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

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

  1. Willy6

    Willy6 AK Subscriber Subscriber

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    Don't quote me on that though it could be the other way around as I haven't been under the hood of an X-1 in over a year..
     
  2. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Yes, it is the other way round, the TP are for bias current adjustment which must be done across the emitter resistors. Therefore the white wire mustn't connect to the 4.7 ohm resistor as they are in turn connected to the bases of the OP transistors. Thus the white wire must go to the 0.33 ohm cement resistor, and emitter of the OP transistor. ;)
     
  3. Willy6

    Willy6 AK Subscriber Subscriber

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    Ya i wasn't sure if I had switched sides with that wire in the pic yet or not since it was taken with my phone camera over a year ago..
     
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  4. slimecity

    slimecity Super Member

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    OK - so like I said. I am a bit slow.....it appears that based on what you are saying here John - my connection is already correct? Or do I need to move it?

    I note that the black testpoint wire is also connected to the emitters, but I presume these ones are getting the opposite voltage power supply.

    I obviously dont want to muck this up.....Cheers!

    IMG_1556.jpg IMG_1557.jpg
     
  5. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    The issue was the white wire in the left hand picture - in the picture above (left) it is correctly positioned.

    Not sure about the black wire position - I might be able to check mine sometime soon.
     
    Last edited: Oct 19, 2017
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  6. Ronito6

    Ronito6 Super Member

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    A bit of captioning on those pics would be welcome.

    Looks correct to me.
    The white wire is soldered to the socket that receives the emitter of TR-703 (or TR-704).
    The black wire (next to that white one) is soldered to the socket that receives the emitter of TR-701 (or TR-702).

    You should be able to visually follow the traces to which those wires are soldered directly to the topside test point.

    So it appears your topside test point is live and correct.

    All that done and said, making it live is for mere convenience and never had an effect on the performance of the unit in as far as I can see.

    My functioning X1 also had the topside test point unconnected.

    Why Sansui chose to stop attaching the topside test point in later X1s it is a question. Was it indeed a mistake or done purposefully?

    Doesn't really matter. Compared to all the other work involved in restoring an X1, THAT issue is a dish of ice cream.
     
    Last edited: Oct 19, 2017
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  7. ghamilton

    ghamilton Super Member

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  8. Ronito6

    Ronito6 Super Member

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    For the sake of more precision:

    • The black wire which originates at inner / first of the two relevant emitters to be measured on the F-2775 driver board is soldered into point 17 on the F-2775 board
    • The white wire which originates at outer / second of the two relevant emitters to be measured on the F-2775 driver board is soldered into point 18 on the F-2775 board
    • Following the trace from point 17 on the F-2775 board will lead you to point 19 of topside test point .
    • Following the trace from point 18 on the F-2775 board will lead you to point 20 of topside test point .

    So in short...
    Black wire: Emitter > Point 17 > TP 19
    White wire: Emitter > Point 18 > TP 20

    TP 19 and TP 20 equal the emitters to be measured in the SM.

    I can’t help but feel that there is a risk in making that test point live.
    It seems real easy to cross multimeter probe tips there.

    What would happen if the emitters touched?

    I imagine...
    [​IMG]
     
    Last edited: Oct 20, 2017
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  9. Willy6

    Willy6 AK Subscriber Subscriber

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    That's why I use mini clips instead of trying to hold two probes on it and then trying to turn the trimmer all at the same time.
     
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  10. Ronito6

    Ronito6 Super Member

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    Yes. Very safe.

    Grabbers are the way to go.

    BUT when people (well I) get rushed, tired, or a little drunk (four fingers pointing back here :D)
    that's when one might get careless.

    Got to respect that live test point. When not in use I think it should covered by a blank molex shroud like this
    [​IMG]

    or maybe a small piece of square rubber (an eraser) cut to size and prepped to accommodate the TP prongs.

    AND its probably wisest to not attach or detach probes while the amp is on. (That is one "hot" test point.)

    Yeah...my suggested precautions are pretty anal, but working on an X1 is supposed to be annoying.
     
    Last edited: Oct 19, 2017
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  11. slimecity

    slimecity Super Member

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    OK - finally got things up and running - have replaced the output module trimpots and have also removed the unconnected middle pin from the bias reading molex connector - to reduce the risk of shorts when taking readings.

    So not very good news all round - on the back module initially had DC offset racing up and down erratically before settling on O volts. Turning the trimpot to either extreme gets no change to this. On this back module I also cannot get any bias readings, despite turning the trimpot to either extreme. I'm very concerned that this could mean my little Sony input FET is kaput.

    On the front module I could initially get the DC offset to within 30mV or so. Once I had that, I could adjust bias fairly easily, to get 20mV. This was all good and then the speaker relays started clicking like crazy and the DC offset on this module was also shooting up and down, between say 500mV and 3V or so. I couldnt stabilise the DC offset again after this, however on this module at least the trimpot was having some effect on DC offset levels. While all this was happening however, the bias was holding steady.

    So at least I have one out of four readings looking pretty GOOD.

