Technics tuner -FD panel

[transistor495]

There's a vintage radio tuner I have which has a dim display panel. Digits and letters are made of white dots so I assume its a fluorescent dot display, Most dots are dim and some are bright. One thing I've noticed is that the bright dots are aligned in horizontal lines so as the dark ones. Do anybody think it's repairable for a clear display or the dots are dead already unrepairable?

Example display panel. This is not my model:

**broken link removed**

 

[transistor495]

burp...

 

[Nigel Goodwin]

You might check for high ESR electrolytics (assuming you have an ESR meter or scope), but the most likely reason other than that is the display itself).

 

[KeepItSimpleStupid]

Not sure. Post a model # and just maybe we can find a free schematic. It could mean in internal short or a bad row driver. If they are external to the display, you may have a shot of fixing it.

You can try something that I've used with limited success, but it has worked and it DID work on a totally dead Vacuum Florescent clock used in a car. REMOVE any power sources external or internal batteries and short it for 30 seconds or so for any nearby CMOS parts.

 

[vtech]

What you have is infact a vacum fluorescent display(VFD) that was used extensively in all sorts of consumer electronic products, mainly stereo's & VCR's. In general, you had a filament pin on either side of the tube assembly that was very much like a vacum tube and HAD to have an AC input(1.5~3.3vAC) from the main power transformer and the rest of the pins were driven by a timer/driver IC.

The two main manufacturer of tubes were NEC & FUTABA and while they were easy to work with, the main disadvatage was the fact that after certain amount of usage, the internal emission would start to decrease which translated in to dimmer segment outputs and often it was not uniform throughout the display. I used to run across many where half or just a section would be dimmer than the rest.
Other than replacing the tube, depending on the configuration of the circuit, you could increase the brightness by increasing the reference zener(segment drive voltage) or increasing the AC but it would rarely be uniformed. If the entire display was rather dim yet working, you could get a much better result but still it would be a matter of a time before having to replace it.

 

[transistor495]

The model# is st-k55 and here's a picture of the unit I got from web.

**broken link removed**

I'll try to analyze the internal of the display.

 

[picbits]

A similar thing happened in an old Aiwa system I had - the display was all over the place in brightness and eventually faded to nothing.

That was a couple of dried out capacitors that were at fault.

 

[Nigel Goodwin]

A similar thing happened in an old Aiwa system I had - the display was all over the place in brightness and eventually faded to nothing.

That was a couple of dried out capacitors that were at fault.

See post #3

 

[transistor495]

I may check for bad electrolytics then. Please is there any schematic sir

Not able to find one yet, which would be helpful to track the display driver circuitry easily..