Hurt my AU-717 (current went wrong way, channel dead )

Discussion in 'Exclusively Sansui' started by delboyko, Dec 28, 2017.

  1. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    Long story short

    I was selling/demonstrating my "old" amp and I connected it to the same speakers as my AU-717, just with another pair of wires that had banana plugs on them.
    Before letting the music play for the buyer I forgot to turn off the Sansui and I noticed that it went into protection mode. He was "playing" like that for maybe a minute or so, I don't know. No smoke or funny smells.

    After the old amp went with the new owner I switched Sansui back on and it came out of protection just normal. The only problem was music went only through one channel.
    I quickly switched to direct coupled amp only and still music coming only through one channel.
    Checked for BIAS and offset on both channels. Working one was in spec while the other was off(don't remember the numbers).

    How bad is it? Where should I start...are things damaged on working channel as well, just not that bad?
    Please help. :(
    (recapped it this summer)

    @LBPete - I posted the SN
     
    Last edited: Dec 28, 2017

     

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  2. LBPete

    LBPete Rolling Along Subscriber

    Messages:
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    If you are getting sound from one channel, it's not likely the amp itself is damaged. The dropout is likely be occurring in the pre amp. Do you get sound from both channels in MONO mode? First step is to just "exercise" all the switches and pots, including the connected/separated switch and see if that brings it back.

    - Pete
     
  3. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    Already tried with connected/separated switch. Only left channel works. When I switch the R and L plug it still works on only one channel so it's not the source or preamp. Checked the speakers as well and both work on left speaker post.
    I think it's something in between right amplifier board and speakers post. What's the first thing that would get fried on the way to the amp and how far can it even get?
     
  4. LBPete

    LBPete Rolling Along Subscriber

    Messages:
    11,281
    Location:
    Long Beach, CA
    What do you mean by switched the R and L plug? Are you just switching the source input? The AU-717 doesn't have a mono switch so to check the amps switch the Connected/Separated switch to separated and jump the left pre-out to the right main in and the right pre-out to the left main in with a pair of RCA cables. If the problem switches to the other channel, the problem is in the pre-amp. If the problem stays in the same side, it's in the amp.

    - Pete
     
  5. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    I meant right(R) and left(L) to verify the source.
    I used a DAC as a preamp so I just turned volume digitally really low and plug it directly in "main in" instead of jumping it with an extra cable. Again only left channel works.
     
    Last edited: Dec 28, 2017
  6. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    UPDATE:
    I've checked the power supply lines to the amp board and compared left and right channel. They are almost identical so I guess the search goes on.
    Here are the numbers:
    - 60,3V on all 4 main filter caps,
    - 6 V on green and purple wires
    - from 0,03V to 0,05V on brown and orange wires. Values are identical but they tend to rise gradually with time

    I've taken the right channel amp board out and everything looks mint. Power supply board fuses are still intact.
    Please instruct me further what to check.
     

     

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  7. delboyko

    delboyko New Member

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    19
    Location:
    Croatia
    BIG UPDATE:

    Tried switching power supply lines from non working to working channel so I can rule out the power supply. Unfortunately, I've got no sound so there must be something wrong with the power supply.
    Then I tried switching power supply wires one by one from working channel to non working and it stoped working only on one wire. It's the brown wire that's causing the problems on working channel.
    Here, I'll show you:
    [​IMG]


    Next, I figured that amp board is not ruled out yet so the quickest way to check it is if I connect it to the power supply from a working channel. Unfortunately no sound again. :(
    Then, out of pure curiosity I cranked the volume to 12 o'clock... nothing... going full blast and YES! I can hear sound coming out, very quiet but loud and clear enough to decide that it has no distortions and it sounds just about right.
    I'm sure you guys could help me with culprits on this with the amp board. PLEASE... I'm sick and tired of mono sound. :D
     
  8. inductor

    inductor Super Member

    Messages:
    1,522
    Location:
    uk
    speaker relay ? try measuring the voltages, much easier than swapping wiring round !
     
  9. Bigdrive

    Bigdrive Member

    Messages:
    98
    Location:
    Kelowna
    Hello,
    I am working on a 717 right now and just read this post. If you get sound at nearly full blast, I would check switching. I have had this on mine. That source push button on the front is very important in this unit. Mine did this and when you get it right the sound will blast so back volume down when playing.

    It's a little unclear to me about this left/right test you did.

