| lscangus |
Todya, just now, i have powered up my Aleph-X with a vairable transformer, and after about 30 seconds, there are smoke coming out from the output resistor, but when i switch it off, i cannot feel any thing whihc is hot.
And i have notice a strange thing is the cirucit does not draw any power from the -V supply, as when i switch it off, the voltage accross the -V supply doesn't drop. but the +V voltage drops quickly.
Thank you for your kind attention to this thread. This is my first aleph. And i want it to work.. Please help!
Angus |
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| Netlist |
Angus,
A nice thing to start with is to tell us (link) which schematic you used, what rail voltage, and possible changes you made to the schematic.
I think with output R's you mean from output to ground but it's guesswork for now. :)
/Hugo |
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| Netlist |
Sorry Angus, I can't go into debugging the board to reconstruct the schematic. Also, I need to know exactly what resistors were smoking.
/Hugo :) |
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| lscangus |
The resistor that is in smoke is the one parallel to the 33ohm resistor, which is in series with the Output.
But i do not understand why it doesn't not draw any current from the -V |
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| eapavant |
| If you post a schematic I am sure Netlist and others can help you. With out one there is not much they can do. |
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| eapavant |
| I found this in the thread from your GB. It looks like KK's. |
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| lscangus |
| quote: | Originally posted by eapavant
I found this in the thread from your GB. It looks like KK's. |
That is the one, thank you for all your help.
Angus |
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| EUVL |
Angus,
Try the following first to see if the diff pair is working / adjusted properly.
Disconnect the power boards completely from your frontend board. Change R3/R53 to 100k. Tie both +ve & -ve inputs to ground. Power up and adjust VR101 until the voltage across R3 & R53 are approx. 3.9V.
If this is OK, you should get about 1A flowing through each of the lower MOSFETs.
I am on trip at the moment. But I am sure other can / will help.
Patrick |
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| lscangus |
How do i know there is a current of 1 A flowing?
Angus |
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| EUVL |
Measure voltage across the Source Resistors of the power MOSFETs (not on your schematics, so I cannot tell you what number) and use Ohm's law to calculate the current I=V/R.
Patrick |
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| Netlist |
| quote: | Originally posted by lscangus
The resistor that is in smoke is the one parallel to the 33ohm resistor, which is in series with the Output.
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Would that be R3 or R53?
/Hugo |
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| jh6you |
| quote: | Originally posted by lscangus
How do i know there is a current of 1 A flowing?
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I think that you have a Source resistor just below each MOSFET, e.g. 0.39ohms or whatever . . . Measure voltage across the Source resistor. When V=R, there is 1A (according to I=V/R).
Regards
Damn . . . I'm always late . . . :devilr: |
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| lscangus |
But it said i have to disconnect all the power boards completely from your frontend board. And i think the source resistor is on the power boards.
So what i have to do is to Change R3 and R53 from 10k to 100k and then disconnect all the fets and then addjust the VR101 and then measure the voltage accross the source resistor on the power board (0.33 Ohm) and use V=IR calulation to calculate the current
Angus |
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| lscangus |
| quote: | Originally posted by Netlist
Would that be R3 or R53?
/Hugo |
Is arround R14-R18
Angus |
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| lscangus |
Here are more information for you guys
Angus |
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| EUVL |
> But it said i have to ....
Angus, you don't have to do anything. It was just a suggestion.
> disconnect all the power boards completely from your frontend board. Change R3 and R53 from 10k to 100k and then disconnect all the fets and then adjust the VR101 and then measure the voltage across ......
.... the Drain resistor of the diff pair (R1 / R51) to about 3.9V. This will prove that at least your frontend diff pair works. The Aleph current source is difficult to adjust without the power MOSFETs, so you'll have to do it in the next step. One step at a time.
Don't worry about your bias current as yet. Just make sure the frontned works. There is little to go wrong at the power stage.
It would help a lot if you read the Wiki and try to understand how the circuit works.
Patrick |
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| lscangus |
So for now, i disconnect all the power boards and then measure the voltage. of R1/R51 or R3/R53
Which pair is correct?
Angus |
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| EUVL |
> So for now, i disconnect all the power boards and then measure the voltage. of R1/R51 or R3/R53. Which pair is correct?
R1/R51, the 2x 390ohm resistors at the drain of the IRP9610s.
Was typing mistake with R3/R53 in post #9. And don't forget to connect both inputs to ground temporarily.
Patrick |
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| lscangus |
| quote: | Originally posted by EUVL
> So for now, i disconnect all the power boards and then measure the voltage. of R1/R51 or R3/R53. Which pair is correct?
R1/R51, the 2x 390ohm resistors at the drain of the IRP9610s.
Was typing mistake with R3/R53 in post #9. And don't forget to connect both inputs to ground temporarily.
Patrick |
Thanks for your help, just ordered some resistor via the internet today,. arive tomorrow. Keep you guys up date and fingers cross... Hope i didn't damage any components.
Angus |
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| lscangus |
I tried that already. changing R51 and R1 ro 100k Ohm, and i got a voltage of about 13 volt across it...
Angus |
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| EUVL |
Angus,
You should change R3/R53 from 10k to 100k, and measure R1/R51 (which were 390 ohm, and you should keep them as that) to 4V while trimming VR101.
Patrick
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| lscangus |
oh... i did the wrong thing.. will i damage the components?
i will try again tonight
Angus |
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| Keith Marrison |
Patrick,you have advised Angus to change R3/R53 to 100k,,do these need changing back to 10k after checking the front end and reconnecting the power mosfets.
Thanks,Keith |
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| Babowana |
| quote: | Originally posted by Keith Marrison
need changing back to 10k
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Yes if the trouble shooting is successful with R3/R53 of the temporary 100K. |
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| Keith Marrison |
Thanks Bobowana.
Keith |
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