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Fixing a by Tim Blythman busted Arduino Uno The Arduino Uno is a hardy beast, but occasionally we manage to let the magic smoke out. Perhaps our attempt to harness the power of lightning to run an Arduino was a step too far . . . who is to say? Regardless, we wound up with a few poor Arduino victims which needed to be resurrected. Here is how we did it, for less than the cost of buying new boards. These techniques should work with other Arduino boards, too. T he Arduino Uno (and its various clones) has been designed to be resilient in the face of poor treatment by both beginners and experienced users. The ruggedness of the ATmega328 microcontroller is a major factor in this. Despite this, we managed to break a few Unos. Most of these have been due to excessive voltages being applied to the DC jack or VIN input. Let’s look at the damage caused and how we can fix it. If you have an Arduino to fix, we’re assuming that you have some experience with Arduino boards and the Arduino integrated development environment (IDE) software. While there is no doubt that some Arduino-compatible boards are very cheap, almost to the point of being disposable, it can still be worthwhile to repair them. Below, we discuss three components that are likely to fail and how to replace them. Clones and DC regulators Some Uno clones use a different 5V siliconchip.com.au regulator from the original, and these cannot withstand as high an input voltage. This stung us twice before we figured out what was going on. Genuine Arduino Uno boards have an NCP1117 regulator, capable of handling up to 18V, while some clones use the AMS1117 instead, which is only good up to 15V. If (like us) you apply more than 15V to a clone, this voltage can find its way to places it shouldn’t, like the USB port of a connected laptop. This can also burn out the regulator. Replacing that regulator can not only fix the board, but you can replace it with a proper NCP1117 or equivalent, giving you the full 18V input range. Note also that the original Uno, and most clones, have an ATmega16u2 microcontroller as their USB-serial converter IC. This chip can also be damaged as it is connected to the ‘outside world’. Some clones use a CH340 instead, and this could potentially also be damaged. Australia’s electronics magazine We haven’t managed to blow up any ATmega328s (yet!), but we did have one that appeared to have a damaged ADC pin and as a result, was giving erroneous (and frustrating!) readings. If it does fail, this IC is easy to replace, as it is usually socketed. One way to quickly check that the ATmega328 is functional is by pressing the reset button and watching the onboard LED. It flashes twice when the Arduino bootloader starts up. If you don’t see this flash, either the micro is not getting power, it hasn’t been programmed, or it is faulty. Clones of the Arduino Mega and Leonardo often feature similar parts to those described above, so the following advice is pertinent to these boards, if not relevant to all components. Things that go pop The most likely component to require replacement on a dead Uno board is the main voltage regulator. Referring to the official schematic for the most common “R3” variant shown in Fig.1, this part is labelled March 2020  61 +5V +5V 100nF 10k 1k 1k K USBVCC 100nF 31 JP2 18 F1 500mA 19 20 USB TYPE B 1 2 USB+ 3 22 D– 30 22 D+ 4 21 29 GND 22 CON2 23 TS1 25 TS2 26 L1 27 5 1 X2 16MHz 1 F UVcc PB4/T1/PCINT4 AVcc PB5/PCINT5 XCK/AIN4 /PCINT12/PD5 PB 6/PCINT6 AIN3/INT5/PD4 U3 ATMEGA 16U2 PB 7/PCINT7 D– PB0/SS/PCINT0 PB1/PCINT1/SCLK D+ PB 2/PD1/PCINT2/MOSI PC7/CLKO/ICP1/INT4 PB 3/PDO/PCINT3/MISO RESET PC6/OC.1A/PCINT8 AIN6/T0/INT7/PD7/CTS PC5/OC.1B/PCINT9 11 TX1 14 ICSP1 15 SCK2 TXD1/INT3 /PD3 AIN0/INT1 /PD1 XTAL2/PC0 22pF OC.0B/INT0 /PD0 UGND 1 2 4 3 16 MOSI2 17 MISO2 5 6 24 RESET2 13 1k XTAL1 A K 10 RX1 UCAP AIN1/INT2/RXD1 /PD2 2 K PC4/PCINT10 PC2/AIN2/PCINT11 D2 RX  LED2  Vcc 12 AIN5/INT6/RTS/PD6 1M 22pF TX LED1 4 32 A A 9 M8RXD 8 M8TXD 100nF RESET-EN 7 6 GND 28 3 1k 1k Q1 FDN340P USBVCC +5V +5V S D 1k G 100nF 6 10k 1k 8 5 100nF 7 IC7b A ON IC7: 4 LMV3581DGKR  LED3 K 10k D1 M7 A U1 N CP1117 VIN K CON1 47 F IN OUT GND 100nF +5V U2 LP2985-33DBVR 5 1 VIN 3 47 F +3.3V VOUT ON/OFF GND BYP 4 1 F 2 SC 2020 ARDUINO UNO REV3 TM U1. It takes its input from