AU-517 AND AU-919 Troubleshooting

Discussion in 'Exclusively Sansui' started by spacemanx1, Aug 12, 2018.

  1. spacemanx1

    spacemanx1 New Member

    Messages:
    10
    Hi folks!:)
    I am a new to this site and was hoping to find a "expert(s)" that would be generous enough to provide some troubleshooting suggestions. I have two separate amps with two different issues. I understand basic electronics and have schematics for these units, I am in need of a "shopping list" of things to start checking to point me in the right direction so I am not going down a blind path.

    AU-517
    Amp powers up and plays fine up to a point.
    I have found that with no low level inputs (cables disconnected) and just speakers connected that as the amp begins to warm up a low level hum appears on the left channel only regardless of volume level. Flipping switches/turning pots etc. on front or back of unit does not affect this. As unit continues to warm up the hum or the level does not change. After about 1 hour the hum gets louder and there are crackles and high frequency "screetches". When the amp is powered down and cools off the entire process is repeatable.

    AU-919
    Unit works fine until it warms up for about an hour and the power "protector" circuit kicks in with the flashing LED. It stays this way for 10-15 seconds and then turns off and operates normally (this may happen 2 or 3 times). Note, than when I power up the unit cold or hot it takes ~11 seconds for the protector circuit to "close" and the LED to go solid red. This time seems long and is much longer than the 517 protector that switches in after 2-3 seconds, don't know if this suggests anything.

    thanks in advance for any guidance.
     

     

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  2. ghamilton

    ghamilton Super Member

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    Do NOT turn them back on until you get several replies! I have the 919 and it is worth the wait. Has any work ever been done on these units? (some history would help)
     
  3. spacemanx1

    spacemanx1 New Member

    Messages:
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    Hi, thanks for the reply.
    My brother bought the 919 new back in the 70's and handed it down to me about 20 years ago. It has been "tuned" and cleaned several times, I had it repaired some years back for an intermittent channel but don't recall the details on what was fixed, quite frankly I believe after this repair is when I noticed that the power protector took longer to shut off when the amp was first turned on.
    The 517 I bought from an audiophile friend and it has probably seen at least 3 owners so I unfortunately don't have any history. For both of these systems the issues are "new", i.e. they previously worked fine.
    Sorry, wish I had more details. :(
     
  4. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    The AU-517 sounds like it might have failing main PSU capacitors for one channel, but really needs a check over by a vintage aware tech.

    The AU-919 will be tired now (as will the AU-517) and in need of a full recondition, again preferably by a vintage aware tech. They are a lot of work to get sorted out but well worth it.

    They are both fine amplifiers, but the AU-919 really is superb in full working condition. But it suffers from the Sansui Glue problem, this and the instability issue gets more and more likely to appear and cause problems unless dealt with by that reconditioning. If the amplifier is used, especially with the fault you describe it could destroy the unobtanium output transistors thought by many to be the key to its marvellous sound.
     
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  5. Overundr1

    Overundr1 AK Subscriber Subscriber

    Messages:
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    Not much to add to what Hyperion mentioned but as always an extra .02 is nice to have---

    AU-517 will require at minimum pulling and rebuilding the power supply board (the large board sandwiched between the main caps and the transformers. Glue has probably corroded components responsible for the +/-35v rails throwing the rest of the amp out of balance. Many many detailed threads about the process here on AK

    AU-919 really should be taken out of rotation till several issues are addressed. Having the protection relay start to kick in after the unit warms up indicates probable dc drift which in turn is due to a variety of possibles from black flags allowing oscillation and overheating to corrosive glue to suspect input differential pairs etc etc.

    Both are very nice examples of Sansui in their heyday and worthy of the time to get them right.

    Welcome to AK as well, especially the Sansui forum.

    -Lee
     
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  6. spacemanx1

    spacemanx1 New Member

    Messages:
    10
    Thanks folks on the thoughts and ideas.
    Well I certainly don't have an EE degree and I know there is nothing more dangerous than a ME trying to do a EE's work! I don't have much more than some voltmeters and scopes, obviously no sig-gens or anything like that. These units have way too much sentimental value so I would rather not screw them up, I was asking to determine if it may be something "simple", but it sounds like it isn't.
    Soooo, it sounds to me your recommendation would be to find a competent vintage tech. If so any idea of a ballpark cost to repair? I understand that you really won't know the issue until you dig into it, but I don't know if this is a $200 job or a $800 job or more :eek:
    Thanks again for the help, any other ideas on what I might suggest to a tech are appreciated.:)
     

     

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  7. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Be brave :)
    The AU-517 would be an excellent unit to learn the tech ropes on, many many folks here to walk you through the process and no expensive test gear really needed. The 919 on the other hand is not for the faint of heart and there are far fewer techs that have been in one.
    Many many first time repairs on this and its sister the 717 have been successfully completed on AK over the past decade.
    -Lee
     
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  8. macyjrm

    macyjrm AK Subscriber Subscriber

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    Your approximate location might be useful. Perhaps we can point you toward an experienced tech nearby.
     
  9. spacemanx1

    spacemanx1 New Member

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    Hmm, my last post is missing along with the reply from Hyperion that I saw via email. Server issues or am I limited to the number of "posts" somehow?
     
