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ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au How to unpack SMDs without losing them Thanks for a terrific challenge with the SMD Trainer Board project (December 2021; siliconchip.com.au/ Article/15127). I am looking forward to getting to the smallest part that I can manage. One thing missing from all the descriptions is how do you get the little blighters out of their capsules (cocoons, packaging, enclosures) without them escaping? I have struggled with this problem more than anything else so far, and am only on the large components above the line. This could be a good competition for us old coots – the oldest person to get the smallest component working. I am 82. (D. L., Clare, SA) ● We usually hold the strips component-­ s ide-up and peel the plastic cover off from the side using tweezers. Peel it back to expose just the number of components you want, then turn it upside-down just above your workbench surface, and they should drop straight down onto it. It helps to have a uniformly coloured, flat mat (or even a sheet of paper) to empty them onto so you can easily see where they land. You usually have to flip them over after tipping them out, but there isn’t much you can do about that. We would be interested to hear about the smallest parts that you can manage. There are three of us here in our early-to-mid 40s, and we struggle with anything smaller than M1206/0402. Even they are a bit challenging. We find M1608/0603 easy enough, and anything larger than that is a relative doddle. USB Cable Tester problem solved I recently put together the USB Cable Tester (November & December 2021; siliconchip.com.au/Series/374). It all went together quite easily and the calibration worked well. 108 Silicon Chip But when I put it together finally with the batteries inserted, it would not go to sleep. For the LCD screen to be initialised correctly, I had to wire an external power switch to switch it on with the box closed, after the LCD had plugged into its socket. With this switch connected, the LCD was initialised correctly and showed the countdown screen, but after the countdown finished, I did not get the main idle screen as shown in Screen 7 on page 92 of the December 2021 issue. Instead, I get the following display: USB Cable Tester DFP: VBUS,SHLD, When I insert a cable, the device appears to work correctly. For example, with a Type A to Type B cable inserted, I get: CABLE INSERTED:OK USB 2.0 0+ 0Check DFP and UFP. 327mV at 1A: 326mW This tallies with Screen 8. If I then press S1, nothing happens, so S1 doesn’t seem to act the way it should. The device remains on and doesn’t go to sleep. I hope someone can point out where my mistake could be. (J. H., Nathan, Qld) ● We think you have a short circuit between the Vbus pin and the shield of one of the USB sockets (hence the “DFP: VBUS,SHLD” message with no cable inserted). Check the resistance between those pins with an ohmmeter and inspect the sockets for solder bridges. Note: J. H. sent us a reply which stated: your diagnosis was spot on. There was a short between Vbus and shield, but you would never guess what caused it! After completing the calibration tests, I inserted the jumpers JP1 and JP2 back on one of their respective pins only. Unfortunately, with the jumper for JP1 sideways, the underside of the jumper came in contact with the shield of the neighbouring USB-C socket. Even more unfortunately, there was a little bit of the jumper’s internal metal connector protruding from the base, Australia's electronics magazine which was enough to cause the short between Vbus and shield. After fixing that, the device works perfectly. I’m so happy it wasn’t my soldering that was at fault, as I would have to go back to soldering 101 and repeat the course. Replacing USB Cable Tester sockets I have bitten off more than I could chew by tackling the USB Cable Tester kit (siliconchip.com.au/Series/374)! I successfully soldered CON5 (Mini USB). I then attached CON8, but in testing it, it detached, pulling one of the tracks off the board. So I really need to start again. I see that I can buy a replacement board, but where do I get CON5 and CON8 in the USA? Can you supply these three parts so I can start again? I’m not sure if I can use CON8 in practice because I don’t think it will ever be strong enough to stand having a connector inserted. The alternative is to proceed without CON8. Will the Tester function without it? (R. T., New York, USA) ● You can certainly leave off any sockets, and the circuit will still function otherwise (naturally not being able to test that cable type). We have all our micro-USB sockets (CON8) tied up in kits, but the specified part, Würth Elektronik 692622030100, is currently in stock at both Digi-Key and Mouser. As they are both based in the USA, you should have no trouble ordering from them. CON5 is a very common type of connector made by many manufacturers. You can use EDAC Inc. 690-005-299043 which is inexpensive and also in stock at both Mouser & Digi-Key (search for the part numbers). We think the problem you had with CON8 coming off the board and tearing tracks might be that you didn’t manage to wet the mounting tabs on either side