USB Connector Resistance: Another reason for slow phone/tablet charging

It was back in 2014 when I first published about USB cable resistance as one reason why your phone or tablet might be charging slowly. At the time, quality cables with good gauge wires were hard to find, and many “cheap” 28AWG cables were bought by unsuspecting consumers without knowing the downsides. Since then, it has become one of the most-viewed articles on this site, and the market has responded positively by advertising cable specifications more frequently.

However, this is only one part of the puzzle, and it is something I had realized almost right after I posted that article. Unfortunately, I couldn’t find the motivation to explain the technicalities at the time. Since then, a number of comments and reviews later, I feel that I’m better prepared to explain another issue which has existed since the dawn of USB but has gotten worse as we attempt to push more current through our cables.

Is that USB connector designed correctly?

USB at its introduction specified the ability to transfer up to 500mA at 5V over the USB A and B connectors. Throughout the iterations, the number of connector types have increased, and so has the current demanded by end-devices. USB “legacy” connectors still remain with us today and still remain relevant to many chargers which feature a USB-A socket.

Unfortunately, the design of USB focused on making things cost-effective, and as a result, these legacy connectors tend to be less-accurately specified from a dimensional standpoint. This means that connector sizes can vary significantly between manufacturers, but “it should still work”. How well this works in practice is a different story.

I’m sure that many readers may have experienced a headphone socket which crackles and might need you to turn the plug a little or pull it out slightly before a good connection is made.

Others may have even experienced a USB charging cable which refused to charge until a little lateral pressure is applied to the connector, and then it worked. Or maybe, you needed to pull it out just a tiny bit.

These are all manifestations of contact resistance which may arise due to connector incompatibility.

The design of the USB connector is such that this problem should be minimised in properly-designed connectors.

I will focus on the USB-A connector, although the principles hold true for most types of connectors. The first feature to look at is the shape of each of the pins in the connector. Properly formed connectors have a tapered design at the front, which leads to a “raised ridge” in the centre. This whole pin is gold-plated to avoid oxidation and maintain good contact.

When mated with its appropriate mate which contains gold-plated contact springs, the raised ridges concentrate the pressure to “break through” any surface dirt. The plastic tongues on the undersides provide a stable “backing” and increase the pressure between the spring surface and the contact while enforcing connector alignment. The outer shell keeps the connectors from pulling apart, provides a continuous shielding path and maintains the alignment of the pins.

This all sounds pretty simple, but in reality, I’ve seen a lot of things go wrong:

  • Some connectors I’ve seen have absolutely no gold plating whatsoever, which makes them liable to oxidation and potentially depositing dirt onto perfectly-good connectors. Others have false “gold-coloured” plating which wears off after only very few uses.
  • Others have tongues which are too “thin” in the vertical dimension, and thus the plug doesn’t make good contact unless it’s tilted downward or upward.
  • A cost-saving measure seems to be the use of “thinner” and more “flexible” shell materials for the plug, which are liable to bending and mis-shaping after the application of a mild amount of mechanical stress. This jeopardizes the tightness of the connection and can lead to premature contact wear due to intermittent contact.
  • Some are “cost-reduced” in manufacturing resulting in “flat” pin profiles that do not achieve as reliable contact as the raised-ridge profile which it should have. This is common on “PCB” style plugs.
  • There are some completely unconventional plugs (e.g. a “reversible A” or a “shell-less A”) which violate the standard and thus rely on other parts of the socket to compensate in order to make the connection work.

Another point is that connectors are not designed to be used forever. Most connectors have data-sheet lifetime specifications of about 10,000 cycles to a maximum contact resistance of 30mohms. This sounds plenty, right? For 10 cycles a day, it’s almost three years to failure.

The truth is that this data-sheet stated lifetime is for ideal circumstances. This means not exceeding any current ratings, using their appropriate mating partner connector, under perfectly clean circumstances with no added mechanical stress. Once you add reality into the mix, these ratings can go right out the door.

