Agilent E3641A repair

[feedback.loop]

This power supply had non-functioning front panel (display, keypad and encoder). It turned out that three chips were dead in the front panel module: Intel 80C51 micro-controller, HV518PJ VFD driver and 74HC02 quad NOR gate. Fixing this took quite a bit of SMD and through-hole rework, and quite a bit of luck, especially finding the firmware for the micro-controller.

https://youtu.be/E3F59nj6Fho

Replacement parts on DigiKey:
AT89S51: https://www.digikey.com/product-detail/en/AT89S51-24JU/AT89S51-24JU-ND/1118890
HV518PG https://www.digikey.com/product-detail/en/HV518PJ-G/HV518PJ-G-ND/4902550

Firmware 34401-88804 rev01: http://www.ko4bb.com/getsimple/index.php?id=download&file=HP_Agilent/Agilent_34401A_E3646A_Display_board_MCU_firmware_dump_EPROM_34401-88804_RE-34401-88804.zip

34401A multimeter service guide with display and keyboard schematic : http://literature.cdn.keysight.com/litweb/pdf/34401-90013.pdf

[HighVoltage]

I have repaired a few of these power supplies in the past but compared to the problems you ran in to, my repairs were trivial.
Thanks for another great repair video.

[Armadillo]

Great repair video with multiple faulty devices and thermal imaging camera and fluke 97 throw in.
Wonder what causes the string of failed devices including the CPU. Run over by a train or strike by lightning?
Lucky firmware and schematic are at hand. 

[glarsson]

Wonder what causes the string of failed devices including the CPU.

The HV518 probably failed and shorted Vpp (up to 90V) to Vdd (5V). Vpp (pin 1) and Vdd (pin 44) are next to each other ... 

[bitseeker]

Great job on another repair. This one was more extensive than HP supplies I've worked on. Always enjoyable to learn new things about fixing them.