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New project. Sansui 8080 recap. Advice appreciated.

Discussion in 'Exclusively Sansui' started by RR--, Apr 4, 2018.

  1. RR--

    RR-- Active Member

    Messages:
    247
    Location:
    Melbourne, Australia
    Hey guys I'm back!

    But I never really left as I have literally been using my AU-719 daily since I recapped it around 2013.

    I came across a Sansui 8080 in rough shape years ago but am only finally starting to use it due to being able to actually fit this monster it in my new house. It sounds absolutely fantastic! the lyrics really leap out at you and the soundstage is really wide and detailed, this amp sounds too good to sell.

    The amp works great except for:
    • A slight distortion in the high frequencies in the left channel only
    • A sloppy bass response and high noise floor likely due to the original aged capacitors
    • A lot of surface rust on the chassis and exterior cosmetic damage to the wood case
    I'm planning on doing a full recap and possibly sanding back and painting the chassis to prevent further rust.

    [​IMG]

    My first priority though is fixing the distortion in the left channel high frequencies.

    Any thoughts on what could be causing this? I took it to a repair shop years ago and they couldn't hear it on their (terrible) speakers. My current thinking is it's a transistor on the pre-amp board somewhere that's on it's way out but honestly I don't know anything about transistors so any advice would be very much appreciated.

    As I'm not that great of an electrician I was planning on taking a shortcut and purchasing this capacitor kit instead of making a list of capacitors again.
    www.audio-high-store.com/product/sansui-8080-upgrade-kit-audio-capacitors/

    This kit includes 73 Elna Audio, Nichicon KZ and FG caps not including the two big ones.

    Again any advice you have is very very much appreciated, I couldn't have done it l the last time without the advice and generosity of this forum.
     

     

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  2. RR--

    RR-- Active Member

    Messages:
    247
    Location:
    Melbourne, Australia
    Some more "before" photos showing the condition it's in. Not bad for $65 at a second hand shop.

    [​IMG]
    [​IMG] [​IMG]
     
  3. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
    1,741
    Location:
    Costa Rica
    Before recap you probably want to address the problems of your unit.
    First....

    Grab a service manual, measure offset and bias, adjust, be sure if the distortion is on the preamp o the amp section (I don't think it is on the PS).
    Then report
     
  4. RR--

    RR-- Active Member

    Messages:
    247
    Location:
    Melbourne, Australia
    Yeah good thinking, I'll have another look at the bias and DC but it was adjusted when it was serviced and made a big difference. I have the manual and an expensive multimetre so that should be no problem.
    Do you know of an easy way to tell if the distortion is on the pre-amp or amp section? The 8080 is my only amp with pre-out jumpers. My AU-719 and AU-4400 don't have them.
    Thanks for the reply.
     
  5. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
    1,741
    Location:
    Costa Rica
    I would use a phone, mp3 player or a computer and connect it to the amp section (main input) and manage the volume from the device.
    If is in the amp section, I would start F-2436 and then F2547, weak points on this fellows are the fuse resistors, VD1212,and IS2473 (diodes), 2SC1313 transistors (can be replaced with the KSC1815) you have some on the preamp.
    If is the pre section, I would start with the pots ( Deoxit)

    BTW, looks like the bottom cover is very rusted, I would soak them on white vinegar for some hours and the clean it very well with WD40 (not use in pots)
     
    RR-- likes this.
  6. RR--

    RR-- Active Member

    Messages:
    247
    Location:
    Melbourne, Australia
    Wow good advice! my Dac (Maverick Audio D1) has a pre-amp volume dial so I did exactly what you said plugging it into the main input and the problem persisted, so that must mean the problem is in the amp section.
    The receiver already has had it's pots cleaned from the previous "service".
    I'll have a look at the components you mentioned as well as tackling the rust. Would you just recommend changing all of them or is there a way I can test them first with my multimeter and moderate talent?
    Thanks again.
     

     

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  7. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
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    Location:
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    On this units a good advice is diagnostic first... a cheap oscilloscope and tone generator app it is a good starting point. So I would do it like this.

    Lets establish first which section is faulty (amp or preamp). Once that's done, we will have a better picture to where appoint our guns, and refresh the units.

    Study this great piece from a fellow AKer... It will give you an outline to where to start to diagnostic (that will make the whole experience MORE rewarding)

    http://www.conradhoffman.com/troubleshoottut.htm
     
  8. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,893
    Location:
    uk.. the middle bit
    owing to the obvious corrosion i would first be cleaning all electrical connectors .
     
    Hipocrates likes this.
  9. RR--

    RR-- Active Member

    Messages:
    247
    Location:
    Melbourne, Australia
    Thanks again I'll give that link a good read, I think we've established the problem is definitely in the amplifier section.
    Electrical connectors have been cleaned although I'll give the inside a proper clean with some shellite soon as well as the rust. Thanks
     
  10. kevzep

    kevzep Its all about the Music Subscriber

    I'd also suspect the speaker relay, I just had this happening in an amplifier I was working on.
    Dodgy old relay contacts can most definitely cause distortion.
     