For starters, any trapped particles can act as an abrasive compound wearing away the precious gold plating and serve to impact resistance. Any contamination from atmospheric deposition can result in corrosion where the plating is broken. Arcing from “loose” connections due to poor “partner” sockets can destroy the coating. Damaged sections increase contact resistance. Once you add the possibility of the outer shell being dimensionally affected by bending due to stress, a good connection is hard to ensure.

Hopefully, now, you can begin to appreciate that a USB connector is not as simple as it appears. But you might not be convinced that this is a problem.

A look at the cable resistance shows that for a 1m 24AWG cable, the cable contributes about 168mOhm of resistance. The connectors are supposed to be up to 30mOhm each at the end of life, or 60mOhm total. This isn’t entirely negligible, especially if we improve the cable. A better cable can be hamstrung by poor connectors!

“QC2.0/3.0 and higher voltages eliminates the problem!” Really?

One of the biggest push-backs I’ve had in regards to the original cable resistance article is a misconception that higher charging voltages solves the problem. The problem is that there are two problems in reality and neither of them are completely solved by higher voltages.

The first problem is under “regular” 5V charging, some devices may show slow charging or no charging at all when connected to long cables. When they upgrade to a QC2.0 charger, they see the device can now take a charge, and think that the problem is solved. Instead, it hasn’t – and it’s merely been masked.

From a simplistic view, to convey the same power at a higher voltage requires less current, therefore the resistance of the cable causes less voltage and loss. This is true. However, the other half of the story is that Quick Charge is developed to help speed charging of the phone, and instead, it tends to use currents in the 1.2-2A region to best optimize the charging where possible. This is, coincidentally, similar to the currents drawn by regular 5V charging and hence results in a similar amount of voltage drop.

However, people then seem to think that because it runs at a higher voltage, a 0.25V drop isn’t going to be a problem because it’s a smaller percentage of the voltage. This is NOT true, and the reason is simple.

Any voltage dropped over the whole cable assembly’s resistance is produced as heat. This is dependent on current and resistance only, so P=I^2*R. As 5V “regular” charging and Quick Charging nominally operate in similar current regimes, the voltage drop and power lost in the cable is pretty similar.

The two dark green lines indicate the maximum resistance of a single connector and two connectors at end of life. The light-green lines are an estimate of a 50cm 24AWG cable with two connectors, and 1m 24AWG cable with two connectors at end of life. Note that at 1.5A for the cable, expected voltage drop is 0.21 to 0.255V, which is right on borderline acceptable for regular 5V charging. The power dissipated in the cable and connectors is 0.315-0.383W. It’s not an unsubstantial amount – it’s about the same as holding your hand in front of a small battery-operated 3 x COB LED torch.

If you are to expect that 12V charging, being about twice as high of a voltage as 5V, can tolerate twice as much voltage drop, this would increase the power loss to about 0.63-0.766W. This is not a wise move, because the heat has to go somewhere, and now the cable gets twice as much energy dissipated per unit length. Where the cable is well made, the power should be somewhat “evenly” distributed across the cable, but if there is a fault with a contact, the lion’s share of the resistance can concentrate at that point. In the worst case, blindly pulling current despite a falling voltage compounded with a localized resistance in the connector can result in melted connectors and damage to devices. A higher charging voltage does not fix the issue of power being dissipated in and along the cable and connectors!

Practical Effects – A “slow” quick-charge?

If this graph looks a little familiar, it’s because it’s basically the graph from my Mi Power Bank Pro review, just with two traces added to the graph.

In order to test charging current profiles, I grab an appropriate wall-charger and throw a modified charger doctor current shunt in line to measure the current with a Keysight U1461A multimeter connected to a PC.

When first testing the “regular” 2A charger, there was no problem. The unit clocked in a 5 hour and 45 minute charge time. But then I tried to test the QC2.0 charging ability and got the grey curve, clocking in a charge slower than with the non-quick charge adapter.

