NEVER found problem??

[220/221]

If you can't find the problem, whatever it might be, you just don't own the right test equipment yet.

 

[petersonra]

I have had a few problems that took some digging but eventually I found them all.

Often you get reports that seem to be more of a conclusion from the guy reporting them then an accurate relaying of the symptoms.

One of the more humorous ones was this.

I was in TN starting up a machine with the chief engineer of a client. He got a call from his boss saying they were having trouble with a machine in GA. The plant maintenance guys and the service technicians were having a real problem with it and eventually the service technician declared it was some kind of software bug because it only happened on Saturday mornings.

I ask if there were any error messages on the operator interface. Service technician says no.

I looked through the PLC code and came to the conclusion that nothing in the PLC cared one whit what day of the week it was.

It was eventually decided that I should go look at it so the next weekend we drove from TV to GA (a very pretty drive BTW).

I start to plug computer into PLC while chief engineer exercises machine. Before computer has even booted up, he calls me over to the operator interface. In big red letters scrolling across the bottom of the screen is an alarm message "low air pressure". I ask service technician about this. He says "O yea, it always says that when it does this".

Turned out the plant used to shut off one of their compressors on weekends and the one they left on was running at about what the air pressure switch on the machine was set to, and when one of the big air cylinders started to move, the air pressure to the machine dropped below the setting on the pressure switch. A small adjustment to the pressure switch and we left.

This stretched out over four weeks.

The worst of it was the the chief engineers boss (VP or engineering) had also flown down there to witness the fixing of the software bug that only happened on Saturdays. They had shown him the problem, and he too had noticed the "low air pressure" alarm message but apparently did not realize the machine would shut itself down if the air pressure was too low. And never thought to even tell us about the alarm message.

 

[mdshunk]

Often you get reports that seem to be more of a conclusion from the guy reporting them then an accurate relaying of the symptoms.

You're sure right about that. I basicly approach the tougher problems as though everything everyone has told me is a lie. Maybe not the case most times, but as you rightly point out, people will relate their own incorrect conclusions and assumptions as part of the reported symptoms. The famous one is 'the breaker is bad'.

 

[acrwc10]

You're sure right about that. I basicly approach the tougher problems as though everything everyone has told me is a lie. Maybe not the case most times, but as you rightly point out, people will relate their own incorrect conclusions and assumptions as part of the reported symptoms. The famous one is 'the breaker is bad'.

Years ago I was at the supply house and an HVAC guy kept comming in and buying the same fuse about every 20 minutes. He would put them in a roof top unit turn it on, it would blow the fuse right away, then he would come back and buy more fuses. I went to look at it ( bad compressor ) fixed it in about 5 min. $75.00 cash , he was happy to have the problem fixed because the supply house was out of fuses in that size. I think the quote is, " the deffinition of crazy is doing the same thing over and over but expecting a different out come."

 

[mdshunk]

Years ago I was at the supply house and an HVAC guy kept comming in and buying the same fuse about every 20 minutes. He would put them in a roof top unit turn it on, it would blow the fuse right away, then he would come back and buy more fuses.

Reminds me of an old man electrician that I used to work with that would put a row of strip lights on a 60 amp breaker to make the ballast that was tripping the 20 amp breaker declare itself. Yikes!

 

[e57]

This is a fun thread.

The most aggravating part of troubleshooting IMO is the person who you're doing the work for isnt being honest with you. This happens most when the person you're doing the work for isnt paying the bill.

Sometime even when they are paying the bill..... I come across this a lot. And simular situations....

Joe Home-owner: "It just stopped working the other day..."
You open the boxes of the circuit and notice that there was NO WAY IT COULD HAVE!

As you're fixing it, 'Sue - Joe's wife' slips you the news that it 'just stopped working' after Joe messed with it.....

 

[electricguy61]

I've posted this story on another topic, but it fits here as well.

