Probably a dumb question...

Thread Starter

Jonathan Dennie

Joined Oct 10, 2019
2
I tried searching about for a definite answer to this, but I wanted to be more certain. I have a device (a rotary engraver) that turns on and parts of it work, but not enough to use it.
I opened the enclosure to look for issues on the boards and first there were 2 capacitors that were piping out smoke like nobody's business. I replaced those and it worked as it should, intermittently.
Now when I have it opened, I hear a "crackling", or "fizzling" noise coming from a rectifier diode (KBU6K).

My ultimate question is, a rectifier diode should not be making noise, right?
If it's making noise, it has shorted or something, right?

Thanks
Jonathan
 

Tonyr1084

Joined Sep 24, 2015
3,470
I agree with @Dodgydave. Fully diagnose the problem before throwing parts at it. The caps were "piping" smoke because they were being overloaded for some reason. OR they may have gone bad and pulled down the rectifier. Or it could be something entirely different that has caused both problems. Hard to diagnose without putting my hands on it. Will do what we can to help, but it's sounding a bit naker'd.

Buzzing is the signal of an AC issue. A rectifier should redirect the current so that it is constantly moving in a single direction (DC). Pulsing DC can buzz, but a diode shouldn't buzz. And there's no guarantee the buzzing is coming from the rectifier. The rec. may be shorted and the caps are trying to handle the AC. Especially if they are electrolytic caps - hitting them continuously with reverse voltage can do bad things to them - like let the smoke leak out. Or pump it out as you said.

Do you have a fuse in the system? If so - is it the right fuse? Or was the wrong value put in either deliberately or by accident? With fuses you can replace a fuse with a lower value fuse or the correct fuse. You should never put a higher rating fuse in that it should be. The fuse is there to prevent total catastrophic failure of the circuit. If one part is damaged and the fuse blows then it did its job. You only have a single component to replace. But if you keep throwing fuses in it in an effort to figure out where the problem is - then the problem is going to be "Everything". So fully diagnose the problem before you start replacing parts. And when diagnosing - take precautions to not cause further damage.
 

Thread Starter

Jonathan Dennie

Joined Oct 10, 2019
2
Thank you very much for the information and the advice. I am not very good with diagnosing electronics, apart from obvious visual things, and we only paid $500 for the machine. Paying someone to work on it would likely cost about as much as we paid, so I went ahead and tried just replacing the rectifier. It was successful! Probably just because I was crossing my fingers. Lol.
Again, thank you very much. What you were saying gave me confidence in trying that option. A $2 part was a satisfying investment.
 

Tonyr1084

Joined Sep 24, 2015
3,470
Glad you were able to get it working.

Few years back my MIL (mother-in-law) bought a washing machine. It failed within two years. The failure was a "Mode Shift Coil". Only you couldn't buy just the coil, even though it was two bolts off and on and a single plug to plug in. You had to buy the entire mechanical assembly at a direct cost of $135.00 (US). Then you had to do all that work to install it. I would have bought a MSC if I could have. But since I couldn't, and having a service tech do the repair at a total cost of around $400, she decided just to buy a new machine. I said "Wait a minute. Let me look at it." Got it home, and sure enough, the MSC was dead. Open. No continuity. Wondering how it could have burned out - I drilled out the rivet and opened the housing. The interior looked pristine. No signs of charring or high temperatures. No foul smell. Just an open "Fusible Link" (FL). It was barely rated strong enough to handle normal washing. And when I investigated on line, there were a lot of failed MSC's.

So I went to RadioShack and bought a new FL. One rated a few degrees higher than the one I took out. Don't remember what the ratings were, but I replaced it with one that was probably less than 10˚C higher. For $1.98 (plus tax) I had her machine up and running.

Just goes to show what one can do when one decides to repair instead of replace.
 

MisterBill2

Joined Jan 23, 2018
3,721
I make it a practice to repair things instead of replacing them, it has become a way to beat the challenge of those who design things to be replaced, not repaired. Those thermal fuses are there because parts are built with cheaper insulation that will not survive a bit of heat. And it is certainly a pain to have a very expensive transformer fail because a 3-cent thermal fuse was such poor quality that it failed on a hot summer day.
And when the filter capacitors have failed the rectifiers are always suspect. Not always guilty, but certainly suspect.
 
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