edge, so I'm going to select 127 VAC.
     
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