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About bui501

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    Bangkok, Thailand
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    Music, Machine Shop
  1. KGSSHV Carbon Build Thread

    Thank you, Wachara. Good to talk to you over the phone this afternoon.
  2. KGSSHV Carbon Build Thread

    Damn!! Thank you, Laowei & Kung. I’ve adjusted my original post so nobody else orders from the same vendor. The link is where I purchased from. The photo I posted was of what I received from them. so does anybody have some spare CREE SiCs they can resell to me?
  3. KGSSHV Carbon Build Thread

    That sounds like what happened to me on the positive rail board a couple of days ago: I thought it was just the thermal paste shorting the 10m90s to the heat sink. I didn’t even make the connection til you referenced your earlier experience. Ive got the 10m90s replacements on order from mouser now. Ah... but you mistakened me for someone more patient and wiser... I was the idiot that fired up his brand newly stuffed Carbon build (amp boards and all) without proper heat sinking. It was what started my headaches in the first place. You’d think I’d learn a little patience from that, but I went with the Chinese vendor because it would save me several weeks of waiting for parts from mouser... so of course, I didn’t test the parts from China before excitedly soldering them in before the delivery guy even left my building.
  4. KGSSHV Carbon Build Thread

    The original 10m90s’es were from mouser... that was on the psu boards that were (mostly) working before I melted the components by running them without proper thermal pads... all of the replacement 10m90’s now on both power supply boards and both Carbon amp boards are from the same batch from the same Chinese vendor...
  5. KGSSHV Carbon Build Thread

    Chinese vendor on AliExpress... :-( i couldn’t find these parts locally in Thailand. I'm looking at mouser.com to reorder tonight... Thanks for all your troubleshooting, by the way, Soren.
  6. KGSSHV Carbon Build Thread

    Drats!!! I’m measuring an open between drain and source and between drain and gate of the 10m90s I pulled off the board... all the other (new, unused) 10m90s from the same batch measured the same...
  7. KGSSHV Carbon Build Thread

    Doh!!! I had the test leads going into the wrong ports on the dmm... These are the remeasured readings: CSS meassured .01mA (i.e., ZERO) between the drain of the 10m90 and the junction of R1/R2. The other CSS also measured 0.01mA between the drain and pin 6 of the regulator... bad 10M90s???
  8. KGSSHV Carbon Build Thread

    These 1st 2 photos are the front and back of the board I’m trying to fix right now. The last 2 are of the board whose 10m90s popped at full voltage. I’ve just finished cleaning most of the thermal paste off. There’s lots of scratches on the back from where I had scraped off hardened flux spots.
  9. KGSSHV Carbon Build Thread

    Soren, I used 2x 9V batteries. CSS meassured 23mA between the drain of the 10m90 and the junction of R1/R2. The other CSS also measured 22 to 23 mA between the drain and pin 6 of the regulator... Looks like I have to replace the 10m90 and DN2540s again. Thanks for the test guide and the link to it.
  10. KGSSHV Carbon Build Thread

    Not yet. Just read the link and am scrounging up a 15-20v supply for the test... Sent from my iPhone using Tapatalk
  11. KGSSHV Carbon Build Thread

    Voyage at SiC drain is 553VDC... Do you think it’s a bad SiC? Sent from my iPhone using Tapatalk
  12. KGSSHV Carbon Build Thread

    I’ll measure tonight and report back (I’m on East Asian time). Thanks, Sorenb. Sent from my iPhone using Tapatalk
  13. KGSSHV Carbon Build Thread

    This is the GRHV board I’m using; no cpc1117 optocoupler. The voltage at the terminal/lead coming from the transformer reads 390VAC. Sent from my iPhone using Tapatalk
  14. KGSSHV Carbon Build Thread

    Help! So... After waiting several months for replacement SiCs, I replaced all the 10m90s, SiCs and DN2540s on both GRHV boards and amp boards. I've only started testing the psu boards. The low voltage outputs measured right around +/-15V. However, the -400VDC lead only measures -5V even though the leads from the transformer correctly reads ~390VAC (measured directly at the pads on the board). The high voltage outputs correct (+/-400VDC) before the SiC and 10m90 meltdowns from a few weeks ago, so the only parts I've replaced are the 10m90s, SiCs, and DN2540s on the board. Any suggestions? On a side note, when a manufacturer advertises their silver-looking thermal paste as "electrically non-conductive", they might not be thinking high-voltage... One of the 10M90S on my other psu board just let off a spectacular spark and a "Pop!" after a few minutes at full 220VAC from the variac. I was using PEEK screws, Protronix Series 7 Silver Thermal Paste, and standard aluminum oxide pads. The paste was advertised as "electrically non-conductive." The little explosion blew the al oxide pad right out from between the component and the heatsink.