Old IFI RC?

[slijin]

So, my team's offseason project this year has been to revive every robot gathering dust in the closet for an end of the year demonstration for the school. One of the problems we have is that one of our robots (formerly our main demo bot, but we stole his RC to revive our 2002 'bot, which hasn't run for 3 years - all of his functions are running now! ) is missing his IFI RC, although we do have another IFI RC in the closet.

Since there's no necessity for it to be competition legal, as it's for demo purposes only, I've opened up the IFI (by this, I mean I've taken the plastic base off, so that the bottom of the circuit board is exposed). From appearances, everything seems to be in proper working order, except the power ports.

Now, the main power port - from what I can tell - had been broken off, and someone had subsequently attempted to wrap solder wick around it and forge a connection, miserably failing. So what I've gotten done so far is pulled that connector off (a horrendous amount of what seems to be enamel or plastic melted onto the IFI), while scratching my head. There are two reasons for this. One is that while testing continuity through the main power port, I'm pulling 9 kilo-ohms of resistance, whereas on the others, it's 1.7 kilo-ohms. I'm also not getting any continuity through the backup power port.

I've already repaired an IFI whose main power port was similarly damaged (by me, inadvertently - the crimp on the quick disconnect was so horrendously done, that I decided to pull it off and redo it, pulling our the tab in the process). I opened the IFI, soldered a short piece of solid copper wire to the bottom of the circuit board, and then soldered it to the tab from the outside. One of the tab's pins was still intact, so I only needed to make the other pin.

However, before I repeat this for the IFI I'm working on right now, I'd like to know if anyone can think of a good reason for the discrepancy in resistance.

[Al Skierkiewicz]

Sam,
A picture would help. Please keep in mind that this circuit board is multilayer and you may have damaged an internal connection. Can you describe the resistance reading? Are you measuring across the two terminals? From one terminal to a powered output?

[slijin]

The IFI I'm working on looks mostly like this one, for the most part: http://www.ifirobotics.com/images/el...ics/rc-350.gif.

Some of the I/O pins are damaged (we probably won't be using all of them, so that shouldn't be too much of a problem), but the main problem I had was that the tab on the ground of the main power was completely pulled out. I made a partial fix today that I plan to finish up tomorrow: I took an uninsulated female quick disconnect, soldered two lengths of copper wire to it (female quick disconnects have two 'tunnels' on the sides to hold the tabs in place; I ran the wires through these, bent them in, then soldered the body of the quick disconnect), and then ran that through the pinholes on the main power ground. I crimped it onto a 12 AWG wire, and then slid some heat shrink on to insulate the connection. It looks something like this (big picture, I know :x), without the heat shrink.



Tomorrow, I plan to add another disconnect to this wire and hot glue the base of the quick disconnect to the IFI to secure the connection. I'll take a before/after picture tomorrow in the lab; I didn't have a camera with me today :d.

To test continuity through the main power today, I measured the resistance from the positive main tab to the wire I attached to the ground; it came out to 8.7 kilo-ohms, which I assume is because of the attached wire. Across the backup power (those tabs are intact) - which was tested with one probe to the positive and the other to the ground - the readout was 1, which is what I always get when there is no continuity within the circuit.

[EricH]

Sam, I think that picture you'll be taking tomorrow is what Al was looking for. Al has been around longer than I've been around, and I came in back when the programming was in PBASIC on an IFI RC. (I'm not going to ask Al for horror stories from the pre-IFI days...)

Something like http://www.chiefdelphi.com/forums/sh...ad.php?t=37296 would work better than the picture of the outside case.

[Al Skierkiewicz]

OK Sam, the resistance measurement from positive to negative terminal only tells you that something is not shorted and that there is some connection to electronics on the board. This is actually a good thing. Since you have the cover off already, you should be able to see a three terminal regulator on the board. As I remember it is the same case style as the power FETs on a Victor. You should have zero ohms (less than 2 ohms) between the negative power input and the center pin or mounting tab of that regulator. The left hand pin should be connected to the positive power input but goes through one of the fuses as I remember. A resistance measurement should also show less than 2 ohms on this path. I think that IFI made a change to a lot of surface mount components somewhere in the life cycle including the regulator but a picture will show that. If the parts are not covered in black, the regulator will have something that identifies it as a 7805 style device. 7805, 78L05, LM340-05, etc.