the DC jack via diode D1, or from the VIN pin header directly. Its output provides the 5V rail. Both the 18V-rated NCP1117 and 15V-rated AMS1117 come in the SOT223 SMD package, and their specifications are very similar, apart from the maximum input voltage. If U1 is damaged, you will not be able to power the Uno from these inputs, but it may work when powered directly from 5V (eg, from USB). While removing U1 may allow the board to operate, we found that it is usually not the only damaged component. On two of our boards, U1 was feeding its input voltage to its output, 62 Silicon Chip which is an expected but unpleasant failure mode. This lead to further failures on these boards. In one case, we found that U2 was also getting quite hot when the board was powered from the USB socket or the DC jack. This is an LP2985 3.3V regulator which runs from the 5V rail. On a typical Uno board, the 3.3V rail does not power anything. It is simply there for anything else that might need 3.3V, such as an attached shield or module. Thus, an overheating LP2985 on a bare Uno is a sure sign of regulator failure. On another board with a failed regulator, we found that U3, the ATmega16u2 which provides the USBAustralia’s electronics magazine serial function, was getting quite hot, even when connected via USB. Since it too runs from the 5V rail, it had probably been irreversibly damaged. In both cases, the failure of U2 or U3 likely provided some protection to ZU4 (the ATmega328 microcontroller), by behaving like a very crude shunt regulator, as in both cases, the micro was still operational. When we say that parts are getting hot, we mean too hot to touch. Sometimes you can smell that there is a problem or feel the general warmth of the board, but it is still entirely possible that some part of the board is hot enough to cause a small but painful burn if you start probing around with siliconchip.com.au +5V +5V 100nF 100nF 100nF K 10k D3 MISO 1 RESET A RESET 1 RESET 9 1M 10 XR1 16MHz RESET/PC6 XTAL2/PB 7 IOH SCL +3.3V GND RESET 23 ANALOG INPUTS 24 25 A2 26 A3 A4 A5 SDA 27 SCL 28 ADC 0/PC 0 13 D3 4 PD2 D2 3 TXD/PD1 D1/TX0 2 RXD/PD0 GND 8 D5 D4 5 PD3 +5V D6 6 PD4 ADC5/PC 5/SCL D7 11 PD5 ADC4/PC 4/SDA D8 12 PD6 ADC3/PC3 D9 14 PD7 ADC 2/PC 2 D10 15 PB0 ADC 1/PC 1 D11 16 PB1 A1 D12 17 MOSI/PB3 SS/PB2 A0 D13 18 PB 4/MISO VIN AREF GND 19 PB 5/SCLK ZU4 ATMEGA 328P +5V SDA 21 AREF RESET VIN 6 XTAL1/PB 6 POWER GND 2 +5V 4 MOSI RESET 5 Vcc IOREF RESET SCK 3 7 20 AVcc ICSP2 D0/RX0 IOL GND 22 SCL SDA M8RXD M8TXD +3.3V 3 1k ‘L’ (IO13) 1 A LED4 IC5a PB5/IO13 2  K VIN Fig.1: the circuit of the R3 Arduino Uno design. The R2 used an ATmega8u2 instead of an ATmega16u2 to provide the USB-serial interface, but was otherwise very similar. your fingers, looking for a fault. So take care when inspecting damaged boards! Also note that we suggest you do not plug any potentially faulty Uno board into your computer’s USB port with external power applied, in case the board is back-feeding power into the USB pins. If you must do this, use something like our USB Port Protector (May 2018; siliconchip.com.au/Article/11065) to provide a measure of protection. You have been warned! The diagnosis The first Uno we repaired was showing two main symptoms: its 3.3V regulator (U2) was getting hot when the siliconchip.com.au board was powered, and it was not showing up on our computer when connected via USB, even though the power LED was on. We didn’t try powering it from the DC jack, to see if regulator U1 was working, as that would almost certainly make things worse. But we assume that U1 was indeed fried and had caused this other damage. In retrospect, the damage to U2 may have caused the 5V rail to sag enough to prevent U3 from working correctly. Because the 3.3V rail is not critical to a bare Uno’s operation, we suggest removing U2 first if it’s getting hot, and seeing if that results in any change. In our case, we jumped straight in Australia’s electronics magazine and replaced U1, U2 and U3, and that fixed it. The second Uno had just one symptom: the USB/serial chip, U3, was getting hot (and naturally enough, the computer wasn’t detecting it). A quick test with a multimeter showed 4.4V on the 3.3V pin, which is about the same as on the 5V pin! Since we couldn’t test U1 without risking further damage, we simply replaced all three