Overtemp Light on constantly

Actually a very simple fix.  Before you turn the power on, set the "max temp" pointer to it's maximum position.  There are break beam sensors in the temperature meter and at power up you will see some deflection of the temperature needle and if it passes through the max temp sensor at all you will turn the light on and the ONLY way to reset it is to turn the power off, move the max temp pointer, and then power up again.  That should take care of it.

Thanks for the reply but I have tried setting the overtemp to 40 degrees first and then switching on. Same thing, light comes on immediately and stays on.

The start button does light up but when you press it the stop immediately comes on without spinning up the rotor.

Next is the rotor temperature sensor I suppose but where is it and how do I get to it?

W

Well, that was the usual fix for that problem. If the temperature sensor, the black nub sticking up in the bottom of the chamber, is the problem you will probably get strange temperature readings. If that is not the case then you need to be considering that the temperature meter itself has become defective as this did happen from time to time especially if the light emitting source for the overtemp sensor has failed which would give you the symptom that you are seeing. There is also nothing in the meter that can be repaired in the field so you are probably looking at replacing the meter or you may have a problem with the temperature control board which is the smaller of the two circuit boards located behind the black plastic back panel.

There were many, and I mean many, different updates done on this very old series of centrifuge and some of them indeed had to do with the temperature control system including replacing the old meter with a newer version that had LED's instead of an incandesant source for the meter sensors. I really don't know if Beckman is still working on this model of centrifuge anymore as it was obsoleted over 10 years ago and most of the old retired dogs such as myself have long since stopped either working on them or even thinking about them. Also, parts availability could be a major problem, especially for the timer. Your only possibility may be a "reputable" 3rd party service group in the area where you are located. I have no information relative to them so I really can't offer any guidance on that situation.

The temperature readings actually look good. The needle is steady and follows if the chiller comes on so I think sensor and meter are good.

What I need to know is why the machine thinks everything is fine, START goes green, but when you press it, STOP immediately lights up. There must be logic that checks a few parameters and decides if it should spin up or not.

How about the door switch? I can hear the latch locking it when START light goes green and then you cannot open it. The vacuum seems fine too, as does the chiller/cooling.

Maybe replacing all the logic chips on the PCB can work? A shotgun approach I know but maybe one has gone faulty.

Everything is not right since the overtemp light keeps coming on. I believe Don has it exactly right. You should truly consider his advice.

Guri

The failure of the MAX TEMP light source within the meter assembly would give you ALL of the symptoms you are seeing.  It is just the way the circuitry responds to the meter being defective.  Replacing the IC's on the control board, aka low voltage board, is probably a waste of time because there are just as many transistors on that board as there are IC's and the temperature control board is about the same.  My experience would be pointing me towards the meter first.  Beyond that, there is not much else I can do to help.

Don

Thanks Don, I shall check that light source and hopefully I can find a suitable replacement and get it going.

What is confucing is that the instrument "aparently" did spin up normally for a long time WITH the OVER TEMP light on! Or so the technician in the lab claims. What I saw in the manual that definitely should not be the case!

Thanks very much for the advice so far, it is much appreciated! Once the light source has been checked I'll report back.

Wynand

I believe you missed something in my post, there is no known way to easily check that source out in the field. For many years the meters were on an exchange part status that Beckman returned to the manufacturer for repair until LED technology became available. At that point the old meters were scrapped after being replaced with the LED source version.  There was also a modification that needed to be done in order for the new style meter to work but what that was I really can't remember anymore.  All of the "old" J2's I was responsible for got the updates back in the 90's so I never had to worry about them again.  I really don't see any way forward on this unless you can find someone that can supply you with either an old style meter or a new style one and the necessary update information, too.

Don

If the light source cannot be replaced easily that will be a problem and I understand that parts are not available. I am an electronic engineer though. Do you think I will be able to take the meter apart and figure out how to modify it? Surely substituting an incandescent bulb with an LED should be fairly simple?

I would hate to scrap a useful (if very old!) instrument because of a bulb failure.

Thanks for all the replies, it helps a lot!

I'm not trying to downplay your skill set about this and you are obviously free to try anything at all to try to repair the meter. I can only speak from experience that Beckman did not believe it was worthwhile of our time to try to make that repair in the field because of what was involved in getting the meter apart far enough to make the repair in the customer's lab. Not only that, the source lamp was never made available to us so I can't even help you with that information either. I wish you success if you are actually able to fix the meter and please publish what you did if you are successful in order to possibly help others in the future.

Don