OT took my plasma cutter in for repair

[J Tiers]

Most factory repair places will replace the PWB, as opposed to doing "component level repair".

This is very reasonable, for several reasons:

1) You get an exact replacement, which has all the functions tested and is as good as what was put in the machine originally

2) Power electronics often fail in a more destructive manner, parts may be vaporized, traces blown off the PWB, holes burned in the PWB itself. It is not uncommon to be unable to repair the PWB in such a way that it can be re-used.

3) It is common for a power device failure to damage other parts. Usually you can determine that, but sometimes the damage is not enough to cause a failure, YET. So repairs are a crapshoot unless you replace more than appears needed.

4) The liability issue is easier if ONLY factory parts are used. You can get in trouble replacing components unless you use the exact original component, and know if they are specially selected, etc. You can hardly go wrong using a factory original assembly, since you make no decisions, redesign nothing, and are not putting in any substitute parts which can later be described as "cheap, inferior, substitutes". There is no "knew, or should have known" involved.

[Sparky_NY]

I have a harbor freight plasma, bought used, which I have been very happy with UNTIL.....

A friend bought a "CUT 50" plasma from ebay for under $200 delivered. He brought it over and we set it up and tried it. It outperformed the HF unit by a LOT. The HF unit struggles with anything over 3/8 thick, the Cut 50 cut 5/8 plate like nothing ! I am half tempted to get one and sell my harbor freight plasma. At under $200 there isn't a lot of risk. My friend has been using it a lot and it works great.

Just a FYI on cheap plasma cutters.

[gaston]

I have 2 plasma cutters a cut50 and a 1980's century 20 the cut 50 will cut 1/2 easy but makes "angry noises and scares the hell out fo anyone in my shop... the century 20 will only cut 3/16 but hums like a kitten purring. Its old ,transformer ,weights a ton , and for 37 years worked like a slave
Take this invert stuff and shove it, I'll take an old transformer machine any day

[OhioDesperado]

OMG, that went in circles.

SO, now real questions.
First, make and model of the unit.
Second, where are you in regards to Ohio?
Third and maybe important and maybe not is I DO repair them at board level depending on what it is, and what got smoked. And if it's a decent unit or a crap import that is under designed, and some of the big name stuff meets that spec as well as the import stuff. Lincoln Pro-Cut 55 was one that didn't have the cooling ability built in for being run hard. And they would burn a board that cost $917.00 to replace and you were burning up 8 parts that cost 3 buck each.
Ask me how I know.
The fan actually would run too fast to leave the air in place long enough to effectively transfer the heat from the heatsink to the air before being blown out the other end.

Anyway. Make Model and specific what's it doing. Pictures of the inside of the cabinet may help as well.
It don't work is nice, but does it power up?
Do the lights come on?
When you pull the trigger does the air flow start and it just don't apply power to the torch and cut.
Does it sound like it's trying to apply power AKA air flow starts and then it sounds like a transformer buzz but it don't cut. That sort of description.

[Puckdropper]

I don't mind paying a diagnostic fee IF the diagnostic comes with a guarantee that it has isolated the problem. I've never found a repairman who would diagnose it, then refund all money paid if the fix does not work.

Dan

Imagine a series of walls between you and the device working. Some walls are small (switch has to be in the on position) and others are large (missing gear) or even hidden (clear gunk over locomotive wheels). All a diagnostic can do is identify some of these walls, but some walls hide other walls so you've got to actually find and fix those problems first.

I can't guarantee the diagnostic will identify your problem, all I can do is tell you what I found and state my hypothesis as to the cause. Sometimes that hypothesis will prove to be wrong or will actually be right and another problem will be revealed.

I'd like to offer you your money back if the diagnostic is incorrect, but I just can't have confidence in my diagnostic until it's tested and at that point the device is fixed.

[J Tiers]

.....

I'd like to offer you your money back if the diagnostic is incorrect, but I just can't have confidence in my diagnostic until it's tested and at that point the device is fixed.

Very true...

The proof of the diagnosis is that fixing the diagnosed problem fixed the unit. So simple, so obvious, and so true.

Goes right along with "fix what you know is wrong".

[danlb]

I can't guarantee the diagnostic will identify your problem, all I can do is tell you what I found and state my hypothesis as to the cause. Sometimes that hypothesis will prove to be wrong or will actually be right and another problem will be revealed.

I'd like to offer you your money back if the diagnostic is incorrect, but I just can't have confidence in my diagnostic until it's tested and at that point the device is fixed.

I understand that. I've made a living diagnosing things and fixing them. But part of my diagnostic technique was to prove a part bad before replacing it. Yes, there are places where you can't do that easily, but charging a customer $1000 for a repair that does not fix the problem seems wrong.

Dan

[J Tiers]

I understand that. I've made a living diagnosing things and fixing them. But part of my diagnostic technique was to prove a part bad before replacing it. Yes, there are places where you can't do that easily, but charging a customer $1000 for a repair that does not fix the problem seems wrong.

Dan

Yes.... Proving the part bad is the reason for replacing it. Otherwise I have no idea why one would do it.

