What is the resistor value?

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Geronimo
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Posted by Geronimo: Tue. Apr 3, 2018 - 09:30 PM
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Hello freaks!

 

Today my dishwasher finally decided to give up after acting erratically for a while (turning off and back on randomly), after lurking for a bit I found the control board and a resistor looks burned, but apart from that I don't see anything else (visibly) burned.

 

Resistor

 

One side of the resistor is connected to one side of a relay (possibly ground, the big green area), the other side is amongst other connections connected to a connector on the edge of the board, there are a load of connectors with many wires in the same color, so I'm not certain what is "out there" that is hooked up to the resistor or why it has burned.

 

Any idea why it burned in the first place? Under dimensioned? Are faults elsewhere probable?

 

What was the value of the resister, I'm reading it as brown-black-brown-black -- white (101 ohms ??? % or possibly 100 ohms?)

What is the rating? 2W?

 

Best regards, I hope you can help me solve my puzzle!

Geronimo

- Brian

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Learning and Information, General Electronics
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Paulvdh
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Posted by Paulvdh: Tue. Apr 3, 2018 - 10:32 PM
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Geronimo wrote:
but apart from that I don't see anything else (visibly) burned.
The grey part above the resistor looks pretty burned too. Is it a capacitor or just apiece of plastic?

 

101 Ohm seems unlikely because it is not in https://en.wikipedia.org/wiki/E-series_of_preferred_numbers#E96

 

Power rating of the resistor is .... Not high enough?

Almost impossible to guess from a picture. Best guess somewhere between 1 and 5 Watts. Power rating is also highly dependent on the max allowable temperature of the resistor, which can also vary a lot.

 

To me the resistor looks like Black Red Black Brown.

A 12 Ohm 1% shunt resistor for current measurement could be part of a circuit to regulate a motor current.

It could be that the motor is stuck and draws too much current, which blew the resistor.

 

-----------------------

Oops. Only now I see a white band on the far left.

According to https://en.wikipedia.org/wiki/Electronic_color_code this may be related to some EIA vibration resistance specification.

When reading form that side my gues is:

Brown Black Red = 1k Ohm

Black = Something none standard ???

 

Following the wires or beeping them through might very well lead to better insight.

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

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avrcandies
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Posted by avrcandies: Tue. Apr 3, 2018 - 11:10 PM
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It could be a choke (inductor), rather than a resistor (but not too likely).

 

If it hooked to a connector, could be wherever it went (panel switch, knob, sensor,etc) has shorted or become defunct...so you should investigate.

 

Sometimes power resistors are not rated high enough & slowly cook the board over years of use, especially when they get dusty. 

 

Test the resistor...they are usually very sturdy & there is a decent chance it is still "good" (but needing replaced) & the problem still exists somewhere in its connection pathway.

 

TAKE A LOOK at this posting...might have some tips

https://www.electronicspoint.com/threads/pcb-for-dishwasher-repair.280427/

You guys are brilliant, thank you so much for your help on this. I swapped out the cluster of blackened surface mount stuff and TNY264, and it no longer blew the resistor. It must have failed fairly catastrophically in order to blow that resistor as must have been a decent voltage spike...! Sadly I still dont have a working machine just yet, though I need to check my connections as my SMD soldering is never great. Hopefully that will be enough, for later this week when I next have time. Too tired now to keep going.

Thanks again,
 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Tue. Apr 3, 2018 - 11:24 PM
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valusoft
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Posted by valusoft: Wed. Apr 4, 2018 - 07:40 AM
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Brian,

 

Did you try googling for the dishwasher's service manual. That is usually my first call when faced with something like this. My neighbour's refrigerator had been declared irreparable by one "technician". I found the service manual on the net and the refrigerator has now been working for more than 2 years. Give it a try.

 

Ross McKenzie ValuSoft Melbourne Australia

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Geronimo
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Posted by Geronimo: Wed. Apr 4, 2018 - 09:20 AM
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avrcandies wrote:
TAKE A LOOK at this posting...might have some tips https://www.electronicspoint.com...

