bui501

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...

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???

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.

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.

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

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

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

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

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.

Hi, Blueman2. Thanks. I was following your earlier post and was happy to hear of your success with the alternate SiC. Unfortunately, I had already went too deeply down the path of ordering (and reordering—and reordering) the CREEs by the time you had confirmed your results with the ROHMs. Sent from my iPhone using Tapatalk

A stack of 20 ea. CREE C2M1000170 SiC’s newly arrived directly from China... you’d think they’d be cheaper from China, but alas, no... and alas, several of the more experienced builders on this forum have identified the parts in my photo as fake. This is where I got the parts from: (as Kung pointed out below, the parts above do not match the photos in the link.) https://m.alibaba.com/product/60636916771/C2M1000170D-C2M1000170-TO-247-4-9A.html?s=p&spm=a2706.7843299.1998817009.1.r8CLBF On a side note, I had originally ordered from Newark.com when they claimed to have some in stock, but they never shipped my order and ended up refunding my money after weeks of delays. I won’t be using newark again. Big lesson for me: Safer to just wait for mouser... Sent from my iPhone using Tapatalk

Thanks, Jim. I’ve got all three transistors on order for replacement. I was so impatient to see the boards all powered up, now I have to wait longer for replacement parts. Besides the math and patience, a bit of common sense could have come in handy: if you guys are all bolting huge heat sinks onto these transistors, it probably should have been a clue that I probably shouldn’t have fired them up without any heatsink.

Thanks, Wachara! I may have to take you up on your offer. My thermal pads should be arriving in the next day or two, but it looks like the replacement SiCs I ordered from Newark haven’t even been shipped out yet. I placed an order with them for some SiCs several days ago. Hopefully, their online stock status is accurate. I think you’re right. The one with the melted metal tab is probably toast. I just didn’t expect the temperature to get SO high SO quickly. :-(

Thanks, Blueman2. I'm double checking the CT connection from the transformer tonight. Re. the molex connectors, I had used something similar for the initial setup when I built my kgsshv -- it really helped when disconnecting/reconnecting everything during the initial testing/setup stage, but I had to remove those molex connectors for my kgsshv because they were only rated for 250v. The ones you see on my in-progress carbon build are rated for 500v, so I should be able to leave them on permanently. Makes it really easy to move things around during troubleshooting even though they don't look as nice and neat as the phoenix terminals.

Damn it! I think you've nailed it, Sorenb and Wink... The 10m90s and SiC's are not properly attached to the heat sinks yet -- I don't have the thermal paste and all the aluminum oxide pads yet as they're still on their way from Mouser. I didn't think the 10m90s and the SiCs would get hot quickly enough to cause a problem if I powered up everything for "just" long enough to adjust the current... The metal tab on one of the SiCs got hot enough to actually melt!!! Thanks guys for your help. I'll try again after the pads and paste arrive and report back. AARRRGGHHH.... This waiting for parts is killing me.

I finally received the last few components for my carbon build and finished populating the boards this weekend. (carbon board v5 + GRHV fat, split boards) I'm using the split fat board version of the golden reference high voltage power supply boards and a SumR toroidal transformer with 2x360, 2x16 secondaries. Actual unloaded measurements from the transformer's secondaries at 220VAC input were 387/387VAC, 17.8VAC. When I hooked up the ps boards to a variac and cranked up the input line voltage to the transformer, the high voltage outputs from the boards measured +400/-400V . The LEDs on both amp boards come on and stay on. Problem 1: The low voltage outputs from the GRHV boards goes up to only +/-10V even at 220VAC input on the transformer (17.8VAC unloaded measurement from the transformer's output, low voltage winding). Problem 2: I hooked up the power supply boards to the carbon boards anyways and started to play with the current adjustment pots. At the test point FURTHEST away from the servo 2 jumpers, I can get the current to 20mA (started out at 18mA). However, at the test point/pot closest to the servo 2 jumpers, the current started out "normal" at close to 20mA, but after 10 or 20 seconds, it rose to 36mA -- I cannot/cannot get the current to go much lower at that test point. This is the same for BOTH amp boards, so I'm assuming it's a problem with the PSU boards. - I've double checked all the solder joints three or four times with a 20X loupe. (FYI, instead of using the phoenix terminals that everybody else has been using, I decided to use molex mini fit jr. cable connectors that are rated for 500V because I was paranoid about messing up and not being able to examine the solder joints underneath the phoenix terminals.) - I've gone through and cleaned up all stray flux and debris several times on both sides of each board. I've read through this forum and have tried some of the suggested troubleshooting suggestions. E.g., measured the resistance between HV+ and GND and HV- and GND leads on the amp boards as suggested by SORENB to INSANITY last sep in this thread, and the resistances measured as expected in the ballpark of "250kohm-ish" (actually, around 280Kohm). Any suggestions on next steps for troubleshooting? I've attached photos of the power supply boards and one of the amp boards (unpowered). I haven't attached the ceramic pads on the 10M90S'es yet -- those are coming in the post from mouser along with the thermal grease for the pads.

That's SiC, man!

Thank you for the tips, Skooby and Kevin. Sent from my iPhone using Tapatalk

Would this work as a substitute for the LSK389? Mouser doesn’t carry the LSK389. This the closest I could find from them for dual JFETs: https://www.mouser.com/Search/ProductDetail.aspx?R=2N3958virtualkey58900000virtualkey106-2N3958 Sent from my iPhone using Tapatalk

Awesome! Thank you. Sent from my iPhone using Tapatalk

I’ve been trying to find a source for the PZTA42 transistors for the Carbon V5 boards, but everybody seems to be out of stock on them. Would this be a suitable substitute? Diodes Incorporated, ZETEX, Manufacturer part FZT657 — it’s a 300V NPN transistor with a collector current rating of 0.5A: https://www.mouser.com/Search/ProductDetail.aspx?R=FZT657TAvirtualkey52230000virtualkey522-FZT657TA

That’s ok. I remembered the advice you and others gave me for my KGSSHV build and just continued with that. Having the components slightly raised made it a lot easier to check every joint on both sides of the board. About the resistors getting in the way of the SMDs: DOH!!!! Sent from my iPhone using Tapatalk

I ran out of scotch. I’m going to bed :-D Sent from my iPhone using Tapatalk

Finally got off my ass and started to populate the boards for my Carbon build... I’m on a roll now... I just hope I don’t run out of scotch before the boards are finished... Sent from my iPhone using Tapatalk