Hi guys!
Been repairing this receiver for a while. The one and only problem so far is DSP. When turned ON (all the logos show well + self check related to DSP is ALL OK) no sound at the outputs, only in Direct mode. Tried reflowing the IC. After that found crystal oscillator XL41 not providing 20MHz, only 100-300Hz ripple.
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Took off and without it DSP does not pass self check and logos are not working. Placed 25MHz crystal as had by the hand, this freq is OK, but of course DSP still no sound. Today bought exactly 20MHz PTH, soldered and the freq is 2..4kHz of nice sine wave on the one pin and not so fine on the other. Tried 3 of the crystals.
Any ideas of what is going on there? Bad DSP and that's it as No Replacement Part Available according to the SM? Why only for 20 MHz crystal?
Been repairing this receiver for a while. The one and only problem so far is DSP. When turned ON (all the logos show well + self check related to DSP is ALL OK) no sound at the outputs, only in Direct mode. Tried reflowing the IC. After that found crystal oscillator XL41 not providing 20MHz, only 100-300Hz ripple.
Imgur: The magic of the Internet
Took off and without it DSP does not pass self check and logos are not working. Placed 25MHz crystal as had by the hand, this freq is OK, but of course DSP still no sound. Today bought exactly 20MHz PTH, soldered and the freq is 2..4kHz of nice sine wave on the one pin and not so fine on the other. Tried 3 of the crystals.
Any ideas of what is going on there? Bad DSP and that's it as No Replacement Part Available according to the SM? Why only for 20 MHz crystal?
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If it stops working once you take off the xtal, isn't that a sign that the oscillator is in fact working fine? Your measurement may just not reflect that - you are not using a DSO by any chance? DSOs have a habit of reducing their sample clock as you increase the time base, which can give some nasty aliasing. To accurately capture a 20 MHz sine, we'd want something like 60-100 MHz worth of fs.
Even in the unlikely event that the oscillator driver should be dead, you could still feed an external 20 MHz oscillator of a suitable amplitude into OSCIN/OSCVSS and hopefully the rest would work fine.
The reference clock is just the first step anyway. No doubt a PLL is being used to generate the actual converter clocks. Look out for shorted SMD ceramic caps and other such fun stuff.
As old as the unit is, it shouldn't be afflicted by the TI DSP issues found on newer models. If the DSP is a BGA chip it may still appreciate a reflow though.
Even in the unlikely event that the oscillator driver should be dead, you could still feed an external 20 MHz oscillator of a suitable amplitude into OSCIN/OSCVSS and hopefully the rest would work fine.
The reference clock is just the first step anyway. No doubt a PLL is being used to generate the actual converter clocks. Look out for shorted SMD ceramic caps and other such fun stuff.
As old as the unit is, it shouldn't be afflicted by the TI DSP issues found on newer models. If the DSP is a BGA chip it may still appreciate a reflow though.
Thanks for reply!
I'm using scope of 100MHz and do not have any problems seeing all others crystals signals on the board. Even with my 25MHz crystal in place of XL41 everything was allright! Only original and my new ones of 20MHz show nonsense (old - only ripple, new - nice sine but freq is ridiculous). Will double check load caps, but nothing short for sure here.