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sorenb

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Posts posted by sorenb

  1. 22 hours ago, demonkuro said:

    When I measure the negative voltage of the battery, DC offset to ground suddenly becomes -150, I go to check R42, and I find that the R42 in the existing battery becomes 5.8V, some become 6V, and some become other values

    maybe start by checkin PSU rails at the AMP boards entry points, and check that all diodes are properly lit

  2. @jokerman777
    Based on your post's I'd recommend disassembling both angle brackets, making sure all holes are properly deburred, and all the tappings are clean, also clean all semi's. Make sure the screws can go into the tapped holes using only finger force -  if not re-tap the hole.
    Re-assemble, using regular compound (the white stuff).

    As for the buzz, you stated to have observed a flash in the region of the negative rails, and showed a burn'ed screw from the positive rail, showing that something was cookin here as well, and might have cause excessive current draw from the transformer causing it to buzz

    • Thanks 1
  3. 59 minutes ago, jokerman777 said:

    Oh I got parts referencing a BOM where it says stth1512D that is obsolete and I used STTH15S12D instead, I suppose not going to make a difference?

    STTH512FP is ready available and fully insulated.
    If you look through the KGSShv thread, some had troubles with un-insulated rectifier tabs shorting.

     

  4. 2 hours ago, demonkuro said:

    It seems that only R+ is always working fine?

    To me it seems R+ is not working correctly as it seems to be stucked at ~0V

    ...does it swing toward B+ at power off? have you tried pull the LF353? does the EL34 heater glow? maybe swap the EL34's in that channel?

  5. 5 hours ago, demonkuro said:

    ... The output R- to GND was -91V, R+ to GND was 0.05V, L+/L- to GND was -28.6V, ...

    Provided the readings are right, I'd look at the right channel LF353 and re-check all the diodes in the right channel servo are properly oriented
    if everything seems right, pull the right channel LF353 and see what readings you get.

  6. 11 minutes ago, Pars said:

    OK, finally getting around to testing the GRHVs I'm building for the Carbon. Using Soren's post on pre-testing, I had some variances.

    kgsshvdualsoftstartclean_jamesUK_markup.JPG.bbab7d15efac3dae13bf848e0729f95e.JPG

    I marked up the schematic from James above.

    1. For the first test, using ~17Vdc thru an ammeter, I'm getting 0.5mA (not 2mA) (points A1-B1)
    2. For the second test, I'm getting ~1.3-1.4mA (points A2-B2), which matches Soren's figures.
    3. For the third test, I'm getting 10.5-10.9mA (points A3-B3). This may be referring to a Megatron HV900 PSU in Soren's notes below, and I'm not sure I'm looking at the correct points anyhow.

    I have a 100K resistor paralleling the two 390Ks. Bringing the positive supply up on a variac until it regulates, it seems to be regulating at 55Vdc, which is about what I calculated. Boards are 1.8 version, single fat sw variants. The voltage appeared to be stable; raising the variac a bit didn't change the output.

    Just checking because the first CCS test was considerably lower than what Soren saw. I did unsolder one end of the 100K resistor and rechecked, but no change.

    Any thoughts, or just go for full voltage?

    "you should get ~2mA" probably a typo, ~1mA is what I usually get, depending on the DN2540 ...0.5mA might be just fine

  7. 8 minutes ago, simmconn said:

    The SiC did survive and still tested good all the way to 1700V on a curve tracer. I guess the ST9360 had a slow death and the BC557s gave up before more current could damage the SiC. 

    I've seen similar. 
    DN2540 leaking usually shows up as the output voltage of the PSU drifting.
    As far as I remember the supplies breaking down was all wired as negative rails.
    However, I have not seen it on any GRHV using the cpc1117. 

  8. 2 hours ago, simmconn said:

    I’ve been using the DN2540 in TO-92 package since my first Carbon build without any problems on the amp board. However I’ve seen two instances where the DN2540 on the GRHV developed a Drain-to-gate leakage. That caused excess current thru the HV PNP. In one case (my own build) it was caught in time and didn’t do any real damage, in the other case (someone else’s board with a TO220 DN2540) the PCB was cooked, the ST9360 failed and brought down both the BC557s. The leakage problem is regardless of the DN2540 package. I’m suspecting in the cascode CCS there may be a corner case where it is stressed beyond the safe limit.

    did the SiC survive (someone else’s board with a TO220 DN2540)?

  9. 3 hours ago, dingding123 said:

    Hi sorenb, thanks for the suggestion. I dont think the CCS was faulty, but I replaced the 10m90s with a new one from Mouser anyway. No change in bias voltage :(

    The main GRHV voltages are normal: +396V and -406V.

    Does the 806k and15k resistors have anything to do with setting the bias voltage?

     

    did you check the zener string is actually seeing ground? and the 3k is actually 3k value, and sees source and gate?

    • Like 1
  10. On 6/2/2020 at 12:11 AM, powertoold said:

    Hi all,

    I have a KGSSHV (not carbon) 500V that has developed some low-level static / distortion with certain resonant frequencies on the left channel. I'm fairly certain it's caused by the KGSSHV since the static is reduced when I adjust the offset voltage to be more positive (currently at 40V offset; I believe ideal is 0V offset and 0V balance).

    Would anyone have any insight into what is causing this static / distortion, especially since it is reduced when I make the offset voltage more positive?

     

    Thanks!

    @mwl168 is right 40V offset doesn't sound right.

    The static may origin from leaking resistors or bad solder joints.
    Check the 175k's (r10+r11) , r14+r29 and r7+r30 ,  as well as their joints

  11. 54 minutes ago, Hirsch2k said:

    So I have finished the PSU and I am getting the expected voltages on all rails except Bias, which reads +380V to ground. But I guess this is expected behavior for Bias voltage without the proper ballast?

    most likely you are measuring at BIAS output, having an output impedance of 5Meg ... and the DMM most likely 10Meg, so the +380V is actually 570V

    Use the test point (TP) rather to get the right voltage

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