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Class D Switching Power Amplifiers and Power D/A conversion

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Old 14th June 2009, 01:58 PM   #21
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Sorry just one other thing. When tracing around the RCA input, do i keep my earth probe (well crocodile clip) attached to the RCA shield the entire time or do i put it onto the earth of the amplfiier?
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Old 14th June 2009, 02:41 PM   #22
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if you look for signal, then I would say keep it on input gnd at all times, since input signal is input
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Old 14th June 2009, 02:45 PM   #23
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Ok, cheers.
I'll post back later with my results of following the input around.

I was hoping it would be something more fundamental though, as the power light isn't coming on...
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Old 14th June 2009, 02:50 PM   #24
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it still could be, like led driver, but since you don't get no sound and we don't even know if output stage is working... we can't say more then this for now
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Old 14th June 2009, 02:56 PM   #25
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Ok, so i need to put the scope across the output fets when the amp is on and there is an input from the RCA's.
Then if get nothing, re-think. .

Thank you again for your help.

I'll post back with scope results. Also some better pics if needed.
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Old 14th June 2009, 03:05 PM   #26
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no no no, why would you look output with input??
input is input, out is out, look at them separatedly

input RCA gnd for input signal... output is with power supply secondary gnd
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Old 14th June 2009, 03:30 PM   #27
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Ok, so which fets do i need to put my probe onto? The set of 8? (output fets) or the set of 20 (supply fets?).

Or do i not need to check fets, does the signal go into toriods?
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Old 14th June 2009, 04:26 PM   #28
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output, since you already know supply is working, right?
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Old 14th June 2009, 09:17 PM   #29
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Ok, from the output side i'm getting very little ac voltage ~0.2v ish.

However on 5 of the 10 (not 8 sorry) fets i get ~110 v in the middle pin DC.

On the other 5 fets i get 0v DC on the centre pin but on all the right legs i get the same voltage (~110v).
When i test the left pins the amplifier goes into protect. No matter where i put the gnd probe, even if its on another left leg.

When the amplifier goes into protect the fan continues to run and i still get voltage on my supply side. However the buzzing noise stops coming from the caps (as the relay clicks out)

Too i have noticed that across those 4 random fets (DP3/4S) in the middle of the board, i get 2 of them with ~230v AC. Wherea the other 2 i only see about 7v DC(DP1/2R)!
Why is that???

Also when i test for voltage across any of these fets the buzzing from the capacitors gets much quieter.


These are the 4 fet's i'm on about.


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Old 15th June 2009, 05:34 AM   #30
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Quote:
Ok, from the output side i'm getting very little ac voltage ~0.2v ish.
That is still ok, if you have load on or not

Quote:
However on 5 of the 10 (not 8 sorry) fets i get ~110 v in the middle pin DC.
This seems ok too, since I is probably full bridge amp, am just not sure, do you really have 10 fets in total, coz in half bridge that could work, but you would need + and - voltages, in full bridge I don't see how whis could be, one voltage is ok, but for every bank of fets you would need the same number of fets [half has 2 banks, full has 4, so in half you have min of 2 fets and any number times that, in full, 4x any number]

Quote:
On the other 5 fets i get 0v DC on the centre pin but on all the right legs i get the same voltage (~110v).
This sounds to me like you do have half bridge and you do have +/-110v. What is the voltage diffrence between pins that had 100v on? Did you at all times had black lead of dvm on gnd?

Quote:
When i test the left pins the amplifier goes into protect. No matter where i put the gnd probe, even if its on another left leg.
Fest are probably same, so what is on the right side most right is on other side most left, Still it doesn't explain why did it go into protect. If you did with scope, you can have much problems, depends on where you put you probes gnd to... I know I could measure voltage on resistors [current] that were on - rail, coz I had to put gnd of scope to - of amp, and it was like short! Only way everything worked was if gnd is on gnd

Quote:
When the amplifier goes into protect the fan continues to run and i still get voltage on my supply side. However the buzzing noise stops coming from the caps (as the relay clicks out)
A bit odd, but I guess amp section stops working in protect mode, or maybe there is some other thing

Quote:
Too i have noticed that across those 4 random fets (DP3/4S) in the middle of the board, i get 2 of them with ~230v AC. Wherea the other 2 i only see about 7v DC(DP1/2R)!
Why is that???
I have no idea, coz I don't know what they do in circuit

Quote:
Also when i test for voltage across any of these fets the buzzing from the capacitors gets much quieter.

Quote:
These are the 4 fet's i'm on about.
I think this are diods, that are part of making 110v dc
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