ICs on the second Uno too. Chip replacement Both Jaycar and Altronics stock spare ATmega328 ICs, conveniently programmed with the Uno bootloader. March 2020  63 Fig.2: one of our boards after removing the defective parts and cleaning the pads. We’ve also removed the residual flux; the result is almost like a brandnew board. If you have a problem with this IC, this part is available over the counter (Jaycar Cat ZZ8727, Altronics Cat Z5126 or Z5125 without the bootloader). For the other parts, you will probably have to order from a larger supplier like Digi-Key or Mouser. For U1, we ordered an NCP1117LPST50 regulator. The part we ordered also had a T3G suffix, but this only refers to how the part is supplied (tape and reel in this case). For U2, we ordered the LP298533DBV. The part we used also had an “R” at the end, again indicating that it is supplied on tape and reel. U3 is an ATmega16u2 in a 32 pin VQFN package, with a part code of ATmega16u2-MU. Again, this had an “R” suffix to indicate tape and reel. As mentioned earlier, depending on how you plan to use your Arduino, you could just remove a damaged 3.3V regulator and not replace it if you don’t Fig.3: if you apply just the right amount of solder to the QFN pins, with plenty of flux, you should get nice clean joints like these. 64 Silicon Chip need the 3.3V rail. Equipment needed U3 comes in a QFN package, which is short for Quad Flat No-leads. It is very hard to solder or desolder without SMD-specific gear. We used a hot air rework station (available quite cheaply online) and solder paste, as well as the tools noted below. Removing U1 and U2 is difficult without a hot air station, but possible. Replacements can be fitted with a temperature-adjustable soldering iron, although you may need a fine tip. Tweezers, flux paste and solder braid (solder wick) are also very helpful. A magnifying glass will make working with these small parts easier. Even a mobile phone camera with digital zoom can let you get in close enough to inspect your work. Note that flux generates a bit of smoke when heat is applied. Use a fume extraction hood or work in a location with excellent ventilation. We set up a small 12V computer fan to suck the fumes away. It probably isn’t good for the fan in the long run, but it is better for our lungs. Flux removal solution is useful for cleaning up afterwards, as the generous use of flux makes the process much easier. Isopropyl alcohol or acetone can be used if you don’t have a dedicated flux removal solution. Take care, as many of these compounds are quite flammable. Remove the old chips Naturally, the first step in replacing Australia’s electronics magazine the defective ICs is to remove the old ones. If you have access to a hot air station, then it will be easy. Grasp the defective part using tweezers with one hand and lift the board by a few millimetres, holding onto the part to be removed only. If you lift it too high, solder is likely to splash around. Aim the hot air at the part, and after around 20 seconds, the solder will melt and the weight of the board will pull the two apart. If you smell burning or see charring, the air is too hot, and the board may be damaged. If you don’t have a hot air station, you’ll need to melt the solder on all the pins together, so they all come away at the same time. One way to do this is to build up a large blob of solder around the part, covering all the pins on both sides. Or if you’re fast, you can alternately heat the two sides of the chip and rely on residual heat to keep one side molten while you lift the part off. Alternatively, you can cut the pins off while the component is still soldered to the board; then desolder the pins individually. But it’s easy to damage the PCB tracks when cutting the pins on such small parts, and this is not possible for U3 as it has no pins. Once the defective components are gone, clean the pads using the flux paste and solder wick. Apply flux to Fig.4: If the ATmega16u2 chip is soldered correctly, Windows Device Manager should show it as a connected device when the board is plugged in. siliconchip.com.au ICSP HEADER FOR ATMEGA 16U2 Fitting U3 The QFN part, U3, is a bit trickier to replace; but without much prior experience with QFN, we aced it two times in a row. The pads are so far recessed that it is really difficult getting