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Hi all- new here, a little help

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Sixtysixdeuce

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Hi guys (and gals?). My name is Nick, and I'm a mechanic with a hobbiest interest in electronics. Unfortunately, my knowledge is not terribly advanced in contrast to what I expect I'll find here, which is my reason for signing up. The project I have right now is one you'll all probably get a chuckle out of, and most people would suggest simply replacing the broken unit, I think. But I don't like not being able to solve problems, which sometimes means enlisting the help of more knowledgeable folks. Ask me to find the problem with your car, I will. But we don't typically repair the internals of control modules on them, just replace the units. So logic circuits I'm still learning.

Anyway, my query. The item in question is a baby swing, fisher-price nature's touch model (6v DC). I have been unable to turn up a schematic, not even with a call to Mattel's tech service department. So I was left trying to figure out the problem for myself. I'm sure for some of you, this is very elementary, but I'm kinda lost. Problem started when batteries were installed backwards. The sound functions still work, as does the simple mobile motor circuit (just an on/off) The issue is with the swing. It uses a small DC brush motor, but instead of being controlled with a potentiometer, it uses a logic circuit with a couple dozen resistors, 8 capacitors, 3 large and 4 small 3-node transistors (both NPN and PNP), one diode, a small calibrating potentiometer, what appears to be a and one LM324N quad op Amplifier. The issue is that, when turned on and with the motor load, it has voltage only briefly, which then tapers off to nothing. At first, I traced that back to one of the resistors. It had 2.3v in and no out. So I simply bridged it. Well, then the drop happened at the next resistor back in the line. So I bridged it too. Same thing. I got all the way back to the amplifier, which will lose voltage at the 8, 9 and 10 terminals when the two resistors are bypassed. I figured the amplifier was dropping because of heat caused by some internal damage with the inverse voltage, so I replaced it. Same thing still happens.

I suppose my biggest question would be what component was most likely damaged by the voltage inversion? I know this is even more difficult without looking at a schematic or the physical unit, but figured it was worth a shot. I've exhausted my diagnostic capabilities but would rather learn something than do the logical thing and simply throw it away.

Here are a few images of the PCB's. For the insulated wires, the distribution is as follows:

Black-ground
Red-6v+
Blue and white-Mobile motor
Orange (2)-Speaker
Green-Swing motor ground
Yellow-Swing motor power

Since three of the text boxes of the first image came out fuzzy, they simply indicate wires (purple) for the auxiliary position on the swing switch, which allows mobile and sound without swing motion, one pointing to a component that I'm not sure if it's a resistor of sorts or a small transformer coil (It is tiny copper wire wound around an insulator), and one indicating the volume potentiometer at the bottom center.

**broken link removed**

**broken link removed**

**broken link removed**

In the following image, I've attached arrows and numbers to show where the voltage drop happens. The circuit goes straight to the swing motor from point 1. At point 1, the initial drop happens. It'll be 2.3 v on the in side, and drop to 0 on the out. If I bridge that resistor, the voltage will drop to zero at point 2. If I bridge the resistor at point 2, voltage will drop at the three point indicated by #3. I never lose ground or 6v at VCC input, or the other inputs and outputs at the amplifier.

**broken link removed**

Thanks in advance for your help!
 
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fisher-price

I see a small SCM. (Micro IC) In a black Poxy glue. This perhaps could be the cause of your problem and it is beyond repair for what I know. There is not much to do with it:(
 
Hi leal. Yeah, I wondered about it too, and it is hard to be 100% sure without a schematic, but I believe that is dedicated to the sound function. The thing has 3 different noises, and they all work, so I believe it to be undamaged. Volume is controlled by the potentiometer in the center of the large PCB, and it also regulates fine. The sound switch was off when the polarity inversion happened, only the mobile and swing were engaged.
 
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Good Show!

Man, I have to admit that this is a bit of a lost cause, but certainly dont expect the manufacturer to be of any help.
I have to say that you have taken a truly logical, and intelligent thought process with everything that yiou have done. The pictures, and notations on the pictures are truly excellent, and are a real example of how someone should ask for support on this board. Im wondering if that big driver transistor (or Darlington, or Mosfet...or whatever) is the culprit. Is there a voltage being applied to it?
 
