J2-MI lid release

First, the high voltage issue on a J2-21 centrifuge does not apply to a J2MI centrifuge.  Electronically and mechanically with respect to the drive assembly, they are totally different centrifuges.

The speed diagnostic is the result of the drive not spinning which therefore does not generate any tach pulses.  Your issue is more complex than the previous discussions.  First, with the lower front panel removed, do you see the LED's on the three switch boards cycling off and on?  If they are not cycling then the circuit board that controls the drive power transistors is defective.

You said that you checked out the switch that contacts the eyebolt.  The switch may be check good but is it coming in good enough contact with the eyebolt so that it actually actuates when the eyebolt comes down on it?  You can check this out by removing the latch cover and actuating the micro switch with your finger or a small screwdriver while hitting the start button.  If it starts, then the switch needs to be repositioned slightly.  Also, you should see and hear the latch engage if there is good contact when you manually actuate the switch.  You did not say whether or not you checked out the other microswitch that is hidden under the top cover that is part of the door latch interlock system.  That also needs to be checked out.

Start with that stuff and get back to me.

Don

Ah, the ol' hidden microswitch trick. It's good as well. I dismantled far enough to trace the cable to the 4-pin block inside the lower front cover, and got continuity across the two contacts with the lid closed. The solenoid coil is good as well (about 100 ohms).

I see two LEDs on each of the three boards, one near each end, and they are all solid off. Just for fun I measured about 126VDC from the red test points in the middle of each board, to frame ground (and about 61VAC, if that matters).

Jeff

Is the circuit board that controls the drive power transistors the one that the three boards plug into?

Jeff, The circuit board next to the three switch boards is indeed the controller for the switch boards.  There is a push button near the rear of the board that if you push it down once, it will put the boards into a cycling mode such that all of the LED's should turn off and on in sequence and the speed display should read 210 but don't be surprised if it bounces around a little.  That will at least tell you that the controller circuit is functioning properly.  Check it out and get back to me.

Don

Hi Don,

The pushbutton did give me a speed display of 220, but there was no response from the switch boards LEDs.

Jeff

Jeff, The fact that you get the frequency display leads me to believe that the board MAY be OK but the fact that the LED's do not cycle also concerns me. Obviously with the power off, slide the electronics chassis out and remove each of the three switchboards. You will see that each board has two power transistors and some associated circuitry which includes a fuse for each transistor circuit. Check out the fuses to see if they have blown. If they have, you then need to check out the Darlington power transistors with a digital multimeter to see if they have shorted out. If they have, then you can either replace each one or replace the boards. The transistors are the cheaper route and I have only very rarely seen any of the associated circuitry fail but anything is possible. Good luck and get back to me.

Don

Don, the fuses are all good, no dead shorts on any transistors (but some very low readings, 0.106 on the diode check function). There is a thermal breaker on the brake resistor that's open though.

Jeff

Jeff, Well, at least it sounds as if your switch boards are good.  What concerns me is why the switch board LED's are not cycling.  You may indeed have a defective control board or there may be a problem with the electronics chassis.  They were problematic for quite some time and had updates done over the years if the centrifuge was under a service agreement.  If I had access to a service manual troubleshooting section then I could help you more but I'm kind of out of ideas other than the board that controls the switch boards.

Don

Thanks Don. I think I'll try the shotgun approach; with nearly everything in sockets as they are it won't be too difficult. Which reminds me, years ago I had a GS-6R that took forever to speed up, and wouldn't go any faster than about 2K rpm. When my troubleshooting broke down I resorted to the shotgun without success and finally ended up replacing the board, which solved the problem. I've still got the old board; have you got anything in the archives on that one? It'd be nice to have a working spare for the two GS-6's I still have.

Jeff

Jeff, Sometimes the old shotgun approach is your only recourse.  Again, it's kind of difficult to deal with a problem like yours without actually having eyes on the centrifuge.  I certainly wish you luck and the next time I get back to where I formerly lived, I will try to dig out my old paper service manuals to find the troubleshooting charts that were very informative.

As to your GS6 issue, I don't really have any input on that one without looking at the schematics.  The biggest issues that I ever had with a GS6 series was with worn out brushes, a loose tack wheel in the bottom of the drive, and occasionally a bad SCR pack.  Again, I can dig out my old paper copies to see if I can help you with this problem too.

Don