Safety capacitor question

Thread Starter

kenzo42

Joined Feb 26, 2014
36
Hi
I blew out my dehydrator. The thermistor wire accidentally touched the circuit board. I replaced the large gray fusible (wire wound) resistor with an identical one since it turned black and started smoking. After replacement, machine still doesn't work. Completely dead. Small glass fuse appears fine.

Can the YELLOW Tenta safety cap have blown as well? I haven't come across a safety cap before. When I test resistance, it is reading open, which I believe means it's ok.

Should this Tenta cap be the next item to replace? Nothing else looks damaged.

Thanks.
board.png
 

Tonyr1084

Joined Sep 24, 2015
6,863
I would expect that the next thing that would have been harmed would be the transistor type device on the big black heatsink. Truth is - without fully diagnosing the problem(s) you can either replace every component one at a time OR replace them all and buy a new dehydrator.

Me? I'd contact the manufacture and ask if there's an available replacement board. Whenever you short something out - there's most often an apparent failure point, such as your resistor. But there are likely several other casualties on the board. Replacing one part at a time may lead to new parts failing because of a fault that may have developed elsewhere. For my money, the BEST move would be, if possible, replace the whole board. Second best move would be to buy a new dehydrator. Otherwise just firing the parts cannon at the problem will likely lead to a bunch more failed parts.

So why did you have the unit open while plugged in? Rule #1 (Safety) is never work on a powered device if you don't have to. And I can tell you there have been many times I've ignored rule #1 only to get a good shocking. OR to blow out a device or two. When the paperwork says "No user serviceable parts - refer to qualified service personnel" THAT AIN'T YOU! It "Ain't" me either. Not in this case.
 

MisterBill2

Joined Jan 23, 2018
11,579
I see an item next to that yellow cap that is tagged as fuse1. With the heat shrink over it there is no way to tell if it has failed or not.
So MAKE SURE THE POWER IS DISCONNECTED and use your ohm meter to check the fuse. A fuse can fail and not look failed.
And I see five small plastic transistors, in addition to that larger device. And it looks like itis covered with black heat shrink, no way you could see if it is failed.

But if you have more money than you know what to do with, by all means buy a replacement board, that might fix the problem. Or not.

And I see what looks like a diode next to that big brown capacitor. I hope that your meter has a diode check function , I suggest checking the diode to see if it is open. Which resistor did you replace?
AND, I also suggest checking the resistance of the heater element, because a serious overload may have damaged that.
 

Tonyr1084

Joined Sep 24, 2015
6,863
But if you have more money than you know what to do with, by all means buy a replacement board, that might fix the problem. Or not.
I respect your opinions. But don't appreciate the sarcasm. And if you feel like you weren't being sarcastic - it comes off that way. But don't fear, my skin is thicker than that. I'm not easily insulted; nor am I going to go away and sulk over the matter.

Repairing the board competently means fully diagnosing the problem BEFORE buying parts and BEFORE you just start throwing parts at a problem. If the reason for the failure is not readily apparent it could be lurking somewhere on the board just waiting for an opportunity to fail.
The thermistor wire accidentally touched the circuit board.
Surely an accident while powered. What blew out is not likely to be just one thing. Sure, if the fuse did its job then great. Just replace the fuse and you should be good to go.
I replaced the large gray fusible (wire wound) resistor with an identical one since it turned black and started smoking. After replacement, machine still doesn't work.
Still doesn't work AFTER replacing a "gray fusible (wire wound) resistor with an identical one since it turned black and started smoking."

If something made this "Gray" item to heat excessively and turned black" then - if it isn't a fuse - something somewhere else got damaged. Something or something(S) (plural) got damaged. Replacing the one damaged thing you suspect to have failed may lead to yet another "Gray" item burning out. And likely harming OTHER stuff. The only SURE way to fix the problem without fully diagnosing the issue is to replace everything. Time consuming and funds consuming. And in the end you can still end up with a non-functional dehydrator.

IF YOU CAN'T DIAGNOSE IT then buying a replacement control board may be the next best option. But it could possibly cost more than a new dehydrator. The TS has to decide how much time and energy can be spent on repairing this problem, versus the time saved and potentially non-wasted money. AND he gets a whole new machine. But if he wants to repair the one single item he has identified as a failed component - that's up to him. And if that's the ONLY issue then "Lucky Him".
 

Hymie

Joined Mar 30, 2018
1,079
X1 type safety capacitors (IEC 60384-14) are tested to withstand a minimum 2kVac – therefore if it is a genuine part, I would say that it is very unlikely to have failed.
 

MisterBill2

Joined Jan 23, 2018
11,579
Probably the failed item is not that capacitor. My suggestion now is to trace the circuit board to find out what other devices the current pased through as it smoked that big wirewound resistor. The same current that damaged the resistor undoubtedly damaged other components as it passed through. By tracing the circuit you will be able to locate additional suspect components. This is how diagnostics are done when there is no circuit diagram available, and no obviously damaged parts. This circuit board is open enough that tracing should be simple.
 

MisterBill2

Joined Jan 23, 2018
11,579
I respect your opinions. But don't appreciate the sarcasm. And if you feel like you weren't being sarcastic - it comes off that way. But don't fear, my skin is thicker than that. I'm not easily insulted; nor am I going to go away and sulk over the matter.

Repairing the board competently means fully diagnosing the problem BEFORE buying parts and BEFORE you just start throwing parts at a problem. If the reason for the failure is not readily apparent it could be lurking somewhere on the board just waiting for an opportunity to fail.

Surely an accident while powered. What blew out is not likely to be just one thing. Sure, if the fuse did its job then great. Just replace the fuse and you should be good to go.

Still doesn't work AFTER replacing a "gray fusible (wire wound) resistor with an identical one since it turned black and started smoking."

If something made this "Gray" item to heat excessively and turned black" then - if it isn't a fuse - something somewhere else got damaged. Something or something(S) (plural) got damaged. Replacing the one damaged thing you suspect to have failed may lead to yet another "Gray" item burning out. And likely harming OTHER stuff. The only SURE way to fix the problem without fully diagnosing the issue is to replace everything. Time consuming and funds consuming. And in the end you can still end up with a non-functional dehydrator.

IF YOU CAN'T DIAGNOSE IT then buying a replacement control board may be the next best option. But it could possibly cost more than a new dehydrator. The TS has to decide how much time and energy can be spent on repairing this problem, versus the time saved and potentially non-wasted money. AND he gets a whole new machine. But if he wants to repair the one single item he has identified as a failed component - that's up to him. And if that's the ONLY issue then "Lucky Him".
Tony, that was not meant to be sarcastic or offensive. I am in a position now where it seems that some individuals with bean-counter degrees keep stating that any sound system equipment that is not digital is trash, fit only for scrap recycling. This despite the fact that it meets all specifications and functions well for our need. They stupidly ignore the fact that it's operation is entirely satisfactory, that it is already paid for, and it is immediately available when required. AND, our organization is not in a position of having excess funds that need to be spent on something.
So having to deal with that slightly sets me up to be les welcoming to the "scrap it" way of thinking.
Also, I am suspecting that analog sound equipment does sound a bit better than most digital sound equipment.
Especially good analog stuff versus cheap digital stuff.
Perhaps some serious audiophile can comment on that.
 
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