The AU-X1 is, like, so hot right now.

Discussion in 'Exclusively Sansui' started by slimecity, Sep 24, 2017.

  1. slimecity

    slimecity Super Member

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    Hmmmm, it didnt go terribly......it also didnt go great either.

    The only bulb I have is 100W - tried that, its glowing half bright. The relay at the back of the main power supply board clicks in a few seconds later. The powersupply I have then drops from 100V to 70VAC on its meter, so nothing appears to be dragging the voltage right down.

    Problem is absolutely no sound. I take it the speaker relays are meant to click depending on speaker selection? Nada there.

    The bulb is half glowing bright. I think perhaps there isnt enough current to make the amp work properly? I tried two 60W bulbs in series however Im not sure if that represents a 120W load, or just confirms that I dont really understand electricity that well.......

    Tried to set DC offset at speaker terminals however of course, I wouldnt have been getting a proper reading if the speaker relays werent engaged. I also tried to set Bias between the two outside pins pictured. The amount went up and down a bit between say 0 and 13mV, then both sides went down to zero.

    I'm going to replace VR 1 and 2 in the power amp boards, then work out where to take the DC offset reading from pre-relay, then try again once the trimmers arrive in a few days.......

    Im really not looking forward to having to work on (and take voltage readings) these power amp modules. I havent actually figured out yet how it would be possible to do this - except by running some extended connection leads from the rest of the amplifier to each module? yikes

    IMG_1535.jpg
     
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  2. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Looks like you haven't worked on the Driver modules yet - failure to be able to set bias (or DC offset) is very likely to be 2 x 390 Ohm resistors per driver that are probably fusibles - because they seem to take a beating and go near enough open - mine were up in the ~200K area. :)

    These are R36 & R37 (near TR13 & TR14). ;)
     
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  3. kevzep

    kevzep Its all about the Music Subscriber

    Can you explain how you have your power supply set up?
    I plugged my variac into the DBT which is plugged into 230V, then plugged the 120V transformer into the variac.
    This way the load on the 230V light bulb is correct. You do not want the 230V bulb on the 100V supply.
    Then I can turn the Variac down to 200V, then the transformer being a 2:1, brings the voltage down to 100V.

    70V is too low, its probably not coming out of protection for that reason.

    Do you have the front panel on so you can see the power indicator LED, that will flash until the unit comes out of protection.
     
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  4. kevzep

    kevzep Its all about the Music Subscriber

    I'm pretty sure he replaced those John, at least I think that's what he did....We all told him about those at the beginning of the thread......I think those modules have been out.
     
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  5. slimecity

    slimecity Super Member

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    Cheers John - these were replaced.

    Mines pretty simple Kev - 230v wall outlet thru to a DBT with a 100W (240V) bulb in it, then to my 2000w stepdown, which is set to 100VAC.

    One idea I had was to set the stepdown to 120VAC, (its selectable between 100-120VAC), taking into account a voltage drop, this could give me enought "headroom" to get the speaker relays to click, while also keeping the DBT in-circuit.
     
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  6. kevzep

    kevzep Its all about the Music Subscriber

    I think you might need a higher wattage bulb, I used a 120watt, and with that, the amp would run, and the bulb was dim, say down at around 10% at a guess, only just glowing.
    I cant remember how much it dropped the voltage unfortunately.
    But I would have thought 100 would do it.
     
  7. slimecity

    slimecity Super Member

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    OK - thats promising.

    I will need to try again - it could simply not be coming out of protect as the offset is too high. Once I get new trimmers in, I can test that theory......
     
  8. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I used a 100W but I can't remember if I got speaker relay activation or not, thinking about it now I think probably 'not' but then I never check for audio output on DBT. I would have been happy enough to see the bulb dim down, even if the speaker relays didn't close. :)

    The thing you Do need to have working is the Soft Start relay - definitely change bulbs to get that working - assuming no very bright bulb showing. ;) You can check for 'normal' bias setting reaction under those circumstances, and also same for DC offset, if you can find a spot to measure at.
     
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  9. slimecity

    slimecity Super Member

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    Cheers John - is this relay RL02 - on the Power supply board?

    That one is working.
     
  10. kevzep

    kevzep Its all about the Music Subscriber

    Connect the power LED up so you can see if it stops flashing when it powers up just so you know for sure. Remember the LED is DC so it has to be the right way round...I know you know that but gotta make sure we are all on the same page...
     
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  11. Ronito6

    Ronito6 Super Member

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    [​IMG]

    This test point usually does not work. For whatever reason Sansui stopped wiring the point to measure the F-2775 voltage.

    The SM actually recomends measuring the voltage from the bottom of the unit by attaching multimeter probes directly to the emitters of output transistors 701 and 703. Just attach them before the resistors, or rather, on the resistor leads that directly contact those emitters.
     
    Last edited: Oct 11, 2017
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  12. slimecity

    slimecity Super Member

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    Thanks Ronito - looks like the best place to take the DC and bias readings in that case is from underneath the power modules.

    Cheers
     
  13. Ronito6

    Ronito6 Super Member

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    Regarding lack of sound. Is the "Power Amp Operation" selector (and this has happened in the best of families) switched to "integrated"? If not, make certain it is.
     
    Last edited: Oct 11, 2017
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  14. slimecity

    slimecity Super Member

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    Yup - its on that setting. I need to wait till the trimpots arrive (1 week) before having another go at this....
     
  15. Willy6

    Willy6 AK Subscriber Subscriber

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    The test points on all four of my units were wired wrong at the factory all you need to do is move the white wire (18) to the other side 20170427_104155.jpg of the op and they will work as they should leave the black wire(17) in place..In this pic the white wire was on the left and I moved it to the right now the tps work..
     
  16. Ronito6

    Ronito6 Super Member

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    Yes!

    I wanted to mention it, but since you were the one to figure out the rewiring to make that test point "live" I thought it only proper that you get as much credit for this discovery as possible.

    Thanks Willy6!!

    [​IMG]
     
    Last edited: Oct 13, 2017
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  17. slimecity

    slimecity Super Member

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    Ok - because I am a bit slow and dont want to muck this up.....can you please confirm?

    That the white wire you show moves from its current pin 18 to the empty hole at pin 15? Is this correct?

    My board IS wired the same way as you show in your pics too.....
     
  18. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    My understanding is that the white wire only - needs to be moved from the 4.7ohm to the 0.33 ohm resistor, as in the picture in post #55 - leave the crimped stake pin where it is in the driver PCB.
     
  19. slimecity

    slimecity Super Member

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    Thanks John - I got it now. I'm moving the wire at the "resistor end" rather than swapping any pins at the "board end."
     
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  20. Willy6

    Willy6 AK Subscriber Subscriber

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    Actually you move the white wire from the 0.33ohm resistor to the 4.7ohm resistor..
     
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