Sony CDP-502 VFD Display - Dark areas are slightly lit

Now to something completely different:
Not the usual "my vfd shas become dull"-question
but the contrary:
Segments that should not be lit are faintly lit.
First I thought the gatter had not enough
negative Voltage, but the effect is independent
from them. Checked voltages, they seem to be
ok. Changed caps in the power supply
for the display voltage, not the slightest effect.
Reduced filament / heater ac voltage, display
becomes darker, slightly lit segments still
visible. Some optical neutral density filter would
have had the same effect.
Whats next? Something wrong in the multiplexing?
Images can be posted later
All the best,
Salar
 
Last edited:

Salar

Member
2006-02-08 8:40 pm
Germany
Strange kind io tyring-i have some aged equipment,
where often lit segments get dim, but not
in this case
 

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Salar

Member
2006-02-08 8:40 pm
Germany
Thanks!
If it was internal leakage, wouldn´t this mean, the display is dimmed?

I have a 2.channel scope.
Tested the oscillator signal on Pin51 of IC 802, (VFD Drive) seems to be ok.
I assumed that the oscillator signal and the pulse signal for the grids are
fixed in a ratio, but triggering the scope to the oscillator signal made the grid
pulse wander - I guess normal?

Then I connected the pulse signal for grid6 and for grid1 to the scope.
Pin 5 and Pin 35 on the schematic, they are connected to Q806 and Q801.
6G is ahead one pulse width, I assume they are meant not to pulse the same moment, but with an offset?
All the best,
Salar
 

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Salar

Member
2006-02-08 8:40 pm
Germany
Sorry for insisting, but would this not mean, that all dark segments would be lit the same?

I.e. the photo in post #3:
Underneath "DISC" all the segments for displaying the track number that should be dark are lit the same.
But on the right, where in the numbers 1 to 20 are displayed, 19 is lit more than the rest...