I’m an idiot!
 

I finally got round to looking at my Heathkit IG18 Audio generator a week or so ago.
Not working, fault traced to power supply. Duff series pass transistors, and although the smoothing caps had been replaced they were still ancient. Whip out caps and transistor. So far so good( this is where the idiot part comes in). Fit new caps, 470uF 63 volt. Even managed to get them the right way round. Quick look at transistor specs. BFX85 should be OK as a replacement. Fitted transistor from several I had sorted, lying on the bench.
Now sort of worked, but HT(?) now low at about 30 volts. Generator appeared to work though. Zenner voltage wrong, with base of transistor more or less at collector. Change zenner resistor and make up a new 43 volt zenner from a 10 and a 33volt. Still the same. 10 volts across the 10 volt zenner, but weirdness across the other.
Tim the idiot shorts out the 10 volt zenner( on the bottom, -ve end) to see if the 33 volt one is working, and BANG. Switch off quick!
Now what? Out with the transistor to check. It’s a 2N5415, which had the circuit called for a PNP transistor ( rather than an NPN)would have been a good choice.
Changed both zenners again and zenner resistor. Check voltage with transistor removed. Spot on 44 volts. Whack replacement tested BFX85 transistor in, but notice sparks as I fit leads into PCP holes. Presumably from 3x 470uf caps at 50 or so volts.
Uh-oh. Murphy is obviously looking over my shoulder, so checked transistor to find I had zapped it, and was dead short in all directions. Goodness knows what would have happened if I had fitted that in!
So I metaphorically poked Murphy in the eye, discharged caps via 47 ohm resistor to common, checked a used 2N2119 and fitted that, with a clip on heat sink. Switch back on with everything crossed and working at last! Correct voltages and mere millivolts of ripple.
It just goes to show we all make a fool of ourselves sometimes!

I was a little surprised that it worked at all with a PNP transistor. Perhaps the transistor was breaking down, and slowing current to flow.

Re: I’m an idiot!
 

We all make occasional silly mistakes;

I once absent-mindedly fitted a bipolar transistor in place of one of the tiddly little plastic-encapsulated 7805 three-legged voltage regulators.

There was smoke.

Re: I’m an idiot!
 

I once blew all 4 filaments in a battery set by shorting out a voltage regulator with a meter probe. We've all done similar stupid things.

Re: I’m an idiot!
 

I remember years ago I blew up a telly by connecting the earth of my scope probe to one of the heatsinks when I was a bit tired and not thinking properly, yes it turned out to be a live chassis set! Didn’t make that mistake again… although I do have an isolation transformer now, and better access to service information!

Regards
Lloyd

Re: I’m an idiot!
 

I did that too, Lloyd by hanging my soldering iron on the chassis of the G11 - and in the customer's house! In my defence the mains switch had shorted live contacts unknown to me.

Re: I’m an idiot!
 

Is there anyone here who does/did practical design or repair work who has _NOT_ made a silly mistake?

I managed to feed 12V up a transputer link back in the day and killed a rather expensive processor as a result.

I disabled the over-current trip on a DEC H754 regulator brick in attempt to find why it was giving no output. The reason turned out to be the crowbar firing at the wrong time, without the overcurrent trip, the short provided by the crowbar blew transistors right off the board.

And many more..

Re: I’m an idiot!
 

I wired up a DPST mains switch 90 deg out, as it were, such that turning it on shorted the mains out. You can imagine......

Re: I’m an idiot!
 

I have seen that done by a boss who used to sometimes come to production to "help".
It left the guy who plugged it in really scared.
There was a 13 amp fuse in the plug. Only the ceramic tube with about half of one of the end caps remained.

Re: I’m an idiot!
 

I doubt it! ;D

Re: I’m an idiot!
 

Oh, the list. One quite memorable one is working on a camera flashgun. They have quite a big capacitor charged to a fair old voltage to supply the flash tube. I got a bit of a bite a couple of times, so decided to discharge the cap. The flashgun survived (I still have it somewhere) but the tip of the screwdriver didn't. Good lesson in source impedance!

Re: I’m an idiot!
 

There are probably a few, but if there are, they are liars!

