1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Fixing an Aune T1 (amp/dac) TUBE DAC Board

Discussion in 'Repairing Electronics' started by bittgata, Mar 25, 2017.

  1. bittgata

    bittgata New Member

    Joined:
    Mar 25, 2017
    Messages:
    19
    Likes:
    0
    Hello,

    I am new to fixing electronics by working on the PCB and I have very little soldering experience but I will probably manage with most of the bigger connections on the board I’m trying to fix.

    The problem is the DAC board which uses a 6922 tube. When the T1 is powered on all it does is produce an audible buzzing sound, the tube never warms up. I know that the tube, the amp board and the power supply work because I have another T1 on which I've tested them.
    On a visual inspection the board with the problem looks, as far as I can tell, just fine with no evident burns, blown up components or bulging capacitors.

    Unfortunately I don’t have any schematics but I do have some stock pictures of the board which are probably more detailed then what I could get right now with mine.

    http://www.digikit.ca/images/D/t1-6.jpg

    http://www.kidultdiagnostic.com/images/aune/aune-t1_06.jpg

    I have or I’ve ordered most of what I will need to test most components but if someone with more experience knows the obvious problem or the most likely problem I would appreciate the information.
     
  2. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,022
    Likes:
    477
    Location:
    James Island, SC
    Welcome to ETO, bittgata!

    If the "buzzing" you're hearing is in the 50-60Hz range (mains frequency), then it would be my guess that the on-board power supply has failed.

    But, without a schematic, it's going to be very difficult to troubleshoot.

    What test equipment are you intending to use?
     
  3. bittgata

    bittgata New Member

    Joined:
    Mar 25, 2017
    Messages:
    19
    Likes:
    0
    Thank you for the welcome! The power supply is external and despite it's weird connector it provides DC and as I mentioned it along with tube and the amp board(which I did not show) have been tested and they work just fine, the problem is somewhere on the board(which is more or less the DAC part of the dac/amp) you can see in the pictures. That said beyond the fact that there are some caps, resistors and a few other electrical components on the thing I have very little knowledge as to how work together so any information would help.
    http://img01.taobaocdn.com/imgextra/i1/179881016/T2lDduXclNXXXXXXXX_!!179881016.jpg a picture of the psu, if it's of any relevance.
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,022
    Likes:
    477
    Location:
    James Island, SC

    (My emphasis).
    upload_2017-3-26_8-15-27.png
    This implies some manner of AC - DC conversion circuit on the board (for the 6922 plates' voltage), which might include a boost SMPS (although not absolutely necessary). Maybe not, but the "buzzing" noise still leads me to surmise that the problem is with the PS circuit on the DAC board.

    Troubleshooting is going to require some very careful probing of the AC to DC conversion circuit(s).

    Is that something you are comfortable doing?
     
  6. bittgata

    bittgata New Member

    Joined:
    Mar 25, 2017
    Messages:
    19
    Likes:
    0
    Oh, I was sure it was DC, must have been blind for a second. I am not all uncomfortable doing this as even if I brake more components it's not going to be any worse than it is now. The problem is the only thing power related that I know regarding the board is the KIS-3R33S, which apparently is a DC-DC converter and I'm not even sure if it's in stock form. Do you have any suggestion as to how I do the very careful probing, where do I start or what looks like it might convert AC to DC or do I just start where the external PSU connects and go from there? If it would help I might be able to get a camera and take same better pictures of my own board.
     
  7. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,022
    Likes:
    477
    Location:
    James Island, SC
    Ok.

    I'd start with checking the Vin of the KIS-3R33S PS (be very careful with your VM probe tips!!:
    upload_2017-3-26_18-19-55.png
    First, with NO POWER to the DAC, check for continuity between the large, tinned hole and the Gnd pin of the IC - if connected use the tinned hole for your ground. Otherwise, use the Gnd pin of the IC for your ground.

    Now, apply power to the DAC.

    Check Gnd to Vin. Should read between 4.75 - 23VDC (I'm going to guess around 10-15VDC).

    If OK, then check Gnd to Vout. Should read between 0.925 - 20VDC.

    Then let us know what you find.
     
    Last edited: Mar 26, 2017
  8. bittgata

    bittgata New Member

    Joined:
    Mar 25, 2017
    Messages:
    19
    Likes:
    0
    If by the large tinned hole you mean the hole that looks gold colored then yes, there is continuity, but I only have a cheap multimeter so I used the 200 ohm function to test this and I got a value of 0.06 or 0.01 for a very short time then it went back to 0.06.
    The Gnd to Vin is about 15.8VDC and the GND to Vout is about 1.59VDC.
    I can't tell if the noise is 50-60hz because it's bit to high pitched though it might very well be 50-60hz and just sounds higher pitched because it sounds like something is almost quietly but continuously shorting, though considering the voltage it's probably a normal amount of noise.
    I've also turned it on by mistake for a second without the tube and the sound was gone, the I turned it on with the tube connected and the sound was there again and I also have a cheap ESR meter on the way but it will probably be a while before I receive it.
    Thanks for input till now and if you have the time I am really interested in this so I would not mind at all if you give me a very short explanation as to why it is that you think I should test what/where you tell to test but I am grateful either way even if I'm just testing and I won't manage to repair it.
     
