This page is intended to help you troubleshoot your BotBoard Plus and/or RS232/TTL cable kit. You will find answers to the most common problems.

Quick Troubleshooting Notes

By far the most common problems with the BotBoard Plus kits have been assembly/soldering errors and PC configuration errors. Perhaps I can set your mind at ease with the following list of wisdom:

1. Relax, you did not fry the CPU! This is the first assumption that everyone seems to make if the board didn't work the first time. I have sold many hundreds of these kits, and to date have only seen 1 fried chip. That was caused by putting 48 volts across the power inputs. The 68HC811E2 is actually a pretty rugged device.
2. The most common problem with the BotBoard Plus starter kit is the serial cable kit. Unless you know that your cable works correctly, you should start your trouble shooting with the cable.
3. I have yet to see a board that could not be fixed by the end user, even kits that are in pretty sad shape after a bad night with the solder iron. This is a very simple board!
4. Did you get a chance to use the BotBoard Plus Testing page? Before downloading your own program, please make sure that Hello World works.

The Serial Cable

I am assuming you have a RS232/TTL kit from me. This is the component where most of the problems show up. The big reason is that the serial cable soldering job is more complex than the BotBoard Plus. To fit the project into a DB9 case, I had to make the board pretty small. If you soldered this together yourself, you understand just how small it is.

The most common problem with the RS232/TTL kit are the pins of the MAX3221 not making good contact with their pads. This appears to be the 95% case. To check this, the best way is to go back and sweat the joints for a moment with a clean soldering iron.

1. Using a sponge, clean the end of your soldering iron. Try to avoid adding solder to the pads at this point.
2. Using your paste flux, make sure there is a thin film of flux available to the pads so the solder will flow.
3. Touch the top of each pin with the end of your solder iron. It should only take a second or two to get the solder to melt and flow onto the pin. Do this to each pin on the MAX3221. At this point, try testing your cable again. It usually works.
4. If step 3 didn't make the cable operate correctly, use a magnifier or other visual aid to carefully check that each pin appears to be soldered, and that adjacent pins are not shorted out. If you must, add a very small amount of solder to pads that don't have an obvious solder connection. Be careful. It is easy to add too much solder and end up bridging several pins together.

Ideally, you would like a little bit of solder to flow up over the edge of the pin. The following series of microscope pictures are my attempt to show you how it should look. However, seeing with this level of detail requires a great magnifier! I used an Intel Play microscope for these pictures. The focus isn't really great since this is a 3 dimensional object we are viewing, but you might find it useful.

Solder pads at 60x magnification

The far right hand pin was soldered completely. The brown substance is residue from the paste flux. Notice how the solder flowed up onto the top of the pin.

The second from the right is an acceptable solder job. The solder flowed, and managed to get up on the edge just a little. The pin has a really good connection on the bottom.

The third from the right is also soldered with an acceptable joint. The entire solder joint is under the pad, which makes it difficult to see.

The fourth from the right is a bad solder joint. Though the solder was melted, the joint did not stick on the underside. Notice that the third and fourth pins look extremely similar. It is often quite difficult to tell the difference between the two, but these are the joints that you should be sure to sweat.

The far left hand pin has no connection at all. When you are looking at these joints under a light, you will usually see some sort of reflection, as in the picture of the left two pins. That is the paste flux reflecting light, not solder!

The following picture shows the far right hand two pins.

Good solder pads at 200x magnification

Note how the solder on the pad is made solid connection to the MAX3221 pin. Yes, it looks a little ugly because the solder melted and the flux bubbled up a little. The solder runs up on the lip of the pad a little.

Bad solder pads at 200x magnification

These two pads have no solder connection, even though they look like they might. The reflection is caused partly by the paste flux, and also by the reflection of the end of the MAX3221 pin into the reflowed solder on the pad.

Other things to check on the cable.

Did you solder the part on with the correct orientation? The orientation of the chip looks something like the following. Note that the 'dot' on the case marks pin 1. Pin 1 on the PCB is marked with a small 1, and is connected to the square pin of the connector.

The next thing to check real quick is that the capacitors are soldered on, and that no bridges or shorts exist. A visual inspection usually does the trick on this. Note that there is a small trace between pins 15 and 16. That trace is supposed to be there. Please don't 'fix' it.

The last thing to check is the ordering of the wires. I usually use the Black wire for pin 1 of the connector (the square pad), followed by Red, Green, then White. Make sure the same order exists on the Molex connector at the other end.

