Neonkev #5 - Agilent/Keysight U8903A Audio Analyzer teardown and repair attempt

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Hi all, thanks for tuning into another episode of neon kev, where we tear down and attempt to repair an Agilent/Keysight U8903A audio analyzer. We will examine the instrument at a hardware level and attempt to replace key components (AD7763, ADSP-21369) in order to resolve an error symptom which occurs during certain measurements. Ultimately, we are not able to complete the repair without further resources. If we are able to acquire the additional resources needed to continue the repair attempt, a follow up video will be produced.

[@mikeselectricstuff]

Would be surprising if there wasn't a checksum on the DSP flash data, which would produce an error message rather than show bad readings.
Would also be unusual for it to not be possible for the host to update DSP firmware - preprogramming may just be a bootloader to allow further programming.

[@neonkev7866]

Hey Mike. It is strange that there are no errors shown if the DSP program is corrupted.
I did reinstall the firmware update package several times too. It has several parts and all of them installed and verified successfully.
I'm not sure if the flash on the ADSP-21369s is updated during this process. The way the flash ICs for each DSP are marked with a custom "U8903-X" part # leads me to believe they are preprogrammed.
I don't think this issue could be the DRAM for the DSP going bad? Each DSP has an external 128Mb DRAM as well.
Besides getting flash from a working unit, the only other routes I can think of are to replace the other DSP processors (the other ADSP-21369 and the one other ADSP-BF535P also on the board).
Keysight condemned the unit outright. Because it is declaired "obsolite" the motherboard is not even available for replacement (they would never do component level repair/diagnostic/reprogramming in the first place).

[@xDevscom_EE]

Could it be some via crack or trace damage on digital bus to DSP? Also did you try to replace SDRAM? Sometimes DRAM chips also die, had few repairs like that.. It's bit funny how UI programmer who designed front panel interface didn't worry much about putting support and processing for gigavolts and teravolts. Totally reasonable signal levels, no worries :D

[@neonkev7866]

Hey Ilya. I was thinking about DRAM recently as well. A friend suggested that I should try heating/cooling DRAM chip while running, this might show change and help isolate part. I don't think unit has any ram test built in software.
I will order some new ram chips anyways because they are cheap. We will see!
Yes, it is strange how the instrument does not detect anything wrong with crazy readings! Self test is also useless on this model. It just checks few basic things on ADC/range switching and always passes...