Identifying an Alps Potentiometer (For Hakko FX-888) - Page 1
Forum section: electronics / repair

author: anfilt
author_rank: Newbie
timestamp: May 16, 2021, 03:37:06 am
content: I have a Hakko FX-888, and recently it took a tumble, and landed on the knob to adjust the temperature. Normally, I just would measure the resistance with my multimeter to find the resistance range and get an idea if it's linear. However, the fall damaged the pot and it just reads open on the terminals. Also it does not have the wiper any more so I can't measure the range.I tried looking on Hakko's website to find either a schematic or service manual, but no avail. I also looked at alps website to see if I can make sense of the numbering on the side of potentiometer, but they don't seem to line up with any part numbers I see in the PDFs I have found. Does anyone here know what potentiometer the Hakko FX-888 uses?

author: bdunham7
author_rank: Super Contributor
timestamp: May 16, 2021, 05:30:45 am
content: You really need to measure every dimension and do your best to measure whatever is left of the carbon track to see what the resistance is. Then you can compare those specs to some actual models.It **might** be this one:https://www.mouser.com/ProductDetail/Alps-Alpine/RK09L1140A65?qs=%2Fha2pyFadugfnIKI4JCdTsv1ifwNhBT5G%2FsKZKTZNB6qkl8CGMrmHw%3D%3D

author: amyk
author_rank: Super Contributor
timestamp: May 16, 2021, 05:33:16 am
content: I believe the 888 has essentially the same circuitry as the 936, whose schematic can be found here:http://dalincom.ru/datasheet/HAKKO_936_schematic.pdf...which means it's probably this one:https://tech.alpsalpine.com/prod/e/html/potentiometer/rotarypotentiometers/rk09l/rk09l1140a65.html(I'm not sure what the difference between a "1B" and "2B" taper is - but they are both linear. A soldering iron with logarithmic temperature range wouldn't make sense.)

author: anfilt
author_rank: Newbie
timestamp: May 16, 2021, 06:11:02 am
content: Well I can at least pinpoint the shaft dimensions since I have a micrometer. But interesting that there are 2 different linear resistance tapers. I wonder what the difference is too might have too look more closely at alps documents to see if I can figure that out.I still need to work out if what you posted has the same resistance ranges.

author: anfilt
author_rank: Newbie
timestamp: May 16, 2021, 06:20:30 am
content: So looking at the carbon it look like it has chips and a couple cracks in it so I am not even sure I can get a good reading, and proping around I only can get from ~1Ω to ~3.3 KΩ before it just becomes an open circuit. If I probe on the other Side of the damage I only get about ~900 Ω. So adding those together is ~4.2 KΩ.

author: mariush
author_rank: Super Contributor
timestamp: May 16, 2021, 06:37:19 am
content: I'd suggest buying a 4.7 kOhm and a 10 kOhm potentiometerIf they're not quite right, you can always parallel a resistor with the potentiometer to tweak it.

author: anfilt
author_rank: Newbie
timestamp: May 16, 2021, 07:53:24 am
content: That's a good point. Although I would need accurate way to measure the tip of soldering irons temperature. I suppose I would need to get something that could let me read a thermocouple. (any suggestions that is not too expensive). However, I suspect from the other comment about the 936 that it's probably the same resistance of pot, and I missing some resistance because the damage when measuring the carbon track directly.

author: amyk
author_rank: Super Contributor
timestamp: May 16, 2021, 08:05:38 pm
content: 5k is what the original markings say.Hakko sells a ridiculously expensive (for a thermocouple holder and a display) tip thermometer, but clones can be had for much cheaper.

author: bdunham7
author_rank: Super Contributor
timestamp: May 16, 2021, 08:31:17 pm
content: I think there's every chance that the model amyk and I have posted is your pot. I would just verify the physical dimensions and order it. If you have doubts or don't like to experiment, you could just order the board:https://www.aliexpress.com/i/33000814237.html

author: floobydust
author_rank: Super Contributor
timestamp: May 16, 2021, 10:37:54 pm
content: I measure 3.695k end-end in circuit and 4.395k out of circuit, and 1/2 way is about 2.2k so it's linear taper.Because a pot's tolerance is loosey goosey ±20% that would be 5k ohms. ALPS seems to only haveone 5k offeringin their lineup.I can't read the controller IC's numbers to see what it's about.I forgot it's like a work of art inside, really nice construction and attention to detail.I swapped in an RGB LED for power/heat indication, Dave did a similar mod too.

author: anfilt
author_rank: Newbie
timestamp: May 16, 2021, 11:26:15 pm
content: Thanks for measuring one you had on hand. So pretty close to what I measured from trying to measure the broken carbon track directly. It likely was one of their standard models was my thought, but ALPs can make pots not in there standard lineup so I was not sure. Just gonna order a 5k pot in my next part order.

author: anfilt
author_rank: Newbie
timestamp: May 16, 2021, 11:28:47 pm
content: Quote from: amyk on May 16, 2021, 08:05:38 pmSeems like you know what the marking mean? I am guessing 50 must mean 5k then?