Voltages to check on the cable.

The following two diagrams are going to show the top and bottom sides of the board. You can check to see if the voltages present are at least somewhat close to what they should be. The numbers on these diagrams are approximate, your measurements are not going to match! However, the polarity ( + or - ) should be the same, and the measurements should be within 15% or so. For example, you might measure 4.95 volts instead of 5.0 volts. That is fine. The tolerances are pretty wide. If, however, you get 3.98volts instead of what should have been around 5 volts, something may be wrong.

You also MUST INSURE THAT YOUR CABLE IS CONNECTED! Just applying power to the RS232/TTL cable is not going to work. The MAX3221 part has an autoshutdown feature. That means if no valid RS232 signal is connected to the DB9 connector, the MAX3221 will shut down, and turn off its charge pumps.

In addition, measuring an active circuit can be difficult and misleading. You should only measure the steady state of the part with no data being transferred.

Please follow these instructions:

1. Connect your cable to your BotBoard (or other device). Put the BotBoard into bootstrap mode. This will normally prevent it from sending data.
2. Connect your cable to an RS232 port, such as on your PC.
3. Set your meter so it can handled at least +20 volts DC.
4. Place the BLACK (a.k.a. COM ) lead on the square pad (pin 1) of the TTL side of the connection. It is labeled GND in the diagrams.
5. Using the RED (a.k.a. DMM, DC, or V ) lead, touch the lead to each of the pads listed and compare the measured voltage against whats on the diagram. If the measurement is more than 20% from what is measured, it indicates there may be a problem.
6. If the diagram shows a negative voltage, and you are using an analog meter, you may need to reverse the RED and BLACK leads for that measurement.

Here are the diagrams:

Frontside of RS232/TTL board

The far left hand pin of the TTL level connector usually isn't connected to a wire. However, it is a great diagnostic pin. It is called the VALID pin, and tells you if the MAX3221 is in shutdown mode or not. If the pin is +5 volts, then the MAX3221 has detected a valid RS232 signal on the DB9 connector. If it is +0 volts, then the MAX3221 has not detected a valid pin, and you will find that the chip has shutdown. In the shutdown mode, the charge pumps are off, so most of the measurements will not be correct.

Backside of RS232/TTL board

The RS232 standard uses a minimum of +5 and -5 for its signals. The MAX3221 attempts to provide approximately +8 volts and -8 volts. Your PC will usually drive the parts at around 10 volts. There is quite a bit of slop in this protocol. The important part is exceeding 5 volts and the polarity. If the polarity is wrong or too weak, the signal will not work properly.

If all the voltages check out, and your cable still doesn't function, then you may need to follow the traces around the board with your meter to insure there isn't a damaged trace.

The BotBoard Plus: An Obvious Checklist

Here comes a list of things that you need to check. Some of these are 'obvious', but please check these through in order. NEVER ASSUME ITS RIGHT, ALWAYS LOOK. I have helped many people get their boards running. People have wasted many hours by assuming that they had done something correctly. First, here is a picture of what an assembled BotBoard Plus should look like.

Note the orientation of the connectors. Here comes the list, in order of most commonly found problems. Please, verify that each item is correct:

1. Is the CPU socket soldered into the correct position? The angled corner is near the crystal. The angled corner on the socket also has a square 'hole', as opposed to the rounded holes of the other corners.
2. Is the resistor network R2 oriented correctly? There is a small dot or mark on the part that should be aligned with pin 1. Pin 1 on this board has a square solder pad, is on the left side as oriented to the picture, and has an extra box on the silkscreen side (the white lettering).
3. Is the serial connector soldered in correctly? The orientation of the connector is important. The locking ramp should be close to the CPU.
4. Are ALL of the solder joints good? There are a lot of solder joints on the backside of this board. Using your good eyesight, or perhaps a magnifier, check through all of the solder joints to insure that they are making good contact, and are not touching their neighboring pads.
5. Did you get the 22pF capacitors into the correct position. The 22pF capacitors are marked with a 220 on the case, and they should be inserted into C3 and C4, near the crystal.
6. Did you solder C1 in correctly? Most capacitors like this mark their '-' terminal. This marking should be close to PORTE's connector.

If you can verify that all 6 of these issues are correct, then it is fairly safe to assume that the HC11 is operating correctly.