Hakko FR-300 Teardown and Mod

       I needed a desoldering gun and looking at my options, I could get a cheap one and enjoy it for a while until it breaks or go all out and get an expensive one and use it a lot longer with better access to spare parts.

       A quick research and I stumbled upon the Hakko FR-300 as it seems to have positive reviews all around. I had extra cash to spend and then I bought one from tequipment.net plus some extra filters and tips.

       It works wonderfully and the parts litterally just falls off the PCBs after desoldering. It was a joy to use, but I had one gripe. The power LED is the same as the old stations where it lights up when the heater is on and blinks as the set temp is reached. Unfortunately, this prevents me from knowing at a quick glance if the unit is turned on or not and I had to double check if it was really turned off. A small mod was performed and it is now much better. Look at the pics below for the teardown and mod.

My FR-300 unit

Removing four self tapping screws on the side and two metal thread screws on the front allows the case to open.

A small detail of the air pump motor and crank.

Crank is brass with a small counterweight added.

Connecting rod also uses a bearing for the spinning joint.

Power cord strain relief and ground point screw.

Temp adjustment pot uses a PCB mount trimmer.

Motor is a typical DC brushed motor, a PCB containing a FULL BRIDGE RECTIFIER and a capacitive dropper is mounted at the back so that it can accept 120VAC input.

Mounting for the front tip assembly uses metal threaded inserts. Nice.

Two screws out and the PCB lifts off.

Detail of the temp adjustment and calibration pots.

8 pin tssop chip is an LM2903 dual comparator.

Overview of the PCB. The other side does not have any components.

Tracing the circuitry, I found the V+ and V- points where I would put in a new indicator LED.

I wanted to make an alternate red-green switchover but the red LED is connected between the comparator output and the triac gate so I opted not to mess with it.

Power to the circuitry was via two 18K resistor droppers in parallel and is half wave rectified so the circuit I plan to add should not draw a lot of current.

A 0603 SMD green LED is placed just beside the original red. Since this was a nitride based green, it is very bright at full current. I only used a 15K current limiting resistor to prevent loading the original circuitry and just enough brightness to not overpower the red.

LED cover placed back and still fits good.

At power on, both red and green LEDs light up.

When desired temp has been reached, the red LED turns off and the green stays lit as a power on indicator.

Page created and copyright R.Quan ©19 Apr 2016.