properly with solder. Next time, you could try adding flux paste to both those tabs and the matching siliconchip.com.au pads on the PCB and make sure you get the solder nice and hot so that it fully adheres to both. Not all software includes ASM files I built the SMD Test Tweezers kit (October 2021; siliconchip.com.au/ Article/15057), but it does not work. I need to find a data sheet for the OLED, as I don’t yet know if the fault is in the OLED or the PIC. Also, I tried to download the .asm file from your shop. I found the .hex file but could not find the .asm file. (L. C., Forest Hill, Vic) ● The OLED modules are based on the SH1106 controller IC, although we have seen some very similar modules with an SSD1306 controller. Both data sheets can be found using web searches. The microcontroller code for this project is written in the C language, so there is no .asm file. Assembly language files usually are only used when the micro is programmed in assembly language (which we are doing less these days as it is more work and harder to debug). The MPLAB X project, including the C source code for this project, can be downloaded from siliconchip.com.au/Shop/6/5948 Troubleshooting AM/ FM/SW Digital Radio I have built the AM/FM/SW Digital Radio (July 2021; siliconchip. com.au/Article/14926). When I power the radio, all I get is a blank LCD (it does light up). I built it using a pre-­ programmed micro. What is likely to be the problem? I tried pressing the Reset button but that did not help. (R. B., Burlington, NC, USA) ● It could be any number of problems. Have you checked the voltages at critical points, such as the supply rails? Do you get anything at all when you adjust the contrast potentiometer on the LCD screen? If LCD is not set up due to program fault or wrong connection, usually just a line of squares will appear. SMD soldering can be tricky, and it’s very easy to have short between adjacent pins of fine-pitch devices. I find a jeweller’s loupe is essential for getting a close-up view. Note: we received a follow-up email that states: I just got the radio working! I decided to check the continuity of connections to each pin of the display and ATmega chip. To be safe, I removed the ATmega chip when doing this test. All connections to the display were fine. When testing the connections to the chip socket, I discovered that I had not soldered two of the pins for the encoder. Fixing that, lo and behold, the radio worked. The writing on the display is visible only when I view it at an angle of 45° or so. I see only white rectangles when viewing it head-on. Adjusting the contrast improved things somewhat, but viewing head-on, the writing is not visible. I will fool around with the contrast control some more. If it is still not good, I will get a new display from AliExpress. Ways of mounting ultrasonic transducers The ultrasonic transducer I ordered from your online shop (Cat SC5629) to build the High Power Ultrasonic Cleaner (September & October 2020; siliconchip.com.au/Series/350) came with a threaded steel ‘slug’. I searched those articles and the internet for an explanation of its purpose to no avail. There is a tiny spike at one end of the slug. Also, given that the transducer has a threaded hole in its face, do you think that bolting the transducer to the bath would provide better results than using epoxy? (G. M., Hughesdale, Vic) ● Our suppliers didn’t give us any instructions regarding those slugs either; however, we think that they are to plug the threaded hole in the face of the transducer if it is not being used to bolt the transducer to its mating surface. Doing so would slightly increase the contact area between the two surfaces, but we don’t think the difference is enough to matter. Still, it probably wouldn’t hurt to insert the slug if you will be gluing it to the surface. Just make sure to thread it with the spike first, and turn it until it is flush with the transducer’s face. The spike is just the result of the way the slugs are cut from a longer threaded rod. SMD Test Build it yourself Tweezers ● Resistance measurement: 10W to 1MW ● Capacitance measurements: 1nF to 10μF ● Diode measurements: polarity & forward voltage, up to about 3V ● Compact OLED display readout ● Runs from a single lithium coin cell, ~five years of standby life ● Can measure components in-circuit under some circumstances siliconchip.com.au Complete Kit for $35 Includes everything pictured, except the lithium button cell and brass tips. October 2021 issue siliconchip.com.au/Article/15057 SC5934: $35 + postage siliconchip.com.au/Shop/20/5934 Australia's electronics magazine March 2022  109 As for bolting the transducer on, you certainly could do that, but you’ll have to be careful drilling the hole to avoid distorting the bath face and clean up any burrs after drilling. The surface needs to be very flat at the mounting point. You’ll also have to make sure it’s sealed properly so that it can’t leak. Keep in mind that when gluing the transducer, the epoxy will fill in the gaps between the two faces to ensure good contact. Waterproof grease smeared on the transducer’s face and/ or bath face is needed to provide a similar effect if you’re bolting it on. Unexpected cause for SC200 