    RR-- likes this.
  11. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
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    As Kev said, visually inspect the relay wich is located on F-2547, plus check F-2436
     
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  12. Overundr1

    Overundr1 AK Subscriber Subscriber

    Messages:
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    Location:
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    2nd the relay comment, had one across the bench recently with occasional distortion artifacts, turned out to be a dodgy relay.
     
  13. RR--

    RR-- Active Member

    Messages:
    247
    Location:
    Melbourne, Australia
    So I think I may be onto something, I pulled a few boards out and noticed most of the transistors on the 'top' boards have black corroded legs which was the issue on my AU-101.

    [​IMG]

    I think this receiver must have been in some weather as the top boards are in a much worse condition then the second layer.
    I took some high res photos of the relay and it looks like it's in pretty good condition in my opinion but I'll let you be the judge of that. I uploaded a few photos here: https://imgur.com/a/dN91o
    If anyone can see anything I can't I'd appreciate it. This amplifier desperately needs a thorough cleaning.

    [​IMG]
     
  14. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
    1,741
    Location:
    Costa Rica
    mmmmm, it seems that a muppet (as my good friend Kevin says) was on the driver board (F-2436)... Can you take a top view picture of that board? Love those nice resolution pics.

    Those black legs transistors are very common this Sansui.
     
  15. RR--

    RR-- Active Member

    Messages:
    247
    Location:
    Melbourne, Australia
  16. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
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    Location:
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    Thanks, those pics help a lot, from my point of view and being just a enthusiast eyeballing without proper measurements we have some stuff to address. (white circles)

    upload_2018-4-8_0-48-3.jpeg

    - Resistors circled are fusistors, they are reported as problematic and love to drift in value.
    - The circled transistors I've read can be noisy and some experienced folks says the are problematic.
    - Those circled red diodes on the top of the image are reported as problematic as well.

    - Finally TR07 was replaced, just barely attached to the heatsink so BIAS can be drifting or unstable, in this particular matter maybe more advanced fellows can chime in and lend us a hand. Me? I would try to get some 2SC984. I got some on ebay a while ago and they are still working fine.

    I tend just to replace the relays, but your does not seems to be to bad.
    If that was my board I would give it the full treatment, (new zeners, diodes, pots, transistors, caps, and resistor replacement)
    But... let's wait others with more knowledge than me say. (this fellows are real experts :thumbsup:)
     
    Last edited: Apr 8, 2018

     

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  17. RR--

    RR-- Active Member

    Messages:
    247
    Location:
    Melbourne, Australia
    Wow looks like I've got my work cut out for me! To be honest I don't know much about zeners or diodes but if the experts on this forum recommend what to replace these with I'll do it for sure.
    Yeah you're right TR07 is pretty ugly! Looks like I can get some NOS ones on eBay for around $15 and have it done properly.
     
  18. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
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    Location:
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    Way more fun, that just recap. :p
    Diodes, that's easy don't worry.... Where to find the source of distortion remotely, that's the tricky part.
    The suspects are.

    - Relay contacts ( you could try clean the relay)
    - Electrical contact (clean very well the socket of F-2436, and check cable connections)
    - Some component on F-2436.

    On F-2436.

    - Check fuse resistors, and replace them; you can replace them with 1/2W metal films types.
    - Visually inspect the work done on the back of the board, look for cold solder joints and traces, you can clean it with alcohol and a toothbrush
    - Check VD1212 with your multi meter in diode function.
    - Check voltages with the schematic as guide
    - Report
     
    Last edited: Apr 8, 2018
  19. RR--

    RR-- Active Member

    Messages:
    247
    Location:
    Melbourne, Australia
    Ok so instead of answers I somehow have more questions.

    I spent quite some time and gave the amplifier, pots, fuses and contacts a thorough clean so I thought to adjust the DC Offset and Bias again.

    The DC Offset was way off at 80mv so I readjusted it within 1mv of 0V.
    For the Bias I pulled the fuse like it says to in the manual and set my multimeter to mA, the amplifier wouldn't power on unless my multimeter's positive terminal was like so in the picture below, the readout was 0.09mA but no matter how much I adjusted pots VR04 and VR03 there was no measurable difference to the readout. I haven't properly tested the amplifier since as I don't know what the bias is set to now and don't want to damage anything.

    Also both the VD1212 Diodes at D06 D07 measured at 0.651V each.


    [​IMG]
    [​IMG]

    However when I was cleaning I did notice a very dodgy repair to a resistor with two resistors which could cause some problems.

    [​IMG]
     
  20. RR--

    RR-- Active Member

    Messages:
    247
    Location:
    Melbourne, Australia
    Also I stumbled across a great website mostly about Sansui QRX receivers but also included 8080's and 9090's. They sell a set of fusible resistors which looks like an easier option for me.
    http://www.qrxrestore.com/parts/
     

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