solder onto them. We tried loading up our iron with solder to get close to the pins, but it didn’t work. You may have better luck trying this technique with a very fine-tipped iron. So we had to use solder paste and hot air. If you have access to a solder stencil to suit a QFN32 part, use it, but this isn’t a requirement. Start by applying a generous amount of flux paste to all the pads, including the large central tab. Squeeze out a small amount of solder paste and mix it into the flux paste along each side of the IC. It should go right into the corners. The amount of paste needed is minimal, perhaps what you could pick up on the tip (not the head!) of a pin for each of the four sides. siliconchip.com.au 16.000 IO2 TX RX IO3 IO5 IO6 IO4 IO8 IO7 IO9 IO11 SC A5 A4 A2 A3 A1 A0 VIN GND 5V 3.3V IOREF GND ATMEGA 328 + RESET + RED DOT INDICATES PIN 1 ARDUINO UNO OR COMPATIBLE 9 1 CON1 IO10 IO12 IO13 AREF 3 2 1 ATMEGA 16U2 Fitting the replacements For U1 and U2, apply flux to the pads and rest the parts on the pads. These parts have a different number of pins on each side, so the correct orientation should be obvious. The flux may help to keep them in place, but it’s best to also hold them with tweezers. Apply some more flux to the top of the pins. Clean the tip of your iron, add some solder and apply the tip to one of the pins. For U1, try one of the small pins, as this will be less affected by the large copper track below. The flux will draw solder from the tip and onto the pin. If necessary, use the tweezers to adjust the position of the part, ensuring it is lined up with the pads and flat against the PCB. Once this is done, solder the remaining pins, turning up the heat for the large tab on U1. If you get a solder bridge, ensure all the pins are soldered down before attempting to correct it. This will prevent the part from moving. Apply flux, then the braid followed by the iron and gently pull away. ICSP HEADER FOR ATMEGA 328 17 25 CON2 GND RED DOT INDICATES PIN 1 4 the pads and rest the end of the braid on the pad. Press down on the braid with the iron and gently slide it to the side. The less residual solder left behind, the better the final result will be. We were able to get the pads nearly looking like they had never been soldered (see Fig.2). 2020 Fig.5: all Arduino Uno boards should have two six-pin in-circuit serial (ISP) programming headers, as shown here; one for each onboard micro. Sit the part on top, ensuring that the pin 1 marking lines up with that on the PCB. If you have trouble seeing it, position the ‘Atmel’ text on top of the chip to be closest to the USB socket. Ensure that the IC is located centrally on the footprint and hold it there with tweezers. Apply heat with the hot air gun directly to the top of the chip; you don’t want the air to move the flux or solder paste too much. The flux should soften and flow, and eventually, the solder paste will coalesce towards the pins. You need to ensure there are no grey smears of solder paste left, although there may be silvery balls floating around. This is fine, as they can be picked off later to avoid short circuits. Once you are sure that U3 has been soldered in place, clean it up by loading the tip of a fine-tipped soldering iron with a small ball of solder. Apply fresh flux paste to the pins and gently drag the tip along one edge at a time. If you have the right amount of solder, a nice-looking fillet should be left behind. If you get bridges between pins, try again with less solder on the tip to help remove the excess. The combination of surface tension and flux should leave a clearly visible fillet of solder to each pad (see Fig.3 – close-up of QFN pins). Testing Before cleaning up the board, you can test that U3 is soldered correctly by trying to connect the Uno to a computer. While the ATmega16u2 does not have any firmware loaded initially, these chips come loaded with a “DFU” (device firmware upgrade) bootloader which means that a Windows computer will recognise that a device is connected (see Fig.4). If you see a similar device appear, then the ATmega16u2 is communicating correctly, and you can clean any excess flux off the PCB. A fine brush (like an old toothbrush) is handy for cleaning among the pins. Note: do not use a toothbrush for brushing teeth after this! If it doesn’t appear in Device Manager, you