Hi,
I’m repairing a small Li-ion powered cat toy (rotating ball, forward/backward motion).
The board uses:
TP4054 (USB Li-ion charger)
SA8301 H-bridge motor driver
One unknown SOP-8 IC with no readable marking
The unknown IC:
Powered directly from the battery (~3.5 V)
Pin 5 and 6 go to INA / INB of the SA8301
Pin 3 goes to a momentary button (to GND) through a 1 kΩ resistor
No crystal, no programming pins
Motor and H-bridge are fine, but INA/INB never toggle.
This looks like a small MCU / OTP controller that handles timing and direction.
Has anyone seen this kind of setup or identified a similar SOP-8 controller used with SA8301 in toys?

 

Has anyone seen this kind of setup or identified a similar SOP-8 controller used with SA8301 in toys?

I have seen them, 8 pin MCU, used in a few applications, the last one was a LED lamp fade in/out sequencer.

 

does +ve go to pin 8 and ground to pin 4? It may not be an ATtiny85 but if the power pins are the same it could be programmed to do whatever it used to do

 

In my case, it was P1, P8 = GND & Pwr, for a picmicro

 

A guess from a random guy on the internet is a Padauk PMS15x-SO8 from Taiwan connected to that Taiwanese (ShenZhen?) SA8301. The cheapest Padauks are $100 for a 4000-piece reel. 11-bit PWMs on pins 5&6, digital input on pin 3, VDD/GND on 1&8, and internal RC oscillators. They sell multiple-time-programable (MTP) flash versions, but yours is likely a one-time-programmable (OTP) PROM for low cost. Many SOP-8 PICs and AtTinys have VDD/GND on 1&8, so you can replace with one of those. Padauk offers other VDD/GND combinations on SOP8, such as 3&4, which could be complicate your drop-in replacement plans. But yeah, I'll go with OTP and VDD/GND on 1&8.

Good fortune on your project.

 

In SOP-8 OTP MCUs used in toys, what are the most common reasons for a controller staying inactive even with valid VDD and input?
Brown-out behavior? Missing sensors? Internal pull-ups holding inputs?
Any common failure patterns seen in cheap toy controllers?

 

Not saying this is it, but allowing for the possibility: Transistor failure due to capturing a high energy particle from space. There is a Veritasium YouTube video about it. He says that as the feature sizes within chips have gotten smaller, there are fewer minority carriers in the transistors, so a single event can cause greater havok. Examples in an OTP MCU would be persistent changes to programmed calls and permanently damaged logic gates. If you believe that the part was not overstressed in use, then fabrication defects and visitors from outer space are the kinds of explanations that remain.

You did not mention any other connections, so I assume that they are NC (no sensors disabling anything). Also I don't think that your USB and Li-ion battery and charging system can exceed the MCU's tolerable voltage, so I don't see an organic overvoltage failure mechanism.

The best-case would be some failure in feeding pin 3, because dealing with a button or resistor would be the cheapest repair available. I mean, it sounds like you think that the power is OK. All I can do is hope that the cause is simple to find and fix.

Just occurred to me: The MCU is in sleep mode (internal clock disabled and drawing a microamp) waiting for pin 3 to change. When it detects the proper pushbutton state, it runs the output sequence for five minutes or so, and then returns to sleep. In this scenario, disconnecting the battery, and then momentarily shorting the VDD and GND pins, and then reconnecting could give you a cold restart of the MCU. This would be about clearing a brown-out behavior.

Again, my cat and I hope that you can get it working.