 

Wow, that PCB looks almost exactly like mine! After skimming the post, I noticed that on my board the TNY264GN is probably also fried! There is a small hole in the top of the IC that I am pretty sure is not supposed to be there (seen something similar before in a blown op-amp).

But the hole is so tiny I didn't noticed it because nothing else in that area looks burned! It's hard to pick up with the phone camera, maybe I can make a macro photo when I get home later.

 

I will look into it in more detail when I get home tonight.

 

TNY264GN

 

valusoft wrote:
Did you try googling for the dishwasher's service manual.

 

I tried, but I wasn't successful in locating it! The washing machine is a Siemens SN46M283SK/52 and the control PCB was in a plastic case marked MELECS EPG60613, apparently this control PCB is common in washing machines of different brands and models.

Not exactly sure where to look, google didn't really help me or maybe my googling skills are getting rusty sad

- Brian

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Kartman
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Posted by Kartman: Wed. Apr 4, 2018 - 01:52 PM
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The input electrolytic capacitor has failed. Usually around 22uF 400V.
I recently fixed a unit that failed similarly. The top blew off the tny ic, so i had to work from the transformer specs to get the ic part number. Element14 had the required parts.

Show us a picture of the whole board so we can identify the failed component.

Last Edited: Wed. Apr 4, 2018 - 02:04 PM
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Geronimo
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Posted by Geronimo: Wed. Apr 4, 2018 - 08:02 PM
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Kartman wrote:
The input electrolytic capacitor has failed. Usually around 22uF 400V.

 

The input capacitor isn't visibly failing, but the previous periodic switching on and off matches with a dead cap.

The value of the cap (big black) is 100uF 400V. The small cap is 16V 470uF. I will probably change both while I'm at it anyway.

 

I can't visibly identify anything else that looks burned, but I will check diodes, transistor, resistors and caps around the IC with a multimeter if I can.

 

Here are a few more pictures:

 

Attachment(s): 

Image icon 01_Board_Full.jpg
Image icon 02_TNY_IC_closeup.jpg
Image icon 03_closeup2.jpg
Image icon 04_board1.jpg
Image icon 05_board2.jpg
Image icon 06_board3.jpg

- Brian

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ki0bk
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Posted by ki0bk: Wed. Apr 4, 2018 - 08:23 PM
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The big cap looks swollen to me, and so is bad, replace it, the small cap looks ok.

The other thing I see is a hole in the TNY chip, so it has let the smoke out, replace it.

 

Jim

 

Click Link: Get Free Stock: Retire early! PM for strategy

share.robinhood.com/jamesc3274

 

 

 

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Paulvdh
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Posted by Paulvdh: Wed. Apr 4, 2018 - 09:47 PM
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ki0bk wrote:
The big cap looks swollen to me, and so is bad,
Nope, wrong conclusion. Bulging capacitors are often a sign of failure, but you are looking at a piece of plastic on top of the capacitor here. These plastic caps get under tention from the crimping foil and often dislodge from the cap and bulge after time. An ESR meter, or measuring the voltage ripple under power are much better methods to check capacitors.

 

Edit

To destinguish as "cap" as short for "capacitor" and the plastic cap on top of the capacitor. Phew.

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

Last Edited: Wed. Apr 4, 2018 - 10:18 PM
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joeymorin
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Posted by joeymorin: Thu. Apr 5, 2018 - 01:26 AM
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So that resistor cooked the plastic case of a nearby relay.  Wonder if that will need replacing, too.

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

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Kartman
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Posted by Kartman: Thu. Apr 5, 2018 - 01:45 AM
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It’s a bit hard to see what the resistor actually does. It is connected to a diode so it maybe some kind of snubber, so the overheating might be ‘normal’ or a result of some other problem. It looks unrelated to the tny switcher. As for the tny chip going pop, the usual cause is the input cap. In this case the board has a large cap so should last some time unless there is a motor drive working off that same cap. On the board i fixed, there was a 22uF cap that was visibly failed. The unit had lasted around 5 years working 24/7.

