Restoring a fast traxx rc, anyone know the datasheets for these parts? "TAIYO 90" "TAIYO 88-R" "A 1357"

[Triode]

I found an old fast traxx RC at a trift store with no controller for a few dollars, it was a childhood favorite of mine which is gone so I bought it.

I have everything I need to make a 2.4 GHz remote for it. I could actually just rebuild a new pair of full H-bridges (it's a tank drive vehicle) but was considering if I could reuse most of the original power circuitry. I'm trying to figure out where to tap in with a logic level Direction and PWM signal to control the power stage.

I realize these are probably proprietary chips, many RC toys I have opened contain Taiyo brand marked chips which I can't find any data sheet for. But I figure maybe this is a recognizable standard someone can tell me about. Or maybe someone knows a source I don't. There is also a bit of educational value here, as this has 2 motors with variable speed in two directions I would expect to see 2 full H bridges, for a total of 8 transistors. Unless the two big SIP packages are handling some of the heavy lifting. I'm not sure. I am guessing the "taiyo 88-R" is interpreting the radio signal and sending out motor control commands, and I would guess the "Taiyo 90" is a mosfet driver, as the transistors all have the same number I'm guessing it's a high/low side N-channel driver. But then where are the other 2 fets on each side?

In the picture I have removed the plates from one side to make the components more visible.

3 pin (transistor I assume) components, 2 on each side, marking: A 1357
Large chip (one on each of the two identical sides): Large text: "Taiyo 90" second row:" M*SIA 9619U"
Main (just one of these that controls both sides I assume): Taiyo 88-R 9506K, in a DIP 16 package

As for circuit board clues, there is glue all over the bottom which I am scraping off. But these transistors seem to have leg 1 connected to +battery, Leg 2 connected to a motor output, and leg 3 connected to the big SIP on each side.

Thanks for any help. I always appreciate the knowledge you all share.

 

[gophert]

Taiyo makes the RC cars and specifies the chips. There are no datasheets.

 

[Triode]

Thanks. You seem to be right on that one, it makes sense they never released any data sheets. Oh well, I've brushed off the glue on the bottom and I can see a few traces that go from the controller to the gate drivers. It can only be so many ways they would be used.

 

[upand_at_them]

If they were produced in great volume the chips wouldn't even be standard, they would be designed and produced just for that product...so no datasheet.

 

[Triode]

With that probable case in mind I went ahead and overlayed the top and bottom of the board in an image editor and traced it out.

Blue lines are caps, black are jumpers on the top and yellow are the paths that go from the main IC to the drivers that I found. All other pins on the main IC either connect to power, or to the radio circuitry.

I think it's a safe bet that these pins are either complimentary PWM, or one for direction and one for PWM speed. I would guess dual PWM. I can probably battery power the circuit and find out the logic level, and maybe observe if it is doing anything while idle. If it's two balanced PWM levels I have my answer about the drive type. In theory with no remote I think it just sits there, I assume it's not likely to be the more sophisticated kind that powers down without it's remote controller present.

 

[gophert]

Nice work!

 

[Triode]

So interestingly here's what the probing shows. The circuit was originally powered by a ~9V NiCad battery. I put it on a 9 volt power supply, and the output pins (with no transmitter controlling it) were all sitting at 2 volts. 2 of the pins on the middle of the radio side of the chip have 9 volts into them, I found that a bit odd. No visible regulator either. It seems like this chip is designed to run on the battery power directly? The top pin on the radio side had a 60 Hz wave with a DC offset of about 2 volts, and an amplitude of 0.5 V. I'm guessing that is the output of the radio receiver stage to the controller chip.

I'm a little hesitant to give it a signal, I'm thinking through the cases that would damage it if I'm wrong.

If it is an H-bridge drive and these are raw inputs I don't want to test it with a full on, full off, they can usually not do 100% duty cycle, it may desaturate and get fried.

If it is direction and PWM input, and I PWM the direction, it might sit there oscilating on direction, which would be bad but probably wouldn't fry anything. Unless there is no dead time protection and it shoots through. After all that logic may be in the chip I'm bypassing (the 88-R) not the big one.

I'm guessing it's safe to try a logic level of 3.3V, but it's odd to me that unconnected it's floating at 2 volts. Perhaps it is inverted?

 

[gophert]

You could simply buy a proper radio, speed controller and change the connectors on the servos & motors to match. Older analog RC radio stuff is all over ebay for good prices. Even non-current digital radio stuff is priced reasonably.

 

[Triode]

I'm just trying to reverse engineer this thing for fun, and it might be cool to keep it closer to the original. But you're right in thinking it's fairly pointless as far as the end result goes. I do already have code to make a remote control device using an nrf24L01 that works just fine, and I have the h-bridge drivers and mosfets to make the power electronics. I also have some RC controller sets and sabertooths if I wanted to use ready made hobby electronics. So this isn't urgent or anything.

 

[Triode]

Just in case anyone follows up or is interested in this in a search, the identified pins worked fine. I have no way to look up the intended frequency or voltage of the driver chip, but when connecting 9-12VDC to the power pins, and sending a 3.3V or 5V PWM signal to the pins indicated in green the motors drove just fine. I tried 10kHz up to 23kHz, and varied the duty cycle. The heatsinks got a little warm but not hot, even when resisting the wheel drive somewhat.

If I were driving the transistors directly I'd be worried that if I chose the wrong voltage I was under driving them, which could result in partial switching and burn them up, so I'd have hooked up the scope to see if it looked like they were saturating (a level off in the mosfet gate voltage), but since these are pins into a gate driver I'm guessing if it responded well that it was enough voltage to trigger it without frying it.

So, while I can't get the exact range of ratings on these chips, I have enough to replace the control with my 2.4G nRF24 and a little microcontroller.