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Old 08-26-2018, 01:55 PM   #1
Th3_uN1Qu3
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Join Date: Jul 2010
City & State: Bucharest
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Smile Bakon 950D "Extra Crispy" mod (19->24 Volt)

Hello, you fine folks.

I've been hearing good things about the Bakon 950D (what a funny name!) soldering station with T12 tips (mistakenly labeled as T3 or T13, i see), so I thought i'd order one and a set of various tips.

The station arrived a couple weeks ago and I was pretty impressed with it, but I wondered if it could do just a little bit better. The replacement tips have arrived last week, just need to pick the package up. Anyway, on to the bacon (pun intended)!

I have noticed that it is usually labeled as 75W. Well, mine is labeled as 50W, so I took it apart to take a look.

The station is made of 2 boards, the power supply and the iron controller. The control chips used are the OB2202 quasi-resonant flyback controller on the primary side and the classic TL431 for feedback. An IRF840 is used as the primary switching device, a 100 volt 20A schottky diode (forgot the number) for rectification, and an AOD425 P-Channel mosfet does the PWM switching of the iron for temperature control. There is also an Atmega processor running the show and a 78M05 regulator providing the iron controller board with power.

The internal build quality is really nice, i was definitely not expecting a full line filter, all big-brand semiconductors (wow! ) and a modern power supply design for the price ($27). The caps are all cheap China brands, but hey, you're getting a lot for your $$.

The power rating on this station I think is the input power rating, because the included tip measured in at roughly 8.8 ohms, and the power supply put out 19.25V which would be an output power of 42.1W to the tip at full drive. So I thought i would boost the power supply to 24 volts, which should be easy, since this is a flyback type supply.

Once i took the iron control board out and read the part number off the P-channel mosfet that is regulating the temperature of the iron by PWM, I noticed that I also had another problem that needed to be addressed before boosting the voltage - the gate of this mosfet was driven by another transistor down to ground, and this device had a 25V gate rating, making 24 volts way too close for comfort.

Since the switching frequency of the PWM is very low, the solution was simple: adding a Zener diode in series with the gate (thanks Chris!). I chose a 5V1 zener, which will keep the gate drive voltage very close to the original. I didn't want to cut the trace so I desoldered and tried pulling up the gate terminal, but the package ended up cracking and the mosfet was damaged. Oops. I replaced the FET with a suitable one from a laptop board. I advise you to cut the trace instead.

Ok, now with that taken care of, time to mod the power supply. The bottom feedback resistor of the TL431 (R24 on the board) was 4.42k. I did the math and it solved to another 15k resistor in parallel with that to give me an output of roughly 24 volts. I soldered the additional resistor on top of the original one. A nice touch is that the turns ratio is printed on top of the transformer, which is 60:8:8 (primary:secondary:auxiliary). So, the auxiliary winding is 1:1 with the secondary. The maximum allowed voltage for the controller chip is 31 volts, so this modification should cause no further complications.

I plugged the iron in, turned it on, the display flashed briefly then quickly went out, and no further signs of life. I measured the primary switching device and it read a near-short from gate to source, so I took it out to verify, but there was no more short either on it, or onto the board. I put the IRF840 back in, removed the 15k resistor and the iron turned on no problem. This must have been the work of some protection circuit... Checking the datasheet of the OB2202 controller showed that it's got an overvoltage protection, which is sensed from the auxiliary winding thru R10 and R11 on the board. Since the aux winding is 1:1 with the secondary, R11 needed to be adjusted down by the same ratio as R24, to change the OVP threshold so it does not trigger at 24 volts output. This solved to an extra 91k resistor in parallel to R11, which I soldered on top of it like for the other one. After this modification was done, the power supply stayed on at 24V.

The output voltage is now 24.14 volts, which should give roughly 66 watts output. This iron was pretty good until now, now it is GREAT! Heats up in no time and handles everything I throw at it with ease. Can't wait to pick up the package with the different tips!

Thus, I present you the "Extra Crispy" mod, because what name would be more fitting for a soldering iron called "Bakon"!
Attached Images
File Type: jpg bakon 950d mod explanation - 1.jpg (1.41 MB, 198 views)
File Type: jpg bakon 950d mod explanation - 2.jpg (1.90 MB, 167 views)
File Type: jpg bakon 950d mod explanation - 3.jpg (919.8 KB, 152 views)
File Type: jpg bakon 950d mod measurement.jpg (2.19 MB, 139 views)
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Last edited by Th3_uN1Qu3; 08-26-2018 at 02:00 PM..
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