I'm trying to fix this little electronic toy. It's really not much, 8 buttons, you push one, the lights go on, and a little melody plays. Now, I really don't know much about this, but really wanna fix that toy :)

There is a single controller, splitting to two circuits, one for diode lights, and another one to a speaker. The way it broke, as it's there is no sound. There is a transistor (or I think it is) for each circuit. For each, one (right) leg is straight to the batteries, the second (left) leg is to the chip (through a resistor), and the third one (middle) is to the outlet (from one it's to the speaker and from another it's to lights).

I was probing both the transistors to see what's going on when a toy is "activated". Dormant, controller leg has the same voltage that is coming from the battery, and the "out" leg has nothing on it. When the button is pushed, the voltage on the controller leg drops a volt or so, and the "out" leg starts showing some for lights. The out leg that goes to the speaker doesn't ever show any voltage, yet its leg that goes to the controller shows different voltage drops (I assume that's the controller "playing" music).

I believe the transistor for the speaker circuit just broke (IMO, sitting an hour in rain would do it). But, the only things I see on this transistor (again, I don't know what is it, really), are: C945 the first line, and P73C on the second line. There is absolutely no markings on this thing, and it has three legs and black solid body. It very much looks like this:

looks like this

For the numbers that I see on it, I couldn't find a scheme that would tell me what it is, and what/where can I get as a replacement.

Some of the answers I've got tell me this is 2SC945, which is then, according to http://www.elexp.com/t_tranmk.htm would be NPN HF transistor. If so, and I were to order a replacement from, say RadioShack, how would I find one that would work?

UPDATE: I was able to replace this transistor with 2N3904 (I should've been more careful picking the replacement that had the same order of pins, but hey, this was the cheapest one available). Thank you for all your help, support, and explanations :)


1 Answer 1


It looks a lot like a 2SC945, whose TO92 packaging matches the image you posted.

  • 2
    \$\begingroup\$ +1, agree. Nearly all transistors that are labeled according to the Japanese standard (JIS) lack the leading "2S". Usually, you just read A123 for a 2SA123, B123 for a 2SB123, C123 for a 2SC123, D123 for a 2SD123, J123 for a 2SJ123, K123 for a 2SK123. (2SA and 2SB series are pnp, 2SC and 2SD series are npn, 2SJ and 2SK are MOS). \$\endgroup\$
    – zebonaut
    Jun 10, 2012 at 21:05
  • \$\begingroup\$ Umm, you don't think 2SC945 is a little high voltage for battery operated? Or I don't understand what "LVceo: 50V min" means? And what's with the P73C part? And also, how do I tell that it would open when the base-emitter voltage drops, not when it will be applied? \$\endgroup\$ Jun 10, 2012 at 21:21
  • 2
    \$\begingroup\$ You need to do some basic reading on transistor parameters. See here page one for LVceo and some other relevant terms. \$\endgroup\$
    – Russell McMahon
    Jun 10, 2012 at 23:21
  • \$\begingroup\$ All right, so just to settle LVceo - 50V min. LVceo means - the minimal collector-emitter voltage to cause a break down is 50V, right? Then the spec for 2SC945 says : max Vbe is 0.65, and on the toy the base was constantly charged at 3V. On the other hand, they say Vebo is 5V max... I'm sorry, this is confusing :) \$\endgroup\$ Jun 11, 2012 at 5:29
  • 1
    \$\begingroup\$ @Pawel - Vebo - is the reverse base voltage, negative with respect to the emitter. This is always low, around 5V. In most applications not relevant. Vbe 0.65V is a typical value, it's a diode junction. You apply the 3V via a resistor which takes care of the voltage difference. \$\endgroup\$
    – stevenvh
    Jun 11, 2012 at 14:35

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