Greetings From Las Vegas -- Personal Vending Machine Kaput

Discussion in 'General Electronics Chat' started by afmobius, Aug 22, 2015.

  1. afmobius

    Thread Starter New Member

    Aug 19, 2015
    5
    0
    (While successfully repairing tube amplifiers to transmissions, I know very little about circuit boards and associated terminology so please forgive the crude descriptions that follow =) )

    Our 15 year old son received a novelty mini fridge that looks like a scaled down soda machine. After 2 or 3 weeks the thing stopped working completely. No noise of any kind although the power light by the on/off slider witch indicates electricity is getting to the unit. Also, there was a burned scent.

    Upon opening the machine, I could see the 2 of the 3 points where the on/off slider switch is mounted on a small circuit board looked scorched.

    Directly above the on/off solder points are 6 copper rectangles laid out in 2 horizontal rows of 3. The bottom middle rectangle the RED incoming wire is soldered; the bottom left rectangle has solder but is empty. At the very top is a row of 4 copper circles with the BLACK incoming wire soldered to the second from the left.

    Where copper/orange indicates unsoldered points and red marks the burned points the board is laid out like this:

    O O O O

    = = =
    = = =


    = = =

    o o oo

    O O O O

    QUESTIONS: (Any insight greatly appreciated)

    1) Does the burned area need cleaning? If so, how?

    2) On the 6 rectangles, why would the bottom left be soldered with connecting anything?

    3) There is a mystery vertical line that starts between the 1st and 2nd rectangle and runs past the 2nd row. It's clearly there for a reason plus it looks like something melted. What was going on here and how to restore?

    Also, I could not upload photos on this site so here are links to my flickr where u can see 2 pix of the circuit board-----
    https://www.flickr.com/photos/25352244@N04/20170191464/in/dateposted-public/
    https://www.flickr.com/photos/25352244@N04/20792802185/in/dateposted-public/

    If anyone is on the paranoid side, you can go to flickr and search lvheretic under PEOPLE and see the pix.

    Thanks for reading.
     
  2. #12

    Expert

    Nov 30, 2010
    16,316
    6,818
    1) Maybe. Alcohol
    2) It doesn't matter.
    3) It's just a jumper wire. Re-solder the ends.

    4) It's just a switch with a light that glows when the switch is on. The switch might be bad. Measure with an ohm-meter to see if it switches. If the LED goes on and off when you move the switch, don't bother measuring. The light already shows if it's switching.
     
  3. afmobius

    Thread Starter New Member

    Aug 19, 2015
    5
    0
    Hi, thanks for the reply. I have a question on your response to # 3... Where should the vertical copper line/jumper be soldered?

    Any idea what caused the burning at the switch and melting at the jumper?

    Thanks
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,061
    3,823
    @afmobius
    Are you supplying the fridge with A/C wall outlet power or DC battery power?

    The wires entering the top of the board (picture of top of circuit board), you can see that there was originally (or originally planned), a switch were the 6 slots are (labelled "SA2" on the board). This switch was to allow the user to switch between AC and DC power sources. On the very top of that board, there are two sets of terminals labelled AC and DC.

    It looks like the switch was removed (or never installed) and the supply was just directly wired for DC (e.g. Battery or supplied by an AC to DC converter of appropriate voltage and current).

    I am guessing that the smoke smell came from either too high of a DC voltage applied or an AC voltage applied to the circuit designed for AC.

    It appears to me that the circuit is designed for 12 V or less (if that resistor is a 1k value (browbeat/black/red)). If it is smaller resistance (brown/black/brown) 100 ohm, then it is designed for 5 v or less. What does the board look like that sends power to this board? Is it just a transformer or something more.

    There is more to this story.

    Note, this is a very simple board and all tracks can be easily traced to duplicate it. Inout power is at the top, a switch allows power out the bottom terminals (both switch at the same time). The green LEd turns on when the switch is turned on.
     
    Last edited: Aug 23, 2015
  5. afmobius

    Thread Starter New Member

    Aug 19, 2015
    5
    0
    Thanks for the insight Gopher. The fridge came with a DC cord for the car and an AC cord that has a box adapter.

    Have posted new pix that should help.

    AC cord was the only one used.
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,542
    1,251
    The board was designed originally to do other things, and was re-purposed for this product. That is why one of the power input wires is soldered to what was a switch contact position (the 6 rectangles).

    My wife always had a small mini-fridge under her desk, and I've resurrected a few. This probably is a peltier device cooler (thermo-electric cooler or TEC). If I read the partially-blocked, upside-down label correctly, there should be two fans running in there somewhere, one to reject the TEC heat into the ambient air and one to circulate the cold air through the fridge (or something like that). If the fan fails, the TEC overheats. The switch is an obvious culprit except for the LED and resistor directly on its output. OTOH, that almost certainly is an AC rated switch, and even though the contacts probably are rated to handle 5 A current, they are rated for AC, and DC requires different contact materials. Measure the voltage across the resistor (should be around 10 V) then measure the voltage across the "element". If the element has 12 V and the fans are running, it's probably an open TEC.

    I suppose there is a chance that there is a 12 VDC compressor, evaporation coil, and all the stuff of a traditional refrigerator, but that would be a first for me.

    ak
     
  7. afmobius

    Thread Starter New Member

    Aug 19, 2015
    5
    0
    Thanks for replying Analogkid... and you are right. The fridge is a TEC device and yes, there are two fans. I googled the fridge before posting and found the majority of the many failures were due to the fan. This thing is like a DeLorean... sleek and sexy at first glance until you look at the 4 cylinder Volvo engine. Looking in this little fridge you can see it is very cheaply made. Wire cut to the minimum lengths; least number of screws to hold things together and the most fragile looking vent fan. Ah well, if things never break, there would not be anything to fix. =)


























































































































































































































































































































































































































































































































































































































































































































































































































































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  8. hp1729

    Well-Known Member

    Nov 23, 2015
    1,957
    219
    Get in touch with the manufacturer.
     
  9. afmobius

    Thread Starter New Member

    Aug 19, 2015
    5
    0
    Thanks for the reply HP. Already tried that... number no longer in service and no alternate from google search...
     
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