An update to my bricked eBay RCA doorbell situation. I acquired a 1GB microSD from Amazon, but this did not bring any different behavior. I tried several ways - FAT and FAT32, with Hik firmware or RCA firmware on the card - each time two copies of the file (original filename and digicap.dav). Followed all of the reset tips discussed recently and from the 101, No luck - I get the same solid red button, with the slight flickers documented in my previous post.
Thinking this might be stuck in a boot loop of some kind, I started googling for hikvision bootloader, thinking there has to be a way for the factory to load software on these during production. That got me down a proper rabbit hole which might have some light at the other end. I found this thread:
Hikvision - Clearing Passwords and/or Loading Firmware via TTL Serial which describes a 4-pin JST-ZH header present on Hikvision cameras and DVRs which can be used for communication to the board via TTL Serial.
I also knew (from having found and posted it here before) that there are FCC teardown photos of a Hik doorbell at
CSDB1 Wi-Fi Doorbell Camera Teardown Internal Photos APPENDIX 1 Hangzhou Ezviz Software
On page 2 of that teardown document, there is a 4-pin header with no connector on it. I figured it would be worthwhile to open the camera up and check the header for DC voltage across pins 1 and 4 (1 should be ground, 4 should be system voltage) to evaluate whether it is a candidate for TTL Serial communication as described in that thread.
I am getting 3.3V DC across pins 4 and 1 - so I am going to find a USB TTL Serial adapter to see if I can communicate to this thing and use the procedures in that thread to get it onto my network and download a firmware image via
TFTP.
Pics of camera guts!
The two brass studs in the back of the camera case (on top in this pic) are the contacts where doorbell wiring attaches. Those brass studs touch two spring contacts on the board when the halves are assembled.
So I connected a couple test leads to those spring contacts on the board so I could power it. At the other end of those green & yellow test leads is a 24V AC transformer (for lawn sprinklers - works great for powering these doorbells on the bench).
Probing for DC voltage across pins 4 (positive) and 1 (negative) to see if this 4-pin header is a candidate for serial communication
3.3 V DC system voltage. There is hope!