Sansui G-5700 Restoration

Discussion in 'Exclusively Sansui' started by TMaster, Jan 9, 2019.

  1. TMaster

    TMaster Transistors for teeth? They do have roots... Subscriber

    Messages:
    101
    Location:
    Austin, TX
    I received my first Sansui G-5700 in the mail today. I bought it to repair and restore as my main receiver. It is not as good cosmetically as I thought; but sometimes that happens with poor pictures and ordering online. After I got it I was thinking I should have paid less... I will have to find some new aluminum looking film for the face sides eventually. Good thing is it is in very good shape on the inside, just dirty and the patented puffed C612. The radio stations display fine, the signal meter works fine, but the Tune center dot never lights up, nor the red stereo LED. There is no sound of any kind, and the power supply relay does not click. Oh and the string/pointer is off compared to the quartz display numbers, but the string can be adjusted.

    I have decided after researching on here, the best thing is to restore the power supply board almost completely. The service manual seems to be lacking on the resistor list with the boards, and I will have to go into the schematic to get the values and maybe even the original resistors themselves.

    First I will do the F-2980, then the F-3000, and so on. Could the MSM5540RS Chip be causing the tune and stereo LED issue?

    Any recommendations would be appreciated!
     

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  2. ghazzer

    ghazzer Senior Member Subscriber

    Messages:
    3,104
    Location:
    Sykesville, MD
    Hello, and welcome to AudioKarma!

    There is a wealth of information here on the G-5/6/7700 series receivers. My suggestion is that you continue your research/reading and then ask specific questions about what YOU want to do with your G-5700. You have already learned a lot about these receivers, but asking for open ended recommendations will only lead you to what someone else would do.

    Call it a "lessons learned", but I think that one of the first things that should be done is to replace the four 100Ω single turn trimmers with multi-turn Bourn style trimmers. The originals are old & brittle and failure can easily lead to secondary failures.

    The F-3060 P/S bd is for the digital tuner circuits. The primary P/S is on the F-2980 bd.

    Good Luck - - -
     
  3. macyjrm

    macyjrm AK Subscriber Subscriber

    Messages:
    1,309
    Location:
    Mississippi
    I had a Sansui receiver (don’t recall model #) with similarly abused side panels. They pop out easily if I remember correctly. I sanded my panels smooth and applied auto aluminum wheel spray paint. They turned out quite nice and were a very good match for the rest of the metal on the unit.
     
  4. TMaster

    TMaster Transistors for teeth? They do have roots... Subscriber

    Messages:
    101
    Location:
    Austin, TX
    Thanks guys, I decided I need to do the F-2980, F-3060, and F-3000 boards first. These seem to be the most problem boards. I am going to try hard to order up everything for them tomorrow. I'm almost done with the list for the F-2980. Are there any resistors that I should replace on the F-2980 besides R44?
     
  5. ghazzer

    ghazzer Senior Member Subscriber

    Messages:
    3,104
    Location:
    Sykesville, MD
    You will be better off to only replace the ones that have failed. Minimize the parts that you replace and try to validate the repair before moving on.
     
  6. TMaster

    TMaster Transistors for teeth? They do have roots... Subscriber

    Messages:
    101
    Location:
    Austin, TX
    I did some probing on the resistors, only a few were wild (might be because they are still in the circuit). Also some by the relay are corroded, I'm going to replace some of them.

    What are you guys using for the Zener diodes? I could not find any info on here for replacements.
    1 ZD601 RD-24F
    1 ZD602 RD-30F
    1 ZD603 RD-30F
    1 ZD604 RD-18F
     

     

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  7. kevzep

    kevzep Its all about the Music Subscriber

    I've never had a bad Zener in a GX700 series amplifier, dont worry about it move on...
    You can't measure Zeners like a normal diode as they do not work the same with regards to reverse bias voltage.
     
  8. kevzep

    kevzep Its all about the Music Subscriber

    Yes, if something is not lighting up on the fluroscan display or a segment is on all the time, quarts lock not working or not working correctly etc etc, that 5540 chip is toast, you'll have to harvest one out of a TU80...
     
  9. TMaster

    TMaster Transistors for teeth? They do have roots... Subscriber

    Messages:
    101
    Location:
    Austin, TX
    Thanks guys, I have finally compiled and added to cart about $75 worth of parts and shipping to redo most of the components on the 3 boards previously mentioned. I'm debating on maybe I should just replace all the elec capacitors and troubleshoot the problem, fix it and let it be. I just feel like I should completely make it last for a long time by replacing a lot of stuff. Let me know what you guys think.
     

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  10. ghazzer

    ghazzer Senior Member Subscriber

    Messages:
    3,104
    Location:
    Sykesville, MD
    I can share first-hand experience with you: It is NOT a good idea to do wholesale replacement of parts, ESPECIALLY on an F-2980 PWA. This is one of the reasons why I am still futzing with my G-6700.

    IMHO you should identify the problem(s); trouble shoot that to a faulty component(s); convince yourself that you have found the cause(s) of your problem(s); replace the failed/faulty parts; verify repair of that problem(s); move on to the next problem.

    If it ain't broke (yet) don't fix it! {35+ year old electrolytic caps & single turn trimmers are exceptions}

    It is just too damned easy to muck something up that was working before you got there. Much easier ID one problem, establish the scope of the problem, do some research (as needed), then work on a solution.

    Observation: If you can, I'd get it working before going after the electrolytic caps, or older caps that are "in the signal path". Then you can safely go back and replace the caps one at a time. This will give you a chance to notice the improvement in the sound, and know that you can easily isolate the problem if it doesn't work.
     
