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Need help finding replacement transformer for oven control board

Discussion in 'Datasheets, Manuals and Component Identification' started by In Kamloops, Oct 22, 2017.

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  1. In Kamloops

    In Kamloops

    20
    1
    Oct 22, 2017
    My in-laws oven and clock stopped working after a tree in their yard fell and hit the power lines.

    I inspected the oven control board and discovered the transformer on it looked like it blew. Sure enough, the primary windings are open.

    Now I want to replace it but I'm having a terrible time googling for its replacement, so I thought I'd ask here.

    It's a Frigidaire stove. Here are pics of the transformer, as well as the OCB.

    If someone can point me to a website that has a replacement, I greatly appreciate it.

    Thanks, in advance, for any help I receive. 20171021_192315.jpg 20171021_192332.jpg 20171021_192355.jpg 20171021_192429.jpg 20171021_192459.jpg 20171021_192516.jpg
    Blaine
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    You have a couple of options:
    1. Find the manufacturer and get a replacement.
    2. Find a replacement board or transformer from a junked unit
    3. Find the specs of the transformer and try to find a replacement
    4. Fix the transformer.
    5. reverse engineer the specs
    1 & 2 are probably the easiest fix, but may not be possible.

    3 is difficult, but you might be able to figure it out based on the circuit or from another unit, or form the manufacturer. Google might be able to help (not much - -apart from others looking for similar transformers).

    4 is the ye olde solution. You may be able to find someone to rewind the primary. Basically this consists of removing the winding, counting the turns, and replacing it.

    5 is kinda similar. Once you have the number of turns of the primary, you divide it by the the incoming voltage. This gives you turns per volt. If you then dismantle the secondary toy can count the number of turns between the taps and multiply these by the turns per volt to determine the secondary voltage(s). The gauge wire on the secondary will be a guide to the transformer rating, but it's total weight is also a good indicator. Next thing is to find a similar transformer.

    However, if the voltage spike was sufficient to damage the primary, there's a reasonable to high chance that something on the secondary side will also be damaged. It's also possible that circuit damage occurred first, leading to an over-current situation which burnt out the transformer.
     
  3. Bluejets

    Bluejets

    4,991
    1,048
    Oct 5, 2014
    Further to Steve's input, you might get some idea of the output by the voltage on the large electrolytic cap nearby or perhaps U1 numbers as I suspect it's a regulator.
    Output appears to be 2 windings?

    I see a 5v test point on the top left area but this could be from a zener somewhere.
    It looks like the black relay may be 12v though.
     
  4. 73's de Edd

    73's de Edd

    3,121
    1,315
    Aug 21, 2015
    Sir Blaine . . . . .

    Replacing the whole board prices out at ~ $141 and some supply places are saying "out of stock" or unk time of availability .

    Just "hoping" to find and buying that SAME identical transformer or finding another one on a used board to pull the transformer unit from it . . . is absolutely being a rats ass chance in hell.

    Do you have the techno skill to analyze the wiring to the primary of the transformer.
    In going on my 99 99 / 100ths suspicion that the 4 leads on the primary are for two windings on
    the primary , each for 120 V operation and that they are BEING tied in parallel to have a 120VAC
    . . . a la Canada . . . operational line voltage connectivity in your situation.
    (Otherwise, they are arranged in series for use in 220VAC operational countries.)

    I am only seeing two terminals on the secondary . . . . indicative of a single low voltage secondary winding . . .that's GOOOOOD !

