Need help identifying components for a 3 tone circuit  - Page 1
Forum section: electronics / repair

author: samvivi7
author_rank: Contributor
timestamp: March 30, 2016, 02:14:14 am
content: Hey everyone,i have a 3 tone circuit which is not working and i a trying to replicate but i am having trouble identifying some of the components. This is for a BMW headlights warning system.the resistors are very easy and the speaker which is 8 ohms.i have a attached links to some pictures and some literature on the chip sab0600.any help is really really appreciated. plz let me know if you need more information.Thank you,Sam

author: fra.gherard
author_rank: Contributor
timestamp: March 30, 2016, 08:43:54 am
content: You can't identify the capacitors, the two diodes also. The bigest diode can be a 1/2W zener, and the other for example 1n4148, but is not guarantee.If you have an LCR tester you can measur the capacitors, but not the diode.The IC is a siemens sab0600, here the datasheet:http://pdf1.alldatasheet.com/datasheet-pdf/view/87236/SIEMENS/SAB0600.html

author: samvivi7
author_rank: Contributor
timestamp: April 02, 2016, 02:41:03 pm
content: Hey fra.gherardThank you for all the help, do you think you could help me with the transistors?again thank you for the help

author: orolo
author_rank: Frequent Contributor
timestamp: April 02, 2016, 04:34:05 pm
content: The lowest four sot-23 components areBAS-21diodes: JSs is their usual marking. There is one of these diodes for each cable in the board, and their polarity implies that black and green cables are ground/sink (in fact, black is obviously ground for the IC), and blue and yellow are positive. I can't discern the upper sot-23 markings, and the wiring is not clear. Since the positive rail for the SAB0600 comes through it, it is either another diode, or some kind of switch, in which case it would probably be a mosfet. The wiring doesn't look right for a bipolar. Can you tell the upper sot-23 marking?

author: samvivi7
author_rank: Contributor
timestamp: April 02, 2016, 11:14:13 pm
content: Hey OroloThank you for the reply I have attached a had hand sketched schematic of the circuit. the upper sot-23 marking looks like 3K or (34), does that sound right?thanks for all the help

author: orolo
author_rank: Frequent Contributor
timestamp: April 03, 2016, 02:05:21 pm
content: Heh. So it is a bipolar switch after all:looking up the marking,3Kis without doubt aBC858B, a jellybean small signal pnp transistor.Your schematic looks right, but you haven't connected pin 4 of the IC to 'ground', between C2 and the speaker. Pin 2 should be connected to high voltage, between R4 and C4, and pin 3 should be connected to C5, if I remember well from when I looked at your pictures.Anyway, the 3K smd is a pnp transistor: when the green wire goes to ground (remember, it's a sink), the transistor turns on, and the circuit is powered by either the blue, yellow, or both cables. The 10K resistor divider is there to drive the base of the transistor, and to pull it up when green is not sinking.R2 and R3 look a bit confusing: could it be that R2 is connected to the left side of C3? Otherwise that pin would be floating, and R2 does near to nothing being in parallel with R3.D1 might be a zener to prevent overvoltage / regulate, since it is directly on the positive rail, and protected by R7.D2 might be a normal diode, of the 1N4148 kind, maybe to clamp the power pin of the IC to no less than -0.6 volts in case of undervoltage. There is a lot of protection going on in the circuit, which I think is normal for an automotive application.

author: samvivi7
author_rank: Contributor
timestamp: April 07, 2016, 01:16:10 am
content: Hi OroloI would like to thank you for all the help and the time you have taken out to help me.I have got a proper schematic together that looks a bit better.I have a question regarding the Cap's since there are no markings on the caps can I just use the values provided in the "test application" of the SAB 0600 data sheet?I have attached some more documents if it any helps regarding the wires that go to the fuse box.Thank you

author: amyk
author_rank: Super Contributor
timestamp: April 07, 2016, 10:38:40 am
content: The datasheet should be enough to make a replacement, it has the typical application circuit.

author: samvivi7
author_rank: Contributor
timestamp: April 07, 2016, 06:31:51 pm
content: Hi amykthanks, so i should be fine with replacing the caps with same values form the datasheet.

author: orolo
author_rank: Frequent Contributor
timestamp: April 07, 2016, 06:50:59 pm
content: Hi. Basing myself on the datasheet and the pictures, I have appended my take on the schematic below.C1 must go to the C pin of the SAB0600, since you need it to set the frequency of the oscillator. The suggested value of 4.7nF seems good enough; together with the 15K resistor should give a frequency near enough to the 13.2KHz suggested by the datasheet.C2 should go to the Q pin: test the continuity with a voltmeter. If it does, I would use the suggested value of 330nF. The L pin can be left floating: the output of the IC will be a square wave, which sounds rather worse than a sinewave; it seems the manufacturers made that trade-off.C3 looks like a RC timer together with the 100K resistor. When green goes low, the Vs node goes up in voltage, and it pulls up pin E through the capacitor. That resets the IC for the duration of the RC delay. I would leave this cap in place unless you are quite sure it is blown. If it is, you'll have to guess the delay time, and infer the capacitance from there.In order to test the circuit, first of all I would test all the diodes and the transistor with a multimeter. If they work, I would consider replacing both polarized caps for equivalents; the yellow one is clearly a tantalum. Respect its 25V rating. Or you can directly try powering the circuit up: get yourself a 12V supply, and connect black to ground, and blue and yellow (and green) to 12V. Note that the IC has a maximum tolerance of 11V, but there are two diode drops, plus the transistor and the 100Ohm and 47Ohm resistor, plus the zener, which probably is around 9V. So a 12V supply should be OK, and is typical for a car battery. Connect the green cable to 12V too, to keep the switch open for now, and test the zener for its voltage. If the voltage in the zener is about 11V, it is there as a protection for overvoltage. If the zener voltage is under 11V but over 7.5V or so, it is there for regulation, and it is working. If the voltage at the zener is under 7V, it is failing and does not give voltage enough for IC operation: replace it for a 9V or more zener, and try again. Now switch the green cable to ground, and wait for a chime. If the circuit chimes, it is working, and the problem is either solved, or elsewhere in the car. If the circuit doesn't chime, there is something wrong: the IC, the speaker, some cap, whatever. To test the IC, watch the Q (sound output) with a 'scope after switching, you should see the chime. If you don't, watch the E pin for the RC decay after switching: if you don't see it, C3 is suspect. If C3 works but the IC doesn't, either the IC is blown, or C1 is failing, and there is not oscillation. If you see the sound waveform but hear nothing, either C2, the 10u cap, or the speaker are blown. If during testing you see the smoke come out, you have your work done for you.And so on. I hope this helps.

author: samvivi7
author_rank: Contributor
timestamp: April 12, 2016, 04:19:05 pm
content: Hi OroloI have been on the road so didn't get a chance to try anything. i just realized that i didn't attache the proper circuit that i had made but you have already made one but i am still attaching my lame circuit. Well first thing i will do when i get back to work is try to test the circuit and in the mean while i will try to make a PCB in Eagle, Still figuring out the software.all your input is very helpful and i thank you for that.will keep you posted