Unknow main IC in a faulty car toy - Page 1
Forum section: electronics / repair

author: dav
author_rank: Regular Contributor
timestamp: January 01, 2019, 11:23:51 am
content: EDIT Jan 05, 2019What could be the unknown main IC on my car toy?Pinout (based on board inspection)PIN1 to the antenna via the series C2 and L1PIN2 VDD (but cannot see any track to VDD, maybe it's internally connected to PIN6; I can only see a track to GND via C6)PIN3 NCPIN4 ? (it just goes to a test point)PIN5 NCPIN6 VDD (3.3V)PIN7 to INA TC118S (U3)PIN8 to INB TC118S (U3)PIN9 NCPIN10 to INB TC118S (U2)PIN11 to INA TC118S (U2)PIN12 NCPIN13 to GND via C7PIN14 to the oscillatorPIN15 to the other pin of the oscillator, via 1k resistorPIN16 GNDOLDHi to all and happy new year.I'm trying to fix a faulty remote control car toy.I found an unknow (for me!) component in series to the power switch.What is it?Thank you

author: mictas
author_rank: Regular Contributor
timestamp: January 01, 2019, 11:35:32 am
content: Quote from: dav on January 01, 2019, 11:23:51 amI'm going to guess, that is a Tantalum capacitor.

author: dav
author_rank: Regular Contributor
timestamp: January 01, 2019, 11:38:34 am
content: I thought the same, but I don't find the value (googled A075 and find nothing).However it's shorted

author: djQUAN
author_rank: Frequent Contributor
timestamp: January 01, 2019, 11:42:21 am
content: It looks to me like a PTC thermistor resettable fuse.

author: Circlotron
author_rank: Super Contributor
timestamp: January 01, 2019, 11:43:31 am
content: Polyswitch for overload protection? Basically a PTC thermistor Like a resettable fuse. Low resistance when cold and suddenly goes high resistance above a certain temperature threshold (current).Edit ^^ Yep.

author: dav
author_rank: Regular Contributor
timestamp: January 01, 2019, 11:46:54 am
content: Thanks to all!So it's normal it's shorted when cold

author: dav
author_rank: Regular Contributor
timestamp: January 01, 2019, 11:52:28 am
content: This car toy is powered via 4x 1.5V AA batteries.When I power it with my power supply, voltage drop down to 1.1V and it takes all the current (power supply goes in protection); the car is motionless.The main board has an unknown IC for the remote control and 2x TC1118s motor drivers (front and rear axis), plus a few SMD components.I tested separately the motors and they work fine.

author: GeoffreyF
author_rank: Regular Contributor
timestamp: January 01, 2019, 03:21:58 pm
content: It is not a tantalum capacitor. It looks like a ceramic capacitor but the nomenclature on it is strange. If it measures as a short, did you assure the switch is not closed across the part of the circuit it is connected too? Having such a device across switch contacts makes sense to avoid arcing across the contacts. Other suggestions do not make sense in terms of where it is in the circuit.If I was trying to find the problem with your toy - this is the last place I would consider.

author: wraper
author_rank: Unknown
timestamp: January 01, 2019, 04:27:50 pm
content: Quote from: GeoffreyF on January 01, 2019, 03:21:58 pmDid you read the question? It'sin serieswith the power switch. It's obvious that it's polyfuse.

author: mikerj
author_rank: Super Contributor
timestamp: January 01, 2019, 04:30:51 pm
content: The yellow wire (antenna?) is very close to C9, check is it's shorting. The crudest way to approach this is to find out which component gets hot when the supply goes into current limiting, e.g. if one of H bridge drivers has shorted out you'd expect it to get warm as it will be sinking pretty much all the current.

author: fzabkar
author_rank: Super Contributor
timestamp: January 01, 2019, 08:09:42 pm
content: Just FYI, the FCC database has numerous circuit diagrams for RadioShack's remote control cars and trucks. These might give some insight into how these devices work.

