Thanks Tonyr, that’s one of the best and simplest explanations of voltage, resistance, amps, watts I have read for a long time.
And misterbill, I will follow your advice!
I have ordered a new one, so let’s see what happens when I solder it in.
Hopefully nothing happens and things go back to normal.
Thanks so much for the help guys, what would we do without you.

 

what would we do without you.

Humanity got this far without my help. I suppose you would still have found the help you need.

Good luck with your repair. I hope the failure was purely mechanical, as it appears to be. Otherwise the best caution I could give would be to fully diagnose the problem before you start throwing parts at it. But in this case I'd go with replacing the resistor and seeing what happens. Can't be too expensive.

 

Okay guys, here is the update.
I resoldered a 47r replacement resistor in place, the equivalent of the ATE 7cs 47r one that the welder had, and plugged it in.
The resistor smoked straight away!

The thing is all of the other components on the board “look” okay.
i have tested all of the other resistors and they all seem to be operating at the right resistance, so wonder what else it could be.

On the 2nd picture in post 3, to the left of the broken resistor is a see though case with what looks like a Wirewound resistor in it and a switch of some sort. The broken resistor seems to feed from or to this, so could this be the problem?
How can this be checked?

There also is a number of mosfet type transistors, they all look okay, but would one of these be the problem.

Any ideas?
thoughts?
Thanks again for the support.

 

Well, we have yet to determine the current and voltage; thus, the wattage. A 47Ω resistor that size "Appears" to be half watt. You DID say (or showed in the spec) that it's a 10 watt component. If you're putting a half watt - or even a one watt resistor in that position - um - it's going to smoke straight away.

So do we KNOW it's a resistor? It may be specked out as a resistor, but given that it's rated at 10 watts per documentation, anything smaller is just going to burn up.

 

“Do I KNOW it’s a resistor?”
Only by what’s written on the side of the broken one, and looking that up on ATE’s website.

I replaced it with this....
https://www.arrow.com/en/products/rs01047r00fe12/vishay
This was (!!!) a 47ohm 10 watt Resistor.

I have Googled it again and came to the same conclusion as I did before about the specs

i don’t know what else to try.

 

The item in the clear case is a relay, an electromagnetic switch.
Mostly components that fail do not change appearance, and if resistors burn up usually it is because some other part has failed and the result is too much current through the resistor. Diodes may fail open circuit or short circuited, likewise transistors. If the resistor that you put in was not rated for the power then no wonder it failed.

 

“Do I KNOW it’s a resistor?”
Only by what’s written on the side of the broken one, and looking that up on ATE’s website. ••• i don’t know what else to try.

My apologies if you felt offended. Wasn't my intention.

I wasn't confident we were discussing the right part. Forgive my error.

Now, if it's burning up immediately then something else must be shorted. That's why you fully diagnose a problem before you begin repairs. Now, if a 3¢ resistor can be thrown in and sacrificed to determine other component failure - I'm all for that. But when doing so there's a chance of further damage to a board.

I had a bad bridge rectifier (BR) in an amplifier. Blew the fuse. When I disconnected the rectifier the fuse didn't blow. So in that case I knew the BR was bad. But why did it fail? Before replacing it I checked the capacitors. They looked good. Checked the transistors. They looked good. And I don't mean visually, I checked them electrically. Fairly confident there were no other issues I went ahead and replaced the BR. The amp has been working beautifully for more than a year now. Oh, and I went up on the specs for the BR. Rather than replacing it with an exact I replaced it with a bigger one, capable of handling higher wattage. I figured if the original BR went short for no other reason than simple over stress - putting a bigger BR would do the same job but not be so prone to failure.

 

One thing I did when checking my BR was to use a 120V 60W lightbulb. In the event of a dead short, the 80 or so volts AC would light the light and not blow something else out. So perhaps putting a similar light bulb (not CFL or LED) can provide further assistance in diagnosing the problem.

Hope this helps. Genuinely hoping so.

