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Old 06-30-2019, 11:29 PM   #21
captainKKK
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

This thing beats me. It always blows the switch diode. The coils can't be bad as they work on lo and hi temp. I realized the small coil is used as resistor to slow the motor speed on lo setting,but why does the low heat and low fan speed take out the 1N5408? My model is just wired weird with only 3 wires running to the heating elements..... I've looked at everything on the net and cannot find any wired this way.

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Old 07-01-2019, 09:12 AM   #22
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

I found one wired like mine, good pics, but not enough detail to help me. https://m.youtube.com/watch?v=kD8ozaHnx3k Interesting at 3:45 minute mark

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Old 07-01-2019, 09:52 AM   #23
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

So which of these is the correct schematic?
Or neither?
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Old 07-01-2019, 11:23 AM   #24
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

Neither one is completely correct....and I will revise and post as soon as I get it open again and give it the fine tooth comb inspection of the heating internals. As you could see in my youtube video reference above, which is exactly like my unit, there is one black wire going directly from the motor rectifier board to the switch.....nothing else in that line. But I will look closer today.
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Old 07-01-2019, 02:59 PM   #25
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

The "top" V1 schematic has a wire from the motor rectifier to the switch... so this one is correct minus the RFI capacitors?

not sure what else could be wrong...if the motor/bridge is not shorted and the auxiliary drop resistor isn't shorted, diode shouldn't blow... but again the fact that the high amount of power dissipated by the diode could be causing problems.

BTW was the replacement 1N5408 the same size as the original at least? Either way it's undersized, probably even a P600M is too small...

(And don't try using two in parallel, in case you were thinking about it... not so simple as that.)

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Old 07-01-2019, 08:53 PM   #26
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

Lol, I already researched the parallel diodes, bad idea. I got some 10A10 10 amps coming, but the diode wire to the switch gets so hot now, the 10 amp will just probably fry something. What I want to do is get rid of that 5408 all together and run another wire into the heating elements, replacing the 5408 with a wire.....most of the HFT guns like mine have 4 wires from the elements, like this. https://www.ifixit.com/Guide/Drill+M...lacement/78060

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Old 07-01-2019, 09:23 PM   #27
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

Problem is that you need to reduce the amount of power going into the heater. For the "low" power, you need to increase resistance into the heater, so add more resistance wire so that less current flows...

You might need to relocate the diode into the intake of the heat gun and add heatsink flaps near the body of the diode...that should solve the problem.
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Old 07-01-2019, 09:28 PM   #28
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

How about I add one of these? https://m.aliexpress.com/item/329861...m.32986191352& on the back end plate of the suction side

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Old 07-01-2019, 09:33 PM   #29
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

Well, that heatsink on the SCR is what you need on the diode

That SCR will be dumping the same heat the diode would have been dumping.
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Old 07-02-2019, 02:39 PM   #30
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

Ok, not knowing what I don't know, I am thinking of using a new (old stock) zener diode 1N11371 in place of the 1N5408, mounted to a heat sink at the air intake, IN THE REVERSE direction. Is this a good idea? See pic of newest crude schematic.
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Old 07-02-2019, 02:55 PM   #31
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

wont work, zeners are different
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Old 07-02-2019, 04:20 PM   #32
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

?

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Old 07-02-2019, 04:29 PM   #33
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

1N1371 is 68V Zener so when you put AC on it, it will conduct in full in half the cycle of the AC, then it tries to clamp down to 68V on another half cycle of the AC, won't work for what you want to do, to conduct only half of the AC cycle only as the original diode does.
https://www.arrow.com/en/products/1n1371/microsemi
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Old 07-02-2019, 04:36 PM   #34
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

did you test the switch yet ? i can see a potential fail that would kill the diode pretty fast .
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Old 07-02-2019, 08:55 PM   #35
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

Ok, thanks to everyone that tried to help and I learned by all your comments . Let's mark this one a SUCCESS.

I have fixed it for good. I tested it on both low and high speeds for at least 5 minutes each. Low speed produced a exhaust temp of 240C, while my added in
heat sink mounted 1N5408 diode performed at no higher than 80F, with my thermal gun. My outside ambient air was 79F at time of test. Note: that bolt sticking out the back, which holds the diode heat sink never even got warm to my touch during testing.

I know I spent $6000 of time and $3 parts to fix this $9 heat gun, and drove all in here crazy, but that's not what I am here for. Thanks again to all, eccerr0r had the solution first and Kaboom was way over my head mathematically, but
Not scientifically....thanks to both, and everyone.

Take a look at my rigged diode heat sink in the intake air side if you are curious......works like a champ. I can fix the next one in 30 minutes for under a dollar.

The end
Attached Images
File Type: jpg IMG_20190702_211817.jpg (734.6 KB, 21 views)
File Type: jpg IMG_20190702_211745.jpg (500.0 KB, 23 views)
File Type: jpg IMG_20190702_211843.jpg (700.1 KB, 21 views)
File Type: jpg IMG_20190702_212026.jpg (652.9 KB, 18 views)

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Old 07-03-2019, 10:24 PM   #36
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

The thermal resistance of epoxy is fairly high so the heatsink won't be too effective. BTW, hopefully you're not blocking the air flow too much, in mine if I did that, it would impede air flow quite a bit...
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Old 07-04-2019, 01:45 AM   #37
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

Quote:
Originally Posted by captainKKK View Post
Ok, thanks to everyone that tried to help and I learned by all your comments . Let's mark this one a SUCCESS.