Amplifier fault I hate having to ask for help, but I’ve spent days on this and I need to move on. My SC200 Amp (January-March 2017; siliconchip.com.au/Series/308) has all the transistors in their correct places. The soldering looks good, so I don’t think there are any dry joints. Transistor isolation from the heatsink measures fine. I’ve put 68W resistors in series with the power supply connections, as shown in Fig.14 on page 80 of the March 2017 issue. I’ve used this arrangement to successfully set up Ultra-LD Mk.3 and Mk.4 amplifiers in the past. When I turn on the power, LED1 doesn’t light up, but LEDs 3, 4 and 5 do light up. I spent a lot of time measuring voltages and couldn’t find the problem. However, I noticed that if I put a DMM probe in the area of the PCB around the bases of Q3 and Q4, LED4 turns off. About 10s to 20s later, LED4 turns on again so that all LEDs are on. That suggests a long time constant, possibly associated with the 1000μF capacitor in the feedback circuit. If I put a DMM probe on the base of Q8, LED1 and LED2 turn on, and LED4 turns off but begins returning to full brightness almost immediately. That said, sometimes when I switch it on, all five LEDs turn on straight away. With LED1 off at first turn-on, the voltages across the safety resistors are very low. With all the LEDs on, the voltages are just less than 1V. There’s no voltage across the output transistor emitter resistors. I tried disconnecting the feedback by lifting one end of the 12kW feedback 110 Silicon Chip resistor and earthing the base of Q2. In this situation, LED1 turns on as soon as power is applied, but all the other LEDs are still illuminated. I’d really appreciate any advice you can give me! (D. H., Sorrento, WA) ● That behaviour is quite baffling and suggests a major fault somewhere, such as an open-circuit or short-­circuit transistor. The fact that probing the base of Q8 causes things to change makes it likely that the problem is around Q7 or Q8. It’s almost as if the base of Q8 is floating. Check carefully around there. You might want to consider replacing Q7 as it is easy enough to do. Also, look at the 22kW and 2.2kW resistors and 1nF and 150pF capacitors in that section to verify they have the correct values, etc. Note: we got a response a couple of days later that read: this is embarrassing. Based on your advice, I decided to re-check every joint and component from the input to the Vbe multiplier. With the benefit of more light and a head-band magnifier, I got to the 10W resistor from input ground to 0V and spotted a green ring. Somehow, a 10MW resistor had gotten into my bag of 10W resistors! I replaced it and all now works well. I will measure all component values in future. More SC200 troubleshooting I have been building your SC200 Amplifier project. I made two modules for a stereo amplifier. One module is working, but the other has some problems. The Clip Detector LED is active, and considering the following measurements, I see it is working correctly. I am using the 5W 68W resistors in series with the power connection as I am still testing. I get the following measurements using the CON2 power connection as a reference: • Positive rail: +55.9V • Negative rail: -57.0V • TP1: -54.2V • TP2: -55.3V • TP3 to TP7: all -54.3V Removing fuse F2 makes no difference to the LED status. Green LED5 stays on while Red LED4 does not turn on under any scenario. On the other side, LED2 and LED3 work as expected. Australia's electronics magazine Measuring around the circuit, I get the following measurements. • D2 A: -54.7V, K: -55.3V • Q7 C: -6.87V, B: -54.8V, E: -55.3V • Q8 C: -55.3V, B: -55.3V, E: -55.9V • Q9 C: -54.3V, B: +54.7V, E: +55.2V • Q10 C: -54.3V, B: -54.7V, E: -55.2V • Q11 C: +56.0V, B: -54.2V, E: -54.8V • Q12 C: -57V, B: -55.3V, E: -54.9V I thought that Q8 might be internally shorted between collector and emitter, but it does not measure as a short. I have not replaced it, though. I have checked the isolation between all the devices and the heatsink. Given the measurements above, I thought there might be a short to the negative rail; however, I cannot find one. Do you have any thoughts as to what would be the cause of the unusual measurements? (B. D., Menangle, NSW) ● The reason that removing fuse F2 doesn’t cause the state of LED4 or LED5 to change is that the entire output stage is being pulled to the negative rail, so there’s never any significant voltage across F2. What we need to figure out is why that is happening. It’s likely to be either due to Q9 not supplying any current (because of a fault in Q9 or incorrect bias) or Q8 being continuously switched on (again, because of a fault or its biasing). You were on the right trail looking for shorts to the negative rail and checking Q8. Q9’s emitter is 0.7V below the positive rail, which is about right, indicating a collector-emitter current of 7mA. So it is probably not at fault. Q8’s base-emitter voltage of 0.6V indicates that it is likely switched on, perhaps too hard. Q7’s emitter voltage indicates that it is supplying enough current to Q8 to be responsible for this. With the output pegged to the negative rail, Q2 should be switched on, supplying current to Q4. As a result, Q3 should also be sinking plenty of current, preventing Q7’s base voltage from rising so high. We suggest you check the voltages across the 68W emitter resistors of Q3 and Q4 to verify that they are similar, indicating that both of these transistors are likely working. If that looks OK, it might be that Q1 is shorted or otherwise faulty and supplying too much current for Q3 to sink. Some measurements of the voltages continued on page 112 siliconchip.com.au Advertising Index AEE ElectroneX........................... 