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sorenb

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Everything posted by sorenb

  1. maybe start by checkin PSU rails at the AMP boards entry points, and check that all diodes are properly lit
  2. Sounds like it's not only the +500V having a problem ... Have you measured the drop across the "current setting" resistors for the various 10m90's? Summing up those per rail, might shed some light on the matter ...
  3. The PSU's I have at hand consumes ~25W unloaded Exploding 10m90's indicate massive current draw ... have you checked for any carbonization in the vicinity of those?
  4. @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
  5. @jokerman777 The thermal compound looks kind of grey'ish ... do you use some exotic compound? The screw needs to be able to slide into the 7721 without any force, otherwise it is too big. Maybe you found the cause of the HV transformer buzzing with "no load" ...
  6. STTH512FP is ready available and fully insulated. If you look through the KGSShv thread, some had troubles with un-insulated rectifier tabs shorting.
  7. @jokerman777looks like you did not use stth512's ?
  8. As I understand, the channel has been working all along, just thrown off by the bal servo. Wonder what the benefit of troubleshooting with the LF353 installed are?
  9. .... are D19/D20 the correct value and both oriented correctly (not flipped)? There are some good advice to be found in the posts from @simmconn, make sure you have read those.
  10. 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?
  11. 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.
  12. Kevin, wish you a UM66T08
  13. "you should get ~2mA" probably a typo, ~1mA is what I usually get, depending on the DN2540 ...0.5mA might be just fine
  14. 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.
  15. did the SiC survive (someone else’s board with a TO220 DN2540)?
  16. Kerry most likely points to the zeners dynamic impedance which varies with current 1.3mA might operate the zeners too close to the knee
  17. did you check the zener string is actually seeing ground? and the 3k is actually 3k value, and sees source and gate?
  18. @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
  19. Check the current source at the front end should source more than ~1.3mA or so look here for more
  20. 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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