Re: I’m an idiot!
 

Snap - almost - In my case I had gone to re-solder the pins of the field output chip before condemning it.

The flash was burned into my retina for hours.

I presume your G11 was like mine in that the on/off switch was part of the control drawer.

Al

Re: I’m an idiot!
 

Made plenty of silly mistakes over the years, but my favourite story is about a colleague years ago, who got a shock while working on a large 32" widescreen TV set. As he rapidly pulled his hand out of the set he hit the neck of the tube and broke it (the tube that is). Expensive!

Re: I’m an idiot!
 

Yes, they do make you jump!

I've had a few little burn holes in the finger ends from accidentally touching primary side capacitors on switched mode jobbies. They don't look much, but they do sting a bit for a few days :angry:

Re: I’m an idiot!
 

Another classic one is from about 30 years ago, when I had a workshop at my mum’s. I was working on a portable TV, and had put the plug in my pocket for safety. I think my mum knocked at the door, and I got up to answer it. With the plug still in my pocket!I managed to drag the TV off the bench, and unfortunately my AVO8 which was attached by test leads st the time. I can’t remember what happened to the TV( so it was probably OK)but that particular AVO was never the same.

Re: I’m an idiot!
 

I could give personal examples but it would take people all night to read....

"Mistakes I made bucket loads, but then again, far too many to mention" should suffice ;D:beer:

Re: I’m an idiot!
 

There is a saying, can’t remember it completely but it goes along the lines of “ The person who said they have never made a mistake never made or fixed anything”

I think we have most if not all made mistakes and Cruising marine sums up mine very well.

Re: I’m an idiot!
 

Snap!!

I should have known better as I wasn't exactly a noobie at the time but the four switch tags were arranged in a square and I obviously didn't interpret the markings correctly......

Re: I’m an idiot!
 

Many yars ago, when I worked on fixing TV's I fixed this one. HMV colour set worth LOTS of money.
Had a convergence fault. The convergence board was one that "folded " up out of the chassis so that you could see picture while adjusting the numerous coils and pots. It was a LARGE board with probably 30 transistors on. So convergence had really gone wonky. Found a transistor that had gone leaky. Replaced that but now I had to tweak the peaking coil to get the picture square. Without thinking, pick up my thin METAL screwdriver and shove it into the coil. Thats weird!! the picture is square. Remove the screwdriver its trapezoid again. Reinsert the screwdriver and twiddle the ferrite tweaking screw to the opposite direction. Whats that smoke ? Its the peaking coil RF heating the screwdriver AND the coil. Bang goes the coil. I pull the screwdriver out of the coil and get a lovely set of stripes from the gnurling on the screwdriver handle. At the same time the transistors, now connected to a smoking shorted coil went off like a string of chinese firecrackers. I ducked as bits of plastic flew everywhere and had another three techs hiding and running. The boss is bright white with fright. I couldnt hide that one !!!. I wasnt fired either. BUT every tech there had a "go " at rebuilding that TV. NOBODY could fix it.
Worst case of egg on face ever. I felt about 1" tall, and considering the other techs were self taught and I had a degree, all the more so.

Joe

Re: I’m an idiot!
 

I readily admit to doing more stupid things than I can remember. It is nothing to be ashamed about.

I'll bet, like a lot of posters here, the number of non stupid things they (I) have done far outweighs the daft stuff.

Let's not make too much of it, everyone has 'sub optimal' days!

Steve.

Re: I’m an idiot!
 

Yes, we have all done it. But this thread is certainly entertaining!

Re: I’m an idiot!
 

Many years ago, while installing a brand new 25W 86MHz trransmitter for the fire service I decided to check the voltages on the backplane.

A slip of the meter probe and there was the magic smoke and a smell of overheated fibreglass pcb. A visual inspection showed no damage, of course not, the power supply tracks were in one of the inner layers of the multi-layer board and the 12V supply track had decided to give up.

Oh well, had to fork out for a new backplane, but luckily no other damage to the expensive kit was caused. Just one of the silly or careless mistakes I have made over the past years.

