Fisher-Price Swing Repair

My son sleeps exclusively in a Fisher-Price Cradle ‘n Swing.  The swing stopped swinging during the night last night, so I took it apart to see if I could fix it before tonight.  The swing is still in pretty good shape, though it is an older model we bought second hand from Once Upon a Child.

When I got the top open, I could smell the odor of burnt electronics.  Fortunately, the bad transistor did me the favor of leaving a scorch mark to let me know what needed replacing.  The scorch marks are a little hard to see in the first picture, but pretty obvious with the transistor clipped off.

Fisher-Price swing control PCB with fried transistor Fisher-Price swing control PCB with fried transistor removed to show scorch marks

The markings on the part indicate that it is most likely an ON Semiconductor MJE171G PNP transistor.  Since we needed the swing tonight, I headed out to the local Radio Shack to see what they have on hand.

There I found a $2 Tip 42 PNP transistor with comparable specs.  The only spec that is not up to the original MJE171G is the maximum emitter-base voltage — 7.0 V for the MJE171G, but only 5.0 V for the Tip 42.  When I probed the drive circuit without a transistor installed, the maximum emitter-base voltage was less than 4.3V for any setting of the motor speed dial, so the Tip 42 will hopefully be fine.  The picture below shows the Tip 42 installed in place of the MJE171G.

Fisher-Price swing control PCB with replacement Tip 42 transistor     Fisher-Price swing control PCB with replacement transistor

The motor still spins when power is applied, but needed a little push to get going.  Rather than to save a second trip to the store for a motor, I also got a replacement motor while I was out.

A helpful Instructables page called Repair your FisherPrice cradle swing describes how to re-purpose the motor from an Air Wick air freshener as a replacement for the Fisher-Price swing motor.  The local Meijer store had one for $5.

It is interesting that the control PCB pictured in the Instructables article has a TO-220 transistor with a big heat sink prominently mounted on a PCB.  It looks like our, apparently older, swing must have had enough transistors blow out that the redesigned with a beefier transistor and better cooling.  Had I read the article all the way through and seen the size of the heat sink on the newer model, I would have bought a heat sink, too.

After replacing the transistor and motor, the swing is back in working order.  I am sure I could have bought the parts online from Digikey or Mouser for much less, but shipping would have eaten up the difference.  Even more importantly, the total price was low enough that getting all the parts fast enough to repair the swing before bedtime was more worthwhile than saving a few dollars.


8 thoughts on “Fisher-Price Swing Repair”

    1. All those years of taking apart broken stuff ought to be good for something 🙂 Now, if I can just get the Roomba working again…

  1. My control board looks a little different. How do I tell what transistor needs to be replaced? I changed the motor, but it still won’t run. The mobile and music work. The motor works when powered directly by the DC. Would appreciate any help. Thanks.

    1. Sorry for the delayed reply. I have not been keeping up with this blog. The first thing to look for on the transistor is burn marks. Often when a transistor dies from overwork, there will be scorching around or on the transistor and surrounding circuit board.

      Otherwise, your best bet would be to use a digital multimeter (DMM) to check voltages around the circuit. A new swing does not cost much more than a DMM, so if you do not already have one, you might be better off just buying a new swing.

  2. So I replaced motor in identical swing motor works but control speed doesn’t and doesn’t swing the motor spring rod just goes back and forth . Old motor was slowing down and needed push. So where do I start. Yeah I can just by another one but knowledge is power. Nothing in close magnified veiw looks off to me but there was alittle rust on connect ing circuit lines”sorry for the lack of Grammer and terms. So I cleaned. Every thing else works just speeds don’t work and some times it’s off when you plug in and switch is on battery mode, flip to DC motor goes. Other times I plug in and just start right away. Either way speed control don’t work and when motor rod goes back and forth doesn’t get swing going. I thought it was because at first I didn’t solder the extra. Whatcha macall it on back of air freshener motor then did and still same issues no change. It’s bugging me because I normally can diagnose and fix just about anything.t

    1. Hmm, I don’t know. Motor turning and no or little motion, could be a mechanical problem. No on some cards the fan speed control his bad when a resistor pack fails. Had the she happen on my stove exhaust fan. So, maybe double check the resistors.

  3. Quick check to see how this replacement worked for you. I have the exact same issue (burned out MJE171 transistor in my swing) and also have easy access to a TIP42C transistor

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