 

Hey tony, no offence taken. I am glad for the help.
i was only quoting your question so that’s why the capitals.

If I understand right, what you mean is to wire in the lightbulb across where the resistor should go, and see what happens.

Trying to trace where the resistor goes to and where it comes from, is proving harder than most other circuit boards i have tested in my limited time.
Would you have any idea as to where I can start tracing this bit of the circuit from, or what part of the circuit even uses this resistor so I can start doing things methodically.

I will start googling welder circuit boards and see what I can find. I did trying finding a circuit diagram for it, but couldn’t find much on it at all.

Once again thanks all for the help, say what you want to me, I want to learn.

 

The light bulb goes in series with the AC supply connection.
BUT please consider that back in post #1 the part spec, probably copied from the parts list, specifies A ten watt resistor. Since those cost a lot more, there must be a good reason for using one with that power rating. So I suggest replacing it with another TEN WATT resistor, which will probably be a bit larger dimensions. BUT avoid getting one of those pretty gold anodized aluminum cased ones because they need a heat sink. The dark brown ceramic case ones are good, but they are a bit fragile. For the initial check you can just have it up in the air on longer leads, but when everything is found to be working then it will need to be supported.

 

Hi bill,
The resistor I replaced the blown one with was a 10w brown cased one and it still smoked it again.
So either,
1) I am misreading the value of what was originally in there as I only have a part number that was printed on its side, and is this posts title, or
2) something else is blown, causing the new resistor to smoke out straight away.
What that maybe I don’t know yet. But will happily take suggestions!
Jon.

 

I thought that part in the first post was from the parts list. Could it be a 47K ohm resistor?
If you still have the broken pieces you can use an ohm meter and get a clue about what the total resistance was. It will be a bit above the sum of the resistance of the two sides.

 

Hi bill,
I replaced it with a 47 ohm one.
Are you saying that 47k is different than 47k ohm?

Just googled it and of course they are different!

 

Okay, so I have just measured the original one that came out the welder with the marking 47r printed in it, and when the multimeter is set to 2k I get readings of .022 on one half and .023 on the other half.
So I get .045 total, but have a bit of wire missing in the middle!

As far as I know that means I need a 47 something to replace it!

Thanks for your patience lads.

 

47KΩ is the same as 47,000Ω. The K stands for "Thousands".

There are a number of ways to call out a resistor's value:
47K = 47,000Ω
4.7K = 4,700Ω
473 = 47 (000) or 47,000Ω
472 = 47 (00) or 4,700Ω
471 = 47 (0) or 470Ω
470 = 47 (no zero's)
47R = 47Ω
4R7 = 4.7Ω
And more. It can get quite confusing to someone who's not accustomed to these numbering methods.

Then there are color codes; 3 band, 4 band, 5 band - it all drives me nuts. I know - short drive.

Without a good diagram I couldn't begin to suggest where to start. But you're going to need to either FIND one or BUILD one. With single layer boards it's quite easy. Two layer boards gets more complicated. Four layer boards and higher are impossible to trace by eye. Unless they're POORLY made. Sometimes I shine a bright light through the board to see the inner layers. If there are large power or ground planes internally - forget about it. Not going to happen.

 

Okay, so I have just measured the original one that came out the welder with the marking 47r printed in it, and when the multimeter is set to 2k I get readings of .022 on one half and .023 on the other half.
So I get .045 total, but have a bit of wire missing in the middle!

As far as I know that means I need a 47 something to replace it!

Thanks for your patience lads.

OK, that measurement shows that you were correct in thinking 47 ohms. So now the challenge is discovering what part has failed that causes the current to be excessive. The very simple process would be to look at the circuit and see what elements are involved. Without a circuit to follow it becomes more complex. So now the choice is either trace out a bit of the circuit related to the resistor. My examination of the topside picture and the underside picture points toward the 680 mFd capacitors near it. But since I am not able to read the voltage rating it is difficult to guess what their rating is. So I would suspect either one or both of those capacitors next, unless there is a power rectifier feeding them.