  10. kevzep

    kevzep Its all about the Music Subscriber

    No, I think the site was restored to an earlier time before those posts, almost everything I posted about two days prior to the site going off line has disappeared...
     
  11. spacemanx1

    spacemanx1 New Member

    Messages:
    10
    Ok, thanks. Wasn't sure if it was something I was doing. In any case what is missing from above.
    I am in Phoenix, if anyone has a good tech they would trust to look at the 919 I would appreciate it.
    In regards to the 517, just to re-iterate I found I found D17, D18, D606 and R621 that was physically clipped with some snippers on one end, but the components are on the board. I have re-capped the left and right channel boards and cleaned up the old glue. The amp does work OK in this condition. I am going hook back up the disabled components and see if it functions.
     

     

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  12. spacemanx1

    spacemanx1 New Member

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    Hi folks.:) Well since the AU571 recap on the L/R channel boards went well and I had to pull the power supply board I opted to just do the recap on this board before hooking back up the disconnected components on the PS board. I measured a few of the diodes and some appear to be bad, one that is next to the relay D608 (10D1), I assume it is flyback protection for the relay. Also thought about replacing the zeners while I am in there also.

    I need some cross reference part number help as a lot of these are obsolete, don't know much about zeners so don't want to pick the wrong ones. Can someone please help me out with the part numbers below and make a recommendation on anything else to replace that is likely to degrade over time while I have it torn apart?

    ZD601; EQA01-06R 500mW ZENER =?
    ZD01,02,03,04; RD33EB 500mW ZENER =?
    ZD602; RD6.2EB 500mW ZENER =?
    D602 DIODE, 10D2, 1S2227 =?
    D608 DIODE, 10D1, 1S2226 =?
    ARE 1S2473 AND 1S2473D DIODES INTERCHANGEABLE TO 1N4148?
     
  13. petehall347

    petehall347 the brandy coffee man Subscriber

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    D608 will test bad in circuit .
     
  14. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Here is a helpful post from another AK member
    The above three types of ordinary diodes/rectifiers shouldn't need to be changed unless they are actually faulty, you are just making work for yourself. :)
     
    Last edited: Aug 26, 2018
  15. Baab

    Baab New Member

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    Location:
    Adelaide South Australia
     
  16. Baab

    Baab New Member

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    Location:
    Adelaide South Australia
    Can you tell me the colors of the wire connection that go for the AU-919 front panel LEDs thank you in advance
     

     

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  17. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Answered in your thread for this question.
     
    Last edited: Aug 30, 2018
  18. spacemanx1

    spacemanx1 New Member

    Messages:
    10
    Thanks John for the feedback.
    Petehall347, thanks for the note on 608 will check out of circuit.

    I took a wag and ordered the following, if anyone thinks these equivalents are a bad choice please let me know.
    D602 1 DIODE 10D2 1S2227 1N4003
    D608 2 DIODE 10D1 1S2226 1N4002
    D606 DIODE 1S2473 1N4148
    D17 1 DIODE 1S2473 1N4148
    D18 1 DIODE 1S2473 1N4148
    ZD601 1 zener EQA01-06R 500mW ZENER BZX55C5V6 or 1N5232B ON SEMICONDUCTOR
    ZD01,02,03,04 4 zener RD33EB 500mW ZENER BZX55C33 or 1N5257B
    ZD602 1 zener RD6.2EB 500mW ZENER BZX5 5C6V2 or 1N5234C

    Baab, not working on the 919 but the 517. Only one LED, it has red and white wires.
     
  19. spacemanx1

    spacemanx1 New Member

    Messages:
    10
    Here is a quick update if anyone cares.
    Finished the re-cap of the 2675 board, cleaning adhesive and damaged components. Hooked all the cut components from the protector circuit and the amp fired up fine. Set all the VR01,02 and 03 pots initially and re adjusted the after the amp was up to temp in about one hour. I measured the +/-31 and the +/-46V test points on both channels, they were within 1V of the schematic and within 0.3 Volts of each other between the two channels. I also cleaned and de-oxed all the pots and switches as well a re-flowed all the rosin flux on the boards I have repaired. I hooked up a precision sine wave sig-gen, and measured the THD, less than 0.01% so I figured it is in pretty good shape. Overall the amp sounds very clean.
    I did have one question regarding the circuitry that affects what might be heard without an input to the amp while the volume is turned all the way up. Before the recap when this was done I could hear a faint hiss, as one would expect from the lower end amps, after the recap no sound is audible from the speakers in this condition, what circuitry affects how clean the circuit is at high output?
    I don't think there is much else to do, if anyone has other thoughts on what to check I would appreciate it, otherwise I will button her up and take my hand at a the AU919 repairs.
     
  20. Overundr1

    Overundr1 AK Subscriber Subscriber

    Messages:
    2,501
    Location:
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    Remember the volume control is an attenuator reducing gain to the amplifier stage which runs wide open. Thus I suspect the tone/eq board, especially if you replaced any of the transistors.
    Nice job on the power supply, getting those voltages right is the largest challenge to rebuilding the 717
    -Lee
     

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