Duane, thanks for sending the schematics and giving me the teardown info so quickly!
(diamaunt, thanks for the info you provided, also.)
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Upon comparing my actual motherboard to the CAD drawings you provided, my board appears to be somewhat different.
• If you look at P.9 of the docs you provided, that board has one tab (4.0mm x 4.17mm) that protrudes out from the right side of the board. My board has two such tabs at that end.
• P.9 also shows a 20-pin connector (for ribbon cable?) in the lower right corner of the board. My board has no connector in that location.
• However, my board has a 26-pin connector (for the ribbon cable) at the opposite end of the board (the end at the left side of P.9). No such connector is shown on your drawings.
So I think my board does not correspond to your drawings.
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The schematics do not clearly indicate the physical location of the various components ... i.e. whether a given part is on the motherboard or on the rear board (with the connectors).
When I first got it apart and looked at the construction, I was hoping that the power circuitry was located on the rear board, which would be easier to access. However I find at least some of the regulators (U300, U301...) on the motherboard.
If "chumbilical" actually refers to the ribbon cable, then it appears that the protection circuitry is also on the motherboard. (I don't seem to find a schematic of that small rear board.)
I was hoping that perhaps the fuse in the RAW PWR circuit had opened (or a diode or choke had gone open). So I tried to power the device using a fresh 9V battery in the battery clip. Upon pushing the power button, still nothing. So, unfortunately, I don't think the problem is in the protection circuitry.
Interestingly, if I connect 9V to the battery clip (through a DMM) I see 0.18 A of current. I see that reading as soon as I connect the battery, and it does not change if I push the CC's power button.
At a quick glance over all the schematics, it appears DC IN PROTECTED goes only to the +5v regulator. However the schematic says "BATTERY signal goes to TS/codec chip..." so that 180mA could be going one of two places.
To narrow it down, I applied the same 9V battery to the rear panel coaxial power connector. Again I see 180mA. So I think that rules out the TS/codec chip.
My conclusion is that both sides of the protection circuitry are OK, the DC is getting to the +5v regulator and to a few other places, as shown on the various pages of schematics.
And something, somewhere, is drawing 180mA. Would a CC normally draw that much in "resting" state, with no backlight, no display, no audio?
To do any further analysis, I'd have to start disassembling boards at the very least. However, I don't have a stereo microscope and micro soldering tools that I'd need to work on these boards. So I'm not sure there is any practical benefit in my going any further.
I'd appreciate your feedback on what I've done up to this point, and any other suggestions you might care to make.
Thanks again for your help!