VFD Multiple Segments on when should be off -

[jjoko]

Got a Pioneer Disc Player where its VFD has segments glowing where and when it shouldn't
Dont know much about VFD's ..been looking for answers but so far stumped!

Any help with this would be most appreciated.

 - Segments do come on as they should when a feature button-switch is selected..but its hard to make out.


One leg of the The Filament/Heater Supply Voltage is reading -24Volts DC to ground and the other fluctuating from between -9 and -14Volts DC  to ground..
The Display Driver Chip is receiving -34Volts DC

Also the Disc Player when on power standby should mean the display is completely off...however there is one segment which is still on!..see picture


.the circuit has the heater/filament voltage on all the time as is the supply to the Display Driver Chip - as long as there is mains power.

[floobydust]

Need a model number to find the schematic.
The VFD bias voltage is likely wrong, it needs a negative grid-cathode (filament) voltage to turn off a segment. It might be a problem with driver IC or open electrolytic capacitor for the bias supply.

edit: note an open connection to a digit grid will cause the entire digit to be OFF - this is counterintuitive but I find the VFD grid actually acts like a screen (acceleration) grid.

[jjoko]

Hello Flooby

Here is what I can get from a Service Manual ....the Powersupply Circuit feeds the display circuit on CN315.

[YetAnotherTechie]

post ac and dc volt readings:
across c216
across d207
verify that the voltages at C315 exist *at the pins* of vfd control chip and vfd. There are several conectors in that path that may be bad.

[jjoko]

post ac and dc volt readings:
across c216
across d207
verify that the voltages at C315 exist *at the pins* of vfd control chip and vfd. There are several conectors in that path that may be bad.

Thanks for posting YAT  - Ive found that the -30Volt VFdisplay Voltage is low at CN315 (pin 2 -24V instead of -30v) ..no other reason other than connector..
Going to solder directly the ribbon to the PSU Circuit board - removing CN315.
Will then retry..and measure Voltages again if needed...will post again tomorrow.

 todays Voltage testing:
(-30V) VFDisplay Voltage at junction of D207 and R201 was -33.5VDC
(-30V) VFDisplay Voltage at CN315, at CN801, at CN805 was all around -24VDC

Heater-/Filament Voltage at CN315, at CN801, at CN805  was all around -29VDC
Heater+/Filament Voltage  at CN315, at CN801, and at CN808 was all around -26.5VDC

[jjoko]

Went Nuts and soldered the Ribbon at CN315 direct to the board just now - Success !

Thanks for the advice - Now its usable again !