Discussion Category: Centrifuge
"Lid" Error Message
I just got my machine running a few minutes ago after a minor circuit breaker repair. For some reason I keep getting the LID error after running the machine at 3200RPM for a couple minutes. The lid is well secured as far as I can tell.
Any ideas what the reason might be for this message?
Here's what happened...
With Lid open, pin 10 reads 4.82VDC and pin 11 reads 4.96VDC
With Lid closed, pin 10 reads 4.82VDC and pin 11 reads 4.96VDC
Am I correct that chip U20 must be replaced?
Is there any upwards play in the lid when it's closed? If you lift up on either corner does it stay tight, or can you hear a click from the latches? Is the emergency release cord tight? There should be a bit of slack in it. Are the release arms on the sides of the latches parallel to the latch cases? If the temperature set point is below ambient, does the refrigeration turn on when you close the lid?
If everything is ok mechanically, how do you feel about some electronic troubleshooting? With the front cover off and laying on the table, looking down on the circuit board, in the far left corner you'll see a flat ribbon cable with a blue connector coming into the board, labelled J8 KBD. Pin 1 is at the far end where the J8 KBD labels are. Counting towards yourself from pin 1, to the right of pins 6-10 you'll see two IC's, first U21 and then U20. To the right of U20 you'll see three circular pads labelled TACH, GND, and 40HZ. Looking at U20 you'll see a dimple in the far right corner on the top of the IC - on the circuit board to the right of the pin at that corner you'll probably see a number 1 printed also. That's pin 1 on the IC chip. Counting to the left you'll come to pin 7 at the far left corner, then coming across to the near left corner is pin 8, and counting to the right you'll come to pin 14 at the near right corner. Pin 7 is ground (GND) and pin 14 is supply voltage (5VDC). Check that you have 5V from pin 14 to GND. Be careful you don't short to a neighbouring pin with your meter probe.
The lid signal comes into U20 on pin 11, and out on pin 10. Whatever you read on one should be the opposite on the other, so if pin 11 is logic high (5V), pin 10 will be low (0V), and vice versa. When the lid is open pin 11 should be high, when closed it should be low. Again, be careful you don't short to a neighbouring pin with your meter probe. With the lid open and pin 11 high, pin 10 should be low. With the lid closed and pin 11 low, pin 10 should be high. (If somenone can help you with this, hold the meter lead on pin 10 and have your helper open and close the lid for you, and you'll see the change of state on your meter real time). If that switching isn't happening then U20 is faulty. If it is happening then the microprocessor may be faulty. That'll be the big IC mounted in the socket on the near side of U20 and 21, with MC68HCP11A0P printed on it. Of the two, it would be better if the microprocessor is bad as you don't need to do any soldering to replace it.
If you want to go there and a chip is bad, make sure you remove all power to the machine and ground yourself by touching a bare metal point on the machine frame before disconnecting the board connectors and handling the board. Ground yourself repeatedly and often when handling IC's. Use a small flat blade to pry the chip out of the socket, and put the new one in by setting the pins of one side just into place in the socket, and pressing the IC slightly against them as you rotate the other side down into place.
When searching for IC's you don't necessarily need the whole number - MC68HCP11 and MC74HC14 will be enough to go on. The IC's you're looking at are old and have been superceded a few times. Just make sure you get DIP (dual in-line) replacements, and not SMD (surface mount).
I ordered a set of new interlock switches and spent my day rebiuilding the latch assemblies. I set my machine to 1500g and waited for something to happen.
After about a minute the damned LID error came on again and the machine slowed to a stop.
I think I'm at a loss at this point.
The connector pins appear tight at the latch connectors as well as the circuit board. Latch mechanisms are working well. The switch attached to the solenoid makes a noticible "click" when pressed. The switch attached to the connectors - do not make a noticble "click" at all. The interlocks are engaged equally when the lid id closed and the eyebolts are currently at equal length.
I just got off the phone with the folks at Ozark. Nice people. They did some quick troubleshooting with me and determined that the issue is most likely stemming from the interlock switches. A have a pair on their way. We'll see how this plays out.
And before you throw it out, try ThermoFisher tech support or Ozark Biomedical. They'll both have more experience than me.
It's been over 10 years since I had a latch issue with my machines so I can't remember every step of the process I had to take then, but ultimately I did have to replace a latch assembly. The switches in the latch are made by Marquardt, and I ordered some p/n 1117.0201's but I don't remember if that was an original or a sub. I'm also looking at p/n 1116.0105, which doesn't come up on their website. You could contact them if you have something different.
It's strange you can't get a meter reading when it will work up to a certain speed. Are all the connector pins tight at the latch connectors and the circuit board? I've seen the socket pins spread open and need to be squeezed back together. You can also clean them with a needle file to ensure a good contact.
Do you have the latches open? Are the mechanisms moving properly? Are the switches clicking over when actuated? The switches themselves can be taken apart by carefully separating the shell with a small flat blade screwdriver, and the contacts acan be burnished. Take it slow and mind the spring on the 1117's - they're a bit tricky going back together but a 6" steel machinist's ruler helps to hold everything in place while you set the other half back in place.
When you close the lid are both interlocks engaged equally and simultaneously? Are the lid eyebolts adjusted equally?
Thanks for your responses thus far. The notes have been extremely useful.
The service manual suggests testing the resistance between pins 2 and 6 on each of the interlock switches to determine if they're working properly. I can't get a reading at all, with the lid up or down which is concerning. I have a feeling that these interlock switches might need to be replaced. A quick google search turned up a few sources for replacement interlock assemblies but they are seriously expensive. Is it possible to replace only the switches as opposed to the entire assembly?
I can't seem to find a replacement part # for the switches. medphysteo, you seem to have more experience than most with this machine. Any suggestions?
This machine is headed for the dumpster if I can't come up with less expensive fix.
It's an older version of an AMP Universal Mate-N-Lok single row 5-position wire-to-wire connector. Current versions are 926299, 770016, and 770019, all of which may be followed by a -1 or -3.
You've probably got an electronics supply place locally that can supply or source them for you. Or you can get them on line from Allied, Mouser, or Digi-Key.