And, as Dan or anyone else who fixes electronics knows, the bad part had to GET "bad" somehow. Yes, it could "just fail". But it pays to look around and find out what ELSE around it is bad as well. And look for root causes.

Once, when I was on vacation, one of the techs built my new prototype PWA. He did not do the preliminary checks, he built it and fired it up. Well, there was something wrong, I don't recall what (I think it was a part put in wrong), and some parts failed. So, genius-boy checked through it, and found a bad part, which he replaced. And turned it on again.....

Of course it failed. So now he found another bad part besides #1, and replaced both of them. And turned it on.... To make a long story short, he managed to blow through my entire stock of the new, hard-to-get semiconductors, that were supposed to build several boards, and he never did get the one working. I was NOT pleased, and suggested that the tech manager arrange some troubleshooting training. offered to help with that (he did not take me up on it) I did get the thing working, because I found a few more sample parts that had gotten set aside. All it took was to find ALL the bad parts, plus the part that was put in wrong, and replace them all at once, instead of one at a time.

Replacing bad boards on a guess is a poor way to do repairs. Especially when it is very likely to result in a "not fixed" situation, possibly with the replacement board now also bad.

[danlb]

Yes.... Proving the part bad is the reason for replacing it. Otherwise I have no idea why one would do it.

It happens quite often when the fault is hard to diagnose or takes lengthy test procedures. It's quicker for them AND they get paid either way.

Example 1: Friends's expensive Mercedes CEL (check engine light) was on permanently. When cleared it would come back on with an hour of driving. The dealer replaced several sensors (one at a time) and an electronic module. They never did find the problem. He paid $3000 trying and eventually sold the car as is.

Example 2: Mom's car currently has a problem where the dashboard goes crazy after a short drive. Local Cadillac dealer diagnosed it as a bad alternator, then a bad battery and finally several bad sensors. It's still broken. She's out $2000 on a car that is barely worth $5000 and it's not safe to drive. That's taking advantage of an 80 year old widow.

Example 3: On a hot day, the house AC would cut out right after starting when temperatures exceeded 100 degrees all day long. Repairman said it needed charging. Did so and charged a small fortune since it was an old freon unit. He said the entire system needed to be replaced if it happens again. Next hot spell it was doing the same thing. I checked all of the electronics, and traced the problem back to the thermostat. Replaced it and it's worked fine for 6 years.

Example 4: On a below zero day in Lake Tahoe, my hybrid did not want to start the first 3 times. The error display made no sense so off to the dealer we went. The Tahoe dealer said that it should be safe for the trip back to the central coast. Got it to my dealer, who diagnosed it in minutes and declared that it needed a new "computer" because my model has a software bug that only shows up in cold weather. When I got the invoice they had replaced several parts including a "fuse relay" and a sensor. A bit of investigation shows that they replaced EVERY PART that the manual said MIGHT throw that trouble code. I'm convinced that they did not test any of the parts.

The thing in common with all four cases was that the companies made money doing things might have fixed the problem, but they were not at all sure if what they were doing was valid. And that's why they do it. They can make more money by fixing it twice or three times.

Dan

[J Tiers]

.....

The thing in common with all four cases was that the companies made money doing things might have fixed the problem, but they were not at all sure if what they were doing was valid. And that's why they do it. They can make more money by fixing it twice or three times.

Dan

Yes, it happens.

And, yet, a guy I know ran a car repair shop for decades, making good money, and his "thing" was that he did not do that. They always knew why they were replacing what they replaced. His shop was well known as "the place" to take the car to get it fixed right, no hassles. Last I heard, he had retired, but the shop was still going on the same lines.

[Abner]

OMG, that went in circles.

SO, now real questions.
First, make and model of the unit.
Second, where are you in regards to Ohio?
Third and maybe important and maybe not is I DO repair them at board level depending on what it is, and what got smoked. And if it's a decent unit or a crap import that is under designed, and some of the big name stuff meets that spec as well as the import stuff. Lincoln Pro-Cut 55 was one that didn't have the cooling ability built in for being run hard. And they would burn a board that cost $917.00 to replace and you were burning up 8 parts that cost 3 buck each.
Ask me how I know.
The fan actually would run too fast to leave the air in place long enough to effectively transfer the heat from the heatsink to the air before being blown out the other end.

Anyway. Make Model and specific what's it doing. Pictures of the inside of the cabinet may help as well.
It don't work is nice, but does it power up?
Do the lights come on?
When you pull the trigger does the air flow start and it just don't apply power to the torch and cut.
Does it sound like it's trying to apply power AKA air flow starts and then it sounds like a transformer buzz but it don't cut. That sort of description.

Answers; - please forgive my terminology if it is incorrect - live green plants are my lively hood(not marijuana).
Thermal Dynamics pak master 38xl (29 amp)
Ohio - Oregon
Powers up, runs a pressure test, fan hums, lights come on.
Ground clamp attached to shiny steel, hold torch down and press button, air comes on but there is no arc, no change in noise from the unit.

Pictures - I will go pick up my unit Thursday, if you don't mind waiting I will get some for you.

Many Thanks,
Abner