While a young TV tech. I persuaded the boss the buy one of the first Philips DVMs with red 7-segment display, not a cheap piece of kit. I learnt the hard way that it was better to keep the probes well away from the line output stage. The repair was not cheap. :censored:

Re: I’m an idiot!
 

As a youngster. I was wiring up some flourescent tubes in an art light box that I made and forgot about including the ballast chokes. When the mains was applied there was a small crack and two wrecked tubes. I think they call it learning by your mistakes or something like that! ;D

Regards,
Symon

Re: I’m an idiot!
 

And the real idiot is the one who doesn't learn, and keeps making the same mistake!

Re: I’m an idiot!
 

When l first started in TV repair l bought an Oscilloscope from RS, because my colleague said "you can take away all my tools, but don't take away my oscilloscope"

So, the first TV l had for repair with frame collapse l fired up the Hameg HM203-6 and set to it with the probe.

On about the third pin the probe slipped and went between two pins. The top blew off the chip and hit the workshop wall.

"Well, at least that TV has a definite fault on it now" said the other engineer.

Re: I’m an idiot!
 

Oh that has reminded me of a similar incident. Many years ago I was showing round a work experience lad in the TV workshop. A colleague was working on a TV; power applied as he worked on it.

I was explaining to the lad that you should NEVER touch anything in the back of one the TVs as they were dangerous and that the engineers were very experienced. The engineer who was working on the set turned round and said that he would demonstrate the danger. He picked up a neon screwdriver and headed for the EHT cap. He slipped though and the screwdriver shorted out the EHT (set running remember), causing a massive bang, large blue sparks and a rather frazzled looking engineer, along with a dead set.

'See' he remarked!

Re: I’m an idiot!
 

Ive made hundreds. Few off the top of my head

- Accidentally sticking an EL84 into the EZ81 socket of a radiogram chassis. Funnily enough there was HT just a little low. Once the EL84 warmed up there were some fireworks. Still worked as an output valve though :D

- Destroyed a Germanium transistor in a jukebox through clumsy application of a scope probe

- Tripped my RCD working on a live chassis radio by touching an earthed soldering iron pin to the chassis. Then falling over finding my way to the house in the dark to flip the RCD back on :D. This has actually happened so many times now I always use an isolation transformer with live chassis radios. I'm pretty good at cutting power, not so good at removing the plug from the socket! :-D

Adam

Re: I’m an idiot!
 

Although statistically improbable, there must be a technician / engineer somewhere who really has never made a mistake. If so I would like to know his or her secret.

For everyone's sake, I hope they happen to be working in something mission-critical like medical instrumentation or aviation.

Re: I’m an idiot!
 

We all make mistakes... My most expensive one being to accidentally hit 'transmit' on a piece of rather powerful VHF transceive gear when its output port was connected to a hired pulsed noise source used to optimise S/N ratio in the receiver.

Said test instrument really didn't like having 250 Watts of RF shoved into it, and I had a lot of explaining to do when returning the now wrecked noise source to the rental company.

Re: I’m an idiot!
 

If it's any consolation I'm currently doing similar silly things with a 5 volt rail in my old Marconi TF2370 Spectrum Analyser. The 2N3055 series transistor looked good so I replaced the uA723 regulator but still the same result showing about 0.5 volts output. I then thought I'd reduce the load to see if the regulator was just current limiting but I put my series resistor in the wrong place and when I next stuck the scope on the 5 volt rail it was showing a ripply 8 volts and retaining that voltage after returning to normal circuit! I'm just hoping I haven't killed a load chips.

Peter :-[

Re: I’m an idiot!
 

I had repaired the ignitor in a xenon projector lamphouse and was about to fire it up for the first time. I needed to see the PCB to make sure nothing was flashing over, so had defeated the interlocks on one side of the lamphouse and left the door open. I secured the area against unauthorised access, connected the mains and operated the ignitor. Just as I pushed the button, the leads of my Fluke DMM moved. They had been parked somehow, around the dowser handle and port, I should have removed the meter entirely before testing but didn't. At the very moment the ignitor fired, the leads flopped down and a spark jumped across from the lamp positive stud in the geartray.

