Aristo Thermostat Adjustment

Discussion in 'Enlarging' started by Sundowner, Dec 5, 2018.

  1. Sundowner

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    I've just finished wiring a photodiode into my Aristo 23C head, and upon getting everything back up and running I've found that the housing gets screaming hot; after five minutes it's literally too hot to touch...and it never got that hot in the past so something is a bit off, somewhere. All of the wiring inside the head was labeled and reconnected correctly - and I know that resistors don't have a polarity, so it can't be "backwards" - so something on the thermostat must have gotten knocked askew. Just to check and see that the thermostat was working, I backed the adjustment screw out until the contacts were no longer touching; now the housing stays totally cool...so my intuition tells me that the thermostat is indeed functional, albeit badly tuned. I don't recall fiddling with that adjustment screw when I took everything apart, but it must have happened because there's no other way that it could've gotten out of adjustment. So...does anyone know how to adjust these things for the correct temperature, aside from trial and error? For that matter, what's the correct temperature? I took my other Aristo head apart (D2 model, from which I copied the photodiode circuit) but the thermostat looks to be set exactly the same as the one on the 23C head...but the D2 head only gets to a pleasantly warm temperature. Any help would be much appreciated.
     
  2. Chan Tran

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    What does the thermostat do? It shut down the power when it got too hot? How can it make things cool?
     
  3. OP
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    Thermostats regulate temperature-altering devices...and to the best of my understanding, this one works like all the rest: by shutting down the power when things get too hot. My guess is that the contacts spread when the ambient air temperature goes up, and reconnect when it gets too cool; I'm going to pull the housing back off my D2 and see if I can watch that happen, but even if I see that happen the settings won't directly correlate to the 23 head. That's why I was hoping that there was a way to check it electrically, or a way to manually get it close without going through a long cycle of adjustment/reassembly/warm-up/take-apart/readjustment.
     
  4. ic-racer

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    I had the thermostat in mine set around 40C. With the lamp on for 5 minutes (maximum allowed) the temp. rose to 44C with a diminished intensity of 0.5 stops. After 10 minutes temp. was back to baseline 40C.

    IntensityTemp.jpg TempRecovery.jpg
     
  5. OP
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    Okay, so you were seeing temperatures around 104° F. I didn't take a reading yet, but I would estimate that my housing was getting up to 175°+; it was physically uncomfortable to hold it. How did you adjust the thermostat? Does the 1212 have the screw--and-contact type, as well?
     
  6. OP
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    What I'm working with, for reference. Ignore the jumbled wires; I'll fix that at final assembly.

    Pictured: Thermostat.

    IMG_20181206_071113.jpg


    Pictured: Current contact setting.

    IMG_20181206_071147.jpg


    I tried to get a good shot that displays the contacts being spread, which is where I set them in order to kill the heat. As best I can tell the resistor is just wired across the main and generates heat when current is applied, and then it kills the heat when the contacts spread...so if there's no "here's how you set it" answer, could I do the following:

    With housing removed:
    1. Set the thermostat to be too hot.
    2. Plug in the heater cord and allow the resistor to start heating.
    3. Take temperature readings on the resistor periodically, and when it gets to somewhere around 40°C / 104°F, back it off until the contacts are barely spread.

    Would this get me "close enough" to prevent the overheating issue, perhaps?
     
    Last edited: Dec 6, 2018
  7. jnanian

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    hi sundowner

    i am sorry i can't help you but people who i know who made a similar adjustment
    put a probe into the light housing which adjusted the light source that way. As you know
    you have to plug in the light/heater cord for 1/2 hour before you intend to print with it
    and as it is being used the intensity of the light becomes brighter ( light output increases ) so you need
    to make adjustments in printing times. to be honest i have NEVER heard of anyone doing what you've done :smile:

    have you called / written aristo /voltarc to see what they suggest ?
     
  8. OP
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    Wait wait wait wait WAIT...I might have not explained myself well. To be clear: what I've done is to wire in the exact same kind of photodiode that Zone VI used to use, and that RH Designs uses now...

    Pictured: ...which are a complete pain to solder, if you suck at soldering like I do...

    thumbnail_IMG_20181204_195216.jpg


    ...which is nothing special, to my understanding. It's a basic Zone VI conversion. Sure, it took awhile to find the right part number for the diode, and I've learned that the entire arrangement is VERY sensitive to light levels (it gets thrown off by the presence or absence of the diffusion plate, or by sitting on a countertop, or just changing the direction you point the head) but I don't think it's anything special...but the diode is also not the problem. What happened is that when I put the whole mess back together, the thermostat stopped telling the resistor to shut off (I think) which is what's leading to the scalding hot temperatures on the housing itself. Like, you can actually smell the paint baking a little bit, which doesn't usually happen until you start pushing 200-ish degrees. So what I'm trying to figure out is how to set the thermostat back to wherever it's supposed to be set without a massive amount of trial and error (because it's a pain to take the casing off, make an adjustment, and then put it back together multiple times). Basically, I made a modification that worked perfectly, and everything I didn't touch started acting wonky.

