Leader 1021 Oscilloscope graticule illumination bulb

[tonedeak99]

Hi everyone. Im new to the forum. I recently bought this oscilloscope and the illumination doesn’t work. I pulled the board, SC-10, and the lights are all blown. I can’t make out any part numbers on the bulbs. As I adjust the illumination knob on the front panel the voltage on the pins, P812, on the power supply board that feeds SC-10 goes from 0vdc to 20vdc. Any help on repairing these lights would be appreciated.

[bdunham7]

In case you don't have the service manual:

https://bama.edebris.com/download/leader/1021/Leader%201021%20Service%20Manual.pdf

They are listed as 14V 100mA and may be all in series in the circuit.  You can check that, I didn't read the schematic to verify.  The Leader p/n 561-020 doesn't cross to anything as far as I can tell, you'll just have to look up some 12-14 volt bulbs of similar size and current rating--anything close will probably do.  There are likely to be plenty available since anything automotive will be the correct voltage and instrument indicator lights will be in the ballpark for current draw.

Something like this will probably work, subject to you checking dimensions:

https://www.parts-express.com/12V-AC-DC-Incandescent-4mm-Grain-of-Wheat-Panel-Lamp-with-Insulated-Leads-070-107

[tonedeak99]

Thank you very much.  I did have the service manual but since I never saw any schematic for the SC-10 board I assumed they didn't go into that detail.  Now I just noticed these lights in the parts section in the end.  Thank you!  As for these lights, I think they will definitely work.  The current lights measure 5mm in diameter and 10mm in height.  What is the amperage spec for these?  Will any 12v grain of wheat light bul work?

[tonedeak99]

Also found this one.  its 70ma.  Do you think it will work?
https://www.amazon.com/GPW05W-Miniature-Pre-Wired-architectural-project/dp/B07DWB9B62

[bdunham7]

Do you think it will work?

I don't see why not.  Almost anything reasonably close to the specs that fits in there should be good.  You typically don't crank of the graticule illumination all that high anyway and most of those scopes had way more bulb than they needed anyway.

[tonedeak99]

Thank you for your help. Ill let you know how it turns out.

[tonedeak99]

Bulbs worked even at full power!!! Thank you again bdunham7.

The only downside to these bulbs was that the wire was stranded and very thin. So it was difficult to feed through the holes. The original bulbs had a solid wire.

[vk6zgo]

At my old work we had a bunch of small Leader video waveform monitors.
That fault was common with them.

For some reason, they all had the PCB (looked identical to yours) reversed, with the tracks on the front, so it was necessary to solder the leads on the same side as the lamp.

The original lamps were Unobtainium, but ones with similar specs were available ex our own stock.
The only problem was that the envelope was longer, so the lamp base had to sit flush with the board, making soldering the leads directly to the tracks impossible.

We turned the PCB round, so it was the same way round as yours, soldered the supply lead directly onto the tracks & the lamp leads through the holes, & all was well.
At least it seems that they learnt their lesson with your one.