author: fzabkar
author_rank: Super Contributor
timestamp: January 01, 2019, 11:26:40 pm
content: Here is a datasheet for the TC118S motor controller:https://datasheet.lcsc.com/szlcsc/Shenzhen-Fuman-Elec-TC118S_C88308.pdfThe application circuit on page 4 could be a match for your toy. The main chip is an SDRX2BD (16-pin).FWIW, here is the datasheet for the SDRX2BD (includes another application circuit):http://superchip.cn/Private/ProductFiles/SCTX2B%EF%BC%88SDRX2BD%EF%BC%89.pdfHere is another datasheet:TX2C ATS302T/RX2C ATS302R, Actions Semiconductor, 5-function remote controller:hackedgadgets.com/wp-content/uploads/2015/10/RX_TX.pdfThe datasheet suggests that the IC is a clone of Realtek's RX2C.

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 02, 2019, 05:43:19 am
content: The polyfuse could still be faulty. If that's in series with the battery it should trip and not let it short. Obvoiusly wouldn't cause the original fault but definately suspect. The H-bridge drivers would be the main suspect for shorts.EDIT: The yellow wire is marked "R" on the switch and board (reverse controls?)

author: dav
author_rank: Regular Contributor
timestamp: January 02, 2019, 12:32:58 pm
content: UPDATEA few seconds later injecting 1.5A, the circuit gone open, so the PTC works fine.So I injected the 1.5A after the PTC, but the only components go hot are the two TC118Ss (I initially expected a capacitor...)I desodered the diode who carries the power supply to the main IC via a 3.3V regulator, but the short is still there (I can exclude the main IC).So I also desoldered the first TC118S and the short is still there, then the second TC118S and no more shortThe track who connects one of the two TC118s to GND swelled up (probably due to high current). I marked this with a purple circle in the pic.Strange that after removing the diode and the two ICs and injecting the current, the C10 elec capacitor shorted itself, too (it's a 220uF 16V 105° Cheng brand). Who knows why?Ah, there was no 0 ohm resistance between the main + and the ground, so the shorts were in the inner of the two ICs.

author: dav
author_rank: Regular Contributor
timestamp: January 02, 2019, 12:35:21 pm
content: Quote from: Cyberdragon on January 02, 2019, 05:43:19 amThe yellow wire is related to the OFF switch position.The switch connects the green wire (PCB ground) to the negative battery pin (switch in ON position) or to PIN6 (Vdd 3.3V) of the unknown main IC via a 100R resistor (switch in OFF position).

author: dav
author_rank: Regular Contributor
timestamp: January 02, 2019, 01:52:43 pm
content: Quote from: fzabkar on January 01, 2019, 11:26:40 pmUnfortunately my main IC is not a SDRX2BD, due to different pinout.Here the pinout of my chip (based on board inspection):PIN1 to the antenna via the series C2 and L1PIN2 VDD (but cannot see any track to VDD, maybe it's internally connected to PIN6; I can only see a track to GND via C6)PIN3 NCPIN4 ? (it just goes to a test point)PIN5 NCPIN6 VDD (3.3V)PIN7 to INA TC118S (U3)PIN8 to INB TC118S (U3)PIN9 NCPIN10 to INB TC118S (U2)PIN11 to INA TC118S (U2)PIN12 NCPIN13 to GND via C7PIN14 to the oscillatorPIN15 to the other pin of the oscillator, via 1k resistorPIN16 GND

author: wraper
author_rank: Unknown
timestamp: January 02, 2019, 02:00:44 pm
content: Power the thing and check if voltages on main IC outputs to motor drivers react to remote control. If they do, then you can just order the driver ICs. If they don't, most likely main IC is dead as well.

