Yihua/Saike 852D++ Soldering/Hot Air Station not quite working anymore

[D4rk1]

Hey there,
I've bought a Saike 852D++ Rework station (Mainboard implies it's an Yihua 852D Version 6) back in December 2016. And whilst it served me a good while, I had a power outage in Feb 2017, which caused the transformer to misbehave.
Back then when I turned the station back on, the transformer had gone hot and dissolved most of the enemal coating on the copperwires.
I suspected that it had only been the transformer and went on to buy a new one which arrived today.

I had assembled most parts when I plugged the unit in and here's what's giving me a headache at the moment:
- The hot air fan works, it heats up - but also to the point where the metal of the fan is glowing red. This was the time I realized it was probably time to fully disassemble the unit to check for more errors.
-- The hot air fan also ran whilst being laid on the holder - while it technically shouldn't, because of a magnet switch or something.
- Hadn't yet tested the soldering iron.
- Neither the power LEDs nor the 7 segment display light up. Just nothing.

Unfortunately I don't know enough about electronics to sort this out all by myself. I tested most of the resistors, which turned out to be fine. Just by the looks of it the capacitors also look fine.
Cannot test the Mosfets (or Triacs?), cause my current backup soldering iron isn't beefy enough to desolder these parts.


I suspect that the s3f94c4ezz-dk94 chip is at fault, guessing that this one is responsible for most of the 'finer' stuff that's going on in the station.
Is there any way to test this chip? Judging by the Google results it might be an EEPROM, so would it be possible to rewrite another one of these chips with the ROM from this station?
If yes - do you know of somebody who could dump their 852D++ Rom or even rewrite a complete new chip with it?

Any help is greatly appreciated, thank you!

[amyk]

The hot air heater on these is powered directly from mains through a triac. The soldering iron is powered through the transformer, it's a typical 24V Hakko 936 clone style.

I'm guessing you had a pretty severe power surge/overvoltage, which damaged the transformer and shorted out the triac.

The S3F94C4 is a Samsung/Zilog microcontroller, and it does have rewritable flash but I doubt rewriting would work if it was killed by overvoltage.

[D4rk1]

Thanks! I've just come to unsolder the Triac next to the mains input/hot air output and put it in a simple test circuit (Connecting a lamp to A2 and +12V, and a switch between +12V and Gate. A1 to GND.) and as far as I know the bulb should extinguish when releasing the switch - this is not the case with this triac.

I also tested it with a multimeter:
No continuity between A1 and A2, ~230-300Ohms resistance when A2 is connected to Gate. I was under the assumption that there should be a high resistance between A1 and A2?

So I can I assume by these tests that the Triac isn't functioning properly anymore?

I'll also test the other TO220 parts on the board and will report back in the next days.

The S3F94C4 is a Samsung/Zilog microcontroller, and it does have rewritable flash but I doubt rewriting would work if it was killed by overvoltage.

Well, it would be quite advantagous to find someone who could clone his - especially since I do not own any re/writing equipment for these kind of microcontrollers. 


Again, thanks a ton for any help!

[KL27x]

Slim to no chance that the device code memory is unlocked, even if someone happened to have this exact model of station AND happen to have a programmer which can read this device.

I'd check the 5V rail, the TRIAC driver, and look for any input protection diodes/fuses that might be blown. I bet you got more problems than the TRIAC. Since the micro is probably connected to the gate of a FET which is driving the TRIAC, it is probably smoked, too. But you might as well check to see if it's getting power. No sense in putting the cart in front of the horse.

a switch between +12V and Gate.

You should need some current limiting. I'm not sure what the max current though typical power TRIAC gate is, but it should only take about 30 to 50mA to trigger, tops. It is possible you burned it out while trying to test it, perhaps.

[D4rk1]

Welp. Checked what KL27x said and both Triacs again today - and both turned out to be fine. So I soldered them back in, plugged the power back in and boom - I've got the 7 segment displays working again.

Soldering Iron works ALMOST like a charm - it just randomly displays a range inbetween the set temperature +- 30-40°C. Like, I set it to ~230°C and the display jumps anywhere from 210°C to 240°C, back and forth.
Any component that could be grilled that would cause such behaviour?


Also the hotair blower doesn't quite work anymore, but that's partly due to the heating element being roasted.
But still I can't figure out how to start the rest of the blower. When I turn the station on, the fan starts spinning (even at the set RPM!) and then it turns off. Can't bring it back to life, no matter what I do.
I suspected it to be the reedswitch in the handle, but circumventing it didn't help either.
I don't want to have more of an firecracker in the house than this thing already is, so before I order a complete new handle, I'd rather have some input first on what could be the cause for this.


Again, thanks a ton for your help!

[KL27x]

If the heater is roasted, the micro may be detectimg an error. The heater probably goes open circuit if u burned it. Maybe do an ohm check to see. If it is burned, you can maybe use a dummy load or even take the heater apart and splice it back together to see if it runs. Of course this is mains and u can easily kill yoirself.

As for soldering iron behavior, i would scope all dc rails to make sure they are stable and not noisy. If issues, check big caps. If no obvious issues replace or augment smaller caps. Replace any opamps if possible. Cross fingers. If spike in rails occurs when heater switches, check for bad snubber diodes.

[D4rk1]

Hey. Finally got my package with the replacement opamps. Decided to replace most of the parts on the pcb anyway, since they were only a few cents each.
I've also checked the snubbers and everything looked fine.
But still no game, so I thought "**** it, I'll just leave the heater unit and use it as a soldering station", and went on to calibrating the temperature only to find out, that the unit even heats the soldering iron when it is switched off. So I guess the micro is roasted after all.

I think I'll contact the manufacturer and try to get a replacement chip :/