JABE UD-1200 JBC clone soldering station does not heat up - Page 1
Forum section: electronics / repair

author: snoopy
author_rank: Frequent Contributor
timestamp: January 01, 2025, 04:40:44 am
content: Recently, when I was using my JABE soldering station and changing tips, I heard a pop sound from the unit. Now, the temp idles/sleeps at 30-40 degrees instead of 200, and when active, the power is at 99%, but the tip does not heat up. I can't see anything obviously blown inside, but there appear to be two Fairchild surface-mount mosfets, and possibly one or both are blown. Has anyone else had experience with one of these failing?

author: Dougmc
author_rank: Contributor
timestamp: January 01, 2025, 05:31:08 am
content: If it pop you should see something blown.Take pictures of the boards then zoom in on the picturesAnd share the pictures

author: snoopy
author_rank: Frequent Contributor
timestamp: January 01, 2025, 08:18:43 am
content: See attached photos. MOSFET is a Fairchild/Onsemi FDB047N10.https://www.onsemi.com/products/discrete-power-modules/mosfets/low-medium-voltage-mosfets/fdb047n10

author: Swake
author_rank: Frequent Contributor
timestamp: January 01, 2025, 03:00:53 pm
content: There is a suspicious black spot on D3 (near the white connector on the left).You have a sofisticated soldering iron, I guess you also have a multimeter and know how to do basic diode tests with that meter?

author: TheDefpom
author_rank: Frequent Contributor
timestamp: January 01, 2025, 09:03:33 pm
content: Agreed D3 looks suspicious, I also noticed that one lead of the fuse is not soldered onto the top side layer, this means current is passing through the plated through hole, that could have failed and gone open, try soldering that fuse on the top side to make sure it is connecting.

author: snoopy
author_rank: Frequent Contributor
timestamp: January 02, 2025, 05:49:50 am
content: I did check all of the diodes, and they appear to be okay. I resoldered the fuse, but I also noted that they use awfully small vias. Possibly, some of them may have gone open.There is about 60Vp-p on the gate-source of Q4 which is way above the max specs of +/- 20V !There are two secondary windings on the transformer. One is a 35VRMS center tapped winding and the other is a 12 VRMS winding so don't how the 60Vp-p is being generated.Wonder if it is similar to the original JBC where someone posted a schematic here ??https://www.eevblog.com/forum/testgear/jbc-soldering-station-cd-2bc-complete-schematic-analysis/

author: Swake
author_rank: Frequent Contributor
timestamp: January 02, 2025, 08:35:50 am
content: 60 Vpp indeed sounds like a lot. A C245 cartridge likes it at about 24 V from what i found on the internet.If the 2 windings somehow get in series you get there: 35 Vrms + 12 Vrms = 47Vrms ~ 66VppThe pop might have come from the transformer.The soldering on the LCD side was not cleaned up. There might be some unwanted solder bridge.Is the tip still good? apparently between 2.5 Ohm and 5 Ohm is a good value. I would not put another tip in the iron without being certain the output is within specs.To test a mosfet:https://youtu.be/RkWy1EirEu8?t=122

author: snoopy
author_rank: Frequent Contributor
timestamp: January 02, 2025, 10:40:53 am
content: Some good news. With the aid of the schematic for the JBC I was able to trace the fault to an open circuit between the source pins of the MOFETS. However, one MOSFET sits directly behind the LCD display so it's not easy to view the trace but I didn't have to look far to find the culprit being a burnt track (see photo below). Because the track was so narrow it's little wonder it burned up and now I recall that it happened when I changed tips and either the tip was faulty with a low resistance heater or there was a momentary short. Anyway rather than bridge the burnt track I just soldered a bit of wire wrap wire directly between the source pins of the MOSFETs and it's back to way it was

author: snoopy
author_rank: Frequent Contributor
timestamp: January 02, 2025, 10:45:51 am
content: Quote from: Swake on January 02, 2025, 08:35:50 amThe tip I used may have have been faulty and had a low resistance heater so best to check them before you use them

author: Swake
author_rank: Frequent Contributor
timestamp: January 02, 2025, 10:49:44 am
content: Good find.That track worked as a fuse, sounds like a good place to put a real fuse as it happened during tip change.

author: snoopy
author_rank: Frequent Contributor
timestamp: January 02, 2025, 11:02:07 am
content: Quote from: Swake on January 02, 2025, 10:49:44 amironically the circuit appears to have some sort of current limit by measuring the voltage across a 5 milliohm resistor and feeding this information to the micro but obviously the current limiting is more than the trace can handle.