QRV-08 power up

[svarthvitt]

Hi,

I have started to solder together the amp now, but I´m wondering how to test the power supply. Can I just power it up before I solder the amp section and see if it lights up? I know many regulators get ruined if you turn them on without a load.

I´m also a little confused on how the options I have on the input. Should I use the pot and c1/c2/r1/r2?

Hope someone can help me out! Thank you!

[peranders]

The regulators works perfectly without load since the voltage reference and opamps are quite enough as load. Good idea to build the power supply first.

[svarthvitt]

Hi again,

I´ve made a real mess now. I was missing some parts for the psu, and impatiently soldered the amp while I was waiting for the parts.

Now I have finished the board and put voltage on it, but its failing. The lights on both positive channels are flashing, then the negative for one channel is flashing, and then its nothing. I´ve tried to resolder most of the missing negative channel, but I see no difference.

I have been having nightmares about searching for an error on this board.. I hope you have some input on where to start looking.


Thank you.

[peranders]

I'll suggest that you do a real good visual inspection first.

[svarthvitt]

I could not find any misplaced parts on the left side of the board, but I´ll try soldering some of the parts again. On the right channel, it seems like I have placed a capacitor on E28. Could this have caused a fault on the right side as well?

I´m all out of 0805 470k resistors now, and it´s too expensive to place another order from Elfa just for this part. Can I fit a regular resistor temporarily, just to see if I can get it running?

[peranders]

Sure you can test with a hole mounted resistor.

[svarthvitt]

I found a new resistor for e28, and found some other errors I made on the boards. I soldered capacitors on c/g41 and 42 instead of leaving them open. I removed them and fired it up again, but the result was the same.

As mentioned, its blinking for half a second, and then the leds go black. The negative on the left channel does not fire at all.

I realise that its almost impossible to troubleshoot this board. Do you have any hints on where to start? I know its likely to be binned, but I´m willing to put some time into this. If some components might be damaged, I´ll order some new one.

[peranders]

I recommend that you once again check all parts.

You can remove R3, then the amp will be turned off. Interesting to see if you'll get a proper stabilized voltage.

You should pay attention to pnp/npn transistors are on the right spot.

[svarthvitt]

Well, I´ve made some progress! I had switched two of the transistors on both amps. t13 and t14.

Now three of the leds are stable, but the left negative is still not lighting at all. All the channels look identical to me now. I´ve been looking at the boards several times a day for a while now, so the channels are symmetric. I have 1.8v drop over the working leds, and only 1.0v over the dark one.

I´m hoping for a new clue here. I obviously have a voltmeter, and also an old oscilloscope, if that helps. I´ve tried to remove r3, but it does not seem to make any difference.


Thank you for your help!

[peranders]

Do you have proper voltage in one channel now?

[svarthvitt]

Yes, one channel seem to be working. I will test it with sound later today.

[svarthvitt]

...and when I soldered in r3 again and connected a source, the negative left channel just lit up. Everything is working now. You never wrote anything about the self-healing properties of this amp!

Thank you very much for the help! I have only tried it from an mp3 player, but it sounds really promising!

[peranders]

Good top hear that you have succeeded. A small review later on would be nice to hear.

[svarthvitt]

Hi again,

How do I disconnect the servo to measure 0v over E1? I think I might have done this wrong the first time around.



Thanks,
Eivind

[peranders]

You don't have to disconnect anything. Just measure the voltage across R1 and adjust with P1. Let J4, J5 be open. Turn the pot to zero and see what you got. A negative voltage means that the input bias current is flowing into the amp. In that case put a positive voltage on the pot (J4).