Thanks, rfs. Yes, the large transistor does distribute power. But it's a primary; I only lose output on one of the 4 amplifier circuits. I'm thinking the amplifier is controlled by the mini transistors, but I haven't had any more time to mess with it today. I ended up finding her another swing, set it up to take an M-type jack for AC adapter (these things eat 4 D batteries in no time) and equipped it with single diode protection on the power side. Was gonna do two, but with the 1500 mA diodes I had, there was a .3v drop. 5.7 runs the thing fine, not wanting to find out if 5.4 is enough, only to have to undue that extra work.

I'm honestly kinda surprised these things arent diode protected to begin with. Seems to me any unit that can be adversely affected by inverted polarity should have an inline diode. Batteries get installed backwards all the time, and many aftermarket AC adapters have interchangeable jacks that can be inserted either way.

I'm gonna keep after this one. It's a personal challenge, and if I get it going, I can recoup what I spent on the other used swing.
 
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Thats the smart way to do it....good job
What I do with all projects that I make, or items that I purchase that I adapt to a external/replaceable power supply, There are VERY few items in my house that are run from batteries, considering a electonics supplier close by offers 1amp, 1-12volt.dc. regulated, variable power supplies for around $5.00. Im just certain to glue down, or cover with a sticker the power selector switch if it is used long-term, so busy fingers wont switch from 3 volts to 12 volts accidentally.
I usually immediatly put in a bridge rectifier into the power input that provides automatic polarity. The two inputs for ac are from the external power supply, and the positve and negative terminals go to the positive and negative inputs of the circuit. So as long as the voltage is carrect, the polarity will always be correct to the circuit, no matter what way the power is applied.
As far as why a simple diode protection is not added...there can only be 2 reasons...the .00001 cent additional cost...or just plain lazyness.
 
OK, guys. I've been painstakingly mapping out this circuit, got my schematics in order-mostly. Problem I'm having is identifying the B-C-E orientation of mini transistors (and whether they're NPN or PNP) and the values of the micro resistors. I can't really figure them out by testing unless I remove them from the board, since everything is so intertwined. Anyone have a good source for decoding them?

The resistors are labeled:

-0
-100
-101
-102
-103
-104
-105
-151
-154
-221
-224
-330
-510
-750
-823
-2402
-3303
-6200

The mini transistors are labeled:

-BDC C6
-BHD C6
-E1Y
-M6.

The standard transistors I'm having trouble identifying as NPN or PNP are

-S8050
-S8550
-7130A-1

I've just googled my brains out, not having any luck. I miss the days of all band-marked resistors. They were easy.

Edit:

OK, I called digikey and the friendly tech there emailed me a micro resister coding chart, so I've got them sorted. Also figured out that my "unmarked resistors" are not resistors at all, but SMD capacitors. How on earth you figure out their rating, however, I still don't know.

I also figured out through a very convoluted search process that the E1Y transistor is a KSC2859OMTF general purpose N-channel amplifier.

Still a little stuck on the M6-labeled one, though I think it's a MMBA812M6 PNP BJT. But it could also be a BSS66 or a BSR58.

Also, the C6-marked ones I'm unsure of, but leaning toward MMBFU310 N-channel JFET.

Got the S8050 and S8550 figured (Both PNP) and the 7130A-1 is a Holtek 30mA voltage regulator

I could use a little help on the pinout of the W103 adjustable voltage regulator and A105J (series capacitor?), too.
 
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OK, so we're not gonna talk about the amount of time I've spent mapping out and trying to reverse-engineer this stupid thing, But I'd very much appreciate if some of the experts could look over my schematic, see if it looks about right, and perhaps try to identify the components I haven't been able to with the aid of this layout. The three transistors filled in with red and the one resistor (or transformer?) outlined with red are the ones I can't figure out.

**broken link removed**
 
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