Mistakes that taught you the most?

When disassembling something, take notes!

I had to play the part of a field engineer once on some Medium Voltage Soft starters that had shorted SCRs. I had never done it before, but I had confidence (too much?) in my ability to figure it out as I went. Long story short, there is an orientation involved in re-assembling them back into the heat sinks. I had a 50:50 chance of getting it right, I lost and shorted the NEW set of SCRs, forcing me to pay for flying out the replacements and costing the end used another day of down time. Had I paid close attention to them during disassembly I would have noticed the orientation, but I was in a hurry because it was an absolutely miserable place (meat rendering plant) but of course because of my haste fueled mistake, I had to spend ANOTHER day of my life there...

... Be convinced that you know the reason why something does not work and at the end discover that it was something totally different

lfe said:

... Be convinced that you know the reason why something does not work and at the end discover that it was something totally different

Click to expand...

Man, I fall into this trap way too often.

Even if you are sure, measure the voltage before you turn on that breaker. I applied 230 volts to a 120 volt PLC input card once because I was "sure". It was the 5th machine we had upgraded and they were all wired the same...except this one. Even when I am sure, I check voltages now after doing anything that might have some chance of affecting the output of a transformer or power supply.

Allways check mA reading from new installations with ammeter before you close any knife contact terminals to analog cards.

The biggest mistake I ever made was not asking what a plant did before I drove there. It was a AB 525 deive that failed and they needed it started up. It was a MEAT RENDERING PLANT. Run away if you ever get called for a rendering plant

JeffKiper said:

The biggest mistake I ever made was not asking what a plant did before I drove there. It was a AB 525 deive that failed and they needed it started up. It was a MEAT RENDERING PLANT. Run away if you ever get called for a rendering plant

Click to expand...

Yep. Or stop at a thrift store on the way there and buy yourself some throw-away clothes and shoes, because that stank NEVER comes out completely.

I had to throw-away all of my clothes, boots,laptop bag. The laptop became my backup to the backup after it sat in the shop for 1 week open so it could air out. Worst smell I have ever smelled. It made me throw up 2 times.

lfe said:

... Be convinced that you know the reason why something does not work and at the end discover that it was something totally different

Click to expand...

Or..... Be convinced that you know the reason why something does not work and someone else tells you they "seen this before" and you listen to them, just to find out in the end you should of went with your gut and stayed the course

I started as a Tech in a bare board PCB factory years ago, it was my 3rd day on the job, I didn't have much going on so helped the mechanical guy swap a pump. Easy Peasey!

"Turn on those valves and i'll check rotation" - So I did. I emptied about 1500 litres of Black Oxide into the effluent plant and ultimately into the the local authority drains.

It's nasty stuff: https://en.wikipedia.org/wiki/Black_oxide

We calculated the copper at around 10k ppm - our limit was 4 ppm!

It shut the factory for around 4 days, we eventually got fined around £60k by Severn Trent (local water authority) and had to spend another £20k to prevent it happening again on a buffer tank system

I spent 10 happy years there and worked my way up to Engineering Director, how I survived that disastrous first week I shall never know! I wish i'd just blown up a £150 PLC!

When you shut off the power always make sure the DC supply has drained out before telling your buddy to go ahead and remove a sensor.


My poor buddy almost got drowned from the 25,000 gallon deluge tank that emptied into the room when he saw the spark, he was soaked. There was a 3' wave of water coming out the door. He is 6'7" and I thought I was dead for sure!

Steve Bailey said:

The question that arises from this statement is why can't you believe what they're telling you?

Click to expand...

Some people will tell you the truth, and over time you can figure out who these are. But of the rest, some tend to tell you either what they think you want to hear. Others, rather than tell you the facts that they know, they tell you what they think the problem is, or just the symptoms that corroborate their diagnosis, regardless of whether or not they've seen the symptoms. Then there are a few people that are just plain dishonest.

My biggest mistake is probably spending a life working on GE PLC equipment

More specifically it's 2019 and Machine Edition will *still* just crash without any warning - training me to manually hit save every time I make a code change (out of fear that I will lose my work). And by *crash* I mean one moment you are looking at the editor, and the next moment you are looking at a blank screen and you didn't even get a dialog box saying goodbye!

And that is without mentioning the bugs I submitted that showed ME 9.5 would *change* code when you exported a block and re-imported it.

A hardware mistake was that even though $2k Genius IO blocks are rated for +24VDC they don't like +24VDC with a superimposed 12VAC component. I burnt out the PSU on a block without knowing, then replaced it, and then replaced the replacement before I realized what I had done. Fortunately the damage was reparable.

@janner_10.
Definitely you were not to blame in that situation.

jraef said:

I had to play the part of a field engineer once on some Medium Voltage Soft starters that had shorted SCRs. I had never done it before, but I had confidence (too much?) in my ability to figure it out as I went. Long story short, there is an orientation involved in re-assembling them back into the heat sinks. I had a 50:50 chance of getting it right, I lost and shorted the NEW set of SCRs, forcing me to pay for flying out the replacements and costing the end used another day of down time. Had I paid close attention to them during disassembly I would have noticed the orientation, but I was in a hurry because it was an absolutely miserable place (meat rendering plant) but of course because of my haste fueled mistake, I had to spend ANOTHER day of my life there...

Click to expand...

Thank god for cameras in every pocket nowadays (within reason)... however, taking pictures still requires attention to detail, focus and white spots (when using flash)...