Logitech Z-10 speakers no sound

[Th3_uN1Qu3]

Got a pair of those from the guy i've fixed the 600W Spire PSU for. They power up, the display turns on, but they don't make any sound on either the USB or analog inputs. The power amps are good, hiss can be heard from the speakers, but no sound output. The touch controls are also very laggy and it sometimes just hangs up. No visible bad caps, output of both regulators is good and ripple-free (tested on scope), but it just ain't working.

It has two 12MHz crystals, one for the CPU and one for the DSP, swapped 'em around but nothing changed. If i mess around with the CPU crystal i can get chip noises out of the speakers, so the hardware is still entirely capable of making noise, it just doesn't want to come thru like it's supposed to. Owner says they just stopped suddenly. The output of the logic reg (LM217) is 5.41v while the absolute maximum rating of the CPU (Zilog Z8F4822AR020SG) is 5.5v, so it's entirely possible that it's fried. The problem is, this is a MCU with built-in flash, so i'd also need a way of getting the firmware out of this one and into the new one, providing the firmware is actually good, of course... At least, the chip supports ICSP and i have a friend which has a Bus Pirate so it's doable. I can't really find anything else that could be wrong here.

The board was an absolute bitch to remove btw. Brown glue AND silicone caulk. Someone needs to be shot.

[tom66]

Re: Logitech Z-10 speakers no sound

Probe the oscillator and make sure it's oscillating at 12 MHz. Use your new scope .
Check the RESET line on the MCU isn't holding chip in reset.

Most of these chips are code protected (write only to the chip, read only unless you decap it and disable the write protection), and while they are usually writeable after factory programming, there's rarely a need to do so as firmware updates are rare (they generally get it right first time.)

Presumably there's a data bus, possibly I2S if it's carrying audio, between the ICs. If so, check if anything is happening there.

You've got 5.4V going into the CPU? It'll be fine. Very unlikely for a CPU to simply fry. I've accidentally run a PIC12F on 12V very briefly. It got very hot and didn't run code (or it did - but all the IOs were stuck high, so I couldn't tell), but once I let it cool down I couldn't find any fault with it.

[Th3_uN1Qu3]

Re: Logitech Z-10 speakers no sound

Have checked the crystals already. I mentioned i also swapped them around to no effect. The USB/DSP chip is a Micronas UAC3556B, i'll check if audio gets thru that. As far as i see the controls are also hooked into the Micronas, so it might not be the main CPU.

I had a PIC12F675 spit out some magic smoke and still work afterwards, but this is a lot more complicated than a PIC.

Edit: The Micronas chip is definitely at fault here. Now the speakers don't boot up at all, backlight goes on and that's it. Windows comes up with "Unrecognized USB device." This issue appears to be common with these speakers and also other Logitech USB audio products with the same chip in them.

The problem is, it is not available to buy anywhere.

[tom66]

Re: Logitech Z-10 speakers no sound

Does it have an EEPROM for the USB configuration? That may have been corrupted and its UID or PID have been lost/damaged.

[Agent24]

Re: Logitech Z-10 speakers no sound

I love how everything now relies on EEPROMs which are proven to lose data after some years... guaranteed failure mechanism!

[tom66]

Re: Logitech Z-10 speakers no sound

EEPROMs do not lose data after a few years. EEPROMs can hold data for 25-50 years. They fail when the microcontroller goes nuts and writes over parts it shouldn't. The solution is page masking the EEPROM so writing is only possible on select parts but that's only available on serial flash, and that's expensive.