    On the frontal panel display, it is using minimal power and on our viewed side of the board, the two white relays and THE heavier BLACK relays 12VDC coils pull the most power required by the system.( Minimal)

    Your power transformers low voltage secondary feeds into the D14-15-16-17 power diodes to create a pulsating DCvoltage to be smoothed to and stored in C1 as pure DC and that will be the main supply voltage for the relay coils with a tap off . . . used to feed to the adjunct U1 for a sub power supply, it is probably going to be a 9-6 or 5VDC regulator.
    Go by its part number numbering of . . . . . a 7805 for 5V . . .7806 for 6V . . .7809 for 9VDC.
    Take a DVM meter in DIODE test mode and confirm that all 4 diodes . . .D14-15-16-17 . . .are giving good diode junctrion readings of ~500-700 millivolts . With no shorted 000 diodes.
    In looking at the "boiled" winding of the transformer, its being on the secondary end, so I'm wanting to think that AC overvoltage / or power spikes coming in and shorting a diode(s) which then severely overloaded that winding and the pimary responded by opening up either of its primary windings or an internal thermal one shot cutout . SO be SURE of those 4 diodes, as I'm expecting problems there.

    My bet is that a conventional transformer of 120VAC input and 12VAC @ 1 amp output rating would be equivalent to what you have . . . or a 2A at the absolute most.
    The C1 capacitor is only letting me get a peek at its side marking of ? 25 ? VDC or ?16 ? VDC, with only half of its numbering showing.
    • Feed back its capacitance and voltage rating for confirmation.
    You can (unfruitfully) search for an identical transformer case and terminal configuration at Mouser or Digi-key,
    but will probably have to use some flying wire leads at points.
    I personally would be using one of my several [email protected] 1 A/ or / 2A "FILAMENT" / "CONTROL" transformers (au gratis), collected from decades past, and then routing its wires to the PCB holes.

    If you are a electronic person or have acquaintances that have some equipment, you could initially hook 12VDC into the C1 and test out with a variable DC supply set at 12VDC, as the display u/p will be run with its own clock oscillator . . . and is not being 50/60 cycle dependant.

    If you do not want to have to "buy it to try it" and have some McGuyverish DNA flowing thru your veins.
    I can give you that type of alternative . . . . if you happen to have use of :
    • A doorbell transformer from your attic and an incandescant table or pole lamp, using a rotary, continously variable dimmer control.
    or a
    • 12 V car battery and a 10 ohm 5 watt resistor (or series/parallel /push pull / tandem/whatever) interconnects of several higher values to end up with that required 10-12 ohms of resistance
    or
    • Scotch tape , 4 toothpicks and a clarinet reed.
    What say ye . . . . .

    73's de Edd

    .
     
    Last edited: Oct 22, 2017
    duke37 likes this.
  5. In Kamloops

    In Kamloops

    20
    1
    Oct 22, 2017
    Thanks Steve, for your time replying. I'm going to try #1 first, and if no luck, then try some of the other responses. Honestly, fixing the transformer sounds likes a good challenge. I've never repaired a transformer before so it would be something I'd be up to doing if I had more time and I knew if I have the right gauge wire, which I'm not sure I do. I seriously thought it would be easy finding the transformer, but I've found out otherwise. Thanks again.
     
  6. Minder

    Minder

    3,103
    664
    Apr 24, 2015
    There is a another scenario where there is a thermal fuse buried or just under the outer insulation, often fitted to these Chinese origin TXFMR's. It might pay to peel off the insulation and check it out.
    Especially if the primary is open.
    M.
     
  7. In Kamloops

    In Kamloops

    20
    1
    Oct 22, 2017

    Yes, the large cap is 25V, and smaller ones are 16V. And the relays are 12 volt, so my guess is output of the transformer would be 12 volts, but 73's de Edd reply has me rethinking. I thought the primary had the 2 pins, and the output had the 4 pins. He says the opposite. Regardless, it's 2 coils on the 4 pin side and ohm readings are 1.4 ohms and 2.8 ohms. No shorts to the core, and no shorts between them. Thanks for taking the time to respond. I appreciate it.
    20171022_133423.jpg 20171022_133434.jpg
     
  8. In Kamloops

    In Kamloops

    20
    1
    Oct 22, 2017
    Thanks. I'm trying to remove the insulating tape and it's terrible. Do you know how I can open the core and remove the coils to make it easier?
     
