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Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

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    Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

    This is a seldomly used electric heat gun that was designed to operate with two fan speeds with two heat settings controlled only by a rocker switch on either high or low. It was working ok and while using on low heat/speed, it suddenly switched to high speed/temp without a change in the switch setting. On disassembly, and testing the 1N5408 Rectifier Diode 3A 1000V, it was found to be bad. It was replaced with the same and it worked as designed .... for 60 seconds and then blew the diode again. Is there a modification I can make to fix this? The heating elements, rectified DC fan motor, thermal cutoff and switch all tested good. Any ideas? See my crude schematic......thanks for any ideas. Would a change to a lower temp thermal cutoff help? How can I keep the 1N5408 Diode for exploding? Would a low quality 1N5408 be the issue here?
    Attached Files

    #2
    Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

    3 amp diode does seem a bit light

    Comment


      #3
      Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

      1st, it cant be a DC motor unless there is another diode we arent seeing,
      your schematic shows it getting AC.

      second, what's the power consumption of the gun?
      the way the circuit works is that the fan motor is getting power via a resistor built into the element,
      and the whole thing is powered either by full waveform (H) or by half the power cycle because of the diode.
      but the diode at 120v is only going to handle 375w (120v 375w = 3A)

      btw, i know it says 1500w - but that is probably bullshit these days.
      Last edited by stj; 06-29-2019, 03:01 AM.

      Comment


        #4
        Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

        Thanks, remember I said crude schematic, so you can take my word That rectifying diodes are on a small board on the back of the blower motor. (I assumed, see new pic with partially exposed fan motor circuit board). Can I just substitute a 10A10 rectifying diode for the 1N5408, or add a resistor before the 1N5408.? Or is this asking for a fried potato? I may take another look inside.....
        Attached Files
        Last edited by captainKKK; 06-29-2019, 02:53 PM.

        Comment


          #5
          Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

          Yep, I was right, the motor is DC, ningbo huana RS-365S, see pics. Any direction appreciated. Note these pics of the switch is missing the 1N5408 diode between the switch 3 and 1 contacts because I soldered it and it got so hot it fell off.
          Attached Files

          Comment


            #6
            Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

            That schematic can't be correct, in HIGH the diode is out of the circuit so the DC motor would be running on full AC

            Is this the same heat gun? https://www.ifixit.com/Device/Drill_Master_Heat_Gun
            Last edited by R_J; 06-29-2019, 03:31 PM.

            Comment


              #7
              Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

              I am not an electronics repairman, only a scientist, and I do not understand it either, but that's the way it was built and worked well on both speeds, for 15-20 minutes at a time for at least 20 sessions during it life......

              R_J, my schematic lacks details of the circuit board on the back of the motor, which I assume rectifies the AC to DC...? And NO that is not the same gun internally, that gun has no circuit board on the back of the motor, nor a 1N 5408 on the switch, and does have WIRES running to each terminal of the switch.

              When I replace the 1N5408, then start it in LOW mode ( which places the 1N5408 in circuit, it works as it should on lower air flow and heat), then after a couple minutes, it switches to high mode by itself, probably b/c the diode has shorted. the diode is only 88F, but the wire between the switch and the anode side of the diode maxed at 150F, before it failed. Any ideas?
              Last edited by captainKKK; 06-29-2019, 04:13 PM.

              Comment


                #8
                Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                Does the motor run properly in high speed? if it does then it must be correct and they just halfwave rectify the whole heat gun for low temp, The only thing I could think of would be if the heat element has shorted somewhere causing it to draw a lot more current

                Comment


                  #9
                  Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                  The heat coils both have continuity, no ground. With a new 1N5408 installed, unplugged from AC, with switch in High, there is continuity from the AC plug. With low switch selected, at the AC plug, my ohm meter shows the same reading as the new diode when it was not in circuit.
                  YES the motor run as expected at high speed when Hi is selected on the switch.
                  Attached Files
                  Last edited by captainKKK; 06-29-2019, 04:36 PM.

                  Comment


                    #10
                    Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                    I suspect the "small heat coil" is just used as a resistor to drop the 120v ac to supply the motor, the motor is likely 12~24 volts dc and the board on the back of the motor supplies the dc voltage. so there is not much that can cause the diode to burn up, the only thing would be exceeding the 3 amp current rating of the diode and if it worked before, the only thing I can think of that would change the amount of current would be shorting in the heat element which would lower its resistance and increase the current. But I doubt that is happening as the heat element looks like it is in good shape and well spaced between the coils
                    Last edited by R_J; 06-29-2019, 05:02 PM.

                    Comment


                      #11
                      Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                      Or the motor is over current-ing and causing the diode to go bad
                      9 PC LCD Monitor
                      6 LCD Flat Screen TV
                      30 Desk Top Switching Power Supply
                      10 Battery Charger Switching Power Supply for Power Tool
                      6 18v Lithium Battery Power Boards for Tool Battery Packs
                      1 XBox 360 Switching Power Supply and M Board
                      25 Servo Drives 220/460 3 Phase
                      6 De-soldering Station Switching Power Supply 1 Power Supply
                      1 Dell Mother Board
                      15 Computer Power Supply
                      1 HP Printer Supply & Control Board * lighting finished it *


                      These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

                      1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
                      2 Hem Saw Computer Stack Board

                      All of these had CAPs POOF
                      All of the mosfet that are taken out by bad caps

                      Comment


                        #12
                        Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                        R_J, i believe you are right when you said, "the "small heat coil" is just used as a resistor to drop the 120v ac to supply the motor, ouch, what a cheap way to do that.....maybe I can get it running while opened long enough to check that blue wire voltage.