Thinking this was a compatibility issue, I decided to use a different QC2.0 source, namely the old Mi Power Bank Pro. As a 10,000mAh power bank can’t fully charge a 10,000mAh power bank due to losses in conversion, I took advantage of the simultaneous charging ability. I connected a regular 2A charger to the first power bank to keep it “topping up” while it output QC2.0 to the power bank under test. Because of the close proximity of the output port to the charge port, I fitted a 20cm 24AWG USB extension cable. Interestingly, the charge was still slower than just doing it from a regular 2A charger.

The fault was not with the power bank, as I reverted to the original QC2.0 wall-charger (to be shown in a future posting), but with a small modification.

I noticed that the shunt was not making quite a solid contact with the USB port on the QC2.0 charger only, so I decided to “crimp” the USB socket to flatten it slightly. This increases the contact pressure, which should improve contact resistance. Guess what? It worked and produced the ~3 hour 40 minute curve.

This is a practical illustration of the following points:

  • Having quick-charge does not necessarily overcome USB cable and contact resistance as this is a dynamic function of the “mating” of the two connectors. Each plug and unplug can produce slightly different results.
  • USB connectors are not made equal – what worked with my Xiaomi 2A charger did not work properly with my QC2.0 wall adapter.
  • While a known good source of the old Mi Power Bank Pro was used, the addition of an extension lead added additional contact and cable resistance, nullifying any benefits. As a result, it’s hard to know if you’re improving the situation or not when juggling around cables and chargers.
  • While it might be easy to fault the charger doctor’s connector as being “cheap and out-of spec”, chances are, most products have connectors which vary in dimensioning enough to create problems at high currents. The device sensed the resistance and backed-off its current draw appropriately to prevent any damage. However, compared to a proper contact with the 2A charger, quick charging proved to be (ironically) slower prior to this “hack”.

While pinching the connector does improve the contact pressure and contact resistance, it is not advisable to do. This is only a “temporary fix”, as by pinching the connector, you can cause permanent damage to the mated connector. This can happen by “grabbing” the tongue too tightly such that it fractures on applied stress or attempted disconnection, additional fatiguing of the contact springs through over-pressure and wear to the plastic tongue which can cause it to “thin” more rapidly and fail to apply proper pressure to other connectors. It will also cause the plug’s pin’s to be “flattened” more quickly, and the gold plating on both plug and socket to wear rapidly.

Other Issues with USB cables

While I have mentioned cable and contact resistance, there is another element of resistance that can come about from the connection of the wire to the plug itself. This point is usually soldered, and depending on the quality of the cable-strip and solder operation, the resistance can vary. It should be quite small by comparison, however, there has been some evidence to suggest that poor quality connections can occur in cheap cables due to over-stripping of conductors resulting in a few strands being fractured at the strip and not making connection. This produces a localized area of increased resistance, and could be responsible for cases where the connector-plug side shows melting.

Some other cables have been made with non-copper wires as well, which will likely have a higher resistance for the same wire gauge. Be careful!

There are “charge only” cables with only the two power conductors connected, but no data connections. Some may have them locally shorted to present as a dedicated charger to the end device. These cables are incompatible with Quick Charge technology which requires the use of the D+ and D- lines for signalling.

Another issue is with insulation wear-out. As USB cables get flexed quite frequently, areas near the plug may be flexed sufficiently for insulation between wires to break within the outer sheath. This is especially probable for specially “thin” or flat cables where regular PVC insulation is replaced by enamel coating (as with headphone cords). While not directly observable from the outside, such loss of insulation results in an internal short circuit within the cable, which can serve to heat the cable and cause it to burn. I suspect this may be what happened in this “viral” image of a burnt cable on a bed. Regular chargers are generally current-limited to source a total of 5 or 10W, whereas fast-chargers can source up to 18W. This is not insignificant, as a hand-held glue gun or battery-operated soldering iron needs just 7W to operate.

This isn’t as rare as it might seem either – I have been approached by a friend who claimed the Xiaomi power bank I recommended was poor because it charged the phone slowly and kept discharging on its own when connected to the cable with nothing attached. The truth was, the cable had a high-ish resistance internal short which was not enough to cause visible damage, but enough to waste energy. Had the cable worn further, a more drastic result may have eventuated, but the power bank was not at fault.