  9. In Kamloops

    In Kamloops

    20
    1
    Oct 22, 2017
    20171022_134816.jpg

    Thanks for the in-depth reply.

    I tested the 4 diodes and all are good. 0.680 on each one. Got lucky there.



    I thought about powering the CB with a spare computer power supply. I guess the best way to do it is start with 5V and then up to 12V, right?

    Lastly, my blood flows McGuyver. My best McGuyver fix ever (not electronics related) was my dishwasher. The rubber water recirculation valve wore out and I replaced it with leather from my old boot. Has worked like a charm for over 3 years now And I kept my old boot just in case it fails again. Can you tell I grew up on a farm?

    Fire away....
     
  10. Minder

    Minder

    3,103
    664
    Apr 24, 2015
    I have opened a few and I know the shellacked winding insulation can be a little of an effort to remove, you don't really want to dismantle the lamination's if you can at all help it, the irony is, when they embed these fuses they save the subsequent circuitry but make it virtually impossible to replace the fuse, if fitted.
    Often there is two wire ends sticking out for the connection to the fuse, so I usually short these out to get every thing going again.
    You need to carefully peel off the shellacked insulation tape to expose the primary winding.
    M.
     
  11. In Kamloops

    In Kamloops

    20
    1
    Oct 22, 2017
    Thanks. I might have ruined the coils already... I used the metal tip of my probe to scratch open the insulation tape around the coil (not knowing that there might be a thermal fuse in there). I appreciate your help. Unfortunately, I have to go now and work. Hope to be back on again tonight. Cheers.
     
  12. Bluejets

    Bluejets

    4,991
    1,048
    Oct 5, 2014
    Appears beyond any thermal fuse fault by the look of the windings they're pretty-much cooked on that one side.
    Also great blob of molten plastic poking out of the core and a blow mark on the board.

    Measurements suggest 2 windings are secondary.
    View of the printed circuit side of the board would help determine but it looks like maybe a 12v and 6v output.
    Is there any reading between the two centre pins of the 4?
     
  13. Minder

    Minder

    3,103
    664
    Apr 24, 2015
    The voltage of the relay coils should indicate what the secondary should be, there is Hammond transformers as a source of possible replacement, if needed.
    M..
     
  14. Minder

    Minder

    3,103
    664
    Apr 24, 2015
    The stove I just fixed was a Frigidaire, it used 24vdc supply for the control board, I don't recall if it was 240v fed from L1,L2, or one line and the neutral.
    What are the relays marked?
    But I would be surprised if it stayed on long enough to cook the winding.
    M.
     
  15. kellys_eye

    kellys_eye

    4,275
    1,147
    Jun 25, 2010
    If it was possible to determine the secondary voltages you could purchase many small transformers that could bold to the board and be wired into position. It would even be possible to mount a transformer off-board somewhere (safe) and take flying leads to the secondary connection points.

    One of the best measurements to make is the pin spacing though. If it fits a 0.1" matrix, so much the better (easier) to find a replacement.
     
  16. In Kamloops

    In Kamloops

    20
    1
    Oct 22, 2017
    No, no reading between middle pins.
    20171022_133450.jpg


    Here is foil side of the pcb.

    20171022_134557.jpg

    for convenience, here's the component side of the board again:
    20171021_192429.jpg
    Thanks.
     
  17. In Kamloops

    In Kamloops

    20
    1
    Oct 22, 2017

    12 volt.
    20171022_123005.jpg
     
  18. In Kamloops

    In Kamloops

    20
    1
    Oct 22, 2017
    Thanks for your response. What surprises me is it seems the ID numbers on the tape seems to be useless... can't find any information about the transformer using them to search online.
     
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    They're probably very useful, it's just that the information it links to is not publicly available.
     
  20. In Kamloops

    In Kamloops

    20
    1
    Oct 22, 2017
    After I posted that, the same thought came to me... perhaps it's internal company info.
     
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