My Aunt and Uncle own a vacation home in Lake Tahoe (about 4 hrs away) They let my family use it whenever we ask.

For two years, they had an intermitant problem of the lights in the house dimming or getting real bright when appliances were turned on. They went through a TV and a refrigerator. Obvious answer: bad neutral.

At my urging, they called the power company. The power company always came out but never found any problems. I called the power company's engineer from my home and he agreed that it sounded like a bad neutral on their side of the meter. They sent out troublemen numerous times, they changed the overhead drop, and then the transformer, and the problem would disappear for a little while, then start again.

Late one night I happened to be there when the problem surfaced again. No question, bad neutral from the utility. I went outside and pulled the meter. No obvious problems, but just for the heck of it, I tried tightening the neutral connection. Guess what? It had never been tightened. I suppose that when under a large load, it would heat up and cause the problem.

It taught me a good lesson: always check the tightness of connections.

 

[acrwc10]

Guess what? It had never been tightened. I suppose that when under a large load, it would heat up and cause the problem.

It taught me a good lesson: always check the tightness of connections.

When I torque down the lugs in a panel I take a marker and put a line across the two parts of the lug. This way I can tell at a glance if it was done and if someone has messed with the lug after I was there.

 

[Energy-Miser]

Sometime even when they are paying the bill..... I come across this a lot. And simular situations....

Joe Home-owner: "It just stopped working the other day..."
You open the boxes of the circuit and notice that there was NO WAY IT COULD HAVE!

As you're fixing it, 'Sue - Joe's wife' slips you the news that it 'just stopped working' after Joe messed with it.....

How about those who stand so close to you the whole time, you are afraid to bump right into them if you make a fast move? e/m

 

[Energy-Miser]

When I torque down the lugs in a panel I take a marker and put a line across the two parts of the lug. This way I can tell at a glance if it was done and if someone has messed with the lug after I was there.

That's a great idea, I will have to tell everyone at my shop about it. e/m.

 

[dbuckley]

The most intriguing unsolved problem I ever heard about was on usenet, and courtesy of Google, can be read here. It's sixty posts long, so will take a while to read through. It starts a bit roughly, but gets more better... I found it interesting as I couldn't satisfactorily explain what was going on, which is fairly unusual; my core skill is basically troubleshooting, so having an unsolvable irked a bit...

The story doesn't have an ending, posts just stopped in 2000, so in 2004 I emailed Chico (the second Nova Scotia Power engineer to be involved in the story), and this is most of his reply:

Wow. That was a few years ago.

Basically still a mystery.

Around that time I was involved with a new piece of recording equipment. The utility also hired a consultant who was a former employee and renound for solving tricky problems. When the $8000 voltage recorder measured a collapse of single phase voltage with no corresponding change in phase to phase voltages, the utility took the position that although we didn't know what was causing the problem, it wasn't coming from the utility supply.

The customer didn't like the answer and went to the regulatory board with a complaint. The regulatory board felt that the utility should be considered the experts on these matters, and more effort should be undertaken to prove our innocence. We were given approval to buy a cadillac, real time Dranetz signature system. This was an 8 channel system installed basically permanently at the location, connected to a phone line. The voltage was measured at the overhead distribution transformers outside the building, and at the customer supply inside the building with all channels fed into a box connected to a phone line.

Whenever the customer experienced a problem, the recordings showed no corresponding activity on the utility side.

In the meantime, the dentist who had his practice in the basement got tired of the whole situation and moved his practice. Since then, things have been pretty quiet. The equipment is still recording, but the complaints are much fewer in frequency.

So I guess we will never know if the problem is solved, or just went away with the dentist, or is simply dormant and will reappear for a future generation of engineers to scratch their heads over.

The End. Or is it?

 

[iaov]

The short answer is 'Yes'. Intermittant problems buck the heck out of people.

Intermittant is the dirtiest word in the English language.

