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KGSSHV Carbon Build Thread

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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. 

29944da55e0ca51c1bf3ed0e85e00278.jpg

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...



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Edited by bui501

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On 1/7/2018 at 9:19 AM, Blueman2 said:

 

 

 

<Despair> noooooooooooooooooooooooooooooooooooooooooooo! </Despair>.  Wait many days and many hours to build my 4th amplifier, of which I only really need one?  Clearly you have overestimated my maturity and patience.  :D

Seriously though.  For the PSU, I wonder if the  755-SCT2H12NZGC11 would be an acceptable substitute.  Just not sure how much of an issue the lower current rating (3.7A vs 4.9A) and slower fall time will be.  It figure it is always nice to have a backup source part for when the primary part goes OOS.  

Here is the parts comparison:

Capture.thumb.PNG.4026cf6a8a10f59ef1af38b72a700cfb.PNG

 

Or you can use the ROHM device as a backup, as it appears to have worked great in my build!  

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Or you can use the ROHM device as a backup, as it appears to have worked great in my build!  

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.


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Yeah, my post is actually somewhat in jest.  I strongly recommend the Cree since it has more proving time behind it.  But if someone is impatient and does not mind risking burning down their house when something goes horribly wrong, then the ROHM is always there! 

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2 hours ago, Blueman2 said:

Yeah, my post is actually somewhat in jest.  I strongly recommend the Cree since it has more proving time behind it.  But if someone is impatient and does not mind risking burning down their house when something goes horribly wrong, then the ROHM is always there! 

:lol:

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On 1/16/2018 at 8:20 AM, bui501 said:

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.

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.":angry:  The little explosion blew the al oxide pad right out from between the component and the heatsink.

Edited by bui501

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5 minutes ago, bui501 said:

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.":angry:  The little explosion blew the al oxide pad right out from between the component and the heatsink.

check the terminal where the leads from the transformer is attached. Might also be that you populated the CPC1117?
 

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check the terminal where the leads from the transformer is attached. Might also be that you populated the CPC1117?
 

This is the GRHV board I’m using; no cpc1117 optocoupler.

adf50e6fa2aacf01d1344ef2fc3d69c5.jpg

The voltage at the terminal/lead coming from the transformer reads 390VAC.


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what is the voltage at the drain of the Sic?

I’ll measure tonight and report back (I’m on East Asian time). Thanks, Sorenb.


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5 minutes ago, bui501 said:


I’ll measure tonight and report back (I’m on East Asian time). Thanks, Sorenb.


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you might find this useful, and be aware that the negative rail is identical to the positive, so the voltage ref 'ground' ref is the negative rail rahter than ground.

Edited by sorenb
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what is the voltage at the drain of the Sic?

Voyage at SiC drain is 553VDC... Do you think it’s a bad SiC?


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9 hours ago, bui501 said:


I’ll measure tonight and report back (I’m on East Asian time). Thanks, Sorenb.


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Have you checked the rail as described in the link I pointed to above?

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Have you checked the rail as described in the link I pointed to above?

Not yet. Just read the link and am scrounging up a 15-20v supply for the test...


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4 hours ago, sorenb said:

detach the HV rails and use the +LV  or two 9V batteries

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.

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not sure how you can measure currents like that using 18V ....sounds like something else is wrong ...

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bui501, are you able to take a clear high resolution picture of the front and back of your board?  That would help us see potential issues.  The good news is that I too have had numerous similar issues during my 4 amplifier builds, but when I diligently listened to what sorenb and other said, I was able to solve the problem so you will too!  My encouragement is to do exactly what sorenb advises, step by step, and you will find the issue.  My issues came when I assumed I had done a step sorenb (and others) advised, but really had not done it correctly.  Particularly in terms of amount of solder and good solder joints.   

 

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5 hours ago, Blueman2 said:

bui501, are you able to take a clear high resolution picture of the front and back of your board?  

 

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.

EC4F9B32-2BF5-4EF5-9A68-A4B49FFB302B.jpeg

ACC6FA45-C0A8-4ED4-9C49-D9220B1225F0.jpeg

BDB5996C-8B5D-415F-92B9-0FFA124AEEED.jpeg

 

AD3FFF56-43E1-4827-838A-52C0AA6C43BD.jpeg

Edited by bui501

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17 hours ago, sorenb said:

not sure how you can measure currents like that using 18V ....sounds like something else is wrong ...

Doh!!!  I had the test leads going into the wrong ports on the dmm...  :palm:

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???

Edited by bui501

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unless you've got bad 10m90's (I've never come across any) I find it peculiar that both seems to be acting up
pull out one 10m90 and test it with a DMM at ohms, test drain-source:

short all legs, before measure drain-source => very low ohms

if you don't get that the 10m90's are probably bad

if you have a breadboard you might find it useful to build a cascoded css including the trimmer, and test as previously described.
If you can't adjust the current using the trimmer, the DN2540 is probably bad (I've seen that a few times)
Or you can use an 8pin IC-socket with resistors+trimmer soldered to build a bug-style test CCS-fixture.

.

Edited by sorenb

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5 hours ago, sorenb said:

unless you've got bad 10m90's (I've never come across any) I find it peculiar that both seems to be acting up
pull out one 10m90 and test it with a DMM at ohms, test drain-source...

if you don't get that the 10m90's are probably bad


.

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...

1C296C91-0C03-4B84-A7D1-4B8F433C2800.jpeg

Edited by bui501

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35 minutes ago, sorenb said:

where did you get those 10m90's from?

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.

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