TeraDak v2.5 (USB DAC) started to be ver noisy - looking for rootcause

emroth

Member
2013-04-26 7:46 am
I own such a USB DAC and there was not a single problem in 2 years - I took it on a journey for few days and when I returned I realized it is no longer working ok. One chanel is dead, another chanel is very noisy - you can hear the signal but noise is much louder than signal itself.

Checked inside for broken parts suspicous soldering points etc. seems to be ok, all capacitors are fine, V supply is ok on each chip, ground seems to be connected everywhere - as long as my multimeter tells the truth.

I checked this dac on several computers on usb input and behaves the same - amp and headphones are ok - working perfectly with another DAC.

Can you suggest where to look for m
 
I suggest check the DC voltage on the output pins of the DAC chips (that's pins 6 & 8). Doesn't this design have passive I/V and use 8 paralleled TDA1543s? My best guess is one of the DAC chips has died - some designs in this mould run at very high supply voltages (close to 8V, occasionally slightly above), so the dissipation in the DAC chips is fairly high, reducing the long-term reliability.
 

emroth

Member
2013-04-26 7:46 am
Yup, you might be right as initial V supply for TDA1543 was ~7V, first thing I did was to bring it down to 5V but ofc that didnt helped at all.

All 8 chips are sittin on sockets so it will be easy to remove them - how to find a faulty dac chip with a multimeter? Or should I just tried it 8 times running each time single chip?
 

emroth

Member
2013-04-26 7:46 am
EDIT: tried out with single TDA1543 and it is working pretty well - it was noisy for a 30s and then music appeared - kind of miracle ;)
No idea why it was "one chanel dead, one chanel digital noise only" anyway I will try with more than 1 TDA1543 and hope for the best :)
 

emroth

Member
2013-04-26 7:46 am
EDIT: one more answer: heat dissipation - if TDA chip is floating loose then there is "one chanel dead, one chanel digital noise only" effect - when I press the pcb board that chip has contact with housing (acting as a radiator) then sound is quite ok - every one of chips is working fine.

Another thing is 1 chip plays ok, but 4 paralleled chips produce distorted sound - I guess 5V supply is not enough for them.

Next stage will be to bring supply back to 7V, mount all 8 tdas and put fresh thermal-conducting fluid on them, and of course screw tightly pcb board to radiator.

I guess it was a mechanical issue - screws were too loose and therefore tda chips were overhitting but I need to collect all the stuff to get it confirmed
 
Some of the TDA1543 chips are dead. The 8 chips are parallel and output the respective current to the common point before the I/V resistor. If one of the DAC is dead, its output current will be noisy and will mess up the other good output. Therefore, the final output is noisy. You can check them by installing 4 chips one time to locate the possible bad ones. Then split the possible 4 chips into 2 batch and install them separately to find the possible bad one. ..... Just find the bad one and replace it. If you can not fix it, you can send it to the Teradak for repair.