    To answer your question: nope, haven't called Aristo...mostly because I didn't know they were still an entity that could handle stuff like this. I know that I can get in touch with Light-Sources for a new tube - which will also be happening, because mine looks a little worn, now that I've fired it up - but I didn't know they had any resources for the rest of the parts of the head. I'll have to touch base with them and see what they say, as well.
     
  9. OP
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    So, update: according to Aristo/Voltarc, there's no thermostat inside the cold light housing... :getlost:

    (Explanation: I wrote them an e-mail this morning, explaining the situation. They say there's no thermostat inside the housing, and that they've never seen anything like that inside the head. There was also some misunderstanding on their part regarding the resistor, because even though I said it was getting very hot, they seemed to think it needed replacing because it wasn't getting hot...and then told me not to try to adjust the temperature. I don't know how you adjust a thermostat that isn't present, but...okay. I also sent a picture of my D2 head with the same "thermostat" shown, but they didn't have a ready answer to that, except to say that the head should get very hot.)
     
  10. ic-racer

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    Here is the thermostat in mine, in the center. The 120V AC goes to the 4 power resistors that safely heat the unit. The temp I recorded is from the outside of the unit.
    I have also attached the PDF instructions that came with my unit.
    temp gun.JPG
    power resistors.JPG
     

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    Last edited: Dec 6, 2018
  11. ic-racer

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    Just re-reading your first post, just make sure you did not bypass the thermostat when you wired the resistors. Also, I don't know the wiring in your unit, but mine has two separate power feeds. A 120V feed only for the heater resistors and a 400V power feed only for the lamp. You would not want to interchange those two.
     
  12. OP
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    Yep...that's the exact same thermostat that I have, as shown in the previously-posted pictures. Same resistors, too! Thanks so much for posting the instructions; I like the fact that you have a switch for the heater circuit...I'll have to add one of those to mine while I have everything apart! I hate unplugging things!

    I think I have a way to set the thermostat; two ways, in fact.

    1. Plug everything in, wait for it to get to temperature, and then back the adjustment screw off to the point where contact is no longer made.
    2. Warm the entire unit in the oven until it gets to about 100-ish F (40-ish C) and then back off the adjustment screw in the same way as the previous idea.
     
  13. OP
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    No, it isn't bypassed...and mine actually has two separate power cords, as well. The 120v plugs directly into the wall (black cord) and the high-voltage feed from the transformer that goes to the lamp (grey cord) from the Zone VI stabilizer. I've also now backed the thermostat switch all the way out - you can see the separated contacts in one of the pictures I posted - and now the resistors never get hot at all...so I know it's working, and I know the resistors are working; now I need to get them working together!
     
  14. ic-racer

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    Seems like you should now be able to set it for an outer housing temp around 38 to 40C.
    If you need a new thermostat, the thermostat from a SEAL press will probably work ($130 from B&H). Also you could check out "Rice Cooker Thermostat" like this for $1.50 from Amazon.[​IMG]
     
  15. mshchem

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    1st thing I would do is get a blow dryer and heat the thermostat and watch it open and close. Something is allowing juice to get to the heaters.
     
  16. AgX

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    The OP has an assembly I assume tyically used in a coffee-machine (though not for boiling but for keeping hot), whereas ic-racer got in relation small resistors. I find that strange.
    But who knows, maybe that assembly was actually cheaper...
     
  17. AgX

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    But a thermostat does not brake, unless actually a bi-metal spring was broken, or the contacts burned, both is not the case. Worst thing that could have happened is springs having been bent, but that should be cared for by new adjustment.
    Or not?
     
  18. OP
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    I did almost that exact thing, but since I don't own a blow dryer I just plugged in the heater circuit and watched to see the movement...and let me tell you: it's microscopic. We're talking half-thousandths, here...but yeah, that assembly is definitely a thermal switch. Also, $150 for one is INSANE.

    Actually, they're the same pieces. His resistors and thermal switch look identical to mine...he just has four times as many resistors because he has that dope-as-f*** 12" housing.

    Also, here's an update: it's working perfectly now.

    Pictured: I even switched the setting to metric degrees, or whatever they're called.

    IMG_20181206_175208.jpg

    That's after ten minutes of preheating. I plugged in the heater circuit with the head at room temperature and then closed the contacts with the adjustment screw, saw the miniature contact arc, and started measuring temperatures and continuing to adjust the screw until I hit 40-ish metric degrees on the housing. Between that and reworking the mounting of the photodiode so that it's only about 1/16" - 1mm? - away from the tube, I'm now seeing stable light output all the way up to the second mark past "L" on my stabilizer! Also, no burning paint smell anymore...:D
     
    Last edited: Dec 6, 2018
  19. AgX

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    I was completely fooled...
    What to me looked lile a heating-element for a coffee-machine is in fact the lamp-assembly...
    Well, over here old cold-light heads are a rarity and that Aristo head totally unknown.
     
