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Dehumidifer - Does not Power On. Faulty Power Supply Board.

Discussion in 'Troubleshooting and Repair' started by wills07417, Dec 26, 2014.

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  1. wills07417

    wills07417

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    Dec 26, 2014
    See attached photos. Yup, it's set on the resistance range. Confirmed the same as open air..., open circuit reading. Just to check i'm doing it right, i checked the other resistor R17 and got the .985k reading. next action, replace the resistor? anything else you suggest i check?

    [Correction: the reading is actually OL.. which i presume is full resistance... it's not 0...]

    [​IMG]
    [​IMG]
     
    Last edited: Jan 14, 2015
  2. wills07417

    wills07417

    18
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    Dec 26, 2014
    I pulled the resistor from the circuit to inspect further and noticed a sort of hairline fracture on the side. Not sure if this is classic symptom of a fried resistor. Confirmed there is no conductivity across the resistor ( 0.L reading ).

    [​IMG]
     
  3. Bluejets

    Bluejets

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    935
    Oct 5, 2014
    It's not a resistor , it's a choke (inductor) and it should have zero resistance.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Nov 28, 2011
    No it's not a choke. The circuit reference marked on the board is RF1 - resistor, fusible. And it doesn't look like a choke; it looks like a resistor!

    I'm not sure about the value. I think the bottom band, which you said was grey, is actually purple/violet, in which case the resistance would be 7.5Ω. What do you think? And based on its size I estimate it's rated at about 2W or 3W.

    Digi-Key doesn't have an exact replacement. I think the best option would be six 47Ω 0.5W fusible resistors (http://www.digikey.com/product-detail/en/FRM50SJR-52-47R/47DVCT-ND/2813217) in parallel (combined resistance 7.8333Ω) or five 1.5Ω 0.5W fusible resistors (http://www.digikey.com/product-detail/en/NFR25H0001508JR500/PPC1.5BCT-ND/614249) in series.

    You could also try to find a direct replacement. I found them at http://www.component.supply/index.php?main_page=product_info&products_id=3466375 but they have a minimum order quantity of 2000! I suspect that will be true for other suppliers too.

    Also check the bridge rectifier diodes D1~4 and the output diode D6. If you can find D5, check it too. For each diode, desolder one end and lift it out of the board. Select the diode test range on your multimeter - next to the Ω range, and you may need to press the Select button to change between continuity and diode test options. Then measure the diode both ways.

    With the red lead to the cathode (the end with the silver band), the meter should indicate open circuit - the same as you see with the probes disconnected. With the black lead to the cathode, the meter should indicate between 0.5V and 1.0V for D1~4. For D6 it may indicate less than 0.5V. But the first measurement is the important one anyway, since diodes don't often go open circuit without some visible indication.
     
    Last edited: Jan 15, 2015
  5. wills07417

    wills07417

    18
    2
    Dec 26, 2014
    IT WORKS!!

    First of all, thanks so much KrisBlueNZ for the quick diagnosis and very helpful instructions! I was about to give up after the numerous trips to the parts store, component switches, and subsequent disappointments. It was definitely great timing that you chimed in to help.

    Some further details.

    The resistor is truly a resistor as you mentioned, and it's actually the irregular 8.5Ω. The way I confirmed is I pulled the same resistor out of my 2nd dehumidifier (same make/model, which coincidentally also flaked out as well couple days ago, but appears to be for a different power board related reason) and checked the resistance (as you showed me). It showed 8.5. I simply swapped it into the original unit and it powered up. I have it up and running for the past 30 minutes with no issues.

    If you don't mind, I am very curious in how you immediately suspected RF1 as bad. Obviously, I'd like to learn as much about this as I've sort of struggled with it for the past few weeks. What clued you in on the bad resistor? As opposed to bad relay, diode, capacitor, etc...

