[sdiy] PCM1702 DAC fakes ? or not ??

[Roman Sowa]

To be sure, check the IC43 opamp first. It is pretty easy if the DAC is 
desoldered, just wiggle a finger over empty DAC pads and there should be 
nasty brooming audible.
IMHO there's no other way now than to check the common lines. Without 
direct access you can solder pieces of wire to QCLK and WCLK traces, put 
PCBs back together and connect scope probes to those wires. To not 
desolder the DAC so many times (one more time and the pads will fall 
off), you may cut the traces on those lines close to the IC29, see the 
clock signals on the scope, then bridge those cuts and observe the clock 
signals again.
I would also check if supply voltages at DAC's pins are correct and if 
those 3 capacitors are not shorted or anything.

You might also consider making test jig for all those DACs you have just 
to see if they are OK. Incrementing data word on every sample would 
create nice ramp. I know you could write simple PIC program for this in 
20 minutes. Seems easy only if you have burn-in/test socket for SOIC20 
though.

Roman

W dniu 2023-12-01 o 15:36, Jean-Pierre Desrochers pisze:
> I’m working on a Yamaha Clavinova CVP900
> 
> That has its right channel dead.. no sound.
> The left channel is ok.
> So, looking at the *_attached PDF file from Yamaha_*,
> 
> They stated that a common issue was found on PCM1702 DAC’s used
> on the main digital board. Noise or no sound at all can be encountered.
> 
> I checked both DAC and, effectively DAC IC29 had no sound
> to its opamp (pin 7 on IC43).
> 
> The only ‘I thought reliable’ source to buy a PCM1702 I found
> was *Syntaur USA* at $36.95 each.
> 
> To make sure I ordered two. Ok.
> 
> So I carefully removed the bad IC29 and soldered a new one.
> 
> The result ? Now both channels were dead !!
> 
> I thought I could have done something on the main board
> while replacing the bad chip.. So I desoldered it and powered back the unit.
> 
> The left channel only came back alive… Hmmm…
> So I picked the second DAC I had left on hand and soldered it
> on the board.. Again both channels dead !!!
> 
> So 2 things could be happening.
> 
> New Fake PCM1702 IC’s that load the common data buses (QCLK, WCLK) when 
> installed
> and keep the good DAC from working.. ?
> 
> Or the driving IC that brings QCLK and WCLK to both DAC’s
> that is getting weak and drop when 2 DAC’s are installed (That I doubt).
> By the way I had no way to check digital waveforms on both DAC’s
> beacause they are placed underneath a big daughter board.
> 
> So what do you think about that ?
> 
> Hmmm.
> 
> 
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