LED alignment in Classics.


I have just noticed in my 45 and 80 the second set of 5 LEDs is slightly below the first.

I thought I bent something in the 45 when I opened it to clean it, but I am wondering if this was like that all along but I never noticed as it seems likewise in the 80, but not as noticeable.

Does this sound like a familiar phenomenon?



Actually, it is specifically the 6th LED from the left. All others seemed in line.

Is this normal? Gosh, I don't want to be tempted to bend something back into alignment if it is otherwise fine....




LED displays in Classics (as you may have noticed) consist in three modules of five digits each, each module in a dual-in-line IC package, but molded in a transparent red plastic, and with individual dome lens molded above each digit. I suppose that a mechanical misalignment is unlikely, because the holes on the printed circuit board contribute to the inter-module alignment. There may be a height misalignment if the module was not properly seated while soldering, and that may cause some optical/visual shift, but I don't think of it as likely, either. And, in the event of a misalignment, it surely will affect all the digits of the block (1 to 5, 6 to 10, 11 to 15). If you unit has been repaired, there may be a chance of inaccurate placement or seating of the middle module, just a guess...

The modules were sorted by brightness by HP Optoelectronics Division at production time (the same modules were available as an electronic component for other manufacturers to buy). There was a letter suffix to identify the relative brightness, and care was taken so the three modules in any given calculator have the same brightness category. Again, a repair work may have used different brightness group, perhaps that may cause an apparent visual shift.

Just some ideas, hope it helps.


Actually there are two different module designs with different size digits. You can usually tell them apart by the color of the leads (silver or gold). Also there is quite a bit of wiggle room for the modules in the holes before soldering. Rather tiny displacements make for rather noticeable shifts in the display.

When changing a display I use a strong magnifier to get the display to match the other ones, solder one corner pin, check again, solder the opposite corner pin, check again, solder the rest of the pins. A display brightness letter code difference of two is usually not noticeable to the unaware. Three is cosmetically OK, four or more can be a problem. It can help if the dim module is on the right end.


David: it is always good to receive your fine corrections, surely it will help Les to solve the situation. Best regards.

Edited: 19 Feb 2007, 9:55 p.m.

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