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Author: Subject: Fisher Sci hotplate common faults
Steve s
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[*] posted on 19-5-2020 at 11:52
Fisher Sci hotplate common faults


Hi All
I'm trying to fix two identical hotplates with what appears to be identical faults. Before i go too much deeper into replacing components on a trial and error basis i thought i'd ask here to see if anyone knows of any common faults on these machines.
Basically the fault is intermittent/random, sometimes i'll fire em up and they work fine but then without moving them or anything they'll just not work next time i fire em up.
I've had a good (magnified) look through the circuit boards checked voltages at various points but still can't seem to find any obvious fault.
The other problem i'm having is finding a manual for them so if nothing else it would help a lot if someone could identify them.
Photo attached;

DSCN6905[1].JPG - 1.6MB
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G-Coupled
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[*] posted on 20-5-2020 at 03:09


Dry solder joint or elderly cap(s), maybe?
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Steve s
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[*] posted on 21-5-2020 at 01:40


No obvious dry joints, i'm currently working my way through checking the IC's, resistors, diodes etc then when i get a capacitor tester i'll go through those too.

Annoying because they are really good hot plates, super quiet and 550C
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G-Coupled
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[*] posted on 21-5-2020 at 13:11


I'd really check/replace the caps as my first port of call - these units appear to be the perfect kind of age where especially the electrolytic caps begin to fail/lose tolerance.

If there's not that many caps and their values aren't too massively varied, it might be good to just buy a couple of bags of half-decent caps and just replace them wholesale.

Please keep us posted on your findings and how you get on - I think it'd be a really good thing to build up some data on the more common failiure modes of equipment like this.

What model is your hotplate, BTW?

[Edited on 21-5-2020 by G-Coupled]
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Keftedes89
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[*] posted on 21-5-2020 at 20:07


Quote: Originally posted by Steve s  
Hi All
I'm trying to fix two identical hotplates with what appears to be identical faults. Before i go too much deeper into replacing components on a trial and error basis i thought i'd ask here to see if anyone knows of any common faults on these machines.
Basically the fault is intermittent/random, sometimes i'll fire em up and they work fine but then without moving them or anything they'll just not work next time i fire em up.
I've had a good (magnified) look through the circuit boards checked voltages at various points but still can't seem to find any obvious fault.
The other problem i'm having is finding a manual for them so if nothing else it would help a lot if someone could identify them.
Photo attached;



What exact problem are you having? No power? No Stir? No heat? Intermittent functioning of any type?
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Mateo_swe
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[*] posted on 23-5-2020 at 09:06


Have you checked the heating element?
Maybe the wire is broken but still have contact sometimes.
It would be helpful to try find out/narrowing down in what region the problem is located.
When the fault is present, is anything else working like stirring, the LED diodes on the front?
When the fault is randomly present its often a faulty solder joint or a broken heating wire.
If nothing works when fault is present the fault is often in the power supply region.
As the 2 units seem ta have same fault you are correct in looking around on the net, maybe its a known issue with this brand and model.
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Steve s
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[*] posted on 23-5-2020 at 16:38


Quote: Originally posted by G-Coupled  
I'd really check/replace the caps as my first port of call - these units appear to be the perfect kind of age where especially the electrolytic caps begin to fail/lose tolerance.

If there's not that many caps and their values aren't too massively varied, it might be good to just buy a couple of bags of half-decent caps and just replace them wholesale.

Please keep us posted on your findings and how you get on - I think it'd be a really good thing to build up some data on the more common failiure modes of equipment like this.

What model is your hotplate, BTW?

[Edited on 21-5-2020 by G-Coupled]


Just ordered 2 of each of the components that i could find in the Farnel catalogue, including all the capacitors (closet values i could find), the VR's, BR's, triacs, transistors and a few opto couplers. The whole lot came to just under £25 inc postage. Should all be with me on Tuesday, in the meanwhile i'm going to try to test as many of the components that i couldn't source.

Great idea re database for the repair of lab equipment, especially useful given the fact that a lot of us are using somewhat dated secondhand equipment.

No model as such but the cat numbers are 11-602-50sh 1200rpm/550celcius 240v (the US 110V ones are 11-602-49sh)
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Steve s
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[*] posted on 23-5-2020 at 16:44



[/rquote]

What exact problem are you having? No power? No Stir? No heat? Intermittent functioning of any type?[/rquote]

Basically all or nothing, sometimes i'll fire em up and they'll work fine, sometimes i'll fire em up and the heat/stir LED will light up for a couple of secs then go and then nothing, sometimes i'll power them up and nothing at all happens.

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Steve s
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[*] posted on 23-5-2020 at 16:55


Quote: Originally posted by Mateo_swe  
Have you checked the heating element?
Maybe the wire is broken but still have contact sometimes.
It would be helpful to try find out/narrowing down in what region the problem is located.
When the fault is present, is anything else working like stirring, the LED diodes on the front?
When the fault is randomly present its often a faulty solder joint or a broken heating wire.
If nothing works when fault is present the fault is often in the power supply region.
As the 2 units seem ta have same fault you are correct in looking around on the net, maybe its a known issue with this brand and model.


Apparently these units do have a fail safe voltage drop system which i believe means that they'll shut down if there is a fault somewhere. Both the heating element and the motor seem to work fine when powered up but yes i might put a tester across them and give the wires a bit of a wiggle just in case i have linked out the TC on both units whilst testing.

I have 12v dc on the output of the BR but then i only seem to be getting 50% voltage at the inputs of some of the IC's 1.3v where there should be 2.5v and 2.6v where there should be 5v
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G-Coupled
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[*] posted on 23-5-2020 at 19:04


Quote: Originally posted by Steve s  
...I have 12v dc on the output of the BR but then i only seem to be getting 50% voltage at the inputs of some of the IC's 1.3v where there should be 2.5v and 2.6v where there should be 5v


It's feeling more and more likely that it's bad caps IMO. :)

How old are these units, and which model(s) are they?

[Edited on 24-5-2020 by G-Coupled]
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Steve s
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[*] posted on 24-5-2020 at 16:41




It's feeling more and more likely that it's bad caps IMO. :)

How old are these units, and which model(s) are they?

[Edited on 24-5-2020 by G-Coupled][/rquote]

I think you might well be correct, one (same one on both machines) of the electrolytic caps i tested today doesn't seem to have any continuity. Luckily it's one of the ones Farnel had in stock so will be able to replace it when my order arrives.

Not sure on year and no model number as such but the cat number is 11-602-50sh 1200rpm/550celcius 240v (the US 110V ones are 11-602-49sh)
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