Is the Display on your IM3003 Faulty?

I had a NuTone IM3003 come into the shop this week with a very unusual problem.  The display on the IM3003 Master Station would not show the correct FM Radio frequency readout, it just displayed 198.9 regardless of how the tuner wheel was rotated.  The tuner worked correctly; it was just the readout that was faulty.

One thing to understand about the tuner/display on a IM3003 is that the tuner is not a digital tuner, like on a modern radio.  The tuner on a IM3003 is an analog tuner (mechanical) that has a digital readout connect to it.  

While it is not that uncommon to have the readout on a IM3003 display be out of alignment or have the clock run fast or slow, I cannot remember ever the last time I saw a unit with a failed display.

The problem was traced down to  IC201 on the display PC.  IC201 is a Sanyo LC7250 CMOS, Digital Frequency Indicator w/Clock LED Function IC.  This is an interesting chip which actually has more features than are used in the IM3003.

Unfortunately this chip is at its "end of life" cycle with chip manufacturers and the availability is limited and somewhat expensive.  The cost is around $18.00 for a single chip.

Removing this 42 IC requires some careful desoldering. A proper desoldering tool should be used.  Installing the new chip is straight forward, being careful to not have any solder bridges between the pins.

With the new chip installed, the display worked correctly again; however, it was necessary to realign the trimmers on the board so the readout matched the radio station that was being played.  I also adjusted the clock to the proper frequency so it will keep the time correctly. These types of adjustments require specialized bench equipment that many Service Centers may not have.

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