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Voltage drops of Placid HD after connecting load (BIII)
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I have a problem with my placid HD. Adjusting it with no load to 5,25 V out and 550 mA. All leds turn on, vout is stable and heat sinks get warm, Vout and V shunt are stable. Measuring shunt is 550 mV wih no load connected. As soon as I connect only bIII DAC with trident installed, only some leds of the tridents turn on.  Voltage drops on Placid HD to 3.25 V, shunt is 0 mV. When I look at the parts the numbers of the QN1, QN2 they differ in number above the J5200, is that maybe the problem? See the pictures for details.  I resoldered everything on the placid, but that did not change this behaviour so far. Edited by user Monday, December 31, 2012 10:25:50 AM(UTC)
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I rembember that a while ago there was a batch that contained the wrong FETS (QN1 & QN2). It could very wel be that you also have a Placid from this batch. |
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I looked up the datasheet for FJPF5200OTU, and ony mention of the marking is this J5200O. And that seems to be the same in this case?
I cannot seem to find anything about the numbers above that marking in the datasheet (Fairchild Semiconductor), but I am not sure they are actually the same?
Can I somehow check the working of these components? Heatsink do get hot, both of them, also with no load.
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I think it's starving.
What's happens if you shunts around 650mA ?
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Originally Posted by: Corpius  I rembember that a while ago there was a batch that contained the wrong FETS (QN1 & QN2). It could very wel be that you also have a Placid from this batch. Thanksm I found a thread where this is described: wrong parts supplied for QN1 or QN2. But that number is really different, so I guess my problem is different and maybe not related to these at all? Maybe it is BIII/Trident related? Not sure where to start here?
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Originally Posted by: avr300 I think it's starving.
What's happens if you shunts around 650mA ? Can I safely do that? Only BIII is connected , should be approx 440 mA + 50 mA = 490 mA, I added some more to be sure it was not to little current (so set to 550 mA).
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Well, it surely runs out of juice "Voltage drops on Placid HD to 3.25 V, shunt is 0 mV."Either there's a short (or defective component) on the DAC side, or you're simply running out of current. Just keep an eye (a finger) on the heat sinks. Edited by user Monday, December 31, 2012 11:35:41 AM(UTC)
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Just for a test, you can disconnect 2 of the 3 tridents. This way you eases up the load of the Placid.
Just to give you an indication whether it's a DAC problem or a PSU problem.
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Originally Posted by: niekos Originally Posted by: avr300 I think it's starving.
What's happens if you shunts around 650mA ? Can I safely do that? Only BIII is connected , should be approx 440 mA + 50 mA = 490 mA, I added some more to be sure it was not to little current (so set to 550 mA). Yes. Increase the shunt current.
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I increased the current and I am now able to connect the BIII and almost all light go on, only one trident misses one light. See this picture.  Current is now set at 650 mA, when BIII with all trident are connected 220 mA is shunted. Voltage is stable now on 5,25 V. I presume all the lights should be on right?
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All leds has to be lit.
That's the AVCC module missing a light. Hmm, strange.
CAREFULLY check the voltage at OUT pads on the AVCC shunt relative to GND.
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And while your in with the DMM, also check the AVCC module IN pads
Careful, don't let your probe slip and short.
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On the side where SRA2 is printed in the board:
5,21V IN and 5,20 OUT
On the other side
120 mV in, 30 mV out.
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Something wrong. In should equal input to the board and OUT should be 3.5v.
Are you sure that the AVCC module lines a 100% up on top of the DAC board ? Check the pins.
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Remeazured, I think I did not apply anough pressure for a correct reading, sorry for that. On the side where SRA2 is printed in the board: 5,24V IN and 5,24 OUT On the other side 5,25 in 2,1 V OUT. Strange values, it should be 5,25V/3,5V both sides? I meazure point IN to GND and OUT to GND, correct? AVCC is correctly alligned on the board as far as I know? See picture below (I highlighted where I meazure; this is the side with 5,25 on in and out). 
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You're measuring correct.
Yes, both sides should read 3.5v at OUT pins and board supply at IN.
Unmount the module, measure the VD pins from the DAC board. See if they are equal.
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Unmounted the module and both sides read 5,29V.
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Now, hand over to Russ and Brian. I can't debug the AVCC shunt without schematic ;-) Something is wrong with your AVCC shunt module. Edited by user Monday, December 31, 2012 1:56:59 PM(UTC)
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 1 user thanked avr300 for this useful post.
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No problem, you are welcome.
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Voltage drops of Placid HD after connecting load (BIII)
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