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Help with 7536A-1 and a 8 pin IC with no numbers

  1. Jun 29, 2009 #1
    I am trying to replace some pieces in a circuit that produces police siren sounds and cant find new ones. one i believe is a transistor with the numbers 7536a-1 and an 8 pin IC with no numbers on it. Can someone please help me identify these. I am new to electronics and not real familiar with a lot of these items.
     
  2. jcsd
  3. Jun 29, 2009 #2
    There is a CMOS microcomputer 7536 (42 pin I think) and an 8-pin 75361A dual TTL to CMOS driver. See www.datasheets4u.com[/URL] for datasheet searches. There is no 2N7536.
     
    Last edited by a moderator: Apr 24, 2017
  4. Jun 29, 2009 #3

    berkeman

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    Welcome to the PF. Can you try to google for info about the circuit board itself? Does it have a name on it, or other numbers that might help to identify it? If you can get a schematic off the web, that will help you a lot in trying to do any component replacements. Especially if one IC has been black-topped (painted to conceal the original identifying info).
     
  5. Jun 29, 2009 #4
    There are no numbers on the ic chip itself, nor are there any numbers on the board. If any one can tell me how to post a pic of the board i will do that. it consist of the ic chip whick has 8 pins another 3 pin that looks like a transistor and has the numbers 7536A-1 on it. then it has 3 caps, one 100uf and 2 104 disk caps and that is it.
     
  6. Jun 29, 2009 #5

    berkeman

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    The little black-topped chip might be a simple microcontroller. In which case, you'd need the program inside the uC in order to duplicate it. If the developer was smart, they used "Secure" at the end of programming their uC, so that others could not easily reverse-engineer their work.

    Which brings up the question -- why are you trying to duplicate this board?
     
  7. Jun 29, 2009 #6
    No just repair it. i think i burnt up the ic, not really sure all i know is it wont work anymore. i have already replaced the parts i know only thing left to replace is the 2 parts i mentioned.
     
  8. Jun 29, 2009 #7

    berkeman

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    Where did you get it from originally? If that's a black-topped uC, you probably won't be able to fix it.

    BTW -- have you tried beeping out the "transistor" to see if it's okay or blown? Have you tried drawing a schematic from the PCB itself? That might ttell you more about the circuit (like, what type of transistor it is).
     
  9. Jun 29, 2009 #8
    i can draw you a pic of the entire circuit board if you want, it only has 5 parts total. It came in a model police car i bought off ebay.
     
  10. Jun 29, 2009 #9
    i think the transistor is a npn because the middle leg is connected to the positive power lead.
     
  11. Jun 29, 2009 #10
    no really sure like i said im new at this electronics stuff.
     
  12. Jun 29, 2009 #11

    berkeman

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    The common jelleybean discrete transistors that I'm used to using have these pinouts in TO-92 (small plastic) packages, read left-to-right:

    2N3904 NPN:EBC

    2N3906 PNP:EBC

    2N2222 NPN: EBC

    So having the middle leg connected to the + supply wouldn't be right for these particular transistors.
     
  13. Jun 29, 2009 #12
    the numbers on the three leg transistor show 7536A-1 but i cant find any info on this anywhere
     
  14. Jun 29, 2009 #13

    berkeman

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    Does your DVM have a "diode test" setting on it? If so, try beeping the trransistor out to figure out if it is an NPN or PNP. Worst case you can unsolder it from the PCB to get full access to the pins without other circuitry hooked onto them (which can confuse your diode test beeping).

    If your DVM doesn't have a diode test setting, you can generally still use a simple resistance measurement instead. Measure between each set of 2 pins, checking both polarities.
     
  15. Jun 29, 2009 #14
    The siren does 4 different tones, if I cant find a way to fix this one is it possible to build a very simple circuit that will do the same thing. not real good with electronics but am willing to give it a try if someone can help i wopuld appreciate it.
     
  16. Jun 29, 2009 #15

    berkeman

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  17. Jun 29, 2009 #16

    berkeman

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    Hey, check out one of those pictures:

    http://www.cpcares.com/media/CK015.jpg

    Looks a lot like what you are describing -- an 8-pin DIP IC and a TO-92 transistor, with a couple of discretes. If you can read the writing on top of the IC (I'm not able to), that might give you one of your answers.

    Maybe see if there is kit information for that board, if it looks similar to yours. Might be based on the same root design.
     
  18. Jun 29, 2009 #17

    vk6kro

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    This is a bit of a guess, but does the IC have the power going to two pins that are diagonally opposite each other in two of the corners? These would have a track going between them on the printed circuit board. Or, at least, does the + supply go to pin 8?
    And does it have pin 1 going to the negative supply? This is unusual among chips.

    The most likely chip someone would use in a siren could be a 555.
    see this site:
    http://www.uoguelph.ca/~antoon/gadgets/555/555.html [Broken]
    No siren there, but info on 555 chips.

    It is very common for producers of circuits to grind the numbers off so nobody can easily copy the circuit.

    Testing the transistor is easier. If you have a digital multimeter look for a diode mode. Test the pins of the transistor (in circuit for a start) for conduction one way but not the other. One of the pins, (the base) should conduct to both other pins in one direction but not the other.
    If any of the pins conduct very well in both directions, the transistor may be faulty and should be tested again out of circuit.
    Testing in OHMS mode usually will not work because the meter tests at a low voltage which won't turn the diode junction on.
    Exact replacement of the transitor probably isn't necessary and anything NPN would be worth a try.

    If you are going to replace the two most expensive things on the board, maybe you should just rebuild the whole thing from new parts?
     
    Last edited by a moderator: May 4, 2017
  19. Jun 29, 2009 #18
    i want to thank everyone for the help. I cant find my exact siren but i have found a few kits online that i can just buy and replace mine. again thanks for all the help. if i find out anything about this circuit i will post and let you know.
     
  20. Jun 29, 2009 #19
    only 5 of the 8 pins appear to be used, 3 of them are not even soldered in. Pins 1,3 and 4 are not even used. pin 2 goes to a wire on the switch, pin 5 goes to ground, pin 6 goes to a speaker wire, pin 7 runs through the positive side of the 2 caps and one of the outer pins on the transistor i beleive it is the c pin, pin 8 hooks to the other speaker wire. if this helps please let me know
     
    Last edited: Jun 29, 2009
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