VFD aging or faulty support components?

[sanchaz12]

Hi all,

Recently I got a Sony MiniDisc deck MDS-JE520 to see how this system works. It works very well for its age (1998), but the VFD is quite dim and lit uneven. Other examples on eBay of the same model show a nice and bright VFD. I do not know much about driving VFD's in general, but what I do know is that VFD's can age and lose their ability to display bright segments over time. I cleaned the screen bezel and VFD, this took the 'haze' that was visible away. It looks crisp now but not much improvement in terms of brightness.

Now the interesting thing for me is the uneven illumination. Along every horizontal filament the segments behind the filament are noticeably darker than the segments not 'covered' by the filaments. Is this (also) a typical sign of wear/age? I checked the main capacitors and measured the voltage test points against the values provided in the service manual and everything seems fine.

Looking trough the service menu I found timers for total play and record times. These total up to about 8400 hours of usage.

Is this considered as normal wear and aging or could there be a fault in the VFD driver or some other components?

If anyone is interested in the service manual, you can find it here (see page 63-66):http://www.minidisc.org/manuals/sony_mdsje520_service.pdf

[bktemp]

VFDs show two different types of failure modes:
Either the cathode (filament) fails (its electron emitting layer), often due to a wrong (too low) filament voltage, or the phosphors on the segments are worn out.
In your case it looks like the phosphors on the segments are worn out, because the area below the filament wires is darker. Because they are closer to the filament wires, they get the highest current.

There is probably not much you can do without changing the display.

[sanchaz12]

VFDs show two different types of failure modes:
Either the cathode (filament) fails (its electron emitting layer), often due to a wrong (too low) filament voltage, or the phosphors on the segments are worn out.
In your case it looks like the phosphors on the segments are worn out, because the area below the filament wires is darker. Because they are closer to the filament wires, they get the highest current.

There is probably not much you can do without changing the display.

Thank you, that was exactly what I needed to know.
It's pretty hard finding a exact replacement, and trying to 'rejuvenate' the VFD will not work in this case I think. Better to leave it alone as it still works. Just one more question. By 'too low' filament voltage I assume you mean the voltage is too much on the negative side. Is that correct?