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5417 C Eppendorf Lab Centrifuge: not working, LEDs blinking

DANGER: THE ENTIRE BOARD IS EITHER LIVE 120V, OR FLOATS AT 170VDC!
If you don't work with such things daily, don't mess with this pcb while it's plugged in.

For the NON-CHILLER version, remove the four side screws, and the entire housing should come right off. If not, turn it upside down and note the rusty crust that's gluing the metal frame to the plastic! Slide a knife, or pry to break the bond. Then invert again, lift the housing carefully and reach inside to remove the ribbon cable from the PCB (pinch the plastic connector sides to release.) There are also two ground cables and the release-string to remove. (Also note, if you want to remove the main PCB, must unscrew the four screws on the BOTTOM of the centrifuge, not the four screws on the PCB itself.

I've now seen more than one 5417C Eppendorf lab centrifuge with the same problem: sudden death after power had been turned off (or, it died right after a local power outage.) No fuses blown. The LCD remains blank. Sometimes the LEDs for "OPEN" and "SOFT" start blinking rapidly. The +5VDC is missing, or giving crazy pulses and never rising up to 5V.

The switching supply for the LCD assembly is repeately restarting: a giant 2Hz sawtooth on the input to the +5VDC regulator. Simple cure: on the main PCB inside, replace a tiny 22uF 35V capacitor labeled "C824," next to IC UC2844AD (switching supply controller chip.) This fixes an apparent problem of slow-aging of the "boot circuit" in the switching supply. The 22uF has dried out and decreased below 5uF, so during power-up, the DC supply cannot wake up before the boot-voltage decreases below 10V. (Yeah right, "simple" cure. Only have to disassemble the entire unit to get to the bottom of the circuit board. SEE PHOTOS BELOW.)

NOTES AND TRICKS:

• Sometimes these units will start up if you unplug the LCD/buttons cable, turn on power, then plug the cable back in. But in older units this requires removing the plastic case! (In newer units the LCD assembly pops out: remove the little side-plug hidden below, and pry. SEE PHOTOS BELOW.)
• To access the LCD/Buttons (newer models only,) find the white plastic plug in the ledge below the LCD, over on the left. Remove it, TURN POWER OFF!!!, then use a tiny philips screwdriver or a 1/16" allen wrench to push out that entire side of the LCD assembly: insert the metal shaft 1" or more, then pull the tip forward. The whole thing pops out. (Do this with power off, of course!) Also, when removing the entire centrifuge cover, the ground-strap on the LCD can easily be unscrewed through here.
• To get to the main PCB without removing the entire cover and case, first remove the motor's round plastic cover inside the rotor-well, plus the four large leveling feet on the bottom of the unit. Unhook the white string at the bottom left corner of the unit (the rotor release cord,) then tilt the entire motor assembly upwards. Don't pull on the wires inside. Also, don't forget about the "rotor detector" that was under the round motor cover (easy to let it slip inside and not re-installed later.)
• If removing the entire door, take a photo of the shaft/springs, otherwise you'll forget how they mesh together. And, DON'T INSTALL THE COVER BACKWARDS.
• If removing the entire case, don't forget to replace the string and white plastic plug, otherwise nobody can manually release the cover latch.
• If removing the entire case, yes, you must first disassemble the door hinge assembly and remove the steel shaft (remove the snap-ring so the shaft can slide slightly. Don't lose that snap ring!)