STFA20
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IKA HS7 - no temp control or actuator response
Please help!
I'm about to shoot myself in the face, here. I bought this thing because my old friend PC320 has the itis' in its stirring motor, and now this fancy
beast that can stir really well is locked on 50C and cannot be adjusted. No errors, just heats to 50C like that's its job, while stirring beautifully.
I'll attach pics in my next post, if necessary, but this thing is immaculate on the inside. It looks like it had one job, did that job for about 6
months, and then was declared defective. I don't have a scope handy to properly test the "rotary"/incremental encoder, but there's so little apparent
use in addition to there being no play in any axis that it seems an unlikely cause, despite being the only part subject to wear and tear that's in the
way to the microcontroller.
I've confirmed with a multimeter that the button/"user input" part of the encoder is functioning electrically (pulled low on actuation), which leads
me to believe the problem is somewhere else, since that button push isn't registered elsewhere.
I also noticed that there doesn't appear to be a Vcc line or any pullup resistors on the breakout board for the encoder. I'm guessing they're on the
display PCB where the Poti Heat connects?
Aside from being a little overly complicated, this is one of the most beautifully designed and assembled bits of tech I've taken apart. I'm really
impressed with all the frills, like the quick disconnects for the heater and stirring motors, as well as the stainless steel spring clamp to ensure
proper heat transfer between a MOSFET/TRIAC (TO-220) and the case.
I don't want to disrupt this thing anymore than I need to as this feels like a loose connection somewhere, though I can't figure where it would be.
Any detailed repair manuals around? Schematics? Any thoughts on the encoder and how it's wired to the board? Any contacts at IKA I can get in touch
with?
I have all the parts to fix anything on this board but I also don't want to touch anything I don't have to. There are no improvements to be made. If
you geek out on electronics stuff, do yourself a favour and open up a digital IKA CMAG HS-7. It will make you feel like someone, somewhere, actually
has a plan. It's like a warm blanket.
Thanks for any assistance you can provide. Requests for specific photos will be honored.
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Heptylene
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I have this hotplate, IKA HS-7 digital. Mine has worked fine for the past 4 years, best investment ever.
So you cannot adjust the temperature at all? There are three modes the hotplate can be in: A, B or C:
A: hotplate maintains set temperature as measured by external probe (PT1000 resistance temperature sensor), which you plug in at the back.
B: hotplate maintains set surface temperature.
C: temperature adjustment locked, cannot be adjusted in this mode at all.
You select the mode by holding the rotary encoder while turning the hotplate main switch on. It cycles through A, B, C, A, ...
From what you describe it looks like you're stuck in mode C.
EDIT: to clarify, mode C is so that nobody can tamper with whatever value is set. You set the temperature you want in mode B, say 42 °C and then
switch to mode C by turning the hotplate off, and turning it on again while holding the rotary encoder knob pressed down. Then you're in mode C with
your temperature of 42 °C which cannot be changed from there.
[Edited on 22-1-2020 by Heptylene]
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STFA20
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YAY! Thank you so much! I was so close to jumping for joy when I read this, and it has cured my beautiful IKA!
Was this in the manual somewhere but I just missed it? I coulda sworn I read that thing back to front.
Are you also using an external pt1000 probe? Is it a proper IKA probe or one of the SciLogix versions? I was thinking of ghetto-fabbing my own.
You completely made my day. Thank you!
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Heptylene
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Yep it was in the manual. Anyway I'm glad I could help!
I got mine with the temperature probe included as part of a package deal, but I got it brand new and it cost me an arm. I've learned some electronics
since then and I'm pretty sure repairing a used hot plate would be a better deal.
Nurdrage has a video on how to make your own probe from a PT1000 temperature sensor (a few bucks a piece). You sound like you do some electronics, I'm
pretty sure you could find out which pins for the back connector correspond to the PT1000 sensor and make your own probe.
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