Conclusion

While the market was quick to respond to the wire gauge problem, it turns out connector resistance is equally as important, or even more important. Problems with connector resistance can arise due to improper connector design, improper dimensions in manufacturing and wear and tear to gold plating on contacts.

Simply upping the voltage may help the symptoms, but does not solve the underlying inefficiency of energy being lost as heat. Where quick-charging is used to improve charge times, the current flow magnitude is roughly the same and there is still a risk that poorly constructed cables with poor contact resistance can heat-up and melt. As a result, even if higher voltages are employed, devices are still sensitive to voltage drops in cabling and connectors to avoid the possibility of excess heat build-up which could lead to fire risk and property damage.

Traditional USB connectors were not specified with close tolerances for dimensions, which results in such problems in ensuring good contact between connectors of different makes. Cost reduction, by reducing materials used, and unconventional USB connector designs also can cause issues. Connectors wear out and become damaged over time. Newer connectors such as USB-C are much tighter on tolerances and should improve the situation, despite the smaller connectors and contact areas.

The solution to the issue is, unfortunately, not so simple for existing “legacy” USB connectors. Most of the time, consumers have absolutely no say about the connectors used in their devices, chargers, cables, etc. and take it for granted that it works well as it’s “USB” standard. Ensuring that products use “name brand” connectors from trusted connector companies (e.g. Amphenol, Molex, Foxconn, Pheonix Contact, etc) that are properly terminated can help. Reducing unnecessary connection/disconnection to avoid wear and avoiding physical strain on the connector is also advised. In a pinch, the situation might be helped by “crimping” the connector slightly, but that is likely to cause accelerated connector wear and is not advised.

Aside from the connector, the wire-to-connector joint is also a potentially vulnerable point, as well as the insulation within the cable assembly. Reports of “phone fires” and “connector melting” often fail to distinguish as to the true cause.

Posted in Computing, Electronics, Power Bank, Tablet, Telecommunications | Tagged , , , , , , , , | Leave a comment

Event: BoM Space Weather Users Workshop (16 – 17 Nov 2017)

Usually, I tend to make an effort to make a few postings throughout the weekends, but this weekend has been a little bit of an exception. That’s because on Thursday 16th and Friday 17th November, I attended the Bureau of Meterology’s (BoM) Space Weather Users Workshop. It is held once every two years, and intended to be a customer forum where space weather product users can discuss space weather effects on their industries. This year, it was held at the Sydney Nanoscience Hub at Sydney University, with a tagline of National Security and Prosperity. Thanks to UNSW, I was afforded the privilege to attend. Here are some of the highlights and some of my thoughts.

The Sun is More Than Just the Light in the Sky

On a day-by-day basis, most people give little thought to the sun, except maybe in a weather sense. Is it sunny? Do I need to put on sun-cream? Or do I need my umbrella?

But the truth is, the sun is (practically speaking) a large nuclear explosion situated eight-light-minutes away from the Earth – one that has a bit of a cyclical temper for throwing out hot gas, charged particles and magnetic fields. These are more accurately termed solar flares and coronal mass ejections (CMEs).

How they affect Earth is less widely publicized. But the truth is, as we grow into a more interconnected, interdependent society reliant on increasing amounts of technology, we become more vulnerable to the effects of space weather. Already, it is known that space weather can affect:

  • Satellites  – causing malfunctions such as single-event upsets (SEU), deep dielectric discharge (DDD) and surface charging. Charged particles can linger inside the Van Allen Belts and result in accumulated damage to semiconductors over time depending on orbit. Solar panels can suffer permanently reduced output.
  • Radio Signals – ionospheric disturbances from X-rays can cause HF black-outs, higher charged particles can cause sporadically enhanced communications increasing interference, scintillation multipath can swamp out signals from GNSS satellites denying availability.
  • Power Systems and Telecommunications – cables can develop geomagnetically induced currents (GIC) from changes in ionospheric currents, inducing slow time-varying currents which can have significant magnitudes for long conductors oriented east-west and can destroy cables associated equipment (e.g. transformers through magnetic saturation) or cause complete grid collapse.
  • Water, Gas and Railway – pipes and tracks can suffer enhanced corrosion effects causing failure.
  • Aviation – loss of radio signals, but also increased exposure to radiation for passengers and equipment when traversing polar routes.
  • Spacecraft and Astronauts – radiation doses could be severe and evacuation plans are probably necessary.
  • Atmosphere – aurora may be visible.

