Class D amp problem

[mika111]

Hi!

I´m a new user on this forum and my english quite bad also, so forgive me already

I have a problem with D -class amplifier, there is noise from speaker even when no signal (only power) is on.

I have already changed TL494, every electrolyte from it, cleaned it up and varnished those transformers.

I´d be very thankful if someone could help me with this.

The noise is quite high Hz and raises and falls at a steady pace.

If I measure DCV from speaker output it shows 25-35mV.

Thank You!!

 

[DUG]

Greetings milla111,

Did you build it or buy it?

Do you have a model number or schematic?

What sort of frequency or waveform is the noise...do you have access to an oscilloscope?

 

[mika111]

Oh...I bought it, brand is Autostudio and model E-1200

I don't have a schematic for this and neither oscilloscope..so my measure -tool at this point is only universalmeter (don't know what it is in English)

I was wondering that could the problem be in HIP4080 or some op -amps controlling that HIP?

The frequency from speaker is quite high Hz and it sails up and down between about 1kHz-15kHz

E: hah..think it's 'digital multimeter'

 

[manojtm]

Hi mika111,

something wrong with your GND line/missing/shield not proper.

measure DCV from speaker output it shows 25-35mV

DC SPK out is ok, no problem found on your amp.

Regards
MANOJ

 

[mika111]

Thanks Manoj..the supply ground is 0,00 ohm at one point and signal ground is 'floating' 1kOhm at that point. From that point it goes to amp chassis via 100nF polko..I changed that polko -> did not solve the problem :/

 

[mika111]

Here is some pictures from the board..

http://kuvaton.com/k/YrWK.jpg
http://kuvaton.com/k/YrW7.jpg
http://kuvaton.com/k/YrWN.jpg

 

[mika111]

Changed those LM393, LM833 and MC14013 from the HIP control -> no effect

Anyone?

 

[Tekko]

Without an oscilloscope, a repair is impossible as theres no way to see if you have the proper signals.

 

[mika111]

Okay, I have now measured some things from the amp. All measurements are from power ground. Oscilloscope is set at AC.

Speaker output http://kuvaton.com/k/Yr3F.jpg
Power FET1 http://kuvaton.com/k/Yr3P.jpg
Power FET2 http://kuvaton.com/k/Yr3q.jpg
Chassis ground http://kuvaton.com/k/Yr3b.jpg
TL494 Vcc http://kuvaton.com/k/Yr3E.jpg
HIP4080 Vcc http://kuvaton.com/k/Yr36.jpg
4013BP Vdd http://kuvaton.com/k/Yr3e.jpg
LM393 Vcc http://kuvaton.com/k/Yr3c.jpg
LM833 Vcc http://kuvaton.com/k/Yr3K.jpg
Amp FET http://kuvaton.com/k/Yr37.jpg

FETs are measured from Drain to Power Ground

 

[DUG]

The big electrolytics...the ones on the right both have + to the right and the ones on the left the + are towards each other.

Verify that they are in correctly.

 

[xrk971]

Wow, that is a lot of discrete components! Not one of the newer single ic class D's I am used to seeing. It must be pretty powerful judging how many fets there are. Do you have a link to the specs?

 

[mika111]

The big electrolytics...the ones on the right both have + to the right and the ones on the left the + are towards each other.

Verify that they are in correctly.

Good point thin they are right way..at least the markings on board tells that. And I believe they would be blown already if they were wrong way.

I was wondering that could the problem be in the PWM because those TL494 outputs are width 8uS up and 15uS down both channels..and measured before the chokes on speaker output it is 8uS up and 8uS down. Woldn't that frequency difference do harm?

Please someone help..a bit lost with this

 

[nigelwright7557]

Try connecting your zero volts on the amplifier to ground.

I had a similar problem when using an MP3 player with my amp.
Because the MP3 player is floating it was picking up junk signals.

 

[mika111]

Try connecting your zero volts on the amplifier to ground.

Tried to connect power ground to chassis -> nothing
Connected audio ground to chassis -> nothing
Connected audio ground to power ground -> nothing

E: Or did you mean to connect amp 0V to power ground?