 

[brother]

Im happy to see the post i started has gotten soo many responses!! The more i read the more troubleshooting KNOWLEDGE i get, and potential test meters to use.

Keep it comming experts. Especially those that had a 'unsolveable' ones. Just be reading those i come up with other ways to test and trouble shoot.

 

[iaov]

I worked for years in a highly automated industrial enviroment. Problems often came and went while we sat and stared at the ladder logic. I agree with Marc that all problems can be found and fixed, but some times in high speed automation you are "shot gunning" things hoping to score a hit. Some problems may take weeks or months to resolve, and once they are resolved we some times wern't sure why. The thing I saw a lot was people did not start out doing logical,orderly trouble shooting. They would try what worked before or would immediatly try the shot gun approach, often creating more problems than they started with. Proper trouble shooting requires the proper equipment, a logical approach, and just a little bit of magic and luck.:smile:

 

[mdshunk]

I worked for years in a highly automated industrial enviroment. Problems often came and went while we sat and stared at the ladder logic.

When you talk about motion control systems and PLC, I've seen some weird stuff happen for no clear reason, but it was resolvable. I've seen I/O's that the ladder logic on the laptop showed were open or closed, but the acutal output was completely the opposite (bad output card). I've seen G-code get spontaneously corrupted all by itself with no human intervention.

 

[Chris6245]

Fastest service call ever completed by me was a call to a retail store at a local mall. Call came in as "back room lights will not come on, breaker is on". I walked into the store got the manager and she was taking me into the back room to show me. As we were walking through the doorway I reached over and flipped the light switch. OMG They haven't worked for days and you show up and they come on right as you walk into the room!!!!... I wanted to tell her it was a "special ability" I had but I just said "lights tend to come on for me when i flip the light switch". She never tried the switch, said she didn't know what it was for...So 2 seconds for a 1 hour service call.

 

[jason]

I have another one.

I went on a service call once where the game room was completely without power. The game room was once a garage or carport that later was enclosed (although this really doesnt matter).

So I get up in the attic to find a feed to the room. I found it, traced it all the way to the other end of the house. Seriously, it was as far on the other end of the house as you could get. It went down into a light switch by the front door. I turned one the switches, a 4 gang box, and the game room has power again.

The home owner told me they bought the house 11 years ago and never knew what that switch went to. They just always left it on and didnt know it was off then. said they had a party recently and someone must have turned it off. I figure at one time there was a flood light, maybe?, and someone used that switch leg as power to the newly enclosed game room.

11 years, and they didnt have a clue.

 

[ptonsparky]

Not having the proper tools is so frustrating, especially when I know they are available, just not in my State and not when I need them.

Changed way to many light bulbs and fustat fuses.

 

[Energy-Miser]

I have another one.

I went on a service call once where the game room was completely without power. The game room was once a garage or carport that later was enclosed (although this really doesnt matter).

So I get up in the attic to find a feed to the room. I found it, traced it all the way to the other end of the house. Seriously, it was as far on the other end of the house as you could get. It went down into a light switch by the front door. I turned one the switches, a 4 gang box, and the game room has power again.

The home owner told me they bought the house 11 years ago and never knew what that switch went to. They just always left it on and didnt know it was off then. said they had a party recently and someone must have turned it off. I figure at one time there was a flood light, maybe?, and someone used that switch leg as power to the newly enclosed game room.

11 years, and they didnt have a clue.

Reminds me of the commercial (forget for what) that went like this: Honey do you know what this switch is for? No, I have never used it. Well he man turns it on and off repeatedly, only to lower and raise neighbor's garage door as she is backing her car out of the garage! I never thought it could happen in real life ! e/m.

 

[jason]

Reminds me of the commercial (forget for what) that went like this: Honey do you know what this switch is for? No, I have never used it. Well he man turns it on and off repeatedly, only to lower and raise neighbor's garage door as she is backing her car out of the garage! I never thought it could happen in real life ! e/m.

Yeah thats pretty funny.