Now I need some references to make sure that calibration is not necessary. Finally I ended up with perfectly working Fluke 8840A for under $100. Thanks to that single LED lights up only one label text. That allowed me to perform an autotest on 8840A that succeeded without any error Final version 2 got an additional PCB with “text mask” and blak 3d printed “light mask”. In version 1 I accidentally mirrored one 4 digit LED and half of the transistor but after many wire fixes it worked. DC powers supply is generated by rectifier + capacitor powered from cathode heating voltage (~5V AC). I used that fact in my advantage and with 1:2 resistor dividers NMOSFETs act as high and low switches for LEDs. High signal (30V) is used to drive both digit selector and segments. The decision was made to build my own LED display! Requirements: -Only discrete components allowed - not ICs -Mimic the look of the original VFD display -Low cost (as always) Original driver outputs 0-30V signals that drive VFD anodes. In addition I didn't like the way they changed display layout. Unfortunately there was no schematic or gerber files. broken After short research I have found Chinese project with LED replacement for VFD.
No damaged capacitor, no visible short circuits, all ICs in place 2) TrueRMS & IEEE488 addons in great condition 3) Testpoints voltage in spec 4) VFD display. In order to remove the display and keypad I had to remove every PCB and cable. disassembly time! First impression was great but after some time I realised that the construction of 8840A is a nightmare. Internal condition was unknown at the time. Hello everyone! That will be my first topic here Few months ago I bought a broken Fluke 8840A in good (visual) condition for ~$50.
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