I opened it up, and I could see ~8.5V volts powering the opamps but no voltage at any of the digital parts, where I would expect 3.3V.
Way back in July 2017 a commenter asked if I knew what the part number for U14 was, likely to be a buck-converter, and that they suspected it was a Texas Instruments TPS62056. The package, function and chips marking all looked like a perfect match so I ordered a few this week to see if it was right.
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| Before |
Desoldering was straight-forward, I used hot air and kapton for protecting parts I didn't want to overheat.
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| During |
The new chip has near identical markings to the old one. Re-soldering was a little harder as there isn't a lot of space, I ended up removing C73 temporarily to get better access. The bridged pins are fine, all those pins are connected together at the PCB.
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| After |
Everything works again with the new chip. Thanks to Shane Bussiere for doing the research and sharing the part number, sorry I didn't help out.
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| All working again. |
Looking at the TPS62056 datasheet, I can guess why this failed. The buck converter chip has a maximum Vin of 10V, the Echo Shifter runs the power jack through a series Schottky diode for polarity protection and then to the TPS. If you use a 9V power supply the chip gets around 8.6V, which is fine, but using a 12V power supply or higher will probably kill it. I couldn't find a compatible chip from TI with the same footprint and pinout but higher maximum input voltage, let me know if one exists.
I would really like to modify this to add a modulation rate control. I hunted around for modulation signals and unfortunately there doesn't seem to be a LFO onboard, it looks like the modulation is done in software in the ADAU1701 DSP. A modulated square wave is run out of the first audio DAC on pin 46.
While I had this open I desoldered the 24AA128 serial EEPROM and dumped the contents, it can be downloaded here. Afaik the ADAU1701 instruction set is not publicly documented, so I don't think the firmware can be easily modified.
