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Class D Switching Power Amplifiers and Power D/A conversion

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Old 14th June 2009, 11:09 AM   #11
luka is offline luka  Slovenia
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amp will probably be ok without heatsink for test..

Do you know how amps work? I mean yea, you can't not have capacitors, and to say, they are part of power supply as are rectifiers [diodes]
what other low voltage? You have 12v input, and signal for amp to work, thats it

Do you have DC on your output? BRW, output is not connected to input
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Old 14th June 2009, 11:29 AM   #12
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Right, but the capacitors are not rated as high as the ones around the fan. I assumed that the ones around the fan were the ones for the high voltage (output) side.

I don't have voltage on the output termianls, no. Neither DC nor AC. Even if i connect a load to the terminals.
However i do get the 110v ish across all the output fets.
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Old 14th June 2009, 11:46 AM   #13
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The big ones are supply caps, highest rated in amp [compared to their C size] Other 2 on other side of fan are most likely part of out LC filter along with those red ones. If they are not, those red ones with those resistors could form RC filter

Does your amp even starts up? does supply start to work? maybe there is a problem even on remote, thing that turns amp on. You will have to check every part of amp, is this and that working, doing so you will find where normal status stops to be.

But as I read, you said you get 110v on output fets, so supply should be working ok, so now question is, does amp section work too? I do hope you have scope, this would be really easy to check
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Old 14th June 2009, 12:00 PM   #14
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I do have a scope (got myself one a few months ago). It all seems well,
Except the power LED is not illuminating. When i put a load across the speaker termianls and power it on, nothing happens.

I hear a relay click in after about 2 seconds of power on. (output protect relay?) The fan spools up immediatly after applying voltage to the remote.

I have connected an input (RCA's and played a tone through them) but where should i be able to find these outputs? As i seem to only be able to pick up this AC across the rca termianls themselves.

I assume the 'amp section' is the 20 fet part? Low voltage high current side?
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Old 14th June 2009, 12:08 PM   #15
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Ok maybe led is dead, amps seems to be working as far as to Damp, did you check if there is signal on output[small sine, high freq.] or befor output inductor?

2s for relay to click, seems ok, output is connecter to output terminals [check if this is true]
And fan is also working

So one of two thing I can think of:
1. input is not conecter anymore or dead, so signal doesn't pass
2. amp section is not working

car amp is made of supply[20fets] and amplifier[8fets], so we have seen that suppy is working, but not amp section, so check this, then, if there is signal, put sine signal on input and check how far it goes, does it even enters amp.
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Old 14th June 2009, 12:21 PM   #16
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Ok, i will when i'm home from work.
The LED itself is ok, i passed a small voltage through it and it illuminated.

So check the ouput on the relay is connected to the output terminals.

When you say input is dead, i have that one hot running resistor (this is from the rca/ gains section to the fets/ toriods). I will replace that when i can.

What makes the power LED illuminate? Is it a feedback sort of thing from the amplication section.
As i just thought that would turn on when voltage is in the power section.

Thankyou very much for your help. I have learned a lot already!
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Old 14th June 2009, 12:27 PM   #17
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Wait a minute, RCA are not connected to any fet by only resistor/s

Mark them on some picture, I must see which ones you are talking about. Maybe it is on if they heat up, but only if the are the right ones. I am thinking you don't think the right ones, since RCAs have small voltage, olmost no current, so based on that, nothing can heat up..
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Old 14th June 2009, 12:39 PM   #18
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Exactly but that is what is concerning me. I mean these resistors are GLOWING they are really that hot.
I'm stuggling to find a picture.
I know RCA's should have little voltage and current. I don't know if these resistors are directly connected to the inputs but they look like they are.

Click the image to open in full size.

The green resistor standing up by that board i was talking about. There is a resistor either side of the pair of capacitors.
It's red hot once the relay clicks in.
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Old 14th June 2009, 12:48 PM   #19
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After relay, ee? Ok you need to find out what are they for, maybe to generate voltage for IC? coz it looks to me there is diode, that would make nice voltage regulator for ICs, and I am thinking on, if IC are dead, there could be short, and full voltage on those resistors, making them way too hot

It also looks like amp was repared before, no?
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Old 14th June 2009, 01:04 PM   #20
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Yes that amplifier i have repaired before. That is not the amplifier which is broken. I don't have any pictures of the amplifier which is broken right now. It looks exactly the same just without that yellwo cap across there.
I'll check IC's when i can.
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