34 Altronics.................................75-78 Analog Devices............................. 9 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Hare & Forbes............................... 5 Jaycar.............................. IFC,53-60 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.............OBC Mouser Electronics....................... 7 Ocean Controls........................... 10 PMD Way................................... 111 SC SMD Test Tweezers............ 109 Silicon Chip Shop............ 106-107 Silvertone Electronics................. 65 Switchmode Power Supplies..... 11 The Loudspeaker Kit.com.......... 67 Tronixlabs.................................. 111 Vintage Radio Repairs.............. 111 Wagner Electronics....................... 8 around Q1-Q4 would help to diagnose this fault further, but given that they are inexpensive devices that are relatively easy to replace, if you can’t find a soldering problem or component value error in that area, you could just replace all four. wide. This can also damage the ignition coil that could arc over internally and short out the windings. That fault is more difficult to check; the easiest method is to swap the coil and see if that fixes it (after checking the IGBT using a resistance meter). Jacob won’t climb his ladder anymore Modifying EA Active Crossover frequencies We bought our son a Jacob’s Ladder kit for Christmas. We separately bought the coil recommended in this kit. Upon original completion, the kit worked fine. While using it, it stopped working and has not worked since. We asked the retailer about this, and they agreed that we had built the kit correctly. Still, they were concerned by the age of the kit on their shelves (which they stated may have been there for many years) and the possibility that components may have dried out over this period, leading to the failure. Do you have any experience with regards to which components regularly fail? (G. D., Redcliffe, Qld) ● Electronic components sitting on a shelf should not fail after less than ten years. The only parts that are likely to age significantly are electrolytic capacitors, and we have plenty of 30-plusyear-old electros that are still fine. Modern electrolyte formulas handle ageing much better than much older devices. The semiconductors, resistors etc will definitely still work. Check fuse F1, which may have blown. The most likely failure is the IGBT (Q1). Usually, when these fail, they end up with a short circuit between the gate and collector (left and centre pins) or the collector and emitter (centre and right pins). The IGBT is most likely to be damaged due to the spark gap being too I recently came across several Twoway Electronic Crossover kits I started assembling about 10 years ago that I would like to complete. They were sold by Altronics, Cat K5570. The problem is that I have lost the instructions that came with them. Also, they were initially designed for crossing between mid-high and high elements. I would like to use them for crossing over at 100Hz. Can you suggest the component values required for sub-bass applications? (M. O., Croydon, NSW) ● Those kits are based on the Active Crossover for 2-Way Speaker Systems project from Electronics Australia, May 1992. A scan of that article is available for purchase from our website (siliconchip.com.au/ Shop/15/6072). To change the crossover to 100Hz, the component values can be scaled using the original crossover frequency versus resistor value tables. You can change the 2043Hz value to 100Hz by multiplying the resistor values by 10 and the C2-C7 capacitor values by 2.043. So R2-R4, originally 39kW, become 390kW and R5-R7 become 470kW (from 47kW). The original 2.2nF capacitors can be 3.9nF in parallel with 560pF (4.46nF total, within 1% of the required value of 4.49nF). Capacitor tolerance (typically at least ±5%) will be the main cause of frequency shifts from the required crossover frequency. SC Notes & Errata Vintage Radio, February 2022: the 100nF capacitor directly below the 6K8M valve in Fig.8 should connect to the GND rail instead of the AGC line. In that same figure, there’s a 33μF 600V HT filter capacitor missing from the 250V rail to GND. USB Cable Tester, November & December 2021: in the circuit diagram, Fig.1 on page 30 of the November issue, the numbers for pins 8 and 10 on IC1 are swapped. Pin ANE2/RE2 connecting to USBU-GND via a resistor should be pin 10, while pin ANE0/ RE0, connecting to USBU-ID via a resistor, is actually pin 8. The April 2022 issue is due on sale in newsagents by Monday, March 28th. Expect postal delivery of subscription copies in Australia between March 25th and April 15th. 112 Silicon Chip Australia's electronics magazine siliconchip.com.au