need to resolder the chip and try again. Loading the firmware As we mentioned a little earlier, the TARGET PROGRAMMER ICSP HEADER MISO 1 2 VTG MISO 1 2 VTG SCK 3 4 MOSI SCK 3 4 MOSI RST 5 6 GND RST 5 6 GND TO D10 PIN ON PROGRAMMER ARDUINO SC 2020 Fig.6: This view of our ISP jumper wire is shown from above (as it would look plugged into the top of the board). The stray male jumper goes to a dedicated pin on the programmer board (pin D10 by default) while the other five pins simply go to the corresponding pin on the programmer ISP headers. Australia’s electronics magazine March 2020  65 Fig.7: here are the required AVRDUDESS programming settings for the ATmega16u2. The port at top left should be the serial port of the programmer Arduino. ATmega16u2 needs firmware to be loaded to operate as USB-serial converter. While the DFU bootloader can be used to upload firmware (using the Atmel Flip software), we found that it did not properly set the configuration fuses, meaning that it did not operate at the correct baud rate. So we’ll describe a more general method. This doesn’t use the DFU bootloader, but does require a small amount of extra hardware. This method can also be used to load the Arduino bootloader onto a blank ATmega328 chip. To do this, we use an ISP programmer, which plugs into the 3x2 pin ISP header. The Uno board has two ISP headers, one for the ATmega328 and one for the ATmega16u2 (see Fig.5). The process to program both is practically the same, but the firmware image is different. These chips can be programmed by using another Arduino board. Any 5V Arduino board with an ISP header should be usable, such as the Uno, Mega and Leonardo (and their clones). A sketch to do this is included with 66 Silicon Chip the Arduino IDE software download. The only extra hardware needed is a simple jumper cable to connect the programmer to the target board (see Fig.6). Make up the cable as shown. You can use a set of individual jumper leads with DuPont headers on each end (packs of these are available from Jaycar & Altronics). Alternatively, do what we did and solder a length of ribbon cable to a pair of 2x3 female headers, with heatshrink tubing used to protect the solder joints. From the Arduino IDE, open the ArduinoISP sketch from the following menu item: File -> Examples -> 11.ArduinoISP -> ArduinoISP. If you can’t find it, try upgrading to the latest version of the IDE. Select the correct board (for use as the programmer) and serial port and upload the sketch. duino IDE, and it is called AVRDUDE, the utility that performs the uploading of sketches to the boards. By the way, AVRDUDE is short for “AVR Downloader/UploaDEr”. To make things easier, we will use AVRDUDESS, a graphical interface for AVRDUDE. You have to download this separately, from: siliconchip.com.au/ link/aaxh As AVRDUDE will have been installed along with the Arduino IDE, once installed, AVRDUDESS should automatically detect its presence. With AVRDUDESS running, you need to adjust its settings to be like those shown in Fig.7. Be careful here since selecting the wrong Fuse byte values (L/H/E at right) can ‘brick’ the chip! From the top, set the Programmer to “Arduino” and ensure the port and baud rate match the Arduino you are using as a programmer. The baud rate should be 19,200 as this is the default for the ArduinoISP sketch (the code snippet shown in Fig.8 is where to change this if you need to). Connect the target end of the programmer to the target board at the ATmega16u2 ISP header, ensuring that the pin 1 designations line up, as shown in Fig.6. The power LED on the target board should light up as the programming cable provides power. If it does not, check the wiring. We occasionally found that connecting the target board caused the USB connection to the programmer to drop out. Try unplugging and replugging the USB cable in this case. To do a quick connectivity check, press the “Detect” button at the top right of the AVRDUDESS window. After a short delay, you should see the message in the lower window: Detected 1e9489 = ATmega16U2 And the MCU selection at top right should match. If you see: ERROR: Unknown signature 000000 Programmer software You also need to load appropriate software onto your PC, to upload the firmware image and fuse settings to the Arduino programmer. Luckily, such a program is also