SQ-80 main board processor hot to touch


I am working on a “bought as parts” SQ-80 that presents a blank display (see earlier post if you are interested in my display problem). Power supply seems okay, giving all the spec voltages.


Right now I am trying to figure out whether I have a bad main board processor, HD68B09EP. It is running quite hot to the touch, specifically in the middle of the chip. I can hold the tip of my finger on it for about 6 seconds before reaching my pain threshold.

My assumption is that the HD68B09EP should not be running at such a high temperature.

I have looked online for guidance as to how to check for shorts within microchips, but the only test that seemed feasible was to check to see if there was continuity between an excessive number of pins on either side of the chip. This basically involves putting on probe of the multimeter to pin 1, running the other probe all along the other side; repeat for pin 2; etc. I did this test, but found only a couple of points of continuity.

I am ashamed to admit that I am not able to interpret the documentation of the chip to the point that I can do much more (I know what Vcc means, but that’s about it). Since I have not yet got my display working, I am not yet able to evaluate the functionality of the processor chip.


(1) Am I right in thinking that the HD68B09EP should not be running so hot?

(2) Is there a better way to check for shorts in the chip than the procedure described above?

(3) Besides shorts within the chip, is there another possible culprit I should be looking for?

(4) Would I be able to replace my (presumably faulty) chip with any off-the-shelf 68B09EP?

Many thanks in advance,