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-   -   Deltec PDM 1.2 (http://www.diyaudio.com/forums/digital-source/110562-deltec-pdm-1-2-a.html)

bertchai 23rd October 2007 06:16 AM

Deltec PDM 1.2
 
Hi,

Does anyone have the schematics for this little DAC?
It uses SAA7320 DAC chip and Sony CX23053 as DIR. Apparently it will not lock. So looks like the DIR is dead. Need to replace it with another DIR like CS4812, etc.

: )

martin clark 23rd October 2007 08:10 AM

The receiver will be OK, it's the uA 9763(?) that will be dead.

This is (I think) an RS422 receiver used to buffer the SPDIF input and located next to digital input. Just replace it, the chip is 8-pin DIL and still available, cheap.

Buy a couple of spares actually, they seem very sensitive to ground currents - plugging my PDM1.2 into a cheap DVD player with a poor SMPS is enough to kill it.

bertchai 23rd October 2007 03:39 PM

Hi Martin,

Thanks for your info. I already replaced the receiver and it still wouldn't lock. : (

martin clark 23rd October 2007 04:18 PM

Have you checked the PSU rails and that the oscillator at the receiver runs when idle (no signal input)?

If you need I'm happy to open mine up and see what I can measure in the way of voltages and waveforms around the pins if that helps.

JohnW 24th October 2007 05:34 AM

Hi,

I've seen cases where when the UA9637 is damaged by input Earth leakage currents / Static it goes S/C between its PSU rails, this also burns out a small SMD resistor in series to supply pins to the UA9637. Check for 5V supply on the UA9637.

Coincidently, the reason the 9637 is damaged by Leakage currents is the fact that the construction of the RCA plug used for SPDIF connects the centre pin first (Signal) before Ground. This results in an "110Va Leakage loop" between the sensitive 9637 input and the SPDIF source. Units with SMPS such as Computers and DVD players are the worst offenders with larger earth leakage currents. Use optical if you can... Also, another reason where BNC is superior for SPDIF - not only can it be a true 75 Ohms interface, but also always insures Ground is connected BEFORE Signal.

If you still have no luck fixing the unit, I'm based in GZ - China and can repair your unit.

John

bertchai 24th October 2007 06:07 AM

That's very kind of you. I will check those once i have time. many thanks


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