Electronics > Repair

Graphite grinder 900W [59G187] Not turning on - mysteriuos 501b-8P IC

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HiddenBear:
Hello Fellow EEVblog Colleagues

As in the title I have a problem with a grinder that have a regulated rotory setings (via a potenciometer). The grinder is not working at all. The thinks I checked :

- Brusches (because it's a brush one) | Maybe a half on them is left, but the contact to the rotor is there. No cracks oraz lose wire, only normal sights of wear.
- Cable  | few ohm, so its fine
- Switch | All contacts work well, no leacked or burned pins
- All components on the PCB that i know how to measure : R, C ,D show correct values. I dind't measured the ESR of the caps because I don't have the equipment for that.
- The triac have a 0.056V drop between A1(+ multimeter wire) and Gate(- multimeter wire) as well Gate to A1, the voltage drop is the same. Changed it for a BTA 12 that has 0.112V drop

The triac replacement didn't help. And there is that 501B-8P IC, I have no clue that this thing is my brain is too smooth to figure it out by it's own. I tried to check on AllDataSheet but didn't find it with the same 214DNWG0a e3 or similar ending. The rotor moves with easy so it's not blocked or jammed.

Below I inclued the worst electronic schematic in my whole history, and photos of the board front and rear.

One think that I could discover was that the R1 20k resistor heats quite quickly after some 3-4 sec of pressing the switch trying to power on the grinder.

If someone had a similar problem maybe not exacly with the same grinder, but a similar issue with a module like that. I'd be thankful for helping to solve with this problem.

fzabkar:
I'm guessing it could be a Sonix SN8P501B-8P (OTP micro?).

inse:
Is there supply voltage across the electrolytic cap?
If not, isolate the IC supply pin.
What is connected to the white cables, some speed feedback from the motor?
P.S. I agree on the schematic ;-)

fzabkar:
The circuit diagram would be a little less confusing if the pin numbering could be corrected.

Perhaps the IC is similar to this (SN8P25011DP)?

https://wmsc.lcsc.com/wmsc/upload/file/pdf/v2/lcsc/2304140030_SONIX-SN8P2501DPB_C337779.pdf (page 8.)

HiddenBear:
I agree with You fzabkar and inse that the diagram could be better made my me. I forgot to mention that the pin names on the IC are taken from a NE555, because it was the easiest to implement in KiCad. That could straighten few thinks in advansed, my bad.

I check the cap as recommended and the voltage is there. So I'm assuming that the IC just broke.

I found today that on Aliexpress there is a 501B-8P but with 1464NSZ01 e3 ending, not the same that is on the PCB.

Link to that : https://pl.aliexpress.com/item/1005008067801762.html?spm=a2g0o.productlist.main.1.67e71d3clccl2W&algo_pvid=7ce4e9b6-265f-41e9-a15f-2d58fb15fad9&algo_exp_id=7ce4e9b6-265f-41e9-a15f-2d58fb15fad9-0&pdp_npi=4%40dis%21PLN%211.97%211.93%21%21%210.46%210.45%21%40210385db17367819171196180e291f%2112000043523675103%21sea%21PL%210%21ABX&curPageLogUid=Ka0z9LlojdAG&utparam-url=scene%3Asearch%7Cquery_from%3A

Gonna give it a try, maybe it will work. Will give a replay in this post about how it worked out or not.

But to be honest I'm still courious what that IC actuall is, because the whole regulator look like a triac dimmer with the adition of the IC (Schematic not made by me). I even builded one for a 3-phase low power USSR wentilator converted to a 1-phase, and it's working quite well (without the IC of course). Checked the PDF link and I'm not sure if it would be a microcontroler unit, seems a bit to expensive for a grinder to me. Maybe it's a circuit that prevents the engine to stop then the grinder is in lowest rotations around ~800 revolutions per minute. Welp, without the schematic we don't gonna know.

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