I was experimenting with out of spec resolution/refresh rates with an HDMI-to-component adapter going into a homebrew BKM-129X. There were sync issues, as expected. After one specific setting (I’m not sure which), the display cut out and has not returned. The overload light never went on. The controls still appear to work because the indicator LEDs actuate as expected, but it is difficult to be certain with no OSD feedback.
My first thought was that a protection circuit tripped, but according to the service manual those should all clear on power cycle. My next thought was that some non-voltaile memory got put into a bad state where maybe the OSD free running frequency is out of spec and immediately trips a protection circuit on power on.
I have tried feeding valid inputs to both the 129X YPbPr (with the composite forwarded to the sync) and 127W composite input.
There is a neon bulb that sits across the flyback transformer, that is labeled IKDET (cathode current detection, I believe). This flashes twice on power on and I can hear an initial sparkle sound, but electrostatic charge does not build up on the display because the high voltage quickly cuts out.
I have tried unseating all cables, taking apart the M boards, removing the MA CR2025 battery, discharging the CR2025 buffer capacitor down to 0.1 V, then reassembling everything. This did not change the behavior.
I have tried to factory reset blind, but so far I have either failed or succeeded and the factory reset did not fix the issue. Here is the sequence I follow:
1. POWER (on). Wait 10 seconds.
2. MENU. Wait 2 seconds.
3. DOWN x4 (highlight SYSTEM CONFIG...).
4. ENTER. Wait 2 seconds.
5. UP x1.
6. DOWN x7 (highlight MAINTENANCE...)
7. ENTER
8. Enter password (0000, 1111, or 9999).
9. ENT.
10. DOWN x5 (highlight restore factory config).
11. ENTER.
12 DOWN.
13. ENTER.
I am not convinced that this is exactly the right sequence.
I have not been able to find a copy of BZI-500 to diagnose and potentially fix this issue through the serial interface. If anyone has a copy they are willing to share, please let me know.
If anyone has experience with an issue like this, please let me know.
Edit: Savon Pat helped me out. The horizontal output transistor (HOT, Q2508, 2SC5450) is blown, along with the HOT dump (D2511, DD54SCLS) and +B regulator dump (D2506, ERD38-06). The +B regulator is still in tact. I think this is an indicator that the FBT is still in tact. Sourcing replacements requires many hours with spreadsheets.