The unit powered up but had nothing on the display. It turned out that the VFD was shattered. A replacement was fitted. Basic load testing was performed.
...
https://www.youtube.com/watch?v=Sj8PMUaCsKg
Another lucky find from eBay. The unit was listed for parts or repair with the description that it quickly flashes an error message. Upon powering up there was a burning smell. The culprit was found to be a tantalum capacitor, which was promptly replaced.
...
https://www.youtube.com/watch?v=FFtiUsgzk2E
The unit was taken apart and examined. 3.3V power rail was found to be low, and tree chips running hot: LD33 voltage regulator, 74HC245 buffer and Xilinx XC9536XL programmable logic chip. The Xilinx CPLD chip was found to be loading the 3.3V rail. The chip is programmable, and, most probably, the program is not available and not readable from such chip (even if a working unit was available). Therefore the unit was deemed beyond economical repair.
...
https://www.youtube.com/watch?v=ja6QE_O-sG8
This is my build of the KX reference designed by xdevs.com. Overall the project went very well. The reference worked on the first attempt. The output voltage was monitored for about 46 hours using HP 34401A and Datron 1071. The graphs look great overall, but with some small unexplained glitches.
KX reference project page: https://xdevs.com/article/kx-ref/
LTZ1000 data sheet: http://www.linear.com/product/LTZ1000
Discussion: https://www.eevblog.com/forum/metrology/kx-reference/
...
https://www.youtube.com/watch?v=mgHhGDRKZjo
This RF power meter was picked up on eBay as non-working, and indeed it did not start up. The problem seemed to be with the keypad on the front panel. Unfortunately, the exact cause was not found. The keypad just started working after disassembly, which doesn't give much confidence that the problem won't come back one day. Also the lithium battery was found to be completely dead, and was replaced by an equivalent FDK one from DigiKey.
FDK 3V lithium battery: https://www.digikey.com/short/pz429fjt
...
https://www.youtube.com/watch?v=KV6pEl5kAUw
Repair of a vintage Fluke 341A voltage calibrator, which was built in late 1970s. Very stable piece of precision equipment. Still within specs.
Manual with schematics: http://assets.fluke.com/manuals/341A_343imeng0000.pdf
Discussion: http://www.eevblog.com/forum/metrology/fluke-341a-dc-voltage-calibrator/
...
https://www.youtube.com/watch?v=mxz3-fGs1Lk
This Mackie Thump speaker has a damaged woofer with a shorted voice coil. The symptom was demonstrated, and the diagnosis was confirmed by measuring the voice coil both at DC and at 1KHz. A good woofer was also measured (not the same model) to show the difference.
Previous Mackie Thump TH-12A repair: https://youtu.be/5zkEzjyKNjg
...
https://www.youtube.com/watch?v=KyfoScucfcQ
Another lucky find from eBay. This Agilent E4400B generator has some problem with fractional PLL. It seems to be unstable, so the instrument periodically shows error 508 "Frac-N Loop Unlocked". The synthesizer was inspected, the block diagram was discussed and the blocks were located on the board. Unfortunately, there was no definite solution to the problem due to lack of appropriate equipment at the moment. If there will be any developments, another video might follow.
Calibration guide: http://literature.cdn.keysight.com/litweb/pdf/E4400-90325.pdf
Document with the block diagram. It is for a different model, which seems to use the same synthesizer:
http://cp.literature.agilent.com/litweb/pdf/E4400-90014.pdf
Discussion: http://www.eevblog.com/forum/testgear/a-look-inside-of-an-agilent-e4400b-signal-generator/
...
https://www.youtube.com/watch?v=JPEmbvUx0JQ
DR600 Li-ion battery pack was taken apart and a battery management system (BMS) was added to it. This was not very easy, but not too bad either having equipment, materials and experience with this sort of thing. If you are going to do something like this, please be very careful. Don't try this if you don't know what you are doing.
Li-ion pack for Roland V-Accordion investigation: https://youtu.be/1obxLWO8zo0
...
https://www.youtube.com/watch?v=a600wjWiT0g