Thermaphot ACP 505 heat exchangers

When making colour prints for the first time for a few months (using fresh and unopened chemistry), I noticed the prints were appearing pale and balanced towards green-blue. Increasing development time to 120 seconds increased density as expected with a slight warm shift but demonstrated the developer and bleach fix were / are working correctly. However, on measuring the temperature of both the developer and bleach fix baths, approx. 20ºC was found in several instances over two darkroom sessions. The pumps for both baths were checked with plain water in-situ and are working.

The Thermaphot manual refers to 'heat exchangers' apparently used to 'save chemisty' however, I'm not entirely clear what the role of these are in this unit; i.e. whether they perform a heating function in this instance. The manual doesn't explain the logic or concept of the machine's operation.

As the Thermaphot ACP 505 operates a valve control for the three print washing baths which is apparently closed when no print is going through; it would seem difficult for the "chemical" baths to maintain a constant 35ºC.





The first image shows the two metal bars, connected to these are solution lines running from one side of each dev & bleach fix tank, through the metal tubes to separate pumps for each line and then back into the other side of the tanks. The off-white goo on the floor of the unit doesn't look as though it should be there and so may be related to the issue; however the could also be an issue with the control circuitry. Tempered wash water is provided by an external Intellifaucet.

I have been using the unit for processing B&W RC prints since the new year; prior adjustment of the controls could mean the baths have never (or not for a while) been at 35ºC / 38ºC. When I first started using the machine in autumn 2008 an amber LED would be lit until the temperature had apparently reached that indicated on the dial (e.g. 35ºC), however this LED stopped operating at some point earlier this year; I forgot to make a note of the date.



Tom.

Can't tell too much from your photo, except those disc shaped units under the clamp look like fixed thermostats. In the second photo, the wires leading into the end under the tubing could be power leads for a heater controlled by the thermostat. Is the white wire from the end of the tube the same braid covered wire going to the thermostat? The corroded looking stuff appears to be a leak from under a thermostat, which may mean the tubing is corroded thru, and took out the thermostat as well. Time to break out the tool kit.

Bob-D659 said:

Can't tell too much from your photo, except those disc shaped units under the clamp look like fixed thermostats. In the second photo, the wires leading into the end under the tubing could be power leads for a heater controlled by the thermostat. Is the white wire from the end of the tube the same braid covered wire going to the thermostat? The corroded looking stuff appears to be a leak from under a thermostat, which may mean the tubing is corroded thru, and took out the thermostat as well. Time to break out the tool kit.

Click to expand...

Bob,

I just had another look. Supported by the clamped rectangular bars, each line contains a circular tube connected to the solution line with another tubular component below; connected to the braid wires, running from the connector block to the tubular component and from the tube to the disc. The discs have some sort of white deposit on them that scrapes off. You may be able to see a slight browning of the braid covered wire on the disc end.

Tom.

Do you have a digital volt meter? If so unplug one wire from the disc units under the clamp and check for continuity, should be approx 0 ohms. Also check for continuity on the two wires going into the heater, which should be the lower tubular component. UNPLUG the unit first!!!!!!!!!! That at least will tell you if the heater or thermostat is gone. You will have dismantle the heater assembly to determine where the leak is. The slight browning of that high temp braid covered wire indicates a poor connection. It could be the crimp on connector, or it just might be due to burnt contacts in the thermostat itself. I'd guess the burnt contacts myself, due to the deposits on the outside, those units are not usually waterproof.

The heat exchangers are heated metal tubes that the solutions are pumped thru in the recirculation system of the processor. I believe you have photographed them in your first photo. They have heating elements imbedded between an outer and inner tube. They are not repairable. You should be able to determine if they are OK or failed by disconnecting each one and doing a continuity check on it. They will have some resistance if OK, and completely open circuit if bad. The only thing I have had fail was a pump. I was able to get a replacement, but it has been so long that I don't remember the parts vendor. These units used to be sold by Calumet, and when they were discontinued, I still called Calumet for a reference to a vendor for replacement parts. They were able to provide one at that time. AFAIK, at least on my processor, the wash tanks are not heated at all, just the developer and blix tanks.

