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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Corning Laboratory Hotplate/Stirrer
A friend of mine picked up a surplus Corning model PC-620 (product info:
http://tinyurl.com/4xmmy) laboratory hotplate/stirrer for a couple bucks. It turns out that the stirrer works but it doesn't get hot. I took the unit apart but didn't see anything glaringly obvious wrong with it. The element shows 14.7 ohms but I don't know what else to look at so I figured that even it's a long shot I'd ask here hoping for a service manual or someone that has some experience with these units. You might wonder why I am "wasting" my time on a hot plate. Well, these things aren't exactly cheap at nearly US$500. Hotplates capable of a very consistent/stable 1000 deg F (550 deg C) don't come cheap. --adam |
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"Adam" wrote in message ink.net... | A friend of mine picked up a surplus Corning model PC-620 (product info: | http://tinyurl.com/4xmmy) laboratory hotplate/stirrer for a couple | bucks. It turns out that the stirrer works but it doesn't get hot. I | took the unit apart but didn't see anything glaringly obvious wrong with | it. The element shows 14.7 ohms but I don't know what else to look at | so I figured that even it's a long shot I'd ask here hoping for a | service manual or someone that has some experience with these units. | | You might wonder why I am "wasting" my time on a hot plate. Well, these | things aren't exactly cheap at nearly US$500. Hotplates capable of a | very consistent/stable 1000 deg F (550 deg C) don't come cheap. In general terms, are you able to safely measure the voltage across the heater while it is running? N |
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"Adam" wrote in message
ink.net... A friend of mine picked up a surplus Corning model PC-620 (product info: http://tinyurl.com/4xmmy) laboratory hotplate/stirrer for a couple bucks. It turns out that the stirrer works but it doesn't get hot. I took the unit apart but didn't see anything glaringly obvious wrong with it. The element shows 14.7 ohms but I don't know what else to look at so I figured that even it's a long shot I'd ask here hoping for a service manual or someone that has some experience with these units. You might wonder why I am "wasting" my time on a hot plate. Well, these things aren't exactly cheap at nearly US$500. Hotplates capable of a very consistent/stable 1000 deg F (550 deg C) don't come cheap. --adam As "stable" it is presumably controlled proportionally not thermostat (either on /off) so some control circuit and triac ? electronic hints and repair briefs , schematics/manuals list on http://homepages.tcp.co.uk/~diverse |
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"NSM" writes:
"Adam" wrote in message ink.net... | A friend of mine picked up a surplus Corning model PC-620 (product info: | http://tinyurl.com/4xmmy) laboratory hotplate/stirrer for a couple | bucks. It turns out that the stirrer works but it doesn't get hot. I | took the unit apart but didn't see anything glaringly obvious wrong with | it. The element shows 14.7 ohms but I don't know what else to look at | so I figured that even it's a long shot I'd ask here hoping for a | service manual or someone that has some experience with these units. | | You might wonder why I am "wasting" my time on a hot plate. Well, these | things aren't exactly cheap at nearly US$500. Hotplates capable of a | very consistent/stable 1000 deg F (550 deg C) don't come cheap. In general terms, are you able to safely measure the voltage across the heater while it is running? Check for power to the heater. If thta's not present, you'll have to trace back to the thermostat or controller (depending on the sophistication). There may also be a thermal fuse in series with the heater that is open. --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
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I'm sorry I should have been more descriptive. The unit is based
arround a 68HC705 micro and has feedback for both the stirrer motor (simple encoder) and the heater (thermistor). The heater is proportionally controlled using triac. As "stable" it is presumably controlled proportionally not thermostat (either on /off) so some control circuit and triac ? electronic hints and repair briefs , schematics/manuals list on http://homepages.tcp.co.uk/~diverse |
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Subject: Corning Laboratory Hotplate/Stirrer
From: Adam Date: 1/6/2005 2:09 PM Central Standard Time Message-id: . net A friend of mine picked up a surplus Corning model PC-620 (product info: http://tinyurl.com/4xmmy) laboratory hotplate/stirrer for a couple bucks. It turns out that the stirrer works but it doesn't get hot. I took the unit apart but didn't see anything glaringly obvious wrong with it. The element shows 14.7 ohms but I don't know what else to look at so I figured that even it's a long shot I'd ask here hoping for a service manual or someone that has some experience with these units. You might wonder why I am "wasting" my time on a hot plate. Well, these things aren't exactly cheap at nearly US$500. Hotplates capable of a very consistent/stable 1000 deg F (550 deg C) don't come cheap. --adam Hi, Adam. The technical literature download doesn't have a schematic, so you're going to have to do a little detective work. It's definitely worth a bit of time -- you've got a good lab hotplate. I'd spend some time trying to get it going. And the 14.7 ohms for the heater itself is also a hopeful sign -- that comes close enough to the 1100 watts rated for 120VAC, which means you don't have a burned-out heater. You didn't mention whether the amber heater light was on. If not, I would look at fusing first. Also check around for a thermal cutoff, probably present somewhere in the enclosure, which will fuse in the event of catastrophic overheating. Another beginning point would be the thermal feedback to the controller. If it's a thermocouple (likely) and the thermocouple is open, all heaters are made to shut down to prevent thermal runaway. If you can find the thermocouple, disconnect one end and ohm it out. If it's more than an ohm or so, you might want to see what needs to be done to replace it. Another possibility is that the thermocouple came loose off the surface it was measuring, leading to thermal runaway and the cutout of the thermal cutoff. Also, I'm not sure which model this applies to, but there's supposed to be an external plug which is supposed to be plugged in if you're going to provide an external temp control (I believe this is for an external RTD or T/C). Make sure that's plugged in if you've got the socket. The lit says that always has to be plugged in if you're not using it (it's a spare part if you don't have it). Once you've looked at these first cut checks, you'll have to get a meter and look at where the power is going. If the heater ohms out OK, and there's no busted fuses, you're probably looking at a problem with the temperature controller board or one of the connections. The connections should be easy to check with an AC voltmeter. The voltage drop will be where the resistance is. If you've got a bad electrical connection, there will be a voltage drop. Usually these will occur over time, which means you will see heat damage at the joint, splice, or connection. Play safe with the cover off and line voltage applied. Other than that, it's probably a controller board issue. Since it's a resistive heater and made for continuous use, you'll probably see a triac control, possibly with a series relay. If the problem isn't there, you'll have to troubleshoot the controller board itself. It would help to know what you're getting on the temperature display (nothing at all might indicate a power supply problem, a dead microcontroller or a shorted component on the controller board, a nonsense display might mean a problem with the microcontroller, and all lines on the display (- - - -), OT or OL might mean a problem with the thermocouple. I haven't worked with that specific model, so I don't have any shortcuts there. But the controller board is also a spare part, available from the manufacturer. I hope this general information is useful. Good luck Chris |
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