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Some questions for my fellow Jobo users

twelvetone12

Member
Joined
Feb 16, 2015
Messages
762
Location
Over the Alps
Format
35mm
So sorry if these may sound a bit stupid, but I could not really find more detailed information on the net. I'm using a JOBO CPA2 from last century which despite the beating works (kinda) perfect and keeps the temperature perfectly spot on.

1) Temperature keeping. I regulate the temperature until che chemicals in the bottles (full to one liter) are at my desired temperature and stable. But I noticed that the tempering bath then is always a couple degrees hotter - is this normal? If I set the tempering path at a perfect 38 degrees, for example,the chems inside the bottles never reach 38. Does this risk temperature fluctuations when I pour it in the tank?

2) How much water in the tempering bath? I fill it so the bottles are submerged, but then filling the reservoir under the tank lowers considerably the water. Should the water be measured to cover the tanks and the upper reservoir? The manual is not very clear on this and I don't want to flood the electronics.

3) Keeping of the tempering bath. How do you guys clean up the unit? I am very careful not to spill anything in the tempering bath, but it still gets very disgusting very fast. if I empty it it leaves a thick chemical residue. I regularly disassemble the unit and wash all the plastic parts with warm water and soap, is this the right procedure? Also, how much do you keep the tempering bath? Is these something that needs to be added to the water?

Thanks!
 
I have had a CPP-2 since the mid-90's, but close enough...

1. I'm sure there is some allowable fluctuation in the temperature of the bath that's still within manufacturer tolerances. I process mostly B&W film on mine--35mm up to 8x10--and I've never concerned myself with the actual temp of the bath; I just make sure my developer is at the correct temp using a thermometer. Btw, it has always been at whatever temp I have set on the dial. Also, I'm sure there are minor fluctuations in temp over the entire process; more important with color developing than what I do.

2. Mine is 18L. I believe the CPA-2 unit is the same size as mine. When filled with the correct amount of water and with the pump running, the bottles are about 1/2 submerged.

3. There is something that can be added to the water, per Jobo's recommendation, if you leave the unit full, but I just dump mine and let it air dry when I'm done. Clean it? Why would it need cleaning? I keep mine covered between uses to keep dust off it and haven't cleaned it in 20+ years of use.
 
Filling instructions for the CPE-2 say:
"The tempering bath must be filled with water. Add water until it reaches approximately the shoulder of the bottles in
the bath. Be sure the water level is high enough to bathe the mounted tank or drum with water (1/8" to 1/4" or 3 to 6 mm, above the tank bottom). Do not adjust the level too high or the non-motor end of the tank or drum will float."
​
On the topic of cleaning:
"The water in the tempering bath should be changed regularly to prevent buildup of algae. Depending on local conditions and water quality, this step may be needed weekly or even daily. For best results, drain the tempering bath at the end of your processing session. Avoid getting water into the motor head (electronics box) when draining the processor.
The inside of the tempering bath should be cleaned periodically to remove any buildup of scum."
​
On the subject of temperature:
"Always monitor for correct process temperature in a bottle or graduate containing chemicals or water. The trough temperature will be several tenths of a degree higher than the temperature maintained in the bottles or graduates. Monitoring the temperature of water or chemicals poured out of a tank or drum, or coming out of the JOBO Lift drain hose, is not an accurate indication of the process temperature.
The temperature of the actual process (inside the tank or drum) is equal to the temperature stabilized in the bottles or graduates, not the temperature of the trough or post-processing effluent."​
 
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I fill the tempering water to cover the shoulders of the chemical bottles.

I wait until the chemicals and the bath have stabilized which can take some time.

I empty the tank when I am finished processing. I do not store water in the processor.
 
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