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Old 22nd October 2010, 08:15 PM   #511
Salas is offline Salas  Greece
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Quote:
Originally Posted by LucasAdamson View Post
Hi Salas,

I am confused about something,
When you have symmetric polarities around earth, then the minus supply capacitors see earth as positive relative to minus output, hence their (+) leg goes to earth where it meets the (-) leg of the positive side's capacitors which see earth as a more negative point than the positive output.
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Old 22nd October 2010, 09:08 PM   #512
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Thanks Salas. It's very clever anyway.
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Old 23rd October 2010, 05:08 AM   #513
TerryC is offline TerryC  United States
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I finally completed installing all the components in the regulator section, and fired it up. All the LED's lit up. Output voltage measured at +10.58/-10.56. Waited a few minutes...... then I notice a bit of smoke rising!

I shut it down immediately and tried to spot which component was smoking, but no visible evidence. I also noticed that the heatsinks on the postive rail MOSFETS were substantially warmer than those on the negative rail.

I then proceeded to power it back up for a few seconds at a time, and take some quick voltage measurements. What I found was that the total voltage across the three current setting LEDs on the positive rail was 7.6v, and should be slightly under 6v. This would explain why the MOSFETS are running hotter, probably closer to 400ma than 200ma (using 10R current setting resistor).

So it appears that the current being drawn from these LEDs is much too high. Could it be that I have a bad JFET between the LEDS and the 100R resistor that is causing the extra current draw?

Now I'm blowing fuses, so I'm having a much more difficult time troubleshooting. Any ideas would be welcomed.
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Old 23rd October 2010, 05:15 AM   #514
Salas is offline Salas  Greece
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First thing I would look for is the K170 CCS JFET that sits on the 100R. Measuring across the 100R, translating into current. Between 6-10mA from a healthy BL. The smoke must have let go from the respective 10R current setting resistor if has 4V across. Then again, a bad CCS Mosfet could not be giving enough Vgs. The one associated with the 10R. Maybe punched through with static when handling.

If blowing fuses, just use DCmA mode on DVM, put it in series with a 9V battery, and feed the K170 as it is on board with power off, pin 1 (+), pin 3 (-). If it will be a short, its the culprit. If it will show normal IDSS, then look for changing the CCS Mosfet, if the leds are beyond doubt. Have you seen them showing weird color?
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Old 23rd October 2010, 02:33 PM   #515
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Originally Posted by Marra View Post
I used 2 MKP1837 0.1uf in parallel. Working well and sounding brilliant.
Great, where did you get them? I've asked Wima for a couple of samples, hopefully I'll get some.
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Old 23rd October 2010, 02:44 PM   #516
Salas is offline Salas  Greece
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They are Vishay. They are available from a very well known Canadian boutique parts vendor in small qty among others.
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Old 23rd October 2010, 02:48 PM   #517
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Great I found them. So, I'll need 2x as many.
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Old 23rd October 2010, 03:09 PM   #518
Salas is offline Salas  Greece
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Choosing those you will need to solder either just one 0.1uF, or one above and one underneath, since they don't come in 0.22uF as far as I remember correctly. Bit strange but entirely doable. In such a case, yes you will need 4 0.1u in total. They are 5mm, the 100uF marked position will suit.
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Old 23rd October 2010, 05:21 PM   #519
TerryC is offline TerryC  United States
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Quote:
Originally Posted by Salas View Post
First thing I would look for is the K170 CCS JFET that sits on the 100R. Measuring across the 100R, translating into current. Between 6-10mA from a healthy BL. The smoke must have let go from the respective 10R current setting resistor if has 4V across. Then again, a bad CCS Mosfet could not be giving enough Vgs. The one associated with the 10R. Maybe punched through with static when handling.

If blowing fuses, just use DCmA mode on DVM, put it in series with a 9V battery, and feed the K170 as it is on board with power off, pin 1 (+), pin 3 (-). If it will be a short, its the culprit. If it will show normal IDSS, then look for changing the CCS Mosfet, if the leds are beyond doubt. Have you seen them showing weird color?
Measured 7.8mA through the suspect K170 (sitting on the 100R). I guess I need to order another 9240 Mosfet along with a gross of fuses, and replace the 10R while I'm at it. Thanks Salas.
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Old 23rd October 2010, 08:30 PM   #520
Salas is offline Salas  Greece
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I would change the 3 associated leds for good or bad too. Just to be on the safe side.
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