Sansui G7500

Discussion in 'Exclusively Sansui' started by Super Noob, Aug 24, 2018.

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  1. Super Noob

    Super Noob Active Member

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    175
    Possible Project. Considering re-capping and refurbishing my G7500.

    [​IMG]

    With that said, I feel like this might be over my head. From reading posts (research) on this set, the G7500 is not of the same quality like the others I own and have rebuilt. Always wanted a G-unit = they look great (to my eye) and this was the only one local in the last 3 years. I feel lucky to have it (had for 2 years), but obviously this not of the quality of G7000 or G8000.

    It works fine, but doesn't get much play based on the fact that this set has been known to grenade and the other receivers that I have accumulated. It is now the only unit not rebuilt in my herd.

    Pretty much thinking of selling it or rebuilding it (and I don't sell anything). I usually don't scare easy = but I think I have a 50/50 chance of turning the G7500 into a parts unit. Could likely unload and get 9090 - but it sure doesn't look like a G-unit.

    Kev / John = what are your thoughts? You are the Sansui guys that have direct experience with the beloved F2980 board. John you helped my on my first expedition into this hobby (Sansui 800) a couple years back = thanks for caring and helping on that set (am infected now and you are a big reason). Kevin your participation on a 300 post rebuild of a lost G7500 is testament to your character, passion, resolution, and selflessness. You as well helped on my SX1250 by suggesting to change all the small semi across the unit. It is as silent as a church mouse and can bring the thunder of a lightening strike in the front yard = she is my favorite unit now. I know you are on the other side / underside of the globe, but thank you for all you do.

    Thanks in advance for your comments.
     
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  2. Robisme

    Robisme Sansui Enthusiast Subscriber

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    Looks of a G-7000, build of a G-7700. Nothing wrong with that. Looks like you put your eggs in two baskets.

    Rob
     
  3. kevzep

    kevzep Its all about the Music Subscriber

    If the unit is working, I can't see any reason why you shouldn't re-cap it. You could also replace the Bias and DC offset trimmers.
    I'd say there's most likely "that Glue" in there as well, and that will need to go.
    Give the switches and pots a squirt, fit some LED, and she'll be good for another 30years...I did that recently to both my G7700's and ended up selling one, and lending the other one to a friend.

    Thank you for the compliment, I like to help where I can, we have to keep all this old gear going.
    I have recently completed a restoration of a SX1250 for a customer, I'm enjoying that for a while until he picks it up in December.
    I am going to do an interesting mod to it that you may be interested in, I will keep you posted.

    Let us know how you get on.
     
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  4. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Well, that was just one puny post, ;) but nevertheless I am very flattered by your kind words, and pleased that you have found interest in this hobby. Clearly, Kev is 'far and away' more of an expert than I am with so many of the aspects of receiver fault finding, test, repair and upgrade. ;)
     
    Last edited: Aug 26, 2018
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  5. KingBubba

    KingBubba "Too Much Stuff" Subscriber

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    I too am a 7500 owner. When I bought it it was reported as not working. The eBay pic showed no jumper cables; so I took a chance. The final bid was low, but not minuscule. When I got it home, I put a jumper and fired it up. Only one channel functioned. I opened it up and someone in it's past had cut a number of wires leading from the driver board. This made no sense to me.

    I have a G-6000 and the G-7500 that are both in need of help. My G-8000 is working fine. I am in a similar situation in that those two are the only units in my playing arsenal that should be rebuilt. The G-6000 was my work receiver and played backstage, at the theater I worked in, for a good thirty years. I have many good memories of blasting great tunes during our long loadins and loadouts. For pure memory's sake the G-6000 will be first. As for the 7500, the left channel that worked sounded great to me and just because it did not have a toroidal transformer did not seem to me to be any kind of factor to even consider as negative. I will have my 7500 rehabbed. I think you should bring you unit up to snuff because it is a great looking and sounding receiver regardless of any negative press about it. Get it going, it will be worth your efforts or costs.
     
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  6. Super Noob

    Super Noob Active Member

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    175
    Thanks... Kevin, John, Bubba. Per Kev comments, I should be in a fair position as it is descent operating condition. Prior to getting the SX850 / SX1250, the G7500 was in my work area and got a fair amount of play. To me the G7500 is very attractive.

    I will rebuild. Need to be careful with the trimmers - so no magic smoke. Need to survey the unit and I will assemble the parts list. Have read there is inconsistenties on the schematic.

    From what I read the bias trimmers work CCW to increase bias in lieu of CW as the manual indicates.

    Am with you on sentimental equipment - I had a Technics SA series receiver when I was a kid. So I wanted a SA800 and was lucky enough to get one cheap needing repair. It was a battle but I won. Though not as desirable as others - it is the one that takes me back.

    The struggles on recent rebuilds has honestly taken me further in my development. I like doing parts list, getting Christmas packages from mouser, relamping units, cleaning up the units internally, and going over the boards with new caps + sealed trimmers + transistors where relevant.

    Yesterday I pulled the Citation 16A back to the center stage. Think I am going to sort out my problem channel then onto the G7500. It has gotten pushed to the side because I couldn’t get it fix. Haven’t given up and know if I stay with it that the persistence will pay off.

