Dim display Panasonic stereo

[Ken G.]

This is a typical 5 disk 2 tape deck bookshelf Panasonic stereo with a
multi color florescent type display .
It is about 1/4 of normal brightness . Any way to fix this ?
Is it the display tube or capacitors .

 

[Meat Plow]

This is a typical 5 disk 2 tape deck bookshelf Panasonic stereo with a
multi color florescent type display .
It is about 1/4 of normal brightness . Any way to fix this ?
Is it the display tube or capacitors .

Another monster created by reading in s.e.r that changing caps fixes
everything.

 

[N Cook]

This is a typical 5 disk 2 tape deck bookshelf Panasonic stereo with a
multi color florescent type display .
It is about 1/4 of normal brightness . Any way to fix this ?
Is it the display tube or capacitors .

These displays are amazingly reliable compared to zebra strip failings etc
of LCD displays. I've never seen a failed or corrupted one , even
in a unit thrown out of a window onto concrete, the display, the only bit
still worked.
I would check for any -30V or so rail failings then disconnect the 3V or so
AC feed to the cross wires and try from another source in case leakage in
the original transformer was producing a problem

 

[Ken G.]

Thanks . i have replaced capacitors in VCRs before for dim display . I
have seen only a few of these stereos this way and if you ever worked on
one you know how difficult it is to get apart & under the boards .
I will note the your ideas and collect more before i dig in .
Thanks !

 

[JR North]

Just like every electrical problem in a car has got to be a 'fuse'.
JR

 

[[email protected]]

Thanks . i have replaced capacitors in VCRs before for dim display . I
have seen only a few of these stereos this way and if you ever worked on
one you know how difficult it is to get apart & under the boards .
I will note the your ideas and collect more before i dig in .
Thanks !

These VFDs typically want +30v for the anode, and filament v depends
on the display, but is very low. They can dim after 20 or more years
of use, if its that old I'd suggest a slight filament boost. One way
is to put a turn or 2 onto the mains transformer secondary and connect
this in series with the filament feed.

VFDs have a huge margin on filament power.

Another poss is to clean up the optical filter, or replace it with a
lighter one, or even leave it out. With these tricks you should get
another century out of it, VFDs just dont die.


NT

 

[Ken G.]

Well thanks again . I dont think this is more than 10 years old . I just
never bothered trying to fix a dim one like this .

 

[Gary Tait]

[email protected] wrote in @z28g2000prd.googlegroups.com:

These VFDs typically want +30v for the anode,

IME, the filments are grounded, with the segments pulled to ground ot -30
as needed.

and filament v depends
on the display, but is very low. They can dim after 20 or more years
of use, if its that old I'd suggest a slight filament boost. One way
is to put a turn or 2 onto the mains transformer secondary and connect
this in series with the filament feed.

If the trasnformer is open framed.

 

[[email protected]]

[email protected] wrote in @z28g2000prd.googlegroups.com:

IME, the filments are grounded, with the segments pulled to ground ot -30
as needed.

VFDs are matrixed thermionic valves, and you cant run what is a valve
mechanism like that. Which bit is grounded doesnt matter, but always
the anode is positive wrt filament to light it. At only 30v anode the
grids should be positive to get light output.

In practical apps the segments are matrix driven, lit one after
another, so you need to scope it to see whats going on.

If the trasnformer is open framed.

If its not one can typically tweak the filament supply cct to get a
bit more V.

But I see this is only 10 yrs old. It may be the display is being
overdriven, which causes them to dim prematurely. If so, removing the
usual dark filter and replacing with something lighter, or possibly no
filter, would enable reduced anode current.


NT

 

[Ken G.]

I guess its the display tube . Fortunately the power transformer has a
small board stickng up in plain sight with the 30v circuits and fil.
circuits on it with the pins labled . All the voltages are fine .

Strange though .. When i push my finger on the back of the display board
across solders the conducting of my finger causes the display to go nuts
and random segments get real bright .

 

[N Cook]

I guess its the display tube . Fortunately the power transformer has a
small board stickng up in plain sight with the 30v circuits and fil.
circuits on it with the pins labled . All the voltages are fine .

Strange though .. When i push my finger on the back of the display board
across solders the conducting of my finger causes the display to go nuts
and random segments get real bright .

Have you tried cutting the traces to the cross-wires, usually the end ones
or end pairs and driving from another low V ac source, assuming there is a
3V or so secondary on the transformer.