    Now, my follow up challenge is to fix the 2nd unit. It also doesn't power up. Obviously I'll need to source another 8.5Ω solution (thanks btw for the links!). I'll also perform the same checks on the diodes and do a full check if there are visible issues. On that unit, i noticed a small ticking sound when powered up...not sure if this helps with the diagnosis.

    It's also quite suspicious that the two units flaked out within 3 months of each other, after having been used for the past 5 years. My wife jokingly mentioned the manufacturers set some sort of timers to commit suicide in order for us to throw away and waste money buying new ones.

    Anyway, I'm again very grateful for all the help from the members here!

    [​IMG]
     
    Last edited: Jan 15, 2015
    Ian likes this.
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Congratulations :)
    You're welcome :)
    What does the multimeter display on ohms range when you short the probes together? They don't normally display 0.0Ω. If it displays 1.0Ω when you short the probes together, then it always indicates 1Ω higher than the true resistance, so in that case, the resistor would be 7.5Ω.

    Of course it is possible that it's 8.5Ω but I kind of doubt it.
    Have a look at this schematic diagram. It's from an example circuit design in a document coded DER-227 on the Power Integrations web site, at http://ac-dc.power.com/design-support/reference-designs/design-examples/der-227-3-w-single-output/. It uses the LNK363, not the LNK364 that's used on your board, but they're very similar. And the circuit design also looks very similar, even down to the reference, RF1, for the fusible resistor! This power supply is called a "current mode flyback" circuit.

    Power Integrations LNK363 example design.png
    On your board, the phase line from the mains supply goes through the glass fuse, then straight to RF1. The other side of RF1 connects to the bridge rectifier formed by D1~4. The output of the bridge rectifier goes to the first smoothing capacitor, then through an inductor (they replaced the other inductor with a bit of wire to save money) to the second smoothing capacitor (incorrectly labelled as a second C1 in that diagram), then to the primary circuit, which consists of the primary winding of the transformer and the Power Integrations LNK363 or LNK364 controller IC.

    When the circuit is working normally, the mains supply is converted into a DC voltage across those capacitors, and the controller IC switches ON and OFF rapidly, sending pulses of current into the primary of the transformer. These pulses appear at the secondary, where they are rectified by a diode (D5 on the diagram above; D6 on your board) and smoothed, and become the power supply's output voltage.

    The components connected across the primary of the transformer are suppression components; they're there to limit the voltage that the control IC is subjected to when it turns OFF. They don't often fail but it's worth checking whether the diodes are short.

    Switching supplies like this often fail because of a voltage surge on the incoming mains supply. The voltage across the smoothing capacitors increases, subjecting the controller IC to a voltage that's too high for it to handle, and the internal MOSFET switching device inside the controller IC overheats and goes short circuit. This may cause a visible sign such as a crack or pit in the IC.

    When the controller IC goes short circuit, the transformer primary becomes connected straight across the smoothing capacitors, and they discharge quickly. The mains supply is still present, and a heavy current flows in RF1 and the bridge rectifier diodes D1~4. This causes RF1 to dissipate a lot of power, and it fails very quickly - that's what a fusible resistor does. This all happens much too quickly to affect the glass fuse.

    I knew from your description that the controller IC had failed (when they fail, they almost always fail short) and that you had replaced it. So I asked you to check RF1, which I assumed would be open circuit, since that's the way things usually go. I also asked you to check the bridge rectifier diodes, because they were subjected to a brief burst of high current when the controller IC and RF1 failed, and the output rectifier diode just in case it had been damaged by the surge (these don't often fail).
    Yes it does. That ticking sound is called hiccuping, and it means that the controller IC is trying to start up, but it is detecting a problem and shutting down. This shutting down is very quick and causes the tick sound. Then it tries to start up again, detects the same problem, and shuts down. And it repeats.

    There's no problem with RF1, the bridge rectifier, or the controller IC - at least, it hasn't failed short. The problem could be an overload at the output, or a failed component in the suppression circuit at the primary. So check D6 for short circuit, and D5 as well. You don't need to lift them out of circuit. D5 is on the underside. Let me know what the markings are on D5 and D6 as well.