That is just some of what can directly happen from regular solar storm events. Of course, not all possible effects will be felt, depending where you are on the Earth (latitude), the design of the systems involved and the alignment of any flares/CMEs and the Earth. However, what isn’t shown is the interdependency of industries on services provided by others.

Such space weather events are not that uncommon and have happened in the past – some of the most famous include:

There have been a number of articles about the potential impacts if a solar storm were to happen today, but yet, it seems that we are still slow in taking actions to effectively deal with the possibility of another major solar storm of the scale of the Carrington Event. The truth is that it’s not that unlikely, with estimations of a chance of 12% in any decade.

Preparing for the Worst

The good news is that it seems that we are starting to take this area with a bit of seriousness. From the conference, it seems that the physics of what drives the ionospheric effects we observe, and the behaviour of the magnetic field and Van Allen belts are much better understood and modelled than I expected. However, we are still at a stage where forecasting the space weather conditions into the future is still riddled with uncertainties, and “nowcasting” the present conditions is still met with some difficulties. When it comes to the human effects of space weather, understanding and mitigating the risks, we are still at an early stage.

A number of US agencies have seemingly paved the way with a National Space Weather Strategy and Action Plan, however, the truth is that the issue is a global one and requires global co-operation to reduce duplication of efforts and ensure consistent approaches. Unfortunately, one barrier to this is the lack of open and transparent data sharing in (traditionally) siloed industries where competitive advantage is the key. One way around this, although imperfect, is to have trusted sharing such as in TISN and partner with an appropriate agency such as CIPMA to do the analysis – both organizations which I was not aware of prior to the workshop.

Addressing and mitigating issues requires a lot of scientific knowledge to understand the issues at hand – this is where academia and research comes in. To prepare for the storm, various industries have done some research to understand whether a “conventional” solar storm causes them any issues:

  • AEMO has set up some procedures in case of solar storms – predominantly involves notification of downstream stakeholders and a strategy to proactively return assets to service to ensure grid stability.
  • Powerlink in Queensland worked with AEMO to monitor geomagnetic induced currents in the neutrals and HV network side of their high voltage transformers on an ongoing basis. Interestingly, they saw some perturbations in neutral currents and 5th harmonic current from a 6th September 2017 X-ray flare and CME event. The magnitude was not particularly great at about 15A for a short duration, although it was probably not worst case. Interestingly, they showed the use of a fibre-optic non-conventional current transformer to monitor the high-voltage side that worked via Faraday rotation effects. This seems quite promising for non-invasive and low-risk (from HV) monitoring despite limited low-current accuracy.
  • Transpower in New Zealand had ongoing neutral current monitoring for a long time, and instead moved to modelling the currents based on magnetometer readings which achieved a good agreement. They had experienced a transformer failure at Islington, which by simulation, is suspected to be caused by a neutral current flow of about 100A. Simulating for Carrington events shows neutral currents of 200 to 2000A (!!) in some of their transformers. Network based simulation showed that removing transformers from the system improved resiliency as current flow is dependent on Earth conductivity and orientation of lines – less lines increases resistance limiting flow.
  • BoM have also done some modelling and work with measured data, reasoning that the difference between modelling and reality is often a scale factor due to simplified ground conductivity assumptions in their simulations. However, it did show that simply being at a higher latitude in itself did not make the grid more vulnerable to large neutral currents – although the amplitudes they simulated seemed to be “tolerable” in their scenario.
  • Jemena looked at gas piping and cathodic protection. GICs make it difficult to ensure continuous protection, but unlikely to break down passivation layer due to short time-scales. May destroy insulating joints, and in coated pipes, concentration of corrosion occurs in pin-prick holes.
  • It seems that widespread GPS degradation has been caused by ionospheric scintillation, however, widespread GPS loss due to radio blackout (increase in background noise) has already been seen. Prolonged loss of GPS on the ground could be major, as position, timing and navigation services all rely on the signals.

Man Made Space Weather?

One of the most fascinating presentations was given by John Kennewell of the Australian Space Academy on Space weather effects of a high altitude nuclear explosion (HANE). This, as he likes to term as “anthropologic space weather” might not be so farfetched given the present political situation.

He makes references to the Starfish Prime experiment and the resulting effects of the EMP, which are well known. What I didn’t realize was the magnitude of some of the induced pulse peaks which have some very short-rise components inducing a (claimed) 2kA on a “telephone line”. The other thing I didn’t realize was the released nucleotides can get trapped in the atmosphere at a high enough altitude to destroy low-earth-orbit satellites over time as they take a while to break-down. As a result, maybe we shouldn’t just fear space weather effects from the sun – but also locally as well.

Not So Scary … But Nifty!

Not all of the workshop was about doom-and-gloom. There was some nifty things I didn’t know about, some of which was elaborated at great detail:

  • SBAS Trial on Inmarsat-4F1 – I’m aware that we had old-fashioned DGPS on MW for maritime uses, and subscription based DGPS systems for on-land uses, but the government is actually running an SBAS trial using an L-band transponder on a commercial satellite to provide three different levels of corrections. The first level is similar to WAAS/EGNOS for regular GPS users. There is Dual-frequency/Multi-constellation SBAS for better performance, although not backwards compatible. The third mode is Precise Point Positioning that requires convergence time but provides solutions better than 10cm.
  • Use of GPS Radio Occultation measurements through the COSMIC/COSMIC-2 missions to help improve weather forecasting through better temperature profiling of the atmosphere by measuring the refraction of GPS signals. A technique I wasn’t aware of until now, and a little ingenius now that I think of it.
  • Military presentations about the Jindalee Operational Radar Network (JORN) and improved ionospheric modelling to improve over-the-horizon radar (OTHR). Also, a presentation about their JP9101 Project Phoenix: Enhanced HF Communications System which will see faster HF communications occupying larger bandwidths become reality, and the phase-out of older technologies (such as TADIL Link-11).
  • Space Weather Services from the Bureau of Meterology including Auroral Alerts which will (soon) have an auroral patrol camera in Tasmania. There is also online HF Radio prediction services (I really like GRAFEX, easy to use and quite accurate I find).
  • A presentation about INSPIRE-2 cubesat of the QB-50 project (and UNSW-Eco got a mention) , which sadly isn’t going so well due to some issues with corrupted filesystems, deployment of antenna issues due to depleted batteries, damage to a comms board temperature telemetry channel and issues with the downlink. I should really get out my antenna just to capture a few frames of telemetry when I can …

Conclusion

I’m glad that I had the opportunity to attend the workshop, as it was quite eye-opening and interesting to be exposed to various aspects of how space weather can directly and indirectly affect our everyday lives. While it was a “Space Weather Users Workshop” targeted as a BoM customer forum, it also had many technical aspects and introductory presentations which helped reinforce concepts which I had only a brief awareness of. It has given me a lot to think about, a few tools to play with and a few numbers here and there to look at. There were also presentations of current research which made references to technology I was not aware of, and investigations showing effects of even mild storms which I was not aware of. For the most part, we live our day-to-day lives thinking that “the sun will come up tomorrow,” rather than “the sun might kill us tomorrow.”

But it’s not all doom and gloom. There’s a lot of interesting technologies that were mentioned as well, and it’s showing us that people are putting thought into it.

But … maybe the biggest message is … it’s not that hard to see an aurora – just take a holiday to Tasmania when the solar cycle picks up again in another five or six years.

