TDA1541A troubleshooting - faulty chip?

[Painkiller]

I bought an unused TDA1541A off e-bay, and have built myself a simple dac. When I power up I get some strange readings, and hope to get some tips from more experienced diyers.

All power supplies work perfectly when not loaded. I use 78xx/79xx series regulators in a pretty regular fashion, but with snubber on outputs. When I connect the chip Vdd2 drops from -15VDC to -5.6VDC. I also get uneven dc offsets on the outputs, 4VDC on the right and 1VDC on the left.

Could there be an external factor in the cirquit causing this, or is it a faulty chip? Board looks clean with no short cirquits or other obvious mistakes.

[Andypairo]

Such a large voltage drop on the negative supply means either a large current draw or a bad regulator.

Try loading the negative supply with 100mA and see if it stays OK.

For the offset.. what do you use as I/V converter?
Output should stay a few mV from 0V.

Cheers

Andrea

[Painkiller]

Thanks for the quick reply.

I'll test the supply later this evening. Hope it's just a bad regulator.

Output offset from the dac was measured without the output connected. Will the I/V affect the measured offset on the dac?

I use a variation of rbroer's I/V-stage posted here on diyaudio. This one:


Having some problems with the I/V also. It seems to read 400mV offset on the output after the coupling caps when loaded. How's that even possible?

[Andypairo]

Hi,
the outputs of the DAC are current sources so their voltage is determined by the load attached. You can use a small value (100R) resistor to gnd for the tests.

Cheers

Andrea

[-ecdesigns-]

I bought an unused TDA1541A off e-bay, and have built myself a simple dac. When I power up I get some strange readings

Could be a bad chip, what is the exact marking on the chip?

I had similar problems with TDA1541A chips with HSH0123 marking:

TDA1541A
11190
HSH0123

What happens when you disconnect pin 27 from VCC?

[dantwomey]

When I was troubleshooting my TDA1541A DAC I used the table on this webpage to check all my TDA voltages. That should get you started.

Regards,
Dan

[Painkiller]

Well, I checked last night, and it's not the regulator.

Into 150R the dac gives 0VDC at Aor and 4VDC at Aol. I've measured around the whole circuit, and there are no short circuits or other obvious mistakes. The supply voltage still drops to -5.8VDC.

The marking on the chip is:
TDA1541A R1
10767
HSH9827 2 Y

What does it mean, by the way? Never took the time to try and understand the inscription.

I'll check voltages on all pins later tonight. And I can try to disconnect pin 27 to see what happens.

Thanks for the help everyone!

[JonHarrison]

Hi,

Any chance you could post a photo of the DAC? Although the date code is believable it could still be a fake. I've personally been caught like this by a seller on Ebay :-(

Cheers,

Jon

[dantwomey]

When I was searching for a TDA1541A I tried to looking for a seller with a previous track record of selling authentic chips. A'af is one such individual.

Regards,
Dan

[Painkiller]

Here's the chip: