Discussion Category: Centrifuge
Unit will no longer power ON
We've had the 5415R for many years. It seems that no one in the lab ever turned it off (it has always been ON). Well, I turned it off and unplugged it the other day in order to clean the rotor.
Now it will not turn back on. I've tried replacing the fuse (slow blow 6.25A, 250 V), but that did not work.
Is there anything else I can check? I did notice that the fuse holder had positions for two fuses, but only one was occupied (I tried putting in two, but could not get everything to fit back in when two were in place).
Thanks for your attention and help!
Reply byGood job Bryan! That's great!
Would you guive some images about the components in the PCB to locate easy in it? specially the 47k resistor that you suggest to replace.
Thanks for your help.
Reply byNice work Bryan, it would greatly help me and others too!!!
Ill try to do what you have mentioned!
Can you provide some pictures of the resistor and location if possible?
Thanks again!!!
Geords
Reply by
Posted By: Bryan Venema
Subject: Unit will no longer power ON
Message:
Solution !
I have an Eppendorf 5415 R that exhibits the same symptoms you describe. Thanks for the display board ribbon cable tip. That led me to investigate the circuit generating the voltage for the display board. The UC2844 Current Mode PWM Controller IC (between C816 and C824) is being powered from 155v through four 47k resistors in series. This is too much resistance as the UC2844 has an undervoltage lockout of 16v and when it tries to start the input voltage drops below 16v. The actual cutout voltage has some variation and the design seems to be marginal. The total resistance should be about 50k or so instead of 200k. I just shorted out three of the 47k resistors (leaving 47k remaining) and now it starts every time. This does put about .4 watts through the remaining resistor which is a little high but should be ok. If you want to be more thorough you could replace each 47k resistor with a 12k resistor putting only .1 watts through each resistor.
Bryan
From Bryan Guys!!!Reply byThank you very much! That is of great help! Is there any way you could provide some images of the resistors and location? I found the IC. Thank you very much.
Reply byHi, were you able to determine the location of the 47k resistors?
Thanks
Reply byI can't figure out how to paste a photo in this thread.
Email me if you would like an image of the resistor location.
Reply byI originally took down my post of the repair because I had to modify the repair but then never went back and revised it. The voltage is too low at 155v to power the UC2844 through the four 47k resistors so I shorted out three of the resistors to get it to start and it works fine and shoudl dissipate .4 watts through the 47k resistor. However, on my centrifuge the voltage jumped up to 320v (?) when the rotor got up to speed and then dissipated 2 watts in my 47k resistor. You can try using a large wattage resistor but you have tomake sure that you can dissipate the 2 watts of heat and the supply has to be able to continuously put 320v across 47k. I was uncomfortable with this so I made a simple circuit to short out three of the 47k resistors when the voltage is low but then open up when the voltage increases. I will email a .pdf of my memory of the kludge circuit to anyone that wants it.
Reply byI made a string of three resistors in series, each one equal to 15K ohms. I then put this across three of the four original 47K resistors. So I left all four of the original resistors in place. I only placed the new resistor string across three of the originals, because I could not get the soldering iron in the tight canyon to the end of the fourth resistor.
This has worked fine for over six months so far.
Reply byI have done extensive research and repair on these units. I can repair the Converter PCB. Very common problem with these units. Labor and parts will cost under $350.
Reply byPhoenix Equipment in Rochester, NY can repair these units for under $350