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PCM1802 in it's simplest application

Other Parts Discussed in Thread: PCM1802

Hi

I have used PCM1802 in it’s basic application (schematic and photos of the issue under a link: https://drive.google.com/folderview?id=0B1h4rvw56X8CflJtU0Y5NFJwX2FpcWRtdmNKVUp1ZlR0TzBGU1Q1dm1ZR1FBUnhDelJFajg&usp=sharing )

It’s a transmitter powered from single mains plug power supply there are two voltages on the board +3.3V and +5V refereed to the same ground.

According to the data sheet on pin three there should be reference voltage of half of Vcc that is approx +2.5V.

Clocks are supplied externally by wireless module, currently no DATA is present (which doesn’t surprise me since Vref is not correct.

What is surprising is that on previous build (some months ago) I had the whole thing working fine, but after I passed the PCB to our subcontractor for him to fit it into an enclosure the module stopped working probably due to handling.

On photos you will see two prototypes from the same batch which I received yesterday, they were powered and voltage vas measured on pin 3, supply voltages were also measured they are +3,3V and +5V, +3.3V comes from +5V by series regulator, +5V is obtained from a series regulator as well from +7.5V mains plug supply voltage.

Why such a simple application cause such anomalies? (one picture shows negative voltage where only positive is available)

What can be done to fix it?

Best regards

  • Hi Greg,

    The ship could possibly be getting ESD damage from wherever you send it off to get fitted for an enclosure. Does the place typically build enclosures for PCBs? Are you making sure to send the PCB in an ESD protected bag?

    It is really difficult to pinpoint exactly where in the process the chip gets damaged. If the device was working prior to getting placed in the enclosure as you stated then something is happening to it when you send the board out. I would recommend talking to the contractor about his process for making the enclosure.

    When you take the board out of the enclosure do you see the same results?

    Regards,
    Mike Ulrich
  • Hi Mike
    Thank you for your answer.
    The problem lies deeper, unfortunately.
    I have contacted our CEM to produce another set of prototypes and it happened that they have some spare boards from a previous build.
    I received two new prototypes build on pcb pattern that worked and first thing that happened is that they are not working and are having the same problem as the first one, that is awkward voltage on pin no. 3 and no data present at the output (both presented under a link that I posted).

    I encourage all of you to take discussion in this topic and will add a suggestion that may bye it could help if someone could drop the internal schematic of 1802 around pin no.3