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Old 26th October 2013, 05:43 AM   #11
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Hi Quan

It is possible you may have a hair line fracture on one of the SMD solder joints.
If you have a needle point soldering tip try and re-solder some of the SMD transistors or post it back to me and I will do it for you.

Cheers

Anthony
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Old 26th October 2013, 06:08 AM   #12
quan is offline quan  Australia
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Hi Anthony, are you refering to the SMD transistor on the amp modules themselves?. But when i tested on heatsink only there is no DC offset problem and the problem only occur when installing within the chassis.
Quan
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Old 27th October 2013, 04:13 AM   #13
rabbitz is offline rabbitz  Australia
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Hi quan

I don't know if these are the modules you got from me, but if they are, I had DC offsets of +26mV and +4mV with my power supply.

You could try swapping the heatsink amp modules to opposite sides to see if the offset follows the amp or stays on the same side, i.e. with the power supply. Try using the power supply with 1 channel at a time with 1 transformer but I don't know the PSU three supply so might not be possible.

If there is no offset problem out of the chassis, then you may want to go back to basics.

1. With the modules out from the chassis make sure the insulators are under all the 3 devices. Check with DMM from module ground to heatsink and you should get no reading.

2. With the modules back in the case, check with DMM from heatsink to chassis ground to ensure continuity. I've had several amps where I had to run a ground wire from the heatsink to the chassis ground as paint or anodised surfaces would not allow continuity. Chassis ground then went to the main earth. The power supply ground went back to chassis ground via a 10R resistor and 2 reversed diodes.

3. Build a fast and easy power supply using 1 transformer, a bridge rectifier and 2 caps for testing purposes. ESP has some schematics for a quick power supply and wiring.

Some builders short the signal input pins when checking DC offset but I usually don't. The only time I have was with a LM4780 ChipAmp.

Cheers rabbitz
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Old 27th October 2013, 09:00 AM   #14
quan is offline quan  Australia
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Quote:
Originally Posted by rabbitz View Post
Hi quan

I don't know if these are the modules you got from me, but if they are, I had DC offsets of +26mV and +4mV with my power supply.

You could try swapping the heatsink amp modules to opposite sides to see if the offset follows the amp or stays on the same side, i.e. with the power supply. Try using the power supply with 1 channel at a time with 1 transformer but I don't know the PSU three supply so might not be possible.

If there is no offset problem out of the chassis, then you may want to go back to basics.

1. With the modules out from the chassis make sure the insulators are under all the 3 devices. Check with DMM from module ground to heatsink and you should get no reading.

2. With the modules back in the case, check with DMM from heatsink to chassis ground to ensure continuity. I've had several amps where I had to run a ground wire from the heatsink to the chassis ground as paint or anodised surfaces would not allow continuity. Chassis ground then went to the main earth. The power supply ground went back to chassis ground via a 10R resistor and 2 reversed diodes.

3. Build a fast and easy power supply using 1 transformer, a bridge rectifier and 2 caps for testing purposes. ESP has some schematics for a quick power supply and wiring.

Some builders short the signal input pins when checking DC offset but I usually don't. The only time I have was with a LM4780 ChipAmp.

Cheers rabbitz
Many thanks Peter for the suggestions. I will try them out. The modules are good off the chasssis. I did measured the modules and heatsink to ensure no short. There are insulators under all trannies. I was thinking of swapping out the PSU and try another simple PSU to see if the problems persist or not. Had such a busy week end and i will endeavor to try all the suggestions.
Quan

Last edited by quan; 27th October 2013 at 09:05 AM.
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Old 29th October 2013, 10:31 AM   #15
quan is offline quan  Australia
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Have try a simple power supply and the Dc offset got stuck at 0.45V still. I think Anthony is right may be there is fracture smd transistor .
Quan
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Old 29th October 2013, 10:48 AM   #16
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Quote:
Originally Posted by quan View Post
Have try a simple power supply and the Dc offset got stuck at 0.45V still. I think Anthony is right may be there is fracture smd transistor .
Quan
I think Anthony was saying fracture in the soldering joint not in the transistor itself. Reflowing the solder on the transistors that Anthony pointed out would do the trick if that's the case.


Chris
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Old 29th October 2013, 10:19 PM   #17
quan is offline quan  Australia
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Yes Chris , my bad writing. I did try to reflow some of the transistors but without the fine tip and magnifying glass plus a pair of steady hands i am in uncharted water. I will take up Anthony offer and sort it out from there.
Quan
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Old 29th October 2013, 10:24 PM   #18
tinitus is offline tinitus  Europe
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or since its multi layer board, could it have hidden cracks inside ?

btw

your amp boards only have DC problem when mounted in a box

is it the box, or just when connecting the two channels together ?

anyway, all those spade connectors and heavy wires can be quite a load for the tiny solder pads
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Old 30th October 2013, 04:05 AM   #19
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Hi Quan,

Was just checking we were all on the same page. Hope Anthony's able to sort it out for you I'm still enjoying my nxv203 amps here!

tinitus,

I could be wrong but I'm pretty sure this is a 2layer board, unlikely to have a cracked via.

You've made a good suggestion about connecting the two so that they share a ground but without the chassis.


Chris
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Old 30th October 2013, 04:31 AM   #20
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Hi Guys

yes it is a 2 layer board, it should not be to much trouble to get Quan's module
working again.
He will be posting it back to me, I will get a look at it and let you know what I found.

Cheers

Anthony
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