    Also have a close look at the output smoothing capacitors - the two blue ones between the transformer and the output connectors. Make sure the tops and bottoms are flat with no sign of bulging or stretching of the plastic sleeves.

    If you don't find any problems, we can start making some measurements.
    Sometimes the manufacturers cut corners with the design to save a few cents - an example is the inductor that they replaced with a piece of wire. Sometimes the components don't meet their claimed specifications. This is common with electrolytic capacitors (E1 and E2 in the primary circuit, and the two blue output capacitors) made by various Chinese electrolytic manufacturers, and was the cause of the "bad capacitor plague" that affected computer motherboards around the middle of last decade. Component counterfeiting is also a significant problem, so even components from apparently good brands may not be what they seem!
     
  7. wills07417

    wills07417

    18
    2
    Dec 26, 2014
    Wow, thanks very much for the awesome explanation! Was detailed yet very easy to follow! I feel truly blessed for your generosity in taking the time to write that all out for me.

    As for the RF1 reading, I've confirmed when I put my probes together, they indicate 0.00. I suspect the resistor is quite unusual at 8.5ohms. Odd I guess, but i'll source both a 8.5 and a 7.5 while i'm at it. Does exact wattage matter? Or as long as I get one rated 3w or higher, should be fine? Also, do i have to specifically find a "fusible" resistor?

    On the second unit, I've tested the diodes as you mentioned. And again, you're right on the money! D6 is short...shows 0.00 both sides. D5 seems fine, showing a reading of .461v or so. No visible signs of any bulging capacitors. So I presume, next action is to replace D6 and hopefully it gets up and running as well.


    Also, would be interested to offer my gratitude by making a donation for the site...This is a great community and good to know there are still kind and generous folks out there! Please let me know how this can be done...
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Nov 28, 2011
    You're welcome :)

    You may find it easier to get an 8.2Ω resistor. That's a standard value and it will be just as good as 8.5Ω. The wattage should be 2.5W or 3W to ensure it will fail quickly and cleanly. Yes, it does have to be fusible. It has to be designed to fail quickly and safely.

    That's cool that you found the problem so quickly! Yes, you should just replace it. I can't think of any other component that's likely to have cause D6 to fail.

    What are the markings on D6?

    You're the first person I know of who has offered to donate to Electronics Point. I don't know how, or even whether, you can do it. I'll start a conversation with Ian, our evil overlord (admin).
     
  9. wills07417

    wills07417

    18
    2
    Dec 26, 2014
    The D6 markings show: SR2100. Already popped down to the parts store for this diode as well as 8.2 fusible resistor. No luck on either.

    Checking Digikey:

    For the SR2100 diode, I see: SR2010-TPCT-ND
    http://www.digikey.com/product-detail/en/SR2010-TP/SR2010-TPCT-ND/950549
    Part number is different (SR2010, not SR2100), but seems to have same specs. Would you say this should be ok?

    For the fusible resistor, I see: RES 8.2 OHM 2W 5% AXIAL
    http://www.digikey.com/product-detail/en/FKN200JR-73-8R2/8.2DMCT-ND/2813100
    This should also be fine, you think?
     
    Last edited: Jan 16, 2015
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    Yes, the SR2010 has the same specs as the SR2100. That is, it's a Schottky diode, 2A current rating, 100V voltage rating.

    I don't know if it's a good idea to use a 2W fusible resistor. The designs in the LNK364 data sheet specify 2.5W and 3W parts. The 2W one you found is convenient, but if you get one, I think you should also get another combination of resistors that will give a 3W rating, see post #24, third paragraph, in case the 2W one pops it clogs one day.
     
  11. wills07417

    wills07417

    18
    2
    Dec 26, 2014
    Thanks for the confirmation and guidance. Will just play it safe and go for a 2.5/3W solution. Probably will take a while to get the parts, but will post once I give it a go with the replacements...
     
