LED alignment in Classics.



#2

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?

Les


#3

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....

Les


#4

Les:

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.


#5

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.


#6

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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