I saw "Demo Clock" as one of the options in the Calibration window's Aux (Output) pulldown menu. It's a 456.35Mhz signal, but I've never seen any reference to it on the Service Manual or the User Guide. Out of curiosity, is there any purpose for the "Demo Clock" signal? Is it used in the self-calibration process?
Yes, it's used in the calibration routine. It will fail the vertical on all 4 channels if the signal is bad or missing.
Any chance you'd know if a 100Mhz or 1Ghz signal is used to test for trigger sections?
I’m not sure I understand your question. Are we still talking about the calibration signals?
Yup. I had a unit with all channel's trigger failed (cannot pick up trigger signals) but it passes vertical. So I wonder if there's a 100Mhz source involved in the trigger section of the self-cal.
It’s been a long time since I’ve worked with a DSO80000, but I think it was more like 125Mhz or 150Mhz. Trigger failures seem to be a common failure mode for the big BGA custom front end part on the DSO80000’s. They typically will fail trigger hysteresis. Also depending on what failed, if it failed on channel1, it automatically fails on all the other channels. So your problem might be only with channel 1. You might start by examining the trigtestCx.txt files found in the scope/temp folder. Cx being C1, C2, etc. indicating channel 1, 2, etc. You might also find the caldebug.txt file of help to you.
Thanks a lot!!! It seems like two tests in Channel 1 and 3 failed in the trigtestCx.txt. The software also complained channel 3 trigger is bad on start (at the message bar) despite I replaced the DAC chip for that channel and replaced the AND gate chip next to it. The scope failed a whole big chain of trigger tests and CalDebug.txt says it can't even autoscale or pick up any trigger signal at all. That's why I wondered if the driving signal source for the trigger tests are dead.
I have another unit that failed trigger hysterisis (only one test over channel 3). There are 3 custom chips in the chain, starting with the attenuator hybrid, the ADC converter (screwed on heatsink) or the the FPGA (heatsink epoxied on)?
If you haven’t done so already, exit the scope app. and then move all the files from the “cal” folder to some temporary folder. Restart the scope app. It will regenerate any needed cal files using default values. Now run the cal again and see if you still have oodles of failures. I suspect, though, that channel 1 attenuator/pre-amp is bad and probably channel 3 as well. That double layer BGA is very difficult to replace even with a high grade BGA rework system. Your second unit definitely has a bad attenuator/pre-amp hybrid.
Cleared and re-run and it's the same failures. I have access to a $5k BGA rework system. Any tips on the tricky aspects of taking the attenuator hybrid from another unit and installing it?
Sorry, but I don’t recommend trying to replace it. I have no idea how Keysight does it, but even with an expensive Air-Vac system and custom nozzles, it is challenging (to say the least).
Yes, it's used in the calibration routine. It will fail the vertical on all 4 channels if the signal is bad or missing.