Yes there is a relay that could be sticking, it's a big one on the back of the machine, visible by taking the back cover off, along the top edge of the upper half in about the middle. Are you seeing Fault 7 when it shuts the run down? My initial suspicion there is the refrigeration system, but with alternatively overheating and overcooling it could be something else. I had the 5V power supply fail on one of mine and it made the compressor go snaky, hammering on/off rapidly, because the logic wasn't getting the right supply. The 5V supply is also on the back, behind the cover, top right corner. You should get 5.2V, anything even slightly less is faulty. I never definitively connected the Fault 7 with the 5V supply, but the compressor problem was for sure and I've been told by a highly experienced Sorvall tech that the 5V can cause all kinds of weirdness. There's a service manual linked under Product Details to the left under the machine photo, and I've sent a larger one with circuit diagrams and parts to the site to post with it. The OEM 5V supply is a Fortron/Source SU40P31L-AZ. I used an Artesyn LPT42 - exactly identical.
Thanks Kaylee and Jeff. The manual was very useful. The flow charts indicated it was Relay K101 the large one to the left of center near the top. It was stuck in. I wiggled it and it came out partially, allowing the compressor to cycle normally, but the fan stayed on. Some more wiggling and it came out all the way and seems to be cycling normally. Is it kosher to put some WD-40 or 3-in-1 oil on the slide?
Jeff - I wasn't getting any fault number. I did do a diagnostic from the manual and found both temp sensors were reading correctly. I looked for the 5V output but only found ~12 volts on two of the pins I checked, and zero on the other two. Does it need to be spinning to get the 5V or did I miss the correct contact or board?
Finally, does anyone know if the K101 relay is a generic part still available (and where) or was it specific to these centrifuges.
Thanks again. Ron
You're welcome, Ron.
Here's the spec sheet for the low voltage supply, with pin-outs. You should see 5V as soon as you power on the 'fuge.
I've never replaced K101 so I don't have a cross-reference for you, but I think it's a common 24V power relay. You should be able to get an ID off the relay itself. Probably Furnass or Potter & Brumfield (now Tyco, I believe), PRD-11DY0-24 maybe.
I did find the 5 V pin - it was putting out 5.08 V on my cheapo meter, and since all was working ok after WD-40 on the relay, I figured if its not broke, don't fix it. There is a little screw next to it that I'm assuming might adjust the voltage?
Thanks for the info on the relay - I'll look at it again. Thermo (or whoever owns them now) wants over $400 for it, so if I can find the part elsewhere, that would be great. Seems to have two outputs, one for the compressor (all in) and one for the fan (all in and partially in). Don't know if that's on purpose or just because mine is getting stuck halfway out.
VR1 does adjust the output, so if you can get a clean 5.2V or better go for it. If you can't you can try replacing all the aluminum electrolytics and adjust for 5.2, it worked for me. Otherwise you're only out $42USD for a new supply. You will have trouble with 5.08V.