Astron SS-30M Meter Light Conversion to LEDs

[xrunner]

Recently my station power supply - an Astron SS-30M, lost the illumination in one of the meters. Apparently they still use incandescent lamps.  Unfortunately, there was no way to easily replace the lamp inside the meter. They were made so that the lamp was sealed inside the meter.

I decided to do a retrofit and convert them to LEDs. The meters were not easy to remove. They had put on the hardest tamper-proof paint I had ever run across. It was so hard I had to resort to using vise grips to unscrew to screws. But, I did manage to remove the meters. See attached pics. I'll post the rest of the story later ...

[SeanB]

They used 6.3V lamps and no series resistor? Use the resistor to drop the lamp voltage to 5V and they pretty much will last forever, at the expense of a dimmer redder light.

[xrunner]

They used 6.3V lamps and no series resistor? Use the resistor to drop the lamp voltage to 5V and they pretty much will last forever, at the expense of a dimmer redder light.

Perhaps, but why are they making these things at all with lamps these days? The supply is only a few years old. C'mon Astron!

Further disassembly of the meters. The lamps are back in there - not designed for people to replace. Should have been made to be replaced by simply removing from the back, but then they couldn't sell people a new meter if the lamp goes out. Removed the lamp board and lamps, in preparation for LEDs ...

[GreyWoolfe]

I did my Astron VS-35M.  I used 110 degree wide angle white LEDs myself.  I didn't have near the trouble that you did getting the meters out, they came out easy.  While it was open,  I also added an inrush current reducer and a bleeder resistor.  I rerouted the power for the LEDs to the 12V output.  I found that using the power point for the light bulbs caused the LEDs to stay on for a couple of minutes.  Now the LEDs go dark the same time the meter reaches 0V.

[SeanB]

Making a new PCB, or just going to tack on some 5050 SMD led dies in series on the existing boards and put the current limiting outside the case. You could run them at 1mA and still have it as bright as the original.

[xrunner]

Well here's how I did it. There's a certain yellow glow I wanted to match, which some other radios have, so I first tried a few LEDs on a breadboard to see how they looked.

I went with 1.6 mm LEDs because the larger ones would have been too close to the back of the meter. The original lamps used a supply of 23.5V per my measurement. For the calculations we have -

23.5V - 4.1V (drop for two LED per meter) = 19.4V drop required for the current limiting R.

19.4V / 0.02 A = 970 ohms

Since 20 mA is max and very bright, I decided to go with a larger R, and had 680 ohm resistors, so I used two of them for a total R of 1360 ohms giving ~14 mA current. I installed the parts in the original lamp boards for the meters. The result was exactly the glow I was looking for. 

[RobertoLG]

nice mod, looks pretty good

[GreyWoolfe]

I used the same board and put the current limiting resistors on the board with the LEDs.  I wanted nice and bright so I stayed close to max current.  I don't use it all the time so I am not worried about the LEDs burning out.

[SeanB]

Nice, reminds me of a display lamp replacement I did on my car, as i got tired of replacing dashboard illumination lamps. Bought 100 3mm orange leds and wired them in strings of 4 with a resistor, and simply used a soldering iron to tack the strings to the plastic  side of the inside of the panel ( plenty of room there)  then used a drop of clear glue to add extra support, and took the wires eventually to the back of the PCB used for the panel.  More even lighting all round, much better dimming using the original Ford dimmer and more importantly no more failures from dead bulbs, as I was tired of the little clip in lamps, even if I did get them by the dozen at the local scrapyard, the work was tedious. I think I used around 50 lamps, running at around 5mA IIRC.

[Jerry D]

My Astron SS-30 meter lamp just went out. If I understand correctly you replace the (2) meters with (2) LEDS each along with (2) 680 ohm resistors in each meter in series with the original Lamp power. Would you be willing to share a part # or source where I can purchase the same yellow style you choose?

Thank you, Jerry D

[xrunner]

Hello Jerry,

My Astron SS-30 meter lamp just went out. If I understand correctly you replace the (2) meters with (2) LEDS each along with (2) 680 ohm resistors in each meter in series with the original Lamp power.

Yes.

Would you be willing to share a part # or source where I can purchase the same yellow style you choose?

I would be happy to share a part number - if i had one. 

I just got them out of my LED collection. But they are of the same variety as these on Ebay. They seem to now be classified as 1.8mm no worries on that. You probably want the yellow ones.

http://www.ebay.com/itm/1-8mm-Water-Clear-Diffused-Round-Top-Warm-White-Red-Blue-Light-LED-Diodes-/122100046749?var=&hash=item1c6dbadb9d:m:mXzKVI3VJPlEwcT9u0v7cOQ

[Jerry D]

Thank you very much for sharing the original fix and for all your help.

Jerry D,