So this Cymatic LP-16 16-channel backing track player came in the other week, from a loyal and "repeat" customer, with the description of "turns on but doesn't output any audio". Additionally, it had possibly been tested also with an AC(!!!) plug-pack. Either way, by the time it got into my hands, it was completely dead.
As the added label reads, this serves two moderate-sized metal bands from the national scene, namely Mad Hatter's Den, as well as Dreamtale. Sadly apparently discontinued nowadays, but still fetching 3-400e prices on Reverb.com, it's a compact answer to a relatively niche requirement. But we're here to have a look-see under the petticoats now, aren't we?
Ok, fine, no more teasing, this time we really DO have a gut-shot...
Not a whole lot to speak of, really - pretty much an all-in-one solution for the purpose.
The brains of the operation is an Archwave DM1100F-CQL - all i managed to find was this brochure. Next to it is an EtronTech EM639165 128Mbit / 16Mbyte SDRAM chip, as well as a cFeon EN29LV320BB 32Mbit / 4Mbyte flash memory for the firmware. Interestingly enough though - even if it's blurry in the photo above - there's an "Archwave Live-Player 16" label as part of the white silkscreen, right next to the flash chip. Cymatic might've just plopped an enclosure around this whole ready-made thing, perhaps?
The output side of things is quite straightforward too - a whole bunch of AKM AK4430ET DACs, followed by a JRC/Nisshinbo NJM4580 for each pair of channels. The DACs are pretty nifty, apparently containing a charge-pump that creates a negative voltage for the output buffer, allowing for the analog output to be referenced to 0V, as opposed to half of the supply rail of the chip (2.5V for a 5V supply, or 1.65V for a 3.3V supply).
Before moving on to the power circuitry, a lone AKM AK5358A stereo ADC handles the "stereo line in" 3.5mm jack input. But with that out of the way...
After the power switch on the back, the 12V input splits off in two directions. One is into a Semtech SC2440 dual buck regulator, which provides (if memory serves) the 5V and 3.3V supplies for the digital circuitry, and the LD1117 nearby further regulates one of those to 1.8V for the processor core. At least that's my best guess / assumption - i know i probed the outputs of the buck converter as part of the troubleshooting, but i failed to take notes. That's anyway not where the problem was, but let's not get too far ahead of ourselves. The other destination for the 12V input is here...
Side-note: One more AK4430ET is shoehorned in this part of the board, in charge of the headphone output on the front of the unit.
You'll have to forgive me for neglecting to take a "before" photo, so you'll have to settle for this "in progress" one - pictured is an Alpha Omega Semiconductors AOZ1051PI buck converter. This, in conjunction with a coupled inductor(!), takes the 12V DC input, and puts out +/-5V for powering all the opamps. As luck(?) would have it, "of course" this was why the whole thing wouldn't even power up at all, when i got my hands on it - dead-short to ground on the DC input...
Ok, so i managed to rip off a couple of pads when removing the three electrolytics hanging off the 12V rail - sue me... Regardless, after that yielded no new data, by sheer virtue of the simpler and chunkier package, i chose to remove this latter chip first, rather than the SC2440, as part of the "divide and conquer" routine - a very effective method for rooting out this sort of "it could be anywhere" type issues. And wouldn't you know it - no more short to ground!.. Oddly enough, just as in some other cases that come to mind, not a lick of solder on the metallic belly-pad of the chip (meant to solder onto a ground plane on the PCB, for extra heatsinking). Coincidence?
After having removed said chip, the (digital side of the) unit started right up, product logo on the display until it finished booting, then the channel activity display. All good there, fortunately
"Of course" i couldn't be bothered to wait a month and/or deal with customs stuff & extra taxes, which is what ordering new chips straight from China would've involved, i spent some time and fortunately managed to find some (in stock, no less) from a Greek company, dealing with spare parts for white goods. Go figure... But hey, in stock, decent price, decent shipping costs, no customs - i ain't complaining!
And sure enough, a couple weeks later, when i finally got around to sticking the new chip in (this time, also actually soldering it to the ground plane, as intended by the manufacturer), we got a live +/-5V output for the opamps. A quick test of the first two channels off the USB pendrive supplied with the unit yielded a metronome on channel 1, and some synth stuff on channel 2. Score another one brought back from the dead!..
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