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Originally Posted by: avr300  Just to check for any problem with the Legato itself, temporary drop the voltage to +-12V and see if the adjusted current is enough @+-12v
I will check Legato 3.1 again and update, may be tomorrow. Do you have any advice about which area I should focus to? I will try to make another simple power supply to test Legato. Thank you very much.
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Originally Posted by: avr300 If you doesn't shunt enough current the output voltage will sag. That's the nature of a shunt supply.
The higher voltage the higher demand for current. That's why I suggest to drop to +-12v, do the test with 350mA, is the rails stable now. If so, and the rig is producing sound, the rig is healthy.
Increasing the voltage is straight forward - as long as you increase the current as well. But we have to make sure that the load is a load and not a short.
Final update for today, Vietnam is night time now :). Thank you for information, after quickly resolder Legato, I reduced voltage to +-12V and do the test with 350mA. Got same result. shunt current on negative rail still = 0mA/11V, positive one is 16mA/4.6V I hope can find something wrong with Legato tomorrow. Thank you.
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Update:
After checked Legato 3.1 and found no issue, I tried with another simple power supply and found it is ok.
Back to my Placid HD BP, if I start with CCS ~ 440mA and 12V, I can power up Legato with +-12V, shunt current become ~230mA.
Is this current too big for Legato or Placid HDBP? Heatsinks are very hot, heatsink compound is melting.
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Now that you have proven that the Legato is ok, you just trim down the current with the Legato in-place and the rig powered on.
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Hi avr300,
Sorry, I forgot to update that I could trimmed down the current with Legato in-place to around 160mA/12V, but voltage on positive rail dropped again on next power up. That's why I have to keep such high current and collecting your advice.
Thank you.
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One thing You can try is to take out the relay at the Legato board. Just for the test. The relay is there to prevent turn-on noise. As long as you switch on your gear source->to->speaker, (DAC, pre amp, power amp) and off again in opposite order you're fine. There has been some incidences where the relay draws a lot of current at kick-in. I don't know why. Edited by user Sunday, September 16, 2012 9:08:57 AM(UTC)
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Today I tried again with Placid HDBP and Legato with CCS less than 400mA. As usual Voltage on positive rail dropped to 4.2V, negative rail seem fine. However, I notice that 02 LME49xxx under bottom of Legato are quite hot. On the Placid HDBP, only heatsink of QP1 and QN1 are hot while QP2 and QN2 are not.
Is this abnormal operation? If yes, which point should I checked. If not, I will proceed with relay removing.
Thank you.
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I am 99% sure you have some transistors swapped.
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 1 user thanked Brian Donegan for this useful post.
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Hi Brian,
As your advice, I checked and found that QN6,QN5,QN2,QN3 were swapped with QPs. I changed them to correct position, however I still got same problem, positive rail of Placid HDBP dropped to 4.2V.
Now I think both Placid HDBP are fine. The problem should reside on Legato, which point you will advise me to check?
Btw, as mentioned in topic about my BIII, now it is fine. But I got problem when connect BIII to 4-SPDIF board by ribbon cable, voltage dropped from 5.2V to 1.5V (I set CCS current at 490mA).
On 4-SPDIF board, I solder 03 Input transformer only. I align pin 1 (with the dot) on BIII with pin 1 on 4-SPDIF board by the red line mark as manual advise.
Could you please help?
Or, if I want to power 4-SPDIF board separately, which pins are used for Vin?
Thank you
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Very likely those transistors which were swapped are dead. You will need new ones.
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Thank you Russ for support.
I already have BC550 in hand but not TP0604, is there any other part can be a substitution for it?
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Hi all,
I found my problem by removing LME49600 in Legato board and put it back one by one. Result is 01 LME49600 was dead.
Legato voltage is fine, no drop, when dead LME is removed. I even can hear music from remaining normal channel (by feeding music signal to in put of Legato).
Thank you very much for helping me on this topic.
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