Resurrecting a VWR Galaxy 14D Benchtop Centrifuge

03

VWR Galaxy 14D, back alive!

It had been advertised as “does not power on” and I got it pretty cheap on eBay, below 100USD including shipping from the U.S. to this beautiful country.  Assuming the usual culprits for a “complete failure”, when the cosmetics are fine: a broken switch or a blown fuse, it should have been an easy fix and a good bargain for a used item sold new for 1400USD.

But nope. Not really: After powering it on, the fan started, so it was neither the fuse nor a switch problem. Just the display kept staying dark and, of course, not any reaction when pressing any key.

Naturally, I decided to disassemble the dingy. First, I had to clean it: The plastic parts of the housing (including the a little bit dusty fan) went into the shower, the rotor went into dishwasher soap for 3 days.

First, I noticed a corroded micro switch which checks if the lid is closed, asking for replacement. An intermediate test to my surprise resulted in a working display and the centrifuge greeting me with a beep! A bad contact probably, I concluded. Thus, I proceeded with checking the connectors and the circuit board (PCB).

It took me some time to find out that there was a real problem with the power supply (although actually obvious: the controller module in the lid didn’t get any power, thus no display :) ). First I assumed it was in the mains, as there are some connectors which might have been faulty (inconsistent results when checking voltages with the DVM, but probably due to oxidized leads) and during measurements (i.e. touching solder points with the probes of my DVM), the display suddenly came alive again. I resoldered them, but it didn’t help.

02

Abrasions on the heat sink

During the further checks I noticed some abrasions at the heat sink which probably originate from a serious mishandling of the centrifuge (either a completely imbalanced run, a failure of many tubes during a run or the poor machine had been dropped). Actually, this must have been a pretty heavy impact, as on closer examination, I noticed that the whole heatsink was shifted. An impact, caused by the motor, had exerted a really high force on the semiconductors mounted on the sink.

01

Detail of the shifted heatsink

Then I began to check the semiconductors on the heat sink: Two voltage regulators (a MC7815C and a MC7805C) and several power FETs (IRF4905 and 532). The MC7815C  (35V (!!!) input voltage, 1A max) was measuring 0V at it’s output, so maybe it was faulty? No! I severed the lead to the PCB and the 15V were back. As the 7815 was feeding (not only) the MC7805C, I severed its input lead, too (after resoldering the 7815). Result: The 7815 was outputting 15V now. Now I resoldered the 7805’s input and severed the output. Result: Again 15V at the 7815’s output. The problem must be after the 7805!

Or in it: I resoldered the 7805’s output lead. Now the 7815 still was delivering 15V. At the 7805 there were 2.5V (with the controller as load 1.8V) . Strangely, I had almost broken off  the output lead of the 7805 during the test (probably it was already damaged by mechanical overload), so I’ll have to replace it anyway. Is this the clue to the problem? Result after replacing the 7805: Nothing. Again 0V at the outputs. I decided to replace also the 7815 with a L7815C which also accepts 35V input voltage (uA types will not survive more than 30V).

After the repair, the controller finally had power: The display lit up and it made “beep” again. The motor still was not working yet. Some more checks and finally I found that I had reconnected one of the micro switches in the wrong way.

Total cost: (8+8+20) NT$, somewhere between 1 USD and 1 Euro, for 2 pcs. 78xx regulators and a micro switch. BaDer-Rd in Taipei City (link) is my place for this (and one of the hubs this world is spinning around). Plus a few hours of measuring and reasoning.
Total reward: a practically new benchtop centrifuge for less than 100 USD.

During the following tests I noticed that the machine is very sensitive to imbalance (which might have caused the previous failure). The rotor is sitting directly on the motor axle. The motor is fixed to the base with 3 rubber dampers on its remote end, so the whole system is somewhat prone to oscillation. The rotor is hollow (in contrast to e.g. Thermo/Heraeus Picofuge machines), thus leaky or breaking tubes may cause a (sudden!) imbalance of the system which might result in disaster, esp. at a higher speed. If being able to acquire a new machine, I would not choose this VWR model, as a massive rotor, preferably made from re-inforced plastics, definitely is the better (and safer) option. One ruined experiment or even injuries and damage caused by a failing centrifuge may incur more cost and hassle than the money you need to spend for a really good machine (like the Picofuge), when you need to use a benchtop centrifuge for your daily labwork.

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6 Responses to Resurrecting a VWR Galaxy 14D Benchtop Centrifuge

  1. Kate says:

    Can you tell me where the fuse is located for this model. I have the same model that’s broken, I think it might be the fuse because the fan won’t turn on, can’t seem to locate the fuse though.

    • luan78zao says:

      Hi Kate,
      in my model, the fuse is accessible from outside without opening the case: Look at the connector for the mains plug at the rear of the machine. There is a small cover, underneath you’ll find the fuse in question. If it should be ok, have the cable and the switch checked.

  2. luan78zao says:

    Hi Kate, then there might be a problem in the mains transformers or a shortcut afterwards (supposing you have tried with an adequately rated fuse). Means that’s not trivial anymore and you might need assistance from someone who can dig into possibly unfamiliar circuits.

    Has your centrifuge failure just happened out of the blue or did you run into a mechanical failure?

    Any signs of burns/scorching inside the machine or evidence that the rotor has hit electrical parts?

    • Kate says:

      Supervisor and I were trying to fix the motor because the centrifuge won’t spin. We opened it up and saw the transformers didn’t look good, so we re-soldered it because we thought maybe there wasn’t enough power. Didn’t work, but centrifuge turned on with same problem where motor won’t spin. We pulled out the circuit board were the motor connects to and saw that it looked bad. Two soldering points for the motor completely burned off and the rest of the circuit board was crusted in some residue. I’ve soldered stuff before, so I re-soldering everything on the circuit board, the centrifuge turned on for a brief second and the fuse blew, now if you replace the fuse and just plug it in (not turn it on) it’ll blow every time. Found a fuse at Radioshack that fits the parameters of the original fuse.

      • luan78zao says:

        That’s strange. If the switch is off, the transformers should not get any power, what makes me conclude the switch is likely to be faulty. What you describe might point to corrosion. Can you maybe post a photograph of the circuit board if WP should permit?

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