  9. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,022
    Likes:
    477
    Location:
    James Island, SC
    I'm just following a fairy normal trouble shooting path, i.e., trace where signals (voltages) disappear. just a starting point.

    It is my supposition that the "noise" is power supply related. Can you locate the noise source to an area of the PCB or, even better, to a specific component (such as the SMPS device (the KIS-3R33S)?
    That Vin seems reasonable. Vout does not.
    Please check and make note of the Vout voltages with, and then without the tube in place.
     
  10. bittgata

    bittgata New Member

    Joined:
    Mar 25, 2017
    Messages:
    19
    Likes:
    0
    The way the Aune T1 normally works is the tube glows as soon as you turn it on and after about 30s a light comes on under the tube, there is also an audible click sound and the DAC starts outputting sound.

    With the tube the voltages are the same, Vin is 15.8VDC and Vout 1.59VDC. The buzzing seems to be coming from the KIS-3R33S, I couldn't say 100% but at worst it could be something right next to it. The tube never glows, there light does not come on and neither does the click.
    Without the tube the light and the click sound come on in about 30s and so does the similar but much louder continuous shorting sound, the Vin starts at a bit above 18.1VDC and it slowly drops to about 17.8-17.9VDC after witch it drops fast till it gets to about 16.7VDC and then it slightly moves around that value, the Vout is 6.22VDC at first and the goes to 6.1VDC after the light turns on. The noise is so loud it's even harder to tell where it's coming from but it seems to be in the same area.
     
  11. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,022
    Likes:
    477
    Location:
    James Island, SC
    Ok. One more test:
    upload_2017-3-28_19-14-54.png
    With the board powered up and the tube removed, carefully check and post the voltages on the tube sockets "Plate 1" and "Plate 2". I don't expect dangerous voltages to be present, but exercise caution just the same!

    When done, perform all the exact same tests on the working DAC board.

    Again, be very careful.

    <EDIT> Plate 2 is mis-identified! Plate 2 is connected to Pin 6, NOT pin 9. Note correction in pic of Post #12!! Thanks to Les for eagle eye...!
     
    Last edited: Mar 29, 2017
  12. Les Jones

    Les Jones Well-Known Member

    Joined:
    May 15, 2015
    Messages:
    1,445
    Likes:
    187
    Location:
    Lancashire UK
    Hi CBB,
    I think one of the pins wrong. According to the data sheets that I have found pin 9 that you have marked as plate 1 is an internal shield. That plate (Anode ) should be pin 6. These are the links to the data sheets that I found.
    https://frank.pocnet.net/sheets/049/6/6922.pdf and http://www.r-type.org/pdfs/e88cc.pdf (6922 and E88CC seem to be different manufacturers part number for the same device.)

    Les.
     
    • Like Like x 1
  13. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,022
    Likes:
    477
    Location:
    James Island, SC
    Oops :banghead:.

    You're right, Les. Pin 6 is the other plate.

    bittgata, take note of my error! Check pins 1 & 6, NOT pins 1 & 9.
    upload_2017-3-29_8-11-50.png


    I'm waiting on a new pair of glasses, and this is why...
     
  14. bittgata

    bittgata New Member

    Joined:
    Mar 25, 2017
    Messages:
    19
    Likes:
    0
    I see in the first picture you also showed me the Gnd but I didn't get if you wanted me to check the voltages between the Gnd and each pin(1 and 6) or between pin 1 and 6 directly so I did all of them:). I did the tests without the tube and all of the results were 0.00VDC both at power on and when the light turned on. I also checked for continuity afterwards and there seems to be continuity between Gnd and Pin6 but not between Gnd and Pin1 or between the 2 pins directly.
    Is there any conclusion to be drawn for this or the different Vout voltages?
     
  15. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

    Joined:
    Nov 17, 2003
    Messages:
    39,203
    Likes:
    640
    Location:
    Derbyshire, UK
    From long ago memory :D

    Pin 1 to pin 9 - A, G, K, H, H, A, G, K, CT

    The double triodes are nice and simple!.
     
  16. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,022
    Likes:
    477
    Location:
    James Island, SC
    bittgata, I have committed a very rookie mistake, and I apologize.

    This is the 6922 pinout, looking at the base (bottom) of the tube:
    upload_2017-3-29_18-7-29.png
    In transposing the pinout to the socket, I inverted the pin locations in my previous posts. Below is the correct pin numbers, looking at the socket from above:
    upload_2017-3-29_18-16-51.png

    So, please check, one more time, for the voltages present on ALL pins with the power on, of both the working and non-working DACs (tube removed). Use the same ground point as before.

    The tube is, really, a secondary issue to your problem. From what you've provided to us, thus far, I'm, pretty confident that the KIS-3R33S power supply has failed.