author: dav
author_rank: Regular Contributor
timestamp: January 02, 2019, 09:13:50 pm
content: My apologies to all, I tested the board with reversed polarity(this is the reason the elec capacitor went shorted)Most probably the two TC118S are good.Now I reinstalled the diode, so the power can reach the main IC again.Without reinstalling the two TC118S and switching ON, the circuit takes 0A at 6V.On main IC I checked PIN7,PIN8,PIN10,PIN11 voltages to GND when pushing buttons on the remote control, but nothing: I read always 0V on those pins.How can I check the remote control? Maybe the fault is there.Remote control Main IC is similar to the one on the car (maybe exactly the same).PIN1 to the antenna via the series C2 and L1PIN2 VDD (but cannot see any track to VDD, maybe it's internally connected to PIN6; I can only see a track to GND via C6)PIN3 NCPIN4 ? (it just goes to a test point)PIN5 NCPIN6 VDD (3.0V - 2xAAA batteries in series)PIN7 to Switch1 (UP button)PIN8 to Switch2 (DOWN button)PIN9 NCPIN10 to Switch4 (RIGHT button)PIN11 to Switch3 (LEFT button)PIN12 to GND via R5 in series with a LED (both components are missing, so this pin is NC)PIN13 to GND via C8PIN14 to the oscillator (16MHz crystal)PIN15 to the other pin of the oscillator, via 1k resistorPIN16 GND

author: dav
author_rank: Regular Contributor
timestamp: January 03, 2019, 09:36:02 pm
content: After taking some infos, I first tested another 100% working RC transmitter toy with my scope and I see both the 27MHz sine wave carrier and OOK waveforms of all available commands (up, down, left, right, up+left, up+right, down+left, down+right).

author: dav
author_rank: Regular Contributor
timestamp: January 03, 2019, 09:37:36 pm
content: Then I swithed to the 16MHz victim transmitter and I do same tests, but here I cannot see anything on the PIN1 (antenna)I can only see 2.7V on pin12 for ten seconds, when any key is pushed.I can desume the transmitter IC is (at least) partially working.But why no interesting waveform on the antenna pin??

author: fzabkar
author_rank: Super Contributor
timestamp: January 04, 2019, 01:45:09 am
content: If you have 16MHz and 27MHz versions of the same toy, then swap the crystals in the remote controls. This should help to isolate the fault.

author: dav
author_rank: Regular Contributor
timestamp: January 04, 2019, 09:26:09 am
content: Quote from: fzabkar on January 04, 2019, 01:45:09 amNo, they are 2 differet toys, one (27MHz) full working and the other one (16MHz) faulty.

author: Armadillo
author_rank: Super Contributor
timestamp: January 04, 2019, 09:42:22 am
content: Those push buttons are prone to failure.Firstly you would check whether they are making true contact.ThenWith just 1 IC, just make sure that the osc circuit from after the buffer is clocking. if not conclude that is IC failure.

author: dav
author_rank: Regular Contributor
timestamp: January 04, 2019, 10:12:02 am
content: Quote from: Armadillo on January 04, 2019, 09:42:22 amI tested the pushbuttons, they're fine.Moreover, when I push any button, there is the above signal on antenna pin (please see pin1_antenna.png), then no other signal within 10 seconds (no matter if I push other buttons, pin1 output is zero for 10s after the first pushing).Waveforms on pin14 and pin15 IC on the transmitter are above.The IC reacts in some way to buttons, but I really don't understand the signal on antenna pin.

author: fzabkar
author_rank: Super Contributor
timestamp: January 04, 2019, 10:44:53 am
content: Datasheet and application circuit for 8A977 & 8A978:http://www.szkxw.com/data/20127301821828953.pdf

author: dav
author_rank: Regular Contributor
timestamp: January 04, 2019, 02:32:44 pm
content: Quote from: fzabkar on January 04, 2019, 10:44:53 amEhm.. 8A977 is installed on the 27MHz working transmitterThe 16MHz one has an unknown main IC; I wrote its pinout above, however it's this:PIN1 to the antenna via the series C2 and L1PIN2 VDD (but cannot see any track to VDD, maybe it's internally connected to PIN6; I can only see a track to GND via C6)PIN3 NCPIN4 ? (it just goes to a test point)PIN5 NCPIN6 VDD (3.0V - 2xAAA batteries in series)PIN7 to Switch1 (UP button)PIN8 to Switch2 (DOWN button)PIN9 NCPIN10 to Switch4 (RIGHT button)PIN11 to Switch3 (LEFT button)PIN12 to GND via R5 in series with a LED (both components are missing, so this pin is NC)PIN13 to GND via C8PIN14 to the oscillator (16MHz crystal)PIN15 to the other pin of the oscillator, via 1k resistorPIN16 GND

