Liitokala Li-ion 9V Repair...

    A fast bob & weave to what the odds predict will probably be my last successful repair before I return to my usual form of breaking stuff.   This little diversion involves a Liitokala 9V battery, and a poor wiring decision, made way back in the mists of time, that came back to haunt me.  The batteries in question were being used in my old detector, and as can be seen below, multiple batteries are needed to power this beastie.

 

 Two are used, in series, to power most of the electronics, while the third, labelled 'S' in the above pic, powers the speaker.  This somewhat complicated wiring setup needed to be routed appropriately, which is what the piece of vero-board, screwed to the battery compartment, aids in doing.  This setup worked perfectly for decades.  But if you look closely, you may notice that the three battery power leads are routed behind, and clamped in place, with the sliver of vero-board, courtesy of a few screws.  Also visible are the multiple soldered vero-board connections, that keep everything civilised.  What is not visible or obvious is that many of these soldered wires protrude through the holes, to the other side of the board.  Although all were trimmed, one, coupled with the clamping effect of the board, and in the fullness of time, still managed to skewer one of the battery leads, forming an intermittent dead short.

    But back to the battery.   Below is the battery PCB, with a replacement transistor fitted (bottom right) - that didn't work!  The original transistor had its identifier code burnt off of it (see pic), so I was working in the dark, and with limited options - all of my 'replacement parts' coming from scrap PCBs.

  

        Fortunately, I got lucky and found a transistor (pic below) that worked!

    More or less anyway.  The On-resistance of the transistor seems to be a bit higher than the original, which results in more of a voltage drop under load (0.2 - 0.3V @ 200mA tested) but still better than a sharp stick to the eye.  I also checked the Li-ion battery capacity, with & without the Boost circuitry;

        Repaired Battery voltage: 4.16V, no Boost - Capacity: 1080mAh

        Repaired Battery voltage: 8.6V, Boosted - Capacity: 350mAh

Interestingly, a capacity comparison between the 'Good' and the 'Repaired' battery, using mAh and Wh's, produced the following;

        Good Battery Capacity: 360mAh and 3.24Wh

        Repaired Battery Capacity: 350mAh and 2.98Wh

Which are close enough to make it a job well done!   Incidentally,  the measured, (1080mAh) versus the stated (1100mAh, by Liitoala)  are satisfyingly close, especially since these batteries have had a fair bit of use.  Of course, stating battery capacity in mAh's for Li-ion (boosted) 9V batteries is completely misleading, which of course, is the point!

Magnum Metal Detector Repair...

    I seem to have been having a run of repair-successes lately, so I figured I'd have (another) shot at a problem that has bested me for over 40 years.  Seriously.

    I may have already mentioned the issue in a previous post, it involved the Magnum Metal Detector's 'pin-pointing' function.  In use, when a metal object is detected while sweeping an area with the detector, the 'auto-tune' will tune out the 'find', zero the meter, and mute the audible find-signal, but only when the head remains stationary over the object - exactly as it should, there's nothing wrong with the auto-tuning!  However, in order to make pin-pointing more accurate, auto-tuning can be disabled, with a push & hold of the pin-point button.

    Thing is, even when I built the detector, the pin-point function never worked 100% - it was closer to 90, then 80%, then getting progressively worse as the decades passed.  What would happen was that, after a detection, and with the pinpoint button pressed & held, the meter would slowly start to swing from zero to fully negative, say, over the course of about 10 seconds.  The faster it would swing negative, the more useless it became.  This negative voltage-swing direction (labelled 'BAD' on the meter) also meant that the 'object-detected' tone, was instantly cut off - whereas a positive-swing (labelled 'GOOD'), retains the, 'object-detected' tone.  Without a tone-signal while trying to pin-point a find, the pinpoint function is practically useless.

    I started off by consulting with my current A.I, LLM of choice, Gemini.  I explained the issue and was advised to brush down the PCB board containing the responsible circuitry with isopropyl alcohol, which I considered a, too 'lo-tech', even insulting, suggestion - implying perhaps that something that trivial, hadn't already occurred to me.  But, try it I did, and no, it didn't work - but it appeared to have improved things marginally.  I then started wondering if the alcohol, running up the legs of the 2N3819 FET, that enables/disables the auto-tune circuitry, could somehow be responsible for the perceived improvement?  Removed from the circuit, it was apparent that time hadn't been kind to the FET in question - its legs once bright & shiny appearance, had become tired & tarnished looking, so much so, that they proved impossible to tin with solder.  So, rather than keep messing, I went searching for a replacement.

    All I managed to find was about half a dozen, genuine, yet equally tired looking  2N3819's, all likely bought at the same time in the distant past.  These proved equally hard to tin with solder, so I was reduced to scraping 40 years worth of grime off of them with a scalpel blade.  Back in-circuit, the replacement seemed to be performing a little better, than the first 'little better' of the original.  It was then I tried cleaning off the underside of the FET - where the legs enter into the transistor's plastic body - and the result was profound, almost a religious experience!!!  Pushing & holding the pinpoint button now, leads to practically no negative voltage drift, no matter how long it's held for (within reason).  The way it was always meant to perform, but never did.

    While all of this was resolving itself,  I happened upon another bizarre problem.  At fault was the shielded wire, that connects the upper PCB to the female socket in the case, that in turn accepts the male plug, that connects to the detector's head.  One of its wires had gone open-circuit.  This 'intermittent break had almost driven me to distraction in the past, exhibiting itself as wild swings of the meter, accompanied by the associated 'beeps' - I had presumed that it was down to circuit instability caused by aging components!  The break wasn't near either end of the wire either, where one would expect a wire to break, but right in the very middle!  Despite my best efforts, I managed to destroy the cable while trying to locate its break-point, and as I (understandably) no longer had any of the specified cable left, I opted for what was to hand, namely a bit of ribbon-cable.  And it seems to work just as well with this!  This turned out to be a huge discovery/fix as far as stability in use was concerned.

    The only other excitement I had with the detector, concerned a poor wiring decision, again, made in the 80's, that resulted in the death of one of my Liitokala Li-ion 9V batteries, as well as a few drained alkalines, before I figured out what was happening - inadvertent short!  On the plus side, though the Liitokala did suffer a fried transistor, I managed to get it up & running again.  I'll probably leave that 'repair-success' for another post. 

Dominox Propane Torch Head Repair.

 

    I got this on Amazon, coming on a year ago, right around the time that I was heavily invested in getting my car back on the road, after a timing chain slip.  As an earlier post here testifies, right about when I had all of the heavy lifting done, I stupidly destroyed the auxiliary belt tensioner.   I managed to get a secondhand replacement on eBay, but figured, as a penance, I'd also try repairing the broken one.

    Hence, the torch head purchase, as well as a tube of aluminium welding rods, also from Amazon.  That was also as far as I got, repair-wise - after all, the car was fixed, which was all the incentive I needed to do nothing!

    But it turned out that the torch I had bought for the job, needed a fix as well, specifically, the igniter didn't work.  I posted the below video as part of my review on Amazon, highlighting the problem.  Prior to purchase, I had noted on Amazon's reviews, that this was a reoccurring problem.  I was also aware that it was a Chinese copy of a 'Western-branded' torch - therefore about a quarter of the cost - so worth the gamble...

 

    ...but which didn't pay off!  So, there it lay for a year, until a day or so ago, when I finally had a look at it.  It may have been cheap, but it's a very nice (copy of the original) design.  The 'fix' was surprisingly easy, whomever assembled the unit was to blame - they neglected to thread the igniter-wire through the 'retaining spring', which keeps it centered in the torch barrel, preventing the ignition spark from shorting to ground.  Once done, the igniter works perfectly - no doubt as well as the torch costing 4 times the price, I'd wager!

    The Igniter's re-assembly sequence can be seen in the below pics.

Dominox Torch

 

Igniter assembly sequence

Igniter-wire centered

Igniter-wire displaced

   

 

Mastech HY3005F-3 Bench Power Supply Repair.

    Over the last two decades, I must have acquired at least a couple of thousand Euros worth of electronics test equipment.  Collecting test equipment, most like-minded individuals would consider understandable, after all, who doesn't like tinkering.  But measuring equipment without components to measure stuff off of, is of no use to a tinkerer, so add to that a few thousand more Euros worth of components to the bill of acquired goodies - while knowing all the while that 99% of them I will never use!  But, as the saying goes, "possession is nine-tenths of the law", and I'd rather possess, when the possession is needed - never mind that most of the unused possessions will eventually end up in a skip at some time in the future.

    Case in point, is the Mastech Bench PSU.  This was bought 10-15 years ago as a replacement, after I had smoked a beloved, though less-capable supply, with high voltage, and which I had 'liberated' from an employer in the distant past.  The Mastech performed well for years.  After a while, I would notice that the displayed voltage would fluctuate a bit, but no biggie.  Over a year or two, that observance became an irritant, then quickly became an annoyance, the voltage jitter increasing in lockstep to my temperament.  I remember at the time, trawling through Reddit, searching for a solution.  On the plus side, I learned that the Mastech - one of a handful of names that it was known by - all in all, was seen by most, as fairly reliable.  Jittery voltage displays was noted however, along with the consensus that either reservoir electrolytics or the voltage pots, needed replacing.

    In my head, I poo-poo'ed the potentiometer solution, mainly because on my PSU, both supplies fluctuated badly, despite, by my reckoning, the right-hand side having been the main work-horse, the left having had sparse usage.  So caps it was, I decided, and promptly ordered some.  But, as an afterthought, I added a bag of assorted pots to the BOM, just in case...

    And there both lay, gathering dust, for the best part of two years - enough time, that I had even forgotten about having ordered the pots!  By this time, the voltage fluctuations had gotten so bad, that I had grown fearful of damaging circuits I was powering it with.  The capacitor-swap was the first thing I tried, and that proved to have zero effect.  I was chuffed to discover, on rummaging around my boxes of components, the bag of pots I had ordered.  Long story short, the potentiometers proved to have been the culprits!  Once replaced, both supplies returned to being fluctuation-free - RESULT!

    Wee!

Frankenstein Fruit

     Possibly my shortest post ever!  I bought these 'fun-sized pears' over a month ago in Lidl.  While not quite 'as green as grass', they were damn close, but I figured, that I could wait a week or two, for them to mature.

    And wait, and wait...  As can be seen, at least one month on, ripe they aint!  There was 7 in the bag originally, and yesterday, selecting the most succulent, I took a bite.  The verdict, medium sweet, but still way too hard, and by no means 'succulent'.

    My question, why are completely inedible fruit like these for sale, and most importantly, what are they doing to these pears to slow their maturation?  It's unnatural to see a bag of pears, placed in an open window (therefore, plenty of sunshine), for this amount of time, to remain green like this.

    It might be interesting to track the above pear's ripening, so I'll try and resist the urge to go chomping on them, till they begin to resemble something edible - the pear, top-right, is likely to be the first contender.  Time will tell. 

26 Days Later.

    The above pic is all that is left of the bag of pears in question, 26 days on from when the 1st photo was taken.   One has ripened somewhat, but as of about 5 days ago, it was still too hard to bite into - and in truth, it has become more wizened than ripe.  I'm just after cutting it into chunks in the hope that the birds will find a use for it.

    In actuality, since the first post, I have already scoffed another bag of these pears, same brand/seller, while waiting for these to metamorphise (seems like a new word, that - think I'll claim it!) into something edible.  They rapidly ripened in to genuinely succulent pears, whereas, as can be seen, the Frankenstein pear that's left, is still bordering on rock-hard, and almost as green as it was over 2 months ago - makes me wonder/worry about what kind of alchemy/chemistry they use to extend shelf life. 

  

    Edit:

    Eleven days on, and some more observations on another bag of frankenstein fruit that is misbehaving (see pic. above).  On the face of it, these pears look promising, for something that's been allowed to ripen for about 3 weeks, going by their colour anyway!  Unfortunately, they appear to have decided to rot rather than ripen.  Two pears from the bag had developed huge blemishes, well on their way to spoiling, so were chopped up and fed to the numerous crows around here.  But despite all of the pears now being a healthy ripe colour, they are all still rock-hard, way too hard for my poor old teeth to attempt gnawing at.

    Lidl  seems to have gotten the message as well, or at least, they no longer had them for sale when I visited them today.