Dim display Panasonic stereo

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

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

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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

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 .

snipped-for-privacy@care2.com wrote in news:1179684751.540124.182250 @z28g2000prd.googlegroups.com:

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

If the trasnformer is open framed.

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 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

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

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on