Post Reply 
TI-45: Rejuvenation of a faded VFD-Display
06-06-2021, 03:48 PM
Post: #1
TI-45: Rejuvenation of a faded VFD-Display
Nice Sunday wishes,

I thought I'd share some calculator rework on a rainy Sunday.


[Image: 0DbnEPM.jpg]


The sample on the left suffers from a considerable dim display. As far as I know, the TI-45 is the only TI pocket calc featuring a vacuum fluorescent display or VFD.

It basically works like a valve tube. A filament wire, the cathode, is heated by a low current and starts to emit electrons. The electrons accelerate to the anode with a potential difference of about 30 Volts, they hit the phosphorized anode coating and the kinetic energy of 30 eV is mostly transformed into photons. The segments of each number are separate anodes and can be switched on and off individually. A grid between cathode and anodes for each digit can be either positive (on state) or negative (off state). This way the driver electronics multiplex digits.


[Image: cOnI2ie.jpg]




The emissive layer on a cathode filament consists of metal oxides which can degrade over time by disuse. But it is possible to bring it back to life by injecting high current pulses. Usually the electronics drive the filament at about 1.5 V AC. Here 6 V DC are directly connected to the filament pins of the display package and the filament wire starts to glow. This treatment is applied about 20 seconds and two times with 8 V. The result is clearly visible.


[Image: ZytPkMo.jpg]


One advantage of VFDs over LEDs is very low current consumption. Only the filament draws some milliamps. Anodes and grid have extremely high impedances and do not contribute to the current consumption. Hence, total current draw does not depend on the number of lit digits.
The pictures below show current draw in off-state (28 uA), on-state one digit (15 mA) and on-state eight digits (16 mA).


[Image: 19SUMdO.jpg]

[Image: VMBXUJf.jpg]

[Image: GURDvI2.jpg]
Find all posts by this user
Quote this message in a reply
06-06-2021, 05:56 PM
Post: #2
RE: TI-45: Rejuvenation of a faded VFD-Display
Very interesting! Somewhat similar to the principle of a TV picture tube rejuvenator.

There were a handful of TI handheld calculator models that used a VFD. I know at least the TI-1025, TI-1265 and TI-1650 four-function models used a VFD. I was surprised to learn that the power consumption was less than an LED model. I would have thought that the high voltage power supply needed to drive the anodes alone would consume more power than an LED model. Thank you providing the data to confirm the lower power used by this model. For many years VFDs were also cheaper than LEDs as well.

The above TI models appear to use a capacitor voltage multiplier instead of a transformer to achieve the required anode voltage.

http://www.datamath.org/BASIC/TI-1000/TI-1025.htm
Find all posts by this user
Quote this message in a reply
06-06-2021, 07:22 PM
Post: #3
RE: TI-45: Rejuvenation of a faded VFD-Display
Here is a photo of my TI-1025. It came with its box and looks like it was hardy ever used. I can't tell if the VFD is dimmer than when it was new but it is very readable.

   
Find all posts by this user
Quote this message in a reply
06-06-2021, 07:45 PM (This post was last modified: 06-06-2021 07:48 PM by toml_12953.)
Post: #4
RE: TI-45: Rejuvenation of a faded VFD-Display
(06-06-2021 05:56 PM)Steve Simpkin Wrote:  Very interesting! Somewhat similar to the principle of a TV picture tube rejuvenator.

There were a handful of TI handheld calculator models that used a VFD. I know at least the TI-1025, TI-1265 and TI-1650 four-function models used a VFD. I was surprised to learn that the power consumption was less than an LED model. I would have thought that the high voltage power supply needed to drive the anodes alone would consume more power than an LED model. Thank you providing the data to confirm the lower power used by this model. For many years VFDs were also cheaper than LEDs as well.

The above TI models appear to use a capacitor voltage multiplier instead of a transformer to achieve the required anode voltage.

There was even a TI with a Panaplex display (TI-150)!

http://www.datamath.org/BASIC/DATAMATH/J...tm#display

Tom L
Cui bono?
Find all posts by this user
Quote this message in a reply
06-06-2021, 08:02 PM
Post: #5
RE: TI-45: Rejuvenation of a faded VFD-Display
(06-06-2021 07:45 PM)toml_12953 Wrote:  
(06-06-2021 05:56 PM)Steve Simpkin Wrote:  Very interesting! Somewhat similar to the principle of a TV picture tube rejuvenator.

There were a handful of TI handheld calculator models that used a VFD. I know at least the TI-1025, TI-1265 and TI-1650 four-function models used a VFD. I was surprised to learn that the power consumption was less than an LED model. I would have thought that the high voltage power supply needed to drive the anodes alone would consume more power than an LED model. Thank you providing the data to confirm the lower power used by this model. For many years VFDs were also cheaper than LEDs as well.

The above TI models appear to use a capacitor voltage multiplier instead of a transformer to achieve the required anode voltage.

There was even a TI with a Panaplex display (TI-150)!

http://www.datamath.org/BASIC/DATAMATH/J...tm#display

Not to mention my preferred one, the SR-22!

Greetings,
    Massimo

-+×÷ ↔ left is right and right is wrong
Visit this user's website Find all posts by this user
Quote this message in a reply
06-06-2021, 08:37 PM
Post: #6
RE: TI-45: Rejuvenation of a faded VFD-Display
Or the TI Minimath early LCD model from 1972 that never made it past the prototype stage.
http://www.datamath.org/BASIC/DATAMATH/Minimath.htm
Find all posts by this user
Quote this message in a reply
06-06-2021, 09:10 PM (This post was last modified: 06-06-2021 09:19 PM by Pjwum.)
Post: #7
RE: TI-45: Rejuvenation of a faded VFD-Display
:-)))) I have to admit the calculator era for me starts with the TI-30.

(06-06-2021 05:56 PM)Steve Simpkin Wrote:  The above TI models appear to use a capacitor voltage multiplier instead of a transformer to achieve the required anode voltage.

The TI-45 uses the exact same 4 ceramic capacitors plus 4 diodes to boost the 30 V anode voltage. No other components beside the TMC chip.
Find all posts by this user
Quote this message in a reply
06-07-2021, 07:06 PM
Post: #8
RE: TI-45: Rejuvenation of a faded VFD-Display
Any chance of getting a picture of the back with the power supply connected?
Find all posts by this user
Quote this message in a reply
06-08-2021, 07:27 AM
Post: #9
RE: TI-45: Rejuvenation of a faded VFD-Display
(06-07-2021 07:06 PM)dhe Wrote:  Any chance of getting a picture of the back with the power supply connected?

Here you go. The filament usually is connected to the outermost two terminals of a VFD and can easily be verified by measuring the resistance (should be < 100 Ohm). Since it is only a wire polarity is irrelevant.

Patrick

   
   
Find all posts by this user
Quote this message in a reply
Post Reply 




User(s) browsing this thread: 1 Guest(s)