I have fixed it for good. I tested it on both low and high speeds for at least 5 minutes each. Low speed produced a exhaust temp of 240C, while my added in
heat sink mounted 1N5408 diode performed at no higher than 80F, with my thermal gun. My outside ambient air was 79F at time of test. Note: that bolt sticking out the back, which holds the diode heat sink never even got warm to my touch during testing.

I know I spent $6000 of time and $3 parts to fix this $9 heat gun, and drove all in here crazy, but that's not what I am here for. Thanks again to all, eccerr0r had the solution first and Kaboom was way over my head mathematically, but
Not scientifically....thanks to both, and everyone.



Take a look at my rigged diode heat sink in the intake air side if you are curious......works like a champ. I can fix the next one in 30 minutes for under a dollar.

The end

If the heat sink that used is to big you could always use a T-220 package heat sink something like this

https://www.ebay.com/itm/20pcs-16x14....c100005.m1851

if this is still too big then can cut it in half and only use half of it which I would think should be enough
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Old 07-06-2019, 01:39 PM   #38
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

Somehow, I am doubtful the diode heatsink was the fix here. If the diode was overheating so badly without the heatsink, then even with the heatsink, you'd see it get quite hot. If that diode is indeed used for cutting power to the entire heatgun's heating elements in half, then you'd have around 4W of power dissipation, as per kaboom's calculations. This is quite a bit of heat to get rid of. And looking at that heatsink you added, it wouldn't take long for it to reach high temperatures again.

That said, I have my money either on the motor bearings going bad or perhaps shorted/touching turns on the heating element. These cheap China permanent magnet DC motors sometimes don't put proper lubrication on the sleeve bearings or just poorly made sleeve bearings. I've had quite a few RC cars go bad due to that when I was a kid many years ago. Took me many years later to find the problem while messing with them with my nephew. When the sleeve bearing start to seize on these motors, the motor may pull 2x to 3x the amount of current it normally draws. The worst one I had (again from one of the RC cars) was an RS-280RH motor that went from drawing 0.3 Amps unloaded to 2.8 Amps unloaded. Basically, after the sleeve bearings on that motor warmed up enough, it would eventually draw normal current. But cold, it would squeal and draw tons of current. I checked the windings and they were all fine. Same with brushes (carbon type - surprising for a cheap RC car, considering most I saw used much cheaper copper brushes that always wore out quick.)

So if the fan motor in that heatgun sounds louder than normal or seems to vary in speed/noise when cold, it may be the motor bearing causing the motor to draw higher than normal current - and perhaps enough to burn out the diode. Otherwise, I suspect shorted/touching turns on the heating element. As others mentioned here, try plugging the heatgun into a Kill-A-Watt (or similar) power meter and have a look at it the next time you use it. Also, try using the heatgun pointed in different directions (i.e. up, down, sideways, etc.) and see if the power draw changes. A loose coil could just be touching another coil next to it when the heatgun is facing in a certain direction. Again, this is something you would see very obviously on a power meter, as the power use would go up.

Quote:
Originally Posted by kaboom View Post
FWIW, these HF heatguns always struck me as having fine chineezium marketing puff: "Ours has two settings."
Eh, they are not too bad.
I have the one that R_J posted a link to in post #6. I've had it for 4 years now and give it occasional use for help with reflowing larger video cards (as a top heater) or to remove large BGA chips. The most demanding job I gave that gun was heating the entire drum assembly of our washer when I was changing the bearing on it. Being a metal drum with plastic housing, I had the heatgun running there on the low setting for a good 10 minutes to heat everything up so that I could remove the drum (drum shaft stuck on bearings due to failed bearings - fun ) from the housing... and then the bearings from the housing.

Last edited by momaka; 07-06-2019 at 01:44 PM..
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Old 07-08-2019, 10:35 PM   #39
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

It's fixed, no qualifications. The motor is fine, purrs like a kitten, the coils are not touching/ shorting. Just two days ago, I used it for 32 minutes on low setting for an under board laptop video reflow, while using a heat gun on the top and the bolt that holds the heatsink was 105F when I turned it off. As I stated earlier it draws 3.5 amps on low and 11 amps on high. Do to worry, it's fixed, the 1N5408 is wrapped in an aluminum holder which is bolted to the heatsink using a thermal pad. Before the heatsink, it blew 3 x 1N5408s and one larger, but now It just works. It's done fixed. The only other thing that may have contributed to the fix, ie lowered the 1N5408's temp, would be the fact that I ran larger solid copper wires from the switch to the 1N5408, so if you need to have another reason there it is.

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Old 07-09-2019, 11:57 AM   #40
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Default Re: Harbor Freight Tools Heat Gun Item 96289 JSRF-601C Repair

Not to worry about the airflow being blocked by the heat sink in the backend, it has plenty area around it, and it keeps the heat sink cooler, sides that the gun has slit cooling opening on the top of the gun too, as seen in my last picture. I suppose that rear red end cap was supposed to go into higher costing heat guns with a mechanical fin to regulate air flow when rotated, thereby adjusting temperature some what but not in this cheap thing. I have hot glued the red end cap to one half of the gun's body to keep it from rotating and shorting the 1N5408 mounted inside it.

Last edited by captainKKK; 07-09-2019 at 12:02 PM.. Reason: answer points of view, concerns
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