AMP4 not working, HELP!

[niiico]

Hi,

I've finished an AMP4 but I was less successfull than with my AMP6...

The amp is not working. I was suspicious since the moment I tried to adjust the offset : the voltage was not measurable.

I tried to connect a source and speakers and as I expected, nothing happened...

So, I tried to figure out what was the pb. Since I don't understand a lot in electronic, this is not easy.

First, I got 5v at J4 pin 7 and when I close J4 pin 5 and 6 (to unmute) the relay is closing. So this part of the circuit seems to work.

Then I checked the diodes. The diode on pin 7 is on and the HMUTE turns of when I unmute the amp. All the other diodes stay off. So, this is correct also.

Nothing is going hot.

I tried to figure if there was a short circuit somewhere. I used the continuity test.

And i don't understand the results! I have a short cut somewhere!

I got continuity when testing between the pins of C10, C22, C24, C35 and C100 or C101. And this makes that I also have continuity between pins 4 and 5, 6 and 7 etc. on the chip.

I also noticed that when measuring D1 on the board (can't find it on the schema), I got 0,6V in one way and 1,9V the other way. D1 is soldered teh right way.

So, can someone help me?
Please, HELP !

[BWRX]

What chips are used in the AMP4? I know one is the TP2050 output stage chip, but what is the other one? The TC2000? And which chip are you talking about in your above post?

Have you soldered the chips in the correct way? I've made that mistake on an amp3 kit once...

[niiico]

Hi,

the chip is the TP2050 associated to the TC2000 as you stated.

I am speaking about the TP2050.

In the document from tripath, in the schema, the caps I'm speaking about are Chbr (.1uF) which are Vcc and the ground. The document is here : http://www.tripath.com/downloads/TK2050.pdf

the C100 and C101 1500uF are stiffener caps which have been added by Jan.

The chips seems to be soldered the right way.

There are some earlier stage pics here : http://blog.niiico.org/index.php?200...-ta2050-tc2000

Clic of the pics to enlarge them.

[BWRX]

Originally posted by niiico
I tried to figure if there was a short circuit somewhere. I used the continuity test.

And i don't understand the results! I have a short cut somewhere!

I got continuity when testing between the pins of C10, C22, C24, C35 and C100 or C101. And this makes that I also have continuity between pins 4 and 5, 6 and 7 etc. on the chip.

I also noticed that when measuring D1 on the board (can't find it on the schema), I got 0,6V in one way and 1,9V the other way. D1 is soldered teh right way.

Ok, thanks for the explanation and deatailed, focused photos! From what you're saying you have a short from power to ground which is not good. Is it a dead short (0 ohms) or is it something else? I would also check the diodes on the bridge rectifier to make sure they're ok.

I don't know what the purpose of D1 is because I can't trace out the connections on the board and it isn't part of the Tripath schematic. Jan added this for some reason.

[Markus2006]

Nicolas,

You have a shortcut between Vcc and the ground. You have to find out whether the shortcut is from power supply or from TP2050. I think that this can be checked by removing J10 (it disconnects power supply). If this is on the power supply side, check C59 (or C50). I think that this is SMD cap and it may be incorrectly soldered. You can also remove R6 just to be sure that it's not due to C50 or Q10. If the shortcut is on TP2050 side, any of C10, C22, C24 or C35 may be incorrectly soldered (or there is a shortcut under the chip, which would be the worst case to fix).
But also let me know whether you have +5V power supply because if you have a shortcut, you shouldn't have any voltage on the board - and this is strange.
Also the masurement of D1 is very strange. How can you have two different voltages? Are you using a voltometer or an ohmometer? I'd say that with voltometer your mesurements are not possible.

Edit: I just noticed on your pictures that J10 is not connected. Is it because of the shortcut?

Marek

[niiico]

Originally posted by Markus2006

But also let me know whether you have +5V power supply because if you have a shortcut, you shouldn't have any voltage on the board - and this is strange.

I have +5V. This is what I found strange.

Originally posted by Markus2006

Also the masurement of D1 is very strange. How can you have two different voltages? Are you using a voltometer or an ohmometer? I'd say that with voltometer your mesurements are not possible.

It maybe because of the tester I use. There is almost no user manual and there are some odd measures.

Originally posted by Markus2006

Edit: I just noticed on your pictures that J10 is not connected. Is it because of the shortcut?

No, the pictures are from an earlier build stage. The amp wasn't finished. On this pictures, only the smd are soldered and the j10 an j5 are not.

I'll make some new test ASAP following your hints and I'll see what happen.

I'll post also some up to date pictures.

Thank you for your help.

[niiico]

Some news...

Jan explained that it may be my power supply which wasn't high enough (only 12V for testing), even if I was earing the relay click.

So, I took my AMP6 transformer (15V) and try. And I have some "almost" good news : I got something!

For the 1st time I got some offset measured by a voltmeter at the output.

One of the channels is reacting well to the offset trimmers (POT1 and POT2) and the other has an odd behavior.

The first can go from -250mV to +150mV while the other goes from -250mV to 0V and nothing else. I put 'em both to -1mV.

So I tried to connect it to some old speakers and my powerBook. I got the channel reacting correctly to the trimmer playing music and the other no...

I turned the trimmer to go back to something like -150mV and I got some music, but with an horrible hiiiisssss (which seems normal with this offset)

The other bad point is that the "thump" in the speakers when the relay goes on and off is very loud.

So, I think we are on the right way, but I still need some help from you

Some pictures of the amp:

[Markus2006]

But this would mean that all your information about short circuit on the board was not correct . How did you test it?

Marek

[niiico]

You're right. I don't understand.

I made some new tests yesterday and realized something I didn't understood.

If I test continuity from ground to power, I get it. If I reverse the pins of my tester (testing from power to ground) I have no continuity.

Can't say why.

Sorry to make you work for me the wrong way...

I had an old 10$ tester before to by a bigger one, but I wonder if I shouldn't use the older one?...

[Markus2006]

It looks like a problem with the tester rather and not with the amp. Just buy any cheap multimeter with continuity tester - I don't think that it will be more expensive than 20$. It will save you a lot of time .
If you have +5V and VCC on the board, there is not short circuit (at least between VCC and ground).

Marek