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TDS220 LED Retrofit

A while back I was very fortunate to receive a working Tektronix TDS220 Dual-Channel 100MHz Oscilloscope from my boss. The catch? The backlight was burnt out. He had taken it apart to see if the problem was obvious, and not seeing anything he re-assembled it and shelved the unit. A couple months later I was talking to him about how I was planning to buy a digital scope, and that was when he reached over to his bookshelf, handed me the scope and said "all yours".

I wasted no time pulling it apart to see about replacing the backlight. At first I assumed the CCFL tube was burnt out, and set about trying to hunt down a replacement. After an hour or so on the net I managed to figure it that the tube was made by Sharp (LM0F2964) but couldn't source it anywhere. Just for fun I decided to measure the voltage the inverter circuit was putting out and came up with about 45V RMS, which seemed pretty low for a back light driver. A quick look at the service manual confirmed that the back light driver should be putting out around 450V RMS; something was amiss.

After poking around at the inverter circuit a bit more I finally decided to scrap the idea of fixing the CCFL driver and instead retrofit the scope with an LED back light strip.

To be continued...

Figure 1 - The CCFL Backlight Tube Sitting in the "Channel" Beside the Polarizer

Figure 2 - Top Half of the CCFL Tube "Channel"