    Please verify, back switch to separated, dac preamp out to 717 power amp in. Volume up on dac and no sound from 1 channel?
    Then, connect CD player or something to line in, switch front to source and either connect voltmeter on ac volts or speaker on preamp out. Does volts rise or you get even a little sound out?

    The brown wire on that unit is ground in on hot side of transformer. I just had out both transformers. Both brown wires go to neautral on the plugs at the back. The fastest way to find out if power is a problem (all be it really bad if you slip up), on the power supply board on the top right and left side you will see a gang of 5 wires. With alligator clips chech do volts black wire to either red, should be around 33-35volts. Now check other side white wire to yellow wire, should be same volts. If you get those readings it's not power supply problem. You said above your caps are at 60v which is right and the other measurements are confusing. Purple to chassis ground should be 39 ish if memmory serves me. But I would not even check that once you get the test above done.

    To test protection circuit I rely on unit. If light stops blinking it's good to go.

    There is no speaker relay, so if driver amp works we get sound.

    So let me know, I am just a newbie hobbyist but I am recap/restoring one right now.

    Cheers
     
  10. Bigdrive

    Bigdrive Member

    Messages:
    98
    Location:
    Kelowna
    I have checked further after looking at you schematic, you mean little brown from pin 28 on power supply. Let me start my computer downstairs and look at the possibilities.

    I would still do my above test anyway.
     
  11. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Actually there is a speaker relay, RL601 fitted centre & bottom of PSU Protector PCB F-2663. ;)
     

     

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  12. petehall347

    petehall347 the brandy coffee man Subscriber

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    the wire you talk about is the speaker out ..it will have dc voltage .measure it at pin 08 ... it should be 0v .i bet its something like rail voltage .
     
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  13. Bigdrive

    Bigdrive Member

    Messages:
    98
    Location:
    Kelowna
    Yes, I was thinking protection relay, ie, not another relay other than that one. Looks like he is saying no output pin 08 on F-2722. I would think that he does power amp in in separated mode and if no output remove left amp and check output transistors.
     
  14. Bigdrive

    Bigdrive Member

    Messages:
    98
    Location:
    Kelowna
    If it had rail voltage on it, say 57 dc would it not blow up the speaker? He never says it stays in protection mode.
    Just a question, still learning.
     
  15. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    25,711
    Location:
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    from what i read it only worked with wire removed . its marked on a post above .
     
  16. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    I've checked power supply voltages in the upper corners and both sides return 36V.
    Also checked the relay and both sides return 0V drop so I guess it's not the relay either.

    When measuring the voltages I reported before on amp boards I used the ground from amp. (ground connections 02 and 03 with other).

    Would sound come out at all if one of the output transistors is bad?
     

     

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  17. Bigdrive

    Bigdrive Member

    Messages:
    98
    Location:
    Kelowna
    Good Question. I do not know but since there is only one set, I would not think so.

    You could prove its the driver. Disconnect all connections both drivers including signal. Switch the amp to separated. Provide a input, then check each preamp out with a voltmeter. If its your driver you will get ac volts when you turn up the volume. If you do, its the driver.
     
  18. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    The saga continues... Episode IV: The last transistor

    Dear audience. I've gone completely immune to mono by now. Nevertheless, my war against it is still not lost!

    I ran my multimeter across every single component on the nonworking channel, and than compared it to the working channel. Everything diode, every transistor, every zener and every measurable cap does what it should and are in close measurement with the working board.
    Still, the sound is very quiet when I max out the volume.

    I've even tried switching the output transistors from good driver board to bad one and again... just a quiet sound. That was a relief to be honest...

    I did notice something different. Resistance on R01 and R02 should be 56K and 2,2K ohm, and they both return 2.2K. Working driver returns as per schematics.
    The same thing happens when I try measuring resistance between point "01" and "02". Working driver returns 56K and nonworking returns 2,2K.

    [​IMG]

    Any help from here?
     
  19. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    25,711
    Location:
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    maybe the parallel capacitor C01 100 picofarad is being a resistor or dead short ? it may well explain the low volume .
    pull C01 and test it .
     
    Last edited: Jan 11, 2018
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  20. Bigdrive

    Bigdrive Member

    Messages:
    98
    Location:
    Kelowna
    Just checked mine for you. Amp is out of chassis. In circuit tests as follows r01 56k, r02 2.2k, pin1 to pin2 57k
     
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