|Voyagers: a fifth m-board layout "found"|
Message #1 Posted by Vieira, Luiz C. (Brazil) on 23 Apr 2003, 9:10 a.m.
Hy, Voyager Fans (and users)
About a couple of weeks ago I got into contact with four HP12C's mainboards. They all belong to one of our regular contributors.
At a first look, one of them called my attention: I had never seen such layout before.
It resembles the first single-mainboard Voyagers but it has "space" for two IC's, instead of the three ones normally found in the HP11C, 15C and 16C. I have never seen the HP10C internals (but I was lucky enough seeing and playing with one HP10C in the 80's...), so I cannot say a word about it. Hey, if there is anyone brave enough to open one HP10C and take a picture, I'd gladly store it with the others.
Anyway, these three scientific Voyagers share the same layout. I also did not see an earlier HP12C (at least not yet) but I am almost sure it has the same layout; it would not make sense having more than one layout in such a factory line, I guess.
This "recently found" layout has space for two IC's and only one is used: the one that was supposed to control the LCD (named RAM/ROM/Display Driver, or R2D2 - thanks, Tony) also scans the keyboard. I thought there was one Voyager-specific IC used to scan the keyboard, but I think that this IC may have other features. The supposed KBD scanner "only" is the same one for the three Voyagers (11, 15, 16), but Tony Duel also mentions something extra about this IC; is it correct, Tony, or I am refering to you wrongly? If so, forgive-me.
And another interesting feature is the LCD's connections. Now I tell you: newre HP12C use a different LCD, EVEN those with 3 batteries. Earlier Voyagers use a different pins/connections arrangment, assymetrically distributed. These "newer" HP12C use an LCD that has connections with uniform distribution, the same number of connections in both LCD's top and bottom surfaces.
I did not remove the LCD from a newer chinese HP12C, the ones with one battery. But I saw its internals, and at components side, connetions are the same and similar cooper trails (PCB) seem to have the same functionality.
I remember reading some posts about LCD exchanging from diferent Voyagers; now I must say that in some cases, even between the newer, 3-batteries type HP12C (Indonesia, Singapore) and other earlier Voyagers, the LCD may be not compatible. Now I am curious about the single-battery Chinese HP12C: what sort of LCD does it use?
One question: I remember that the major concerns about changing LCD's in newer HP12C were related to Power Supply voltage (3.3Vcc against 4.5Vcc). I agree with the fact a 3.3Vcc LCD shoul not be used in a 4.5Vcc circuitry; LCD's timelife would be significantly reduced. Otherwise, if we consider the opposite situation, an LCD designed to work with voltages below and about 4.5Vcc could work in 3.3Vcc circuitry; dimm and viewing angle could be "adjusted" with a new polarized filter and scanning schemes.
As soon as I find a lpace to hold the scanned image I'll post it again.
I must apologise to those who kindly offered a place to hold some of my pictures and I have not yet given them a return. Thank you all; I'm just trying to find my own place, so I'll feel myself a lot more comfortable uploading stuff without disturbing host's piece..
Also, I want to apologise to those still waiting for the "HP28S explodeded view" picture. I'll surely need to scan the original article and filter image again. One of our contributor mentioned having another site with HP stuff where the original article is available.
Well, I think that's all for now. I'll collect some more data about Voyager internals and, if applicable, I'll build an article about this subject. I just want to be sure you all understand that I like Voyagers a lot for many reasons, but I'd like having more information about them.
Luiz C. Vieira - Brazil