Discussion Category:  Centrifuge

"Lid" Error Message

Hey all,

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?

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Asked by

mrwright
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avatar placemarkReply by
medphysteo

I don't know what to say to that. By unplugging J1 from the board you have electrically isolated both latches from the rest of the machine. Unless there is a wire inside one of the latches that is pinched so badly that the insulation is broken and a strand of wire is making contact with the housing, while at the same time the same thing has happened with the neutral side of the power line somewhere inside the machine casing.

On my machine both latches have a tab attached to the emergency release arm pivot, where a ground wire could be attached (I'll send a picture to your gmail). Does yours have a wire at either location? The insulation would either be green, or green with a yellow stripe spiralling around it. If there is you could pull it off and see if that changes anything.

My only suggestion other than that is to dismantle the whole machine again and make sure there are no pinched wires anywhere. Sorry to make you go there again, but what you're describing shouldn't be physically possible.

Jeff

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avatar placemarkReply by
mrwright

Yes, that is exactly what's happening.

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avatar placemarkReply by
medphysteo

Okay, let me see if I've got a bead on this.

With the machine unplugged and J1 pulled from the board, you get an open circuit (OL) across pins 1 and 2.

With the machine plugged in and J1 pulled from the board, you a short circuit (0) across pins 1 and 2.

So if you unplugged J1 from the board, inserted your meter leads into the side of J1 where the wires go in, and plugged in the machine power cord you would read a short circuit, and then if you unplugged the power cord you would read an open circuit?

Jeff

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avatar placemarkReply by
mrwright

I am measuring across pins 1 and 2 of J1 with the harness removed. Should I be measuring the female connectors in the harness itself? Even so, I get no reading.

And to clarify, what I meant by no reading is that the multimeter displays "OL". This is what I get when the machine is unplugged from the outlet. If I plug the machine in and measure across pins 1 & 2 of J1, the multimeter displays 0.00

-Chris

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avatar placemarkReply by
medphysteo

You should have the machine turned off and J1 unplugged to measure across pins 1 and 2 of the connector you unplugged.

What exactly do you mean by "no reading/resistance"? (sorry, I meant to ask you that on an earlier post but got sidetracked). Are you getting zero ohms with the lid either open or closed, or are you getting "OL" (or however your meter shows an open circuit)? Is there a numeric reading, and does it change when the lid latches?

Jeff

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avatar placemarkReply by
mrwright

I've attempted to measure the resistance across pins 1 & 2 on J1 with no luck. When I attempt these measurements with the machine off, my multimeter does not detetct any resistance.

When I plug the machine in, I get a reading of 0.00 on J1. 

This is ultimately why I thought the interlock assemblies might need to be replaced but that hasn't addressed the issue. I feel like I've come full circle.

-Chris

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avatar placemarkReply by
medphysteo

Assuming the switches are opening/closing with the lid (J1 pins 1 and 2 as per  p37-38 in the service manual) then yes, U20 is your next step.

Any one of these will work for you:

http://www.newark.com/webapp/wcs/stores/servlet/Search?catalogId=15003&langId=-1&storeId=10194&st=MM74HC14N&pageSize=25&showResults=true

The link you have above is a surface mount version.

(Optional - you might want to grab a socket too:

http://www.newark.com/harwin/d0814-42/connector-dip-socket-14-way-pc/dp/91K6952

The notch in the socket goes to the pin 1end of the chip)

If you have cutters that are small enough, cut the body of U20 off the pins first, then heat each pin and pull it out with needle-nose pliers or tweezers, then remove any solder left in the holes with a  vacuum desoldering tool or braid.

http://www.newark.com/desoldering-guns-pumps

http://www.newark.com/desoldering-braid

Then solder the socket in, then put the new chip in the socket.

Jeff

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avatar placemarkReply by
mrwright

Jeff,

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?

-Chris

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avatar placemarkReply by
medphysteo

Chris,

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). 

Jeff

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