Re: Help with Display problem

Got it fixed thanks to your advice
There was no -24V which was generated from a voltage doubler.Seemed odd that
they would put a winding in just for this voltage and then double it
All the caps and diodes were fine but the 4.7ohm 1/4 watt limiting resistor
between the transformer and the diodes was open
I put in a 5 ohm 1/2 watt unit and its running fine 24V source is at 23.5
Thanks again
Bob

"Arfa Daily" <arfa.daily@xxxxxxxxxxxx> wrote in message
news:_7dTe.4233$Aa1.1658@xxxxxxxxxxxxxxxxxxxxxxx
>
> "James Sweet" <jamessweet@xxxxxxxxxxx> wrote in message
> news:tF8Te.14618$QN4.26@xxxxxxxxxxx
>>
>> "BoborAnn" <trottier@xxxxxxxxxxx> wrote in message
>> news:ZomdnVc_PYxyk4DeRVn-gw@xxxxxxxxxxxxxx
>>> I have a Sony DTC 700 DAT tape transport that the display has gone blank
>> on.
>>> This is a blue display that can be turned off entirely or partially or
>>> the
>>> intensity changed
>>> I don't know the technology but it appears to be a gas based display
>>> given
>>> the display unit shows the remains of the glass connections used to
>> evacuate
>>> it and has an intact getter
>>> I've probed around and it seems odd that the unit is provided a 4-5 VAC
>>> source.
>>> Hoping somebody can provide some guidance on what these displays are
>> called
>>> and how they work so I can keep this unit out of a landfill
>>> Aside from the display the unit runs fine
>>> Thanks in advance
>>> Bob
>>>
>>>
>>
>> It's a VFD, vacuum fluorescent and works on a similar principal as a CRT.
>> The AC voltage is for the heated cathode wires, there should be several
>> stretching horizontally which may glow a dull red if you turn the lights
>> out. IIRC you need about 30v on the anodes (display segments) to light
>> them
>> and there's usually also a control grid in between sections of segments
>> and
>> the cathode wires.
>>
>>
>
> All agreed except one thing I would say is that the display segments are
> invariably driven by a negative voltage, so you will be looking for drives
> at -30v. It is usually this supply that's missing. Check for it by
> measuring from ground to one or other of the filament connections which
> you have already discovered at either end of the display. Although the
> filament overall has around 2 - 5 v AC across it, it is floated -30v below
> ground so that there is not a huge potential diference between the
> filament wires and the display drives.
>
> If this supply is missing, go looking for a voltage multiplier in the
> power supply, as this is the way that this supply is almost always
> derived. It will comprise 3 or 4 small diodes in close proximity to 3 or 4
> small electrolytic caps. These are often around 47uF at 50v working. The
> input capacitor to the multiplier is particularly stressed by having large
> amounts of AC across it all the time, and has a tendency to fail open
> circuit. If you have a 'scope, it's easy to find the offending cap. It
> will have a dirty great AC waveform at line frequency at one side, and
> nothing, or very little at the other.
>
> Hope this helps
>
> Arfa
>


.

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