    But I am intrigued by the 6922's wiring. For instance:
    upload_2017-3-29_18-57-59.png
    Note how pins 1 & 6 (the plates) are tied together. Very difficult to use that configuration for stereo.

    And pins 2 & 3 (grid & cathode of triode2) appear to be tied together. That would make that triode2 non-functional.

    They do seem to have the filaments (pins 4 & 5), apparently, being powered from the USB port. That would explain the filaments lighting up.

    Anyway, a very curious circuit.
     
    Last edited: Mar 29, 2017
  17. bittgata

    bittgata New Member

    Joined:
    Mar 25, 2017
    Messages:
    19
    Likes:
    0
    So the diagram is viewing the tube from below, that's so counterintuitive, I'll do the tests tomorrow as soon as I can.
    To clarify a few things, maybe I didn't explain something properly or I'm not quite understanding you, the tube filaments never light up on the defective unit, there is an LED below the tube socket that lights up when the dac should turn on and start outputting an audio signal. Also I did not connect the USB to the defective unit. On the functioning unit the filaments light up as soon as I turn the power switch and I think it does so even without the USB connected but I will confirm this when I do the tests.
    If this changes anything leave me a reply otherwise I will be back with the results.
    Also the KIS-3R33S is powered by DC, where exactly is the AC turned to DC?
    Regarding the design I don't really know how they use it for stereo but people that have tried it agree the sound is nice at least for the price.
     
  18. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

    Joined:
    Nov 17, 2003
    Messages:
    39,203
    Likes:
    640
    Location:
    Derbyshire, UK
    Not really, you can't access the pins from above as the valve is in the way - so all access is from below.
     
  19. Les Jones

    Les Jones Well-Known Member

    Joined:
    May 15, 2015
    Messages:
    1,445
    Likes:
    187
    Location:
    Lancashire UK
    Hi CBB,
    They maybe using that half as a diode. Don't forget that there will still be current between anode and cathode when the grid and cathode are at the same potential. The grid needs to be negative of the cathode to stop the valve conducting. (Like a depletion mode jfet.) By the way I had not noticed that your pin numbering was mirror image in post #12. I had built things using valves from the age of about 10 (before the days of transistors) so I was used to looking at valve sockets from below when wiring them up.

    Les.
     
  20. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,022
    Likes:
    477
    Location:
    James Island, SC
    Hey Les,
    Agreed. But useless as an amplifier or cathode foll0wer. And with only one triode operational, how in the world does the whole rig produce a 2 channel "stereo" output. That's what makes the circuit curious to me.
    Post #12 just needs to be deleted - :arghh:.
    Ditto, even to the age started. After the requisite crystal radio construct, I got this kit:
    upload_2017-3-30_9-35-15.png
    But, I'm somewhat dyslexic, and the inverse numbering of multi pin components (tubes, transistors, ICs and the like, for instance), topside to underside, caused me no end of frustration then and to this day. I learned to put a marker "dot" for a component's pin #1 on the bottom side of a chassis or a PCB for orientation. Even then I make mistakes... :woot:

    bittgata,
    My SWAG (Scientific Wild A**ed Guess) is the cluster of components below:
    upload_2017-3-30_8-50-28.png
    with the arrow pointing to what I'm thinking is a full wave rectifier bridge with associated components, notably the two silver topped caps. This grouping has the "look" of a circuit that is converting the "15V-0-15V" AC from the transformer PS (noted in Post #4) and converting it to the DC voltages you noted in Post #9 (≈18VDC).

    And since your tests indicated what I consider an appropriate Vin for the KIS-3R33S IC, this is the basis for my conclusion that the KIS-3R33S is defective, given the Vout value you noted on the failed DAC, as compared with those values noted for the working DAC.
    I should have been more specific about what I meant by "power up", the term implies that any and all power sources are connected, unless otherwise specified. Since the PCB traces appear to run from the USB connector directly to the filament pins of the 6922, it seemed reasonable that the USB was the source. But, I should note, filaments are current hogs, and using the USB's 5VDC line for that purpose, with its limited current capability (generally, 0.5A max), is not something I would think prudent.

    Also, I'm sure that you appreciate the difficulty of trouble shooting any device by "back engineering" (because of a lack of a schematic, and I looked for one), which is what we're attempting to do.
     
    Last edited: Mar 30, 2017
  21. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

    Joined:
    Nov 17, 2003
    Messages:
    39,203
    Likes:
    640
    Location:
    Derbyshire, UK
    E series valves have 6.3V heaters, and usually 300mA as well - however, while I can remember the pin connections I can't remember if the double triodes are 300mA per triode, or for the complete valve. The audio versions have a tapped heater as well, so you can wire it as 6.3V or 12.6V - obviously with double current at 6.3V (but again I can't remember if it's 300 and 600, or 150 and 300 :D). No idea where my valve data books might be.

    While I think the idea of using a valve in something like this is particularly silly (and just a con for the gullible), I'm even more bemused that they use an RF twin-triode rather than an audio one.
     
    • Like Like x 1

Share This Page