Hiopos - Cash Touch - Doesn't turn on

[samstown]

Hello,

I have this Hiopos Cash system running on android that stopped working without notice. The power supply is ok, there's light on motherboard but when pressing power button it doesn't turn on.
I've google for schematics but no luck. Motherboard is S2802_V1.3B. I've took some measure and maybe it could be a transistor, the one I am pointing on with the orange arrow on the pics. Does anyone knows this board ?


Thanks
Sam

[mon2]

Start with the main 12v power rail. Is it a stable 12 volts to ground?

Next, suggest to review the Sipex RS232 transceiver which is on the bottom side of one of the posted pics. You can download a full datasheet for this component from Maxlinear (who purchased Sipex/Exar). From this transceiver, you can locate the Vcc rail. Given that all pins are @ 0 volts, the Vcc for this RS232 xcvr is lost so you are missing at least this power rail.

Once you locate the Vcc power pin, remove all power (no pun) -> meter in resistance mode (not diode mode) -> measure the resistance to ground of this Vcc pin. Varying with the age of the design, this Vcc may have been the 5v0 rail or the 3v3 rail. These are charge-pump RS232 xcvrs which will then accept this rather low voltage and then perform a voltage multiplier to often 2x the Vcc rail to support RS232 voltage interfacing.

Start with this review and then perhaps we can determine which power rail(s) are defective. At the very least, the 12 volts used as the input must be present and stable. The onboard xcvr is 16 pin SSOP so my earlier post had the incorrect pinout.

See the correct one below. Remove all power -> meter in resistance mode -> measure the resistance to ground of the VCC pin. We know from your first post that this Vcc rail is at 0 volts. Is this due to a shorted cap or some other reason?

[samstown]

Hello, thank you very much for your reply and your help.

You are right, VCC is shorted to ground. Should I try to inject 1V on SP3232E Pin 16 and look for heat component with thermal camera ?

[mon2]

Can you share the exact resistance measurement? Confirm also that your meter is reporting the reading in ohms (not k; not M; not OL).

If truly a low resistance than yes, it will most likely be one of the shorted / partially shorted caps but to be determined.

Will be great to use your thermal camera if available or you will have to resort to pour IPA (alcohol; we use the Costco stuff). Which ever part evaporates the alcohol quickly, it is running hotter than room temperature. Caps are the first suspect but do inspect for possible cracked regulators, etc. Someone is tanking down this required power rail.

1 volt injection is fair to use at the highest current your power supply can support.

[samstown]

It looks like a short to ground.

[mon2]

The meter scale appears to be in diode mode so select another scale to confirm. If testing in diode mode, place the red probe to ground and the black probe onto pin #16 of this transceiver. Post your measurement.

[samstown]

Thanks. If I set to 20K, I get 0,00

[mon2]

Yup, dead short. Hope it is only a bad cap (most likely). Proceed to apply a voltage for injection. Your (injection) DC power supply @ 1 volt should peak to the max current which in turn should cause the shorted part to heat up. If not enough, increase the current if possible and then the voltage (in this order). Often, the cap will split open and usually it is the tantalum capacitor. Curious on your updates.

[samstown]

resistor in red was getting hot. I removed it but short was still there. I removed the litle cap, not the big one. short is gone, I measue 0.25 when set to 20K. Device doesn't turn on, still 0V on VCC on that spirex chip PIN 16

[mon2]

Place back the resistor that was getting hot. It is probably a ferrite bead that is in series with this Vcc rail. Then test again.

Update:

On the right side of the shared pic there are a few USB connectors. Review the voltage to ground for the pin with 5V label. This is used to power the USB connector VBUS pin.

[samstown]

Thank you for all your help. I had two of those. Following your instruction, I was able to fix the second one, the issue was on the Wifi module, the chipset was getting hot. I remove it and now it boots.
I will try to place back the resistor one the first one tomorrow morning.

Have nice end of day and thanks again.

[mon2]

Excellent. Good job!