That meter was almost part of me, had followed me around 18 countries over nearly 25 years, survived being buried in the Sahara, falling in the North Sea and the Thames, ridden around a baggage conveyor naked when my toolbox split open and had accidentally gone to Japan without me. It was fitting that the first incident to disable it would be a 40kV flashover, not just a broken range switch or something mundane. It will be repaired.

Re: I’m an idiot!
 

My personal favourite: I ran up an old radio with a ratty old mains lead to see what it would do. It worked sufficiently well that it was worth continuing, so I turned the set off and removed the said lead with a set of snips. Should have turned it off at the supply end, not the radio end! House mains tripped out with a bang, left me shaking with 'what could have been'.

Posting these 'events' here is excellent. We should learn from the mistakes of others was we don't have time to make them all ourselves...

Mark

Re: I’m an idiot!
 

Many years ago we had an Interdata 70 minicomputer. We had a service contract with Interdata but as time went by we became more and more convinced that we were being ripped off. Eventually we decided that we could maintain it ourselves and save money. The plan went well right up until the first attempt to do anything, at which point the resident hardware man managed to connect one of the signal lines to far more volts that were good for it. Lots of smoke appeared and the machine stopped working. There were blown chips on every board in the machine.

Luckily it was all fairly standard 7400 series logic and replacement chips were readily available. A couple of days later and it was all working again.

Re: I’m an idiot!
 

....not helped by too much alcohol and being only 18 at the time! My first 'goof' was one Christmas eve although the problem didn't actually manifest itself until about 6 months later.

My first job at a small family-run business. I was tasked with finding the cause of a frame collapse on a 17" Pye TV. Being Christmas Eve there was a certain amount of urgency to get the last few remaining sets out. Nice easy job, cathode resistor, bypass electrolytic and a new PCL82 and the frame on the Pye Pioneer was restored. The chief engineer tapped me on the shoulder pointing to his watch which indicated lunchtime and a motion to join him down the pub for a traditional Christmas pint...or two. I decided to leave assembling the Pye set until the return from the pub. An hour and a half later with three pints of Youngs Special inside me and a slightly muzzy head, we returned to the workshop to finish off the last couple of sets. It took me no time at all to reassemble the Pye set and a final test showed all was well and it was duly returned to the delighted customer. Fast forward 6 months and the Pye set once again appears in the workshop....different fault of no sound. A quick check proved the customer was right so turned the set off and proceeded to remove the back. As the back came away, there was a clattering sound and a strange whooshing noise as the chassis together with the neck of the tube fell out and dangled on wires....!

The story had a happy ending. The chief engineer who saw the funny side of it, when he had recovered from laughing, set about helping me sort it all out. He also handed me a box of screws which should have gone back in the Pye set on Christmas Eve....! He'd been wondering where they came from for 6 months.....! He found a good tube in a scrap set and I set about fitting it and then sorting out the original fault of no sound (which was another PCL82 and cathode resistor). I made absolutely sure that all screws were fitted this time but it was a 'sobering' experience!

Re: I’m an idiot!
 

I did exactly the same thing around about 1977. I can still hear my dad "what the bl:censored:dy hell have you done now"

Graham.

Re: I’m an idiot!
 

While I am on this subject does anyone remember a certain "Brainless Bertie" he was a sort of cartoon character in a trade mag in the 50's/60's.I cannot remember which one. I have some copies somewhere must dig them out.

Re: I’m an idiot!
 

Hi to all,

Anecdote #1:
Circa 1968, i was +/- 15.
Had purchased a Kyoritsu KEW-3 Scope from RIM Electronics supplies in Germany while on a language school trip.
The Scope is all tubes 3 MHz bandwith, no DC, no calibrated positions, very basic.
While poking in the innards, wanted to measure the CRT filament voltage, only 6.3V, right?

Well knew nothing then that CRT Filaments & Cathode are at high negative potential and received the full 1200V EHT when my multimeter test probe slipped & touched Fil pin with bare finger.

Was a good lesson! purchased a book on CRTs & Scopes and started filling in the gaps.

