Douglas Taylor wrote: Well, you could start by tracing out the power pins from the chips, and working out what they connect to. Obviously the TTL will want 5v (possibly at quite a high current). The analogue supply voltages would be more difficult, but have a look at the voltage ratings of power decoupling capacitors - that will give you an "absolute maximum" idea. The "real" voltage will probably be somewhat less. Gordon.

I've started working on my small pile of SAIC V2-LC computers, but run into some snags with the disk drives. For those that do not know of them, these are OEM-for-military portable computers with a 386 or 486 processor. The hard disk is generally a Conner CP30204 IDE drive, enclosed in a special case. The drive is the same dimensions as the common IDE drive used in PCs today. The 3.5" form factor, and about 3/4" tall. The Conner CP30204 has the following specs: size = 212 MB CYL = 683 Heads = 16 Sectors = 38 WP = 0 LZ = 683 One necessary feature of this kind of drive is a an additional small 3-pin connector for power, on the opposide end of the IDE connector from the usual PC-style 4-pin connector. I have seen this only on Conner drives. Might be on others, don't know. Herein lies the issue.. Me needs more of these or similar drives (small sizes up to 500MB perhaps, (due to DOS or 486 limitations). They need to have the small 3-pin power connector, and that's the issue. I dug through all my 3.5' IDE drives, and found only one 120MB one, and it's kaput.. The computer looks like this, shown with the disk drive case in front of the machine and the 'ac adapter' to the left: http://itweb.salisbury.edu/~rafantini/IMAGES/saic4.jpg In any case, I am looking for either cased or naked drives. I have 6 machines and two 'good' hard drives. If anyone has an IDE drive with the aforementioned small 3-pin connector, please let me know. I'm willing to take a shot. -Also looking for 4 or 8 meg 30-pin simms for same. I have managed to cram windows 95 onto one of these little beasts, and it is quite nice, even if slow. Please! reply to my e-mail address, so i can be sure to receive any messages timely. Thank you very kindly, Patrick

What fun! [...] Good luck! I've traced out a fair few schematics over the years, so can possibly give you a few hints. Firslty, difficulty of reverse-engineering depends on the complexity of the components. Easiest first, it goes like this : Large LSI chips that are known (e.g. microprocessors, LSI I/O devices). These can essentially only be used in one way, so yu can identify a lot of signals from one chip (like address and data buses) TTL gates and flip-dlops. Harder. A NAND gate could be doing a million different things (it could be half of an SR, too...). Disvretes. Even harder. A transistor might not even be a digital function (it might be part of a power regulator even on an essentially digital board, for example). Do not pick the HP9100 as your first reverse-engineering project :-) Unknown/custom LSI parts. Painful. You don't know what the pins are. If you can power the thing up you can make some good guesses as to some of them by examining the signals (I did this for some of the HP calculator chipsets, I did know roughly what signals to expect, I just had to find out which was on each pin). Assuming you know what all the ICs are, start by indentifying the power and ground rails (shouldn't be too hard on a board of TTL). Do watch out for chips not powered from the main rails, though. Make a list of all the ICs and the sections in them. It will look something like this : U1 a b '74 U2 a b c d e f '04 U3 '163 U4 a b c '10 Then, as you draw out each gate/chip, cross it off the list. That way you'll know what you've not done, and conversely you'll not draw out the same stuff twace. If the ICs are house-coded and you know the equivalents, you put the standard number on the list. If necessary, list the transistors (and even R's and C's) too. If there are no 'U1' etc numbers on the board, you have to assign them. Either sketch out the layout of the board and write a number for each chip, or stick labels on the actual ICs. I normally do the latter -- the local stationary shop sells sticky lables numbered 1-160 (3 times over in different colours) about 6mm in diameter. They sitck nicely onto most ICs. Make sure you have data on all the chips. A TTL databook is essential, often asking here will get pointers to info (it's worked for me in the past :-)). Use any info you have about external connections to identify signals. Not a lot of help in your case, but if, say, you're doing an ISA card, obviously use the slot pinout. This way you'll get a schematic of the board. How much help that is in linking up to the mechanical/optical side is another matter. -tony

Thanks for the hints, I was uncertain whether to use a continuity tester, but it sounds safe. The circuit boards are multi-layer and from what I can see, looking at one side you can see writing on the layer below that says either +5 plane or ground plane depending on which side you are looking at. I have never seen this before, the buried ground and +5 buss, is this normal? Some pictures of the device are at: http://users.starpower.net/dj.taylor/ BTW: I love the 'non-causal' nature of the list here, I get answers to my post before it even appears! Doug At 08:49 PM 11/11/2005, you wrote:

I must have traced out over 100 boards in my life. I've always used a continuity tester (firstly a homebrew one, then the Fluke 85), and have never damaged anything. The chips on the boards have been a mix of TTL (plain, L, H, LS, S, F, HC, HCT at least), 4000-series CMOS, NMOS and PMOS LSIs, bipolar and FET-based analogue, etc (not all on the same board, of course ;-)). AFAIK I've never damaged a single chip. I would be wary if there were tunnel diodes on the board (from what I've read, those are easy to damage), but I doubt that will be the case on your boards. Yes, it've fairly normal to have the signal traces on the outside layers and the power/ground planes inside. -tony

I don't think that's essential. Maybe it's because I can remember most of the common TTL (and other) ICs and their pinouts, and only have to look up the more obscure ones, but anyway. Much more important is the abiliity to uniquely identify each IC (and other major components) on the board, giving each one a U1, U2, U3... number. You may need to add labels to do that. Not so important. I never, for example draw out decoupling capacitors unless there are very good reasons for doing so (e.g. it's a single capacitor on a derrived power line, output of a potential divider) If you draw out connectors, be cosistent as to how you do it. For example, I always draw edge connectors looking into the socket. Drawing 2 mating connectors as mirror images drives me mad!. For complete units, I often put arrows on the connectors showing the orientation -- pointing, say, to the back and left of the machine. All such references refer to the unit in the normal operating position (again, be consistent about this). Actually, I find it better to stick to A4 (or equivalent) paper and not try to pack too much on a page. It makes copying/scanning a lot easier, it also makes the schematic easier to follow since it's divided up into functional blocks. Of course this means you have to think a lot when drawing it out in the first place (which is no bad thing!) Yes. I have been known to make copies of IC pinouts or connector pinouts (e.g. the ISA slot pinout if I'm working on PC stuff) and pin them up over the bench where I'm working. And have at least 4 databooks open at once. You don't waht to have to keep on stopping to look stuff up :-) -tony