9/3/2023 0 Comments Cathode led segment fading out![]() ![]() Message #5 Posted by McAllan on, 2:27 p.m., Has anybody tried this with a classic? Did it make any difference? See the results of todays repair of a 1975 Prinztronic Scientific here. I have no such experience with the clasics or any LED calculators for that matter, but on VFD calculators it is often solved by replacing the electrolytic capacitors in the power supply. Message #4 Posted by Bart (UK) on, 12:58 p.m., Else it's not the same calculators we're talking about ) Quite "funny" on it's the last module that has been defective on all mine although not the same digit. Except for the heavy one the displays are readable but of course very annoying and you need to read it carefully. Guess I shall keep my eye out for cheap non working / barely working / trashed / heavy worn ones then )īut still wonders what's the cause and whether the modules have been defective from start and tolerances for build errors where higher back then or from what reason they've become defective since. Pretty much the conclusion I've come to myself after hours of carefully (de)soldering. In response to message #2 by Geoff Quickfall Message #3 Posted by McAllan on, 5:21 a.m., Replacing the three digit module which contained the ghosting digit corrected the problem on three classics that I have. Message #2 Posted by Geoff Quickfall on, 7:36 p.m., Re: Classic repair - ghosting digits - What's your experiences? If not small discrete ones aren't available to just put enough on a PCB. ![]() Yeah the modules are long out of production but guess small discrete SMD diodes on a PCB and a mask could do the trick. If only someone would display replacements for the classic series. Of course here the bonding wires are exposed to air and a bit of moist (incorrect storage) and the weak fastened ones let go on either the PCB or the LED chip - here I've both HP, TI and others. Sure the ones which are a PCB with plastic lenses heat seated or glued on top it happens from time to time they have faulty segments. I've _never_ seen a display module fault on neither TI nor Sharp or any other less known using molded or window chip like encapsulated LED modules. Normally calculators with molded LED displays are very robust. Or is it the module themselves that can't cope with the reverse voltages they see as a result of the complex multiplexing or simply bad quality so some go bad with time? Which makes me wonder - did the classics suffer from ghosting digits even back then? Seems like it's pretty much the displays themselves. Seems it's not the driver circuits to blame as I read on some page where one also corrected his 35 with a resistor pulling cathode on a digit. Is it really that hard to come by perfect samples? So what's your experiences with the classics? Can be pulled with a resistor to perfect visible result but raises power draw around 10-15 mA depending on how many digits visible. Guess I should try taking the last intact module from the worn 35 and put in the 80 and see it that solves the ghosting here. No visible difference though so I'm happy. Yeah the 4th had I marked (luminosity) and the modules in the one with dead segment was H marked. Presto! The 4th edition works perfectly - without any pulling resistors. Took a module from the one with the dead segment. That leaves it up to the displays themselves. Kept the original anode driver as I just relied on pressure to try the swap out. Since I already have swapped around the cathode driver of the 4th edition with another from one of the worn ones still no change i also tried swapping the anode driver. ![]() While that works for the 80 and with a low value (high current drain) also for the 35 4th edition that raise power consumption between 10 and 30-40 mA depending on needed value. I read somewhere some one else "corrected" such issue by loading the cathode of a bleeding digit. One segment dead this is also pretty worn and UV exposed so perfect for spares.Ī 4th edition 35 (the one with molded key caps). Shortening with a resistor of the driver coil of the corresponding segment doesn't seem to change power draw any significant value.Ī 3rd edition 35. Found a value which caused no visible fade but also made sure it was dark when supposed to. Corrected it by "shortening" one of the coils with a resistor. Not severe but made difference between 0 and 8 not as clear as it could be. The junk box one: Slight enlightening of the middle segment of all digits. Including the one in my junk box all exhibit some kind of ghosting. Lately I've bought 3 classic 2x 35 and 1x 80. Message #1 Posted by McAllan on, 3:46 p.m. Classic repair - ghosting digits - What's your experiences? The Museum of HP CalculatorsĬlassic repair - ghosting digits - What's your experiences? ![]()
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