    So not sure where to look now. I would ideally like to remove the amp module boards to take voltage readings at points set out in the SM. Does anyone have a method for doing this, and is it fairly straightforward, ie: Can I disconnect the speaker zobel coil as that is really getting in the way......

    Cheers.
     
    Last edited: Oct 22, 2017
  12. slimecity

    slimecity Super Member

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    So in terms of powersupply voltages - I get 125VDC at the caps where the wires from each module solders directly to the cap rails. Then I also get 125VDC from the terminal blocks that connect to pins 06-08 on each module. So it looks like I am getting correct powersupply readings.

    What Im not sure about is the wire that stays connected to each power amp module, which has a plug on the end, and which connects to pins 12 and 13 on the power supply main board. I am currently getting .6V relative to ground on both pins seperately and wondering if this is correct - cant find any guidance on the schematic on what I should be getting here.

    If there is an issue here then I may have @kevzep 's issue with a dodgy SCR, so either Im getting too much DC coming from the preamps, or the SCR could be faulty. Having very similar DC offset issues in each module is a bit fishy....

    I have also tested all the semi conductors in the board where I couldnt get any DC offset or bias and they all check OK. Havent been able to test the zeners or the SV-03s - am replacing all the zeners.....
     
    Last edited: Oct 22, 2017
  13. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Yes, those pins 12(D), and 13(E) are connected to the gate of the thyristor, so 0.6V there probably isn't good, my AU-X1 is out of action at present, but when it is back in one piece I'll take some measuments for you.
    Faulty thyristor is definitely a possibility, you could try disconnecting those 2 wires and see if things settle down? - if they do settle, it will very likely be a faulty thyristor, if they don't settle then it's something else.
     
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  14. slimecity

    slimecity Super Member

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    Magnificent - cheers John!

    Im going to go thru and check all the semis' in the other module, replace the zeners in that one too, put some sacrificial 93s and 94s in both modules (i found some pics on AK showing how you had done this) and then I will try again with pins 12(D) and 13(E) disconnected from the thyrister.

    Look forward to getting your measurements too. Cheers!
     
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  15. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    As promised, I finished rebuilding the rear capacitor bank, and thus was able to power-on and do the promised voltage check for you.

    Pins 12 & 13 = 0.8 mV
    Note that the voltage you are seeing could be coming from one channel only. If you unplug the grey wires that come from each driver board (pin 16) one at a time, (from the PSU/Protector PCB) and see which one (hopefully) has the excess voltage.

    Note that it is an advantage if the sacrificial transistors are fitted in the heatsink sockets that have the TP wiring attached, - I didn't think of this when I did mine and used the wrong sockets - it still works just the same - it just means you can't use the driver board TP's for measuring bias. ;)
     
    Last edited: Oct 24, 2017
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  16. slimecity

    slimecity Super Member

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    Thanks for those readings John - they arent too far off mine.

    Another question - I have checked all the semis in both boards - they all read well on the meter however that of course isnt definitive.

    However just wondering - someone has been in here before me - in the output modules anyway. Note that the wire to the middle pin of the plug connected to pins 06-08 (pin 7) isnt connected thru the molex connector and it solders straight to the PCB on both sides.

    The other thing I am wondering about is R's 47 and 48. I have piles of solder in both boards that look like something was originally here but has since been removed. Also on the component side, there are signs that something has heated up, but is no longer there. The SM states that these area meant to be 3.9kohm 3W resistors. Do others have these resistors in their output modules, or not?

    Cheers!

    IMG_1566.jpg IMG_1567.jpg
     
    Last edited: Oct 25, 2017
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  17. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I am not sure about your comments regarding the molex connector? - it has 3 pins (06,07,08) and all of them are soldered to the board, there are 3 wires going to the mating molex female plug, and these go back to the PSU/Protector PCB, I can't see that one/any of the pins isn't connected. :idea: - they are the low current +68V 0V -68V feed to the driver board.

    As for those resistors - they are seen on the schematic as 3.9K ohm 3 watt, but are not present on my driver boards - take a look at my thread...

    http://audiokarma.org/forums/index.php?threads/restoring-an-au-x1.709469/page-2

    They seem to be bleeder resistors for the main PSU capacitors, but were later relocated onto the metal straps at the PSU capacitors themselves.
     
    Last edited: Oct 25, 2017
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  18. Ronito6

    Ronito6 Super Member

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    Positions R-47 and R-48 are not used. Add nothing.
    If ever used Sansui stopped populating those positions very early in production life.

    The buffer amp F-2774 is bearly like in the SM in terms of components you will actually find on that board.

    With the X1 expect the SM to let you down on many components.
    The SM was issued for an early version of that amp.
    A version so early no one has one. Sansui changed it a lot in a rather short time.
     
    Last edited: Oct 27, 2017
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  19. Ronito6

    Ronito6 Super Member

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    So Sansui put them here?
    upload_2017-10-27_18-34-26.png
     
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  20. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Correctamundo.

    I assume Sansui thought there was no point having hot components on the driver board when you could put them somewhere else. :)
     
    Last edited: Oct 27, 2017
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