How was the 3S and 2S connected to the ESC? Sounds like the ground for the servo wasn't at the same voltage as the ground for the ESC, effectively creating a short through the receiver.

Here's hoping. I emailed holmes and briefly let them know what happened. Hopefully I will hear something positive back from them, but I'm not expecting much aside from a replacement servo. Probably going to have to come out of pocket on the rx and esc I'd imagine, which really stinks. Few hundred more dollars that I'd rather not have to spend :(

Standard serial connection for batteries, as pictured.

If I'm not mistaken, the spc port on the rx (which was receiving 5s voltage direct from the esc battery terminals) is internally separate from the ch 1-4 ports, so I wouldn't expect any issues there, but what do I know, lol. You might be on to something.

If the +ve terminal of the 2S was wired to the -ve terminal of the 3S battery in that serial harness, then the effective voltage sent to the -ve terminal of the servo via the balance connector was the voltage of the 2S battery. The servo has a ground wire connected to the receiver (I doubt it's isolated from the ground wire of the power input), which is connected to the ground wire of the ESC BEC output. That'll definitely create a short (Edit: this would also explain why all the charring/melting you've observed is on the ground wires). It's irrelevant whether you had something connected to the SPC port in this instance.

If you had the +ve terminal of the 3S wired to the -ve terminal of the 2S battery, there shouldn't have been a problem, as everything would have had a universal ground reference point.

Fml. I totally see it now. Thanks gigaplex!! Should save me from cooking the replacements I'm going to have to order.

Aha, so for the servo you did drain the power from the 2nd battery counted from the ground, so the ground of the 2nd battery has the voltage of the 1st battery and finally making a shortcut.

I have been making these adapters for years, drawing 2S power from any balance port up to 6S, here's a close up of how I do it:
FS: High Voltage Servo Harness to 2S Balance Port <Updated 5-JAN-2015> - For Sale: Parts, Miscellany - veteran members only @ URC Forums

https://farm9.staticflickr.com/8797/...b4f1c60e_z.jpg

Technically you don't even need a JST-XH adapter so long as you know which female pin to plug into, which is always the 3rd over from true positive, use a voltmeter to double check you draw 8.4V then mark the balance wire with a sharpie, etc...

I always had a knack for turning a negative into a positive.

Ba dum dum

Just did a little testing, and although I will need to replace the wires, the servo still works. ESC and RX are toasted though. Neither will power up whatsoever. Already ordered a Hobbywing Max8 and another Proton 4 RX. Hoping for better luck during round 2.

Probably going to pick up a voltage regulator which I'll feed full 5s voltage, and set the output to 14v to feed the servo. I was planning on doing this anyway eventually just so the servo would always have the full 14v, but if it prevents the magic smoke from accidentally escaping again it'll be worth the effort. Just need to decide on which regulator to go with at this point because I'm eyeballing a couple of them.

(Sorry, deleted)

You want to always keep "true negative" + signal wire through the ESC and servo... use the red wire from servo to desired "positive voltage" from the balance port.

If you use the negative lead from the battery, then you can get a "dirty signal" and will more than likely run into random glitching on power. Use post#22 for your wiring reference.

Ya got me, lol. After I posted I realized that I would still need to be mindful of where in the series the 3s pack was, because even if I prevented a short by going to the esc negative terminal for ground, if the 2s and 3s packs were to be installed backwards I would end up sending the full 5s to the servo.

I'll just have to pay close attention if I go direct to battery again. Still leaning toward a dc-dc voltage regulator though, but that's for another thread. Lol