  12. wills07417

    wills07417

    18
    2
    Dec 26, 2014
    Having some difficulties sourcing the 8.5ohm 2.5-3w fusible resistor. I know some solutions were provided for 7.5ohm in the earlier posts. Seems like 8.5ohms is a bit trickier for series/parallel configurations. Can anyone provide some suggestions?
     
  13. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    The value isn't very critical. 8.2Ω would be fine. Or a 10Ω 4W or 5W fusile resistor. Or a combination of series or parallel resistors, as long as they're all fusible and all the same value, and their wattages add up to at least 2.5W.
     
  14. wills07417

    wills07417

    18
    2
    Dec 26, 2014
    Just wanted to close out this thread. Replacing the SR2010 diode did the trick. Also went with a 10 ohm 3W fusible resistor and working like a charm. Got two wonderfully working dehumidifiers chugging away in this horrid Hong Kong humidity. Just in time!

    KrisBlueNZ, I know you're no longer with us, but wherever you are, hope you're in a good place. Thanks so much for your time and kick ass troubleshooting! Your kindness and generosity was unsurpassed.
     
    Last edited: Apr 3, 2015
    Martaine2005 likes this.
  15. Anon_LG

    Anon_LG

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    Jun 24, 2014
    Well Kris would be very happy to hear this.

    This I am sure he would be/is pleased with this, that one of his final contributions helped someone fix a problem.
     
  16. jdog375

    jdog375

    3
    0
    Apr 28, 2019
    Hi guys,

    Just wanted to revisit this as I have a Frigidaire FD20EN with the exact same power supply board, which also will not turn on. Going through the thread I identified that R32 was blown and D6 was an open circuit. Additionally FUSE1 (T3.15AL250V) was blown. It seems as soon as one component failed it led to a chain reaction of other components failing. R32 should be a 10.5 ohm resistor? So, aside from those parts what should I assume has also failed? Maybe VR1, IC3 and IC4, and linear voltage regulator L7805CV? Is there a reliable way to test the IC's and capacitors/varistors (don't have a breadboard or many diagnostics tools, just the multimeter)

    I took several classes in mechatronics although have not tinkered in a long time. Thanks in advance all.
    20190427_145316.jpg 20190427_145500.jpg
     

    Attached Files:

  17. HellasTechn

    HellasTechn

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    Apr 14, 2013
    The black 470uf capacitor also looks bad. I would just replace them all to be on the safe side.
     
  18. Bluejets

    Bluejets

    4,411
    935
    Oct 5, 2014
    Firstly a word of warning. High voltages in here AC mains and over 300V dc.
    After power down, discharge any large caps with a 1K5 5W resistor.
    If you are unsure, get it to a repairer.
    TV tech should know what to do.

    It's a small smps .
    The first 3 items fail is fairly typical of a power surge or similar.

    Note the replies above that this is a "fusable resistor".

    As well as checking any bulged capacitors, take a peek at the enclosed pdf for the switching IC (IC3) as it is the likely culprit.
    Enclosed diagrams (lower of the 2) would be a similar arrangement so you could possibly follow the traces on the board and compare.
    Also check the 4 "bridge rectifier" diodes, D1 through D4.
    I doubt any of the other items you mention would be a problem.
    D6 would more than likely give an incorrect reading if you checked it "in-circuit".


    Will be difficult if you have limited experience.
     

    Attached Files:

    Last edited: Apr 28, 2019
  19. jdog375

    jdog375

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    0
    Apr 28, 2019
    D1-D4 are ok, I pulled D6 out of circuit and it is showing open both directions. I'll order some parts and check back
     
  20. jdog375

    jdog375

    3
    0
    Apr 28, 2019
    Well, I replaced R32 (1MΩ 2W) , D6, IC3, IC4 and the fuse and it works now!
     
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