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Old 09-06-2018, 03:53 AM   #48
Francescocy
I've made a post!
 
Drives: 2007 Yaris D-4D 4-door hatch
Join Date: Sep 2018
Location: Florence, IT
Posts: 1
Got the same issue, tried a few things

I had the same issue on my 2007 Yaris (got it used on the cheap as my first car and there are some minor issues with it) the ICs in my unit are clearly burnt, they seem to be 6 BJTs or MOSFETs in parallel each with a 22 Ohm resistor to balance load. This part of the circuit seems to provide power to the cathode filaments in the fluorescent display and the parallel design makes it so that if one of the ICs gives up the ghost, the other 5 will follow soon after, since they have to split the load across 5 instead of 6. The clock is not an LCD, but rather a Vacuum Fluorescent Display (VFD), I could't find any information on this specific panel, but in general a voltage of about 2-3V is used on the cathode filaments; I first tried to replace the 6 ICs with a single powerful MOSFET, this kinda worked, but at 12V source to drain and you don't want that going to the filaments! Next step was to cut out the MOSFET and use a buck converter to provide steady 3V DC power. The screen turnes on, but the filament glows dimply orange and the numbers are dimmer than they should; probing the pins with the display on reveals that the anodes are only getting about 2V, if I understand this correctly, they should have a much higher voltage (10-30V), maybe some other part of the circuit is faulty? Another possibility is that the original power circuitry provided a negative bias voltage to the cathode filament respective to the anodes hence why my approach works, but dimly. At this point this is just speculation; I could disassemble the main VFD and probe that, but I'm too afraid of ruining it since I'd like to still be able to see how fast I'm going at the end of all this :)

If any of you has suggestions or can point out things I did wrong, I would be grateful!
Attached Images
File Type: png Schermata 2018-08-27 alle 11.00.20.png (506.7 KB, 372 views)
File Type: jpg vfd yaris.jpg (394.6 KB, 369 views)
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