TDS1012C-SC has a difficult problem, please help（Resolved）

[lern01]

A TDS1012C-SC, which was working normally, was placed for a period of time. When it was turned on for the first time, sometimes three green lights were stuck. Generally, CH1 CH2 diagnosis failed, and the error log reported CH2 diagnosis failure. After shutting down and turning on the machine again, the self-test passed, but it occasionally crashed after entering the system, but generally everything was normal. Sometimes the USB self-test failed. Re-soldering the EPROM and carefully cleaning the entire motherboard with board washing water, cold machine startup was normal, but CH2 diagnosis failed occasionally. Suspecting that some part had poor contact, I put the whole motherboard on the heating table and used a hot air gun to solder some ICs. After starting the machine, the CH2 diagnosis always fails. I used other oscilloscope probes to connect to the calibration waveform output port of the machine, The output frequency is 3KHz, and other parameters are normal.
I don’t understand the startup and self-test process, and now I don’t know how to check it. I urgently need the help of all the experts, thank you in advance! !

[lern01]

The power supply motherboard is normal.

[lern01]

I have another question for you, where is the factory calibration data stored in the EPROM? I used a new chip to burn the firmware of the oscilloscope, installed it and turned it on, and it showed that the factory calibration failed.

[lern01]

Channel diagnostics failed, what are the related components, friends.

[factory]

The 3kHz cal output signal indicates a faulty mainboard, it could possibly be one of the surface mount capacitor arrays, I had the same problem with a TDS2014 causing channels 3 & 4 to fail, this thread helped with my repair; https://www.eevblog.com/forum/repair/tektronix-tds2024-oscilloscope-repair-log

David

[lern01]

Thank you very much. After referring to the link you provided and checking repeatedly, I finally fixed the motherboard. I also understood the correlation between the frequency change of the self-calibration source and the detection of related circuits during the self-check process of some startups. Starting from the frequency of 5KHz, when the self-check process reaches the USB control chip U900, the frequency rises to about 7.56KHz, and then drops to 5KHz---4KHz--3KHz respectively. At 3KHz, the self-check reaches the acquisition and amplification chips U301 and U400, and then drops to 2KHz---1.8KHz---1.4KHz---1.2KHz---1KHz.
My motherboard was checked and found that U301 had a cold solder joint. After adding soldering, the first startup card had three green lights. At this time, the frequency was 7.56KHz. After restarting, it can enter the system normally and work normally. After careful inspection again, it was found that the C901 pin next to the crystal oscillator of U900 was not in good contact (it also verified that the first startup would get three green lights. I previously thought that the three green lights must be a problem with the firmware.), after adding soldering, it started normally and all problems were solved.
Please tell me whether the above is correct. In addition, please tell me which parts of the other frequency bands are self-checked. Thank you in advance!

[factory]

Well I wasn't aware of the other cal output frequencies during startup.
Also interesting to see pictures of the board from your newer C version, seems Tek stopped using those quad ceramic capacitor arrays, that seem to occasionally fail short circuit in the older models from the TDS1000 & 2000 range.

David