  11. kevzep

    kevzep Its all about the Music Subscriber

    With all due respect Steve, I think yours is a special case, I have blown through 5 of these units in the last year, 2 x G7700, 3 x G6700, oh and a G7500 (same F2980 board). They all came up great, recapping them actually solved issues, what you cant see is how the glue corrodes the legs off some of the electrolytic caps on the F2980 board. The regulated supply underneath which they call the Digital supply board, definitely needs recapping, and it does not hurt to replace the pass transistors (regulators)
    You must recap the F2980 at least, all the ones I have worked on have the glue disease.
    Replace the trimmers.
    Replace the relay.
    But do not worry about any transistors unless you have to.
    Be VERY careful desoldering on these boards, the copper tracks are very fragile, and this is where the problem starts, its easy to put a hairline crack in a track and not even realise as you cannot see them, and then POOF!!! The magic smoke comes out...

    Do not touch anything but the caps on the F3000 board unless you have to, but it sounds like you have issues there anyway with the 5540 chip....
    Use ESD protection when soldering/desoldering the MSM5540, they are fragile as F%^K and its easy to damage them.

    I actually really like these amps, they have a great sound, shame that Sansui weren't a little more diligent with fail safe in the design.
     
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  12. TMaster

    TMaster Transistors for teeth? They do have roots... Subscriber

    Messages:
    101
    Location:
    Austin, TX
    Thanks again for the info. I've been soldering various electronics for over 18 years, so I am not worried. I actually have spent close to 8 hours already on my list for this. This service manual is so messed up because of all 3 receiver versions. Also my F-3000 board is way different than the service manual. I had to go look at the physical board to make my capacitor list.

    I've been trying to source a M5540, MSM5540RS, MSM5540.... But unfortunately I have not found a supplier yet. I really wont want to spend $70-100 for a T-80 just to harvest the chip. Since it seems my chip is running except the tune center dot, I may have to run it that way for a while. Maybe new caps would fix it?

    I was planning on replacing ALL the transistors on the F-2980 and F-3060. That is a big chunk of the cost. Being this thing is close to 40 years old, and it came from garage use, so it has been up and down in the temperatures. I could always just do the caps first then go from there and trouble shoot it. This will be my main receiver so I want it to last without having to fix it all the time! I do want to find a 7900Z....when one comes around also.
     
  13. kevzep

    kevzep Its all about the Music Subscriber

    You will not find one, there are none, 10 years ago I bought the last one off a "obsolete components" supplier.
    The only way to get one is from a working T-80.
     
  14. kevzep

    kevzep Its all about the Music Subscriber

    All the segments in the Fluroscan display are turned on and off by that 5540 chip, if one is on all the time or does not come on, the chip is usually faulty.
    Sometimes I have had these tuners where the alignment is off a bit and as a result the Dot wont illuminate, but you would need to blow on through an alignment to verify.
    I have never seen a fault cause by a bad cap on a F3000 board. There are many different revisions of these boards, none documented...
     
  15. kevzep

    kevzep Its all about the Music Subscriber

    If the silicon is working, leave them. There is no need to replace them, they are not like some units where they go leaky and crackly, the transistors used in these amps are excellent quality and hardly ever give trouble.
     
  16. TMaster

    TMaster Transistors for teeth? They do have roots... Subscriber

    Messages:
    101
    Location:
    Austin, TX
    Is it possible for someone to design a new 5540 version from existing components using a blank board? Is there a datasheet out there? Maybe modify a different IC, like that from the Z series?
     

     

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  17. TMaster

    TMaster Transistors for teeth? They do have roots... Subscriber

    Messages:
    101
    Location:
    Austin, TX
    It has begun.... A diode in place of R615 resistor? Must be a G-5700 thing... Replace with a 1N4148 ?
     

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  18. kevzep

    kevzep Its all about the Music Subscriber

    Why are you wanting to replace it, and it might actually be a Zener Diode, so do your due diligence because you do not want to put a regular diode where a Zener would go.
     
  19. ghazzer

    ghazzer Senior Member Subscriber

    Messages:
    3,104
    Location:
    Sykesville, MD
    Weird! I have a parts F-2980 that also has a diode in the position that is marked as R615, and no R 614 installed. And I cannot locate an R615 in the schematic. The "diode" is connected between ground (at C615) and TR04/B. TR04/B has a ~15KΩ resistor tacked to the track side of the PWB to TR603/C. This appears to be an attempt to insert the "missing" R614, but the tracks for R614 are between TR604/B and the +30vdc bus at jumper pin21.

    Looks like I need to revise my schematic, again.

    G-6700 Partial Pwr Sup-009.jpg

    Also, what is with the 2W(?) resistors tacked in parallel to the two 390Ω(5W) resistors for R605 & R606?
    My SM calls for 2?0Ω(5W) on the G-5700 but I cannot read the middle digit. The G-6700 clearly reads 270Ω(5W), which agrees with the parts PWA that I have.
     
  20. TMaster

    TMaster Transistors for teeth? They do have roots... Subscriber

    Messages:
    101
    Location:
    Austin, TX
    Oh, that diode in R615... There's a resistor on the back side of the board soldered to it, then to the Collector on TR603.

    I think the Diode says 13 on it. But I'd have to pull it to be sure. Really, I ordered some new diodes to replace some of them, I just missed that one, because it was hiding and in a R slot. haha.
     

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    Last edited: Jan 17, 2019

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