Posted in Event, Opinion | Tagged , | Leave a comment

Repair (?): ICOM IC-R75 that won’t turn on!

Returning home from holidays is not easy. In some sense, I’d like to call it a holiday hangover. You start walking on the wrong side of the road, sleeping at odd hours, and in perpetual need of energy to unpack everything and resume life “at home” as usual. Part of that was getting all of my HF-gear back up and running so I could enjoy the airwaves for a bit.

The ICOM IC-R75 is a receiver I hold dear – it was an expensive purchase for me as an undergraduate uni student back in 2010, but it was an investment I was prepared to make as I decided that I wanted to do some shortwave listening, utility monitoring and amateur-radio monitoring. I bought an ICOM IC-R20 just a few years prior, and it proved to be another expensive but good buy, as it got me into amateur radio satellites and scanning the analog transmissions (which are sadly, drying up).

While the IC-R75 I have is not one of the prized earlier models with the S-AM capability, nor one retrofitted by Kiwa to actually make it work, it was one that has travelled with me between houses and received a host of upgrades including the DSP board (meh), two IF filters (useful) and a high stability ovenized crystal oscillator (very useful).

Interestingly, it is one of ICOM’s success stories, being introduced in 1999 and only just being discontinued in 2016 (or so they say). SDR has finally come of age, and their new standalone table-top receivers are SDR based (such as the IC-R8600), with advanced features but also … an advanced price tag. Not long after getting the IC-R75, I did get my Winradio Excalibur G31DDC which became my primary unit, but the R75 still had lots of “work” to do, as it was still a bit more sensitive.

Imagine my dismay when I couldn’t get the thing to power up after getting it all plugged in.

The Cause

I suspected the power plug to be the issue. It uses a barrel plug and surprisingly, there was lots of corrosion or dirt on the barrel. I gave it a good wipe down and rub, and it became shiny as new. I plugged it back in, still no dice.

Then I realized that the tongue of the connector on the radio had a lot of white fluffy corrosion on it too. As a result, I got a jeweller’s flat-blade screw driver and scratched most of it off, and polished it with a fine fragment of wet-and-dry sandpaper.

Plugging it in gave an occasional click of the relay, but the unit still didn’t power up consistently. When it did, it sometimes reset on a loud audio transient, and then eventually it stopped working again.

Because there was some play in the connector on the board, I feared the worst, and decided that the jack might have a broken connection to the board somewhere.

As no stranger to servicing the inside of the radio, I opened it up only to find that the jack is encased from all sides even with the outside covers removed. There was no shortcuts to getting the board out.

Instead, all the screws would have to come out, all the flexible flat cables and coaxial jumpers. The UT-106 lead would have to come out too, noting one end is soldered to the mainboard, and two clips to transistor/regulator packages that use the side of the radio as a heatsink.

After undoing all of it and taking the mainboard out, guess what? The solder joints were absolutely pristine and intact, and the slight play in the plug was bending of the legs of the plug. That wasn’t good, but it was no fault found here. Reluctantly, I reassembled the unit, and replaced the CR2032 coin cell which was down to just 0.6V now.

The fault, as it turns out, was related to the two “springy” contacts that make contact with the centre post in the connector. Some plastic had worn off from the connector, and collected over time on the leading edges. The metal also seemingly had fatigued somewhat, so the centre connection wasn’t reliably being made. Scratching off the dirt and blowing it out helped, but bending the side pins back towards the middle to give it a little more tension finally fixed the problem. The metal will probably fatigue in due time, in which case, replacing the connector is probably the best solution. At least, I’m back monitoring the air!

Conclusion

Sometimes some problems are really simple ones … and to convince yourself otherwise is going to lead you to do a lot of unnecessary work. At least it’s back up and running … and opening it up wasn’t entirely worthless since I did replace the CR2032 for the onboard RTC. But who would’ve guessed that my first guess was so close to the problem – it was the plug after all.

Posted in Electronics, Radio | Tagged , , , | Leave a comment