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 04, 2019, 02:58:43 pm
content: 16 MHz seems a strange frequency for a remote, are you sure it's not multiplied to a higher output frequency? That would explain that you see no modulation on the fundamental frequency.

author: dav
author_rank: Regular Contributor
timestamp: January 04, 2019, 03:15:29 pm
content: Quote from: PA0PBZ on January 04, 2019, 02:58:43 pmI think you're right. I just went on website manufacturer and I read Frequency bandwidth: 2.408 - 2.448 GHzThat 16MHz crystal oscillator misled me.Any suggestion for further testings?

author: Armadillo
author_rank: Super Contributor
timestamp: January 04, 2019, 03:24:12 pm
content: When the;1.0 Input push buttons are working2.0 Power Supply is Correct3.0 Crystal Clock is Clocking,Then the output buffer inside the IC is defective. That's why no output not even attenuated output at Pin 1.0 [only slow moving saw-tooth wave].It would be really interesting if someone can crack this.

author: gamalot
author_rank: Super Contributor
timestamp: January 04, 2019, 04:33:08 pm
content: It's a 16V/0.75A PPTC from AOLITTEL.http://www.aolittel.com/sale-10825659-fast-time-to-trip-16r300gpr-radial-leaded-through-hole-pptc-polyswitch-ptc-resettable-fuse-16v-3a.html

author: dav
author_rank: Regular Contributor
timestamp: January 05, 2019, 01:02:02 pm
content: Quote from: gamalot on January 04, 2019, 04:33:08 pmThank you.But now the question has become "is there a way to repair the toy?"What could be the unknown 16pin main IC on the transmitter and on the car?

author: amyk
author_rank: Super Contributor
timestamp: January 05, 2019, 07:22:28 pm
content: Does it have an FCC ID?That would probably be the best way to find out more information about it.

author: dav
author_rank: Regular Contributor
timestamp: January 05, 2019, 09:24:44 pm
content: Quote from: amyk on January 05, 2019, 07:22:28 pmUnfortunately no (at least I cannot find it on the manual, on the website manufacturer and on the toy itself).The only technical data on the website are:Bandwidth: 2.408 - 2.448 GHzMaximum transmission power: 1 mWHowever, the 16pin main IC pinout is very unusual: pin16 for the ground!

author: fzabkar
author_rank: Super Contributor
timestamp: January 05, 2019, 11:51:47 pm
content: Who is the manufacturer and what is the model number of the toy?

author: siggi
author_rank: Regular Contributor
timestamp: January 06, 2019, 05:46:42 am
content: Maybe the same pair of ICs as in this kit:http://www.icstation.com/mobile/txrx-channel-remote-control-wireless-transceiver-module-robotmotor-p-13271.htmlSent from my iPad using Tapatalk

author: fzabkar
author_rank: Super Contributor
timestamp: January 06, 2019, 06:03:34 am
content: attach01.oss-us-west-1.aliyuncs.com/IC/DIY-Manual/13280.pdfThe pinouts don't match.

author: dav
author_rank: Regular Contributor
timestamp: January 06, 2019, 09:55:30 am
content: Quote from: fzabkar on January 05, 2019, 11:51:47 pmhttps://www.chicco.it/prodotti/8058664079339.bobby-buggy.giochi.macchinine-radiocomandi-piste.html

author: dav
author_rank: Regular Contributor
timestamp: January 06, 2019, 10:00:04 am
content: Quote from: siggi on January 06, 2019, 05:46:42 amUnfortunately no, as this one is not pinout compatible with mine (example on pin16: mine is GND, yours is forward function)

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 08, 2019, 06:24:56 am
content: Dumb theory, but is that a tiny pi filter on the output? Did you check for a short?

author: dav
author_rank: Regular Contributor
timestamp: January 10, 2019, 08:17:50 am
content: Quote from: Cyberdragon on January 08, 2019, 06:24:56 amNo short