  20. OP
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    Evidently they're unknown here as well, because even the people that made it don't know that it has a thermal switch / thermostat inside it!
     
  21. mshchem

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    You got it. I've repaired big old lab hotplates, same basic set up. I have a couple Zone VI VC heads, I use the now no longer around, Metrolux II control, similar to RH design Vario. Dream machine . Good work!
     
  22. jnanian

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    dude
    aristogrid went oOb when rick retired IDK 10-15 years ago ...

    this is on their website for installation of the metrolux temperature probe
    https://www.light-sources.com/wp-co...cl4500_temperture_probe_installation_info.pdf
    ( it is the probe i mentioned previously )
    have you looked through the "archives" there to see if they have info on your light's schemiatics
    or when you called did you ask louise for a schematic diagram for the light that you have ?
    https://www.light-sources.com/solutions/specialty-fluorescent/products/aristo/aristo-archive/

    you probably already did this
    but there was someone on pnet a few years ago maybe doing something similar ?
    https://www.photo.net/discuss/threa...e-to-an-aristo-vcl4500-2-tube-vc-head.497807/
    you might see what they did and call louise ( maybe that is who you spoke with ? ) she was around when
    rick was there still ... and she might be able to help you with obtaining some of the parts you needed...

    you might also post your question over on largeformatphotography.info some of the same people are here
    but there are others on that site AND an archive there that might be useful. the old lusenet archive from the original
    large format site has some info too

    good luck !
    john
     
  23. OP
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    Oh yeah, I know they went tits-up a LONG time ago, which was why I posted here first instead of going to Light-Sources; as best I knew, Light-Sources only manufactured replacement lamps and had nothing to do with the mechanics of the head. After you suggested getting in touch with them I shot Louise an e-mail and looked through the archives...which was where I found the 23C sheet you linked and where I confirmed that the dingus I was dealing with was, in fact, a thermostat. That's why I got really confused when Louise e-mailed me back and said:

    The units did not have a thermostat but had one or two resistor bolted to the reflector plat.
    You should not be adjusting the temperature.. if the resistors have died- (no heat)
    then you need to replace them…the info printed on the resistors.

    That's a direct copy-and-paste quote from the e-mail. When she mentioned "no heat" I realized that I hadn't clarified my problem; I had just asked if there was a guide for adjusting the thermostat, and not told her that it was trying to melt itself from runaway resistor heating. Her response thus makes sense, but what doesn't make sense is her saying "you should not be adjusting the temperature" IF THERE'S NO THERMOSTAT. So, I sent her the same pictures I posted here, and I got back:

    This thing I don’t have a clue of what this is…..not apart of the Aristo products I knew …

    There was also still some confusion about why I wanted to turn the heat down; I had explained the issue thoroughly, but I think she was still under the impression that I wanted more heat on account of a bad resistor...so I honestly just kind of dropped it at that point and asked them to go ahead and build me a new lamp, because I want to make sure that the old lamp isn't causing unknown issues (this is all part of a massive darkroom rebuild that's focused on making sure that the only thing causing bad prints is ME). I was also getting some decent information here, that was actually addressing the questions I was asking.

    Regarding your other points:

    - I'm not that familiar with how the MetroLux works, but it does seem similar to the Vario. I have the StopClock Pro, and I love it.

    - I haven't seen that thread on photo.net, but I can sympathize with the guy that's trying to do the retrofitting; it took me several days to find the part number for the photodiode that Zone VI used to use...which is very similar - if not identical - the one that RH Designs uses, and then another several hours to find a place that carried those particular photodiodes in small quantities. Then I had to find three-pin DIN panel connectors, and then scrounge up some wire, re-learn soldering, modify the housing, test-install a photodiode, figure out what I did wrong and where it needed to be mounted for correct operation, interrupt all of that to fix my thermostat, and then finally finish it off last night. Exhausting!

    - I didn't think about posting on LFF; I just kind of lurk around there and occasionally buy things.

    Anyway, it's working well, now...and as it turns out, the Zone VI conversion is super-easy once you know what to do!
     
  24. jnanian

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    excellent !
    glad it worked out :smile:
    as i had mentioned i am clueless about conversions
    and knowing about neon/cold cathode lighting systems and
    how they work whenever i read about peoples messing with voltage &c
    it makes the little hairs on the back of my neck stand up .. the same thing
    happens when i read about people who decide they are gonna make their own
    silver nitrate from their spent fixer tailings or people using nasty chemistry
    and selenium toner where they prepare dinner .. im kind of a fraidy cat some respects
    but ill hang off a 15story skyscraper or be lashed on to a deadman and document clif faces
    of a quarry knowing the ledge might drop
    but then again i take precautions :smile: and the people who say they are gonna do these things just vanish
    im still here LOL who knows maybe they are taking portraits with the grimm reeper ?
     
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