                        Comment


                          #13
                          Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                          i think the heat is always 100% and the hi/lo and diode are just for the fan motor.
                          so does the fan spin freely, and are any diodes bad on the back of the motor?

                          Comment


                            #14
                            Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                            It IS as DC motor; runs on AC with an internal rectifier, usually 1N400x's.

                            Heater has a tap for the motor with 12-14V across, similar to a hair dryer. The latter usually having a separate "dropper coil" in their heaters, allowing the main heaters to be shut off with a "cold freeze" feature.


                            Check the current draw on "Hi"- a bit much for a 5406, even at 50% duty cycle as expected when chopping off one half of the sine wave. 3A average= 6A for half the time...

                            These always ran on the edge. Heater may have shorted turns- ohmmeter tells you nothing other than the ckt is complete. Use an amp clamp or "Kill A Watt."

                            FWIW, these HF heatguns always struck me as having fine chineezium marketing puff: "Ours has two settings."

                            Better ones ran at constant power and varied temp with an air shutter.
                            "pokemon go... to hell!"

                            EOL it...
                            Originally posted by shango066
                            All style and no substance.
                            Originally posted by smashstuff30
                            guilty,guilty,guilty,guilty!
                            guilty of being cheap-made!

                            Comment


                              #15
                              Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                              The fan spins freely, and the armature looks good on the brush plates. The circuit board on the back of the motor is soldered, with the back of the board facing outward and the rectifier diodes between the board and the motor, and I can see the four diodes and some small resistors. I would probably destroy that circuit board if I tried to remove it to check the rectifier circuit. The heat is NOT 100% all the time, as when it worked, I would switch to hi, the fan cranks up and the heating elements go to bright red, which doesn't make sense, since I would think the hi mode would be when the 1N5408 would blow. But it blows while on lo mode, which then bridges the inside of the 1N5408, and it goes to hi mode without touching the switch, essentially making the same circuit in the low and hi modes

                              Comment


                                #16
                                Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                                Thanks guys for your input. What do you think about getting some 10A10 diodes and replacing the 1N5408 with one of those?

                                Comment


                                  #17
                                  Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                                  Well.. it's a PM DC motor, but this time with an external PCB/diodes to run on AC. Jumped in before looking at motor pix.

                                  Try an 8-10A, 400V diode instead. The 800-1kV diodes tend to have higher junction drop, which means more dissipation for a given current.
                                  Bare minimum would be a 200PIV part, but this only gives a 30V margin on top of peak line voltage.

                                  With a half wave rectifier, a heating/resistive load draws 1/2 the power it would as on full voltage.

                                  750W at 120V is 6.25A If it's thru that half-power diode, it'll be 12.5A, but for half the time, so the same 6.25A average.
                                  One diode drop of .7v * 6.25A=4.375W in the diode. No wonder the solder melted.

                                  This is true even if it's a 10A diode, you just have a bigger package to spread the heat.
                                  If you must keep the half power option, either try to stay around 2mins (or less) on/5mins minimum off.
                                  Or use a TO-220 part on a small heatsink tucked away.

                                  Using 1kV PIV diodes, which have close to 1v drop, you'd end up with 6.25W instead...

                                  This is initial dissipation- as the diode heats, it's voltage drop will fall, to a point.

                                  As I said above, the dual heat option always struck me as a gimmick, and a dubious one at that- literally using a part that's half of the minimum required.

                                  Another example of Hazardous Freight.
                                  Last edited by kaboom; 06-29-2019, 08:08 PM. Reason: additions and formatting :-)
                                  "pokemon go... to hell!"

                                  EOL it...
                                  Originally posted by shango066
                                  All style and no substance.
                                  Originally posted by smashstuff30
                                  guilty,guilty,guilty,guilty!
                                  guilty of being cheap-made!

                                  Comment


                                    #18
                                    Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                                    I have an older version of the HFT heat gun (orange), still works last I used it (knock on wood) and had it probably for almost a decade. For kicks I stuck it into a kill-a-watt a few years ago and it does get to at least 1300W at high, around 700W low.

                                    Comment


                                      #19
                                      Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                                      Originally posted by eccerr0r View Post
                                      I have an older version of the HFT heat gun (orange), still works last I used it (knock on wood) and had it probably for almost a decade. For kicks I stuck it into a kill-a-watt a few years ago and it does get to at least 1300W at high, around 700W low.
                                      Does your gun look like this pic?, if so I would sure like to get a good pic of the insides!
                                      Attached Files
                                      Last edited by captainKKK; 06-30-2019, 08:33 AM.

                                      Comment


                                        #20
                                        Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

                                        No, even older I think (HFT 35776, "Chicago Electric Power tools" brand instead of "Drill Master"). Orange, and no trigger guard. But I suspect it's pretty much the same. The motor is DC and you can see from the intake slots in the back that there's a 1N4007 bridge rectifier soldered straight on the motor terminals.

                                        Any of these new ones have GFCI cords? If hair dryers have them... these should be even cheaper to make....
                                        Last edited by eccerr0r; 06-30-2019, 07:31 PM.

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