included with the ArAustralia’s electronics magazine Fig.8: this small fragment of the ArduinoISP sketch is where the serial port baud rate is set. siliconchip.com.au Here a Mega board is connected as a programmer, with the Uno board as the target. The “ArduinoISP” sketch transforms the Mega into a programmer, although any 5V board with an ISP header is suitable. Then the target processor is not being detected. Check your connections and try again. To upload the firmware, select the “Write” radio button under the "Flash" heading at upper left and then select the firmware file. You will have a copy of it hiding somewhere in your Arduino IDE folder (on our system, it was in C:\Program Files (x86)\Arduino\hardware\ arduino\avr\firmwares\atmeg axxu2\arduino-usbserial\Arduinousbserial-atmega16u2-Uno-Rev3.hex). If you are updating the firmware on the ATmega16u2 installed on a Mega board, you need to use the version with “Mega” in the name instead of “Uno”. To make your life easier, we have included the current version of both files in a download associated with this article on the SILICON CHIP website. Having selected the file, click “Go” under the Flash section. You should see messages like this in your output window: avrdude.exe: verifying ... avrdude.exe: 4034 bytes of flash verified avrdude.exe done. Thank you. This means that firmware has upsiliconchip.com.au loaded correctly. Once that’s done, under the section labelled “Fuses lock bits” at right, click “Read”. The L, H and E (low, high and extended fuses) values should read 0xFF, 0xD9 and 0xF4 respectively, just like our screenshot. We read these from another working Uno. If not, change them to match, then click the “Write” button in the same section. We only had to change the low fuse byte on our chip. Once this has completed, the ATmega16u2 is correctly programmed. You can now unplug the programming cable from the target Uno and connect it to a computer via its USB cable. The ATmega16u2 chip should now show up as a USB Serial Device. Reprogramming the ATmega328 You can also use this approach to install or repair the bootloader firmware on the ATmega328. This is necessary, for example, after plugging a new, blank ATmega328 chip into the Uno board. The arrangement is the same as shown above, except that you connect to the other ICSP header on the target board. Australia’s electronics magazine The required file is called "optiboot_ atmega328.hex". Optiboot is the name of the bootloader firmware. We have included this in our .ZIP download to make your life easier. Once the boards are connected, click the “Detect” button to identify (or manually select) the MCU, write the HEX file to flash and then change the fuse bits. In this case, they should be 0xFF, 0xDE and 0xFD for the low, high and extended fuse bits respectively. We used AVRDUDESS to read these from another Uno to confirm that they were correct. Similar firmware files exist for the Leonardo (ATmega32u4) and Mega (ATmega2560) boards and their main processors. By the way, it’s also possible to use an ISP programmer to upload sketch files directly to the ATmega328 on an Uno, bypassing the USB-serial connection. The connections are the same as for writing the bootloader to the ATmega328 chip. From the Tools menu in the Arduino IDE, select Programmer -> Arduino as ISP. To upload the sketch, press Ctrl-Shift-U or select the Sketch -> Upload Using Programmer menu option. Note that doing this will corrupt the bootloader settings, so if you want to use the USB-serial link for uploading in the future, you will have to re-instate this using AVRDUDESS, as described above. Pre-built ISP programmers If you don’t have a separate Arduino board, or find the above procedure awkward, you can purchase a dedicated Atmel in-circuit serial programmer like Jaycar Cat XC4627. This comes with a 10-pin cable, but a 10-pin to 6-pin adapter is also available (Cat XC4613). Or use Altronics Cat Z6540, which has sockets for both 10-pin and 6-pin cables. These programmers may need their own drivers installed, and will have a different programmer type, rather than “Arduino as ISP”. Conclusion We used the process described here to resurrect two Uno boards with around $10 of parts and some time. And we learnt quite a bit about the Arduino system in the process; hopefully, so will you. SC March 2020  67