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avrcandies
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Posted by avrcandies: Thu. Apr 5, 2018 - 02:36 AM
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Not sure WHY they'd put a big 'ole pwr resistor right on top of a plastic case, when there is plenty of room to scoot it another 0.2 inch away!!

 

wonder if this is a poor man's fuse, some other purpose, or just bleh layout?  Doesn't really seem accidental.

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Paulvdh
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Posted by Paulvdh: Thu. Apr 5, 2018 - 04:36 AM
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@avrcandies #12.

Yep, such traces are sometimes uses as fuses.

 

MikesElectricStuff has a nice anecdote on it.

He was diagnosing such a blown fuse, which apparently turned in a plasma ball before smothering out and metal was sputtered on an ajacent PCB, where it caused a secondary short.

The secondary short caused more damage and the whole Microwave was toast.

 

If my memory serves me right the reason for the PCB trace fuse blowing was because of a failed lamp in the microwave oven itself, which apparently can generate over current conditions when failing.

 

Mike also noted though that these fuses are allright if some care is taken for where they are put, so the (short) spark / plasma can not do more damage.

The holes in the pads are also a nice touch. These help in adherance of the pads to the PCB material. It will prevent the whole track from being ripped of if for example a weld spot occurs inside the edge connector. Via's under the "mechanical pad" of SMD connectors also give them a lot of extra mechanical strength.

 

 

 

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

Last Edited: Thu. Apr 5, 2018 - 10:49 AM
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avrcandies
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Posted by avrcandies: Thu. Apr 5, 2018 - 07:41 AM
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and the whole Microwave was toast

Put some butter on it surprise

 

The holes in the pads are also a nice touch. These help in adherance of the pads to the PCB material

Interesting trick of the trade!!

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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DocJC
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Posted by DocJC: Thu. Apr 5, 2018 - 03:42 PM
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The holes in the pads are also a nice touch. These help in adherance of the pads to the PCB material.

 

I think, also, they help convey heat to the back side of the board, where one might well have a large fill heat sink in addition to the one on the top of the PCB.

 

JC 

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Kartman
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Posted by Kartman: Thu. Apr 5, 2018 - 04:15 PM
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Or the more obvious method of increasing the contact capacity if the edge connector is double sided.

When filament bulbs fail, an arc is usually generated. The problem with an arc is the more current that is available, the lower the impedance of the arc. So what starts out as a 40W lamp becomes a dead short circuit. A similar thing happens with fuses.

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Geronimo
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Posted by Geronimo: Fri. Apr 6, 2018 - 07:11 AM
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I ordered a new TNY chip, resistor, large and small electrolytic cap and another relay (even if the old is still working, i Prefer non-charred components).

I might as well change the caps, they are "usually" on of the first things to fail from my experience - and I would like if the dishwasher would live at least another 5 years without me having to disassemble it. wink

 

Unfortunately there is about 2 weeks delivery on the TNY chip (either that or I had to buy a reel of 50), so it might be a while on any updates.

- Brian

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meslomp
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Posted by meslomp: Fri. Apr 6, 2018 - 11:03 AM
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what tny chip did you order?

in your text you write about a "TNY264" but the chip marking to me looks more like a "TNY254" both ac/dc converters but mort likely not identical.....

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Geronimo
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Posted by Geronimo: Fri. Apr 6, 2018 - 01:25 PM
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I ordered exactly that chip, the TNY264 wink

 

I can see what you mean that it looks like a "5" in the one picture, but if you look at the close-up picture I have attached in another post it's more clear that it's actually a "64" but with some charring/blackened area on the numbers.

 

Geronimo wrote:
Here are a few more pictures: Attachment(s): Image icon 01_Board_Full.jpg Image icon 02_TNY_IC_closeup.jpg

- Brian

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