Patrick, RobS, Hugo:

This one has had me puzzled since we on the BBS first became aware of it. On many players, the cs4231a chip mysteriously "dies" at some point. Hijack automatically works around this, but a dead chip means no mic input, and no visuals for AUX/Tuner.

Apart from that, it's pretty harmless.

But what, exactly, has died? All software accesses to the chip return 0x80 under this condition. Which just happens to match what the datasheet says the chip should return when it is not initialized yet.

The chip has a PDOWN pin, which can be pulled low to "power down" the chip, causing it to return 0x80, until the PDOWN pin goes high again. The datasheet says that this pin can be tied to Vcc (as done in the empeg) if that functionality is not needed.

BUT.. I wonder if it *really* wants a pulse on that line to wake it up regardless? In the empeg, the chip's clock signals come from elsewhere, and don't become valid for quite some time after power-on, and may jitter for a short period there.

What if, this cs4231a is normally just working by accident, and after a while as capacitors and the like degrade slightly, things change just enough that the chip no longer comes out of reset properly after power-on + clock-on ?

What if, it merely needs a PDOWN pulse to awaken it under those conditions? If this were true, then it could save a lot of possibly unneeded repairs.

I have at least one player here with a "dead" cs4231a still onboard, and I'm thinking of modding that machine so that I can pulse that line under software control.

Or maybe I'll just try connecting it to pin 42 of the DSP, which is given a proper low reset pulse sometime after power-up. This could be all that it needs.

...



Edited by mlord (07/02/2008 04:27)