    Kev - outside of the caps, trimmers, LEDs, do you recommend any small transistor changes. Looks like your G7700 is similar.

    Sanui 800
    Pioneer SX850
    Marantz 2325
    Realistic STA2100
    Realistic STA2000
    Technics SA800
    Pioneer SX750
    Pionner SX1250
    Realistic STA2100

    I need to complete one more to get to double digits. Will update as I get rolling - thanks for the recommendations to proceed.
     
    Last edited: Aug 26, 2018

     

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  7. Young46

    Young46 AK Subscriber Subscriber

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    Good luck.
     
  8. Super Noob

    Super Noob Active Member

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    I have the new parts... will post a fully verified list I assembled for the G7500. It will help anyone who might try a rebuild.
     
  9. ghazzer

    ghazzer Senior Member Subscriber

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    There is lots of temptation to just go in and replace all the parts that you want to replace, but that is an almost certain road to frustration with the F-2980 board. It seems like Sansui created a finely balanced design and probably had to tweak each one before it was released. Replacing any component may introduce more tolerance swing than the rest of the circuit(s) can tolerate, and then ZING!

    My suggestion is to make a plan, then go in and replace the components one at a time, one channel at a time. Then you can check that one out with a good listen and a compare back to the other channel. Take good notes. You should be able to replace most, if not all, of the components without removing any boards or jumpers.

    I try to pay attention to the speed and transition frequency of replacement transistors, as I suspect there may be timing problems. "Fast" transistors in a "slow" circuit can switch before other circuits are "ready", causing problems (oscillations???) down the line. The transition frequency (F sub t) is the frequency at which the transistor's gain is 1 (one). I am not sure how this effects performance of a circuit, but the F-2980 boards have gone WONKERS on me more than once with no specific explanation. So I advise caution and good rational thoughts.

    Good Luck - - -
     
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  10. kevzep

    kevzep Its all about the Music Subscriber

    I disagree, if the unit is working and the replacements are the right ones, there is no problem.
    There's no point in being scared its going Chernobyl itself, I recently just ploughed through my old G7700, Originally I used MJE15033/32 for the drivers and MJE340/350 all through it, when I re-recapped it, I had some NOS Toshiba's and some KSC1220/KSA2690.....I blew through and replaced them all, and promptly forgot I designed my bias circuit so instead of turning it down, i had it wound right up when I turned it on.....Hilarious!!
    I blew through and did all the caps, did that modification to the 2980 to remote mount a speaker relay....

    The problems start when the unit has a fault, when they have a fault, this is when these cascading Chernobyl events happen.....

    The key is, positive attitude, and set your mind to fix it, don't worry or tip toe around it otherwise you're heading for trouble...
     
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  11. ghazzer

    ghazzer Senior Member Subscriber

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    I disagree, respectfully. I don't have your knowledge and experience, so I think it is wise to step into something like this with caution and a plan.

    I do concur that the ones that have already failed are more likely to give problems. However, the others are not immune, just less likely.

    Kevzep, Hyperion, Overundr1, or a double fistful of other AKers could probably solve one of these in an afternoon, but I still have too much to learn.

    And I am enjoying the learning. Thanks - - -
     
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  12. Super Noob

    Super Noob Active Member

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    Got a plan... well underway. Will post results.
     
  13. kevzep

    kevzep Its all about the Music Subscriber

    Well, perhaps I could have said "as much as you feel comfortable".
    I haven't done anything particularly amazing in terms of method and/or approach to the 2980's I worked on, I just removed parts and fitted new parts and they worked, even with me getting tricked by my own clever bias circuit.
    If its working, its going to be no more difficult than any other amplifier, where it gets difficult is when it has had a failure, as you know.

    We'll see how this one works out....
     
  14. Super Noob

    Super Noob Active Member

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    175
    It’s done and dialed in nice... will post the final pictures next weekend. Am traveling this coming week.

    Need to figure out new speaker terminals... a few of my plastic leavers are broke. Need to search up what people do with those cheap clips . Repasting those outputs was fun.
     
  15. kevzep

    kevzep Its all about the Music Subscriber

    I knew you'd do it.....Crank it up and let us know how it sounds...
     
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  16. KingBubba

    KingBubba "Too Much Stuff" Subscriber

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    My G-8000 had 1 CW and one CCW VR. If I had not checked the VR with my meter beforehand, I would have cooked my unit doing DC offset. I know not to trust the Sansui and Pioneer SMs, although the Pioneers don't seem so unreliable.
     
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  17. kevzep

    kevzep Its all about the Music Subscriber

    I made my own VBE controlled Bias circuit, I designed it so it the VR went open for any reason, the bias would go to minimum, I got caught out by my own cleverness!!
     
  18. Super Noob

    Super Noob Active Member

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    I spend a lot of time figuring out the bias trimmers when replacing. This unit was easy due to the bias trimmers having two legs on same trace = so it was easy figure the leg to leg for the minimum resistance for initial setting.
     
  19. KingBubba

    KingBubba "Too Much Stuff" Subscriber

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    I definitely learned from my experience and am much more cautious now.
     
  20. Super Noob

    Super Noob Active Member

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    [​IMG]
    Changed some fuses and clips too...

    Before:
    [​IMG]
    After:
    [​IMG]
     
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