TDS 744A Scope Teardown Fixes Dodgy Channel

There are a lot of oscilloscopes from around the 1990s which are still very much desirable today, such as the Tektronix TDS 744A which [DiodesGoneWild] got his grubby mitts on. This is a 500 MHz, 4-channel scope, with a capture rate of 500 MS/s (4 channels) to 2 GS/s (1 channel). It also has a color display and even comes with a high-density (1.44 MB) floppy drive. Unfortunately this particular unit was having trouble with its fourth channel, and its NuColor display had degraded, something that’s all too common with this type of hybrid CRT/LCD (LCCS) technology.

Starting with a teardown of the unit to inspect the guts, there was no obvious damage on the PCBs, nor on the acquisition board which would explain the weird DC offset on the fourth channel. After cleaning and inspecting the capture module and putting the unit back together, the bias seen on channel four seemed to disappear. A reminder that the best problems are the ones that solve themselves. As for the NuColor display, this uses a monochrome CRT (which works fine) and an LCD with color filters. It’s the latter which seems degraded on this unit, with a repair still being planned.

We covered NuColor-based devices before, which offer super-sharp details that are hard to capture even with modern-day LCDs, never mind the ones of the 90s. Fixing these NuColor displays can be easy-ish sometimes, as [JVG] found when tearing apart a very similar Tektronix TDX-524A which required a power supply fix and the removal of goopy gel between the CRT and LCD to restore it.

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Sharpest Color CRT Display Is Monochrome Plus A Trick

I recently came across the most peculiar way to make a color CRT monitor. More than a few oscilloscopes have found their way on to my bench over the years, but I was particularly struck with a find from eBay. A quick look at the display reveals something a little alien. The sharpness is fantastic: each pixel is a perfect, uniform-colored little dot, a feat unequaled even by today’s best LCDs. The designers seem to have chosen a somewhat odd set of pastels for the UI though, and if you move your head just right, you can catch flashes of pure red, green, and blue. It turns out, this Tektronix TDS-754D sports a very peculiar display technology called NuColor — an evolutionary dead-end that was once touted as a superior alternative to traditional color CRTs.

Join me for a look inside to figure out what’s different from those old, heavy TVs that have gone the way of the dodo.

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