Anecdote #2:
1970. Was given an all-tube non-working 1967 25" SECAM colour TV, an Oceanic TV-600 (30 valves, transistorized UHF tuner).
Purchased a thick book on colour TV theory, the set's schematics and got to work.
The set had 4 failures. Took my time, 4 months, learned circuit by circuit & fixed it.
Decided that for reliability would replace with all-new H & V scan valves, EHT shunt, etc.
Local dealer sold me RFT valves made in the DDR. The EL519 & GY500 were shorted from defective QC.
When the plates started glowing red, boy did i switch off fast! no damage.
Purchased only Philips, Telefunken, Valvo valves thereafter.

The TV ran faultlessly until 1978 when i moved and purchased a new 12" Trinitron with my first salary.

Best Regards
jhalphen
Paris/France

Re: I’m an idiot!
 

We all am idiots - Fortunately in different ways, and at different times, so that we can all cover for each other :-)

A group of synchronised idiots is a fearful thing.

David

Re: I’m an idiot!
 

I can remember helping to remove an internal partition wall.
There was a socket strip on it that clearly looked like a retrofit.
I lifted a ceiling tile and sure enough there was three wires in the box.
The wire I wanted to remove was on its own with the other two on the other side of the block. I took the short cut of undoing the screws and pulling it out.
I was informed with a bang that the spur was something else and that there was another terminal block hidden under a flap of itchy rock wool.

Re: I’m an idiot!
 

I quite regularly forget to put my meter lead back into the volts socket after measuring current and the next volts measurement results in a short circuit.
Not good when checking a car battery voltage.


Recently purchased a dc/ac clamp meter to try and resolve this.

Re: I’m an idiot!
 

I recently killed my trusty Fluke 177 but I won't say how I did it other than it is scrap!

Re: I’m an idiot!
 

Done that!

Re: I’m an idiot!
 

I did a really silly thing yesterday.

I recently purchased through the Forum a working 12 volt 12.5 amp switched mode power adapter, which just needed a kettle type mains lead.

To test it I borrowed a cable from one of my cassette recorders but the power adapter appeared dead.

I was thinking that I would have to go inside the adapter and start fault finding when the penny suddenly dropped.

I fuse (the mains plugs) of most of my equipment with 1 Amp fuses, occasionally going up to 3 Amp. Checking the fuse it was indeed 1A and blown (it was working before I borrowed the cable). So even though the adapter had no load connected it was obviously drawing > 1A

Fitted a 13A fuse and then all good.

Edit Update - The label on the adapter shows the mains input to be 1.8A, so should be able to drop the fuse down to 3A


David

Re: I’m an idiot!
 

Some of the better meters, ie, modern Flukes, will beep at you if you select a non-Amps range while the leads are still plugged into the Amps sockets. I don't know how they know.

Re: I’m an idiot!
 

Regarding that PSU. Remember that the device is probably (in fact almost certainly) a switched mode power supply. So when first switched on, regardless of any output current, there will be a surge to charge the capacitor on the input. That will be pretty high albeit for a short time. You can't simply rely on the device ratings.

Re: I’m an idiot!
 

I always assumed there was a switch in the bottom of the socket. Didn't stop many muppets where I worked.

Re: I’m an idiot!
 

I will now confess to what I did with the aforementioned meter, it was being used to test current flow from a solar panel to charge controller, a battery test was then performed without changing the red lead to volts instead of the 10A socket, the internal fuse was dead so I used a piece of fuse wire instead, the PCB track was the fuse!
The only settings to work are Volts and that's it, the other settings are giving random readouts.

Re: I’m an idiot!
 

idiotic tricks!
i recently had a stroke and already have dementia. the doctors asked me to send video of arm (medication reaction). still cant find folder for camera stuff, i was high on tech all my life, so feel a right gonk

Re: I’m an idiot!
 

Not me but a colleague. he was measuring the filament current on the electron gun on a linac. This is normally about 8A. When the machine is generating x-rays the gun is pulsed to -40kV. guess what happens to a meter in series with the gun.

Re: I’m an idiot!
 

Good point.

I dropped the fuse in the plug from 13A down to 3A.

Out of interest I connected an AVO in series with the fuse to see what current it was drawing.

Surprised that it is as low as 25mA and no obvious sign of a surge at switch on, it is maybe too fast to register on the AVO.

David