Earlier Nutek made processors, sold under the Durst label had heating elements in the bottom of the developer and blix tanks and were not part of the recirculation system.

You can get replacement parts directly from Thermaphot: rkuemmerl@thermaphot.com Phone: 0049 911 277990

Schlger,

Thanks for that information. I have some more photos to post here showing the various components under discussion.

Tom.

Here are the photos:



The insulation has been pulled back to enable access to the connecting wires; resistance across the heater was measured at 185 Ohms.



The above components (one on each line) were measured at 0 Ohms.



As can be seen in the above image, the paste-like substance was or is sandwiched between the 'microtherm' components and the metal support bars for the solution and tube heaters.



The bare wire seen in the temperature control unit in the above image connects to what looks like sensor in-line with the pumped solution system.






Tom.

The Microtherm components are fixed thermostats, the white paste is standard heat conductive heat sink compound. They would be for overheating protection cutoff.

Bob,

Can you suggest any other tests I should carry out? Would the thermal paste have leaked out due to overheating?

Tom.

Measure the resistance of both of the heaters at the terminals on the ends of the wires with one end disconnected. 185 ohms sounds kind of high. Also measure the voltage on the terminals the heater is connected to. Without knowing the supply voltage, it is hard to determine a reasonable range for the resistance of the heating elements. Careful when doing this, you don't want to make any sparks.


The thermal paste would thin when heated, it is a suspension of zinc oxide in a light grease and if over applied it would drip off.

Bob-D659 said:

Measure the resistance of both of the heaters at the terminals on the ends of the wires with one end disconnected. 185 ohms sounds kind of high. Also measure the voltage on the terminals the heater is connected to. Without knowing the supply voltage, it is hard to determine a reasonable range for the resistance of the heating elements. Careful when doing this, you don't want to make any sparks.


The thermal paste would thin when heated, it is a suspension of zinc oxide in a light grease and if over applied it would drip off.

Click to expand...

I'm on UK mains voltage which is around 240V. The ACP505 does however contain a small transformer which I assume is used for the control circuitry.

Tom.

Ok, yes the thermal paste might drip off when over applied, it is probably just a suspension of zinc oxide in a light grease. That resistance measurement of 185 ohms of the heating element sounds way high. Try measuring again at the terminals at the end of the braid covered wires with one of the heater terminals disconnected. Also check to make sure the crimp connection to the wire looks good. You should also measure the supply voltage to the heaters when the heater is disconnected. That is needed to determine what range the resistance of the heating element should be in. For example, if the supply voltage is 12 volts, the element would only draw very little current and produce no heat at all. Careful here, don't short anything out.

Sorry about the sort of double post. If those are mains voltage heaters, that would explain the high resistance. Be more careful even.

Bob,

Each of the inline heaters are 230V / 250W spec. I wonder if an overly high mains supply voltage (say 250V) could cause the heaters to "burn out"...

Tom.

Well that resistance is about right for a 230v/250 watt rated heater, so I doubt they are burnt out. I'd trace the circuit back and see if some other component is "open", possibly like a fuse on a circuit board, or maybe that silver coloured controller.

acp 505

Hi Tom

I have been working with these machines for many years.
From what has been described, the heating problem does not seem to be the heat exchangers or the thermal cut outs. I would recommend testing the thermostat, the two mechanical relays on the thermostat board and check the ciculation!

Regards

Paul

Paul,

Thanks for your post. Did you repair the machines at one point in time? The circulation is working, you can see (and feel) the solutions (or plain water in the test case) coursing through the system.

Tom.

Some additional photos:



Above: the reverse of the thermostat board







Above: this component connects to a knob that controls the temperature of the developer and bleach fix baths. This device produces a mechanical 'click' sound when the knob is turned through a certain point.







Above: I'm not sure what this component with the screw is.

Tom.

Tom, the last device is an adjustable resistor or potentiometer. But in contrast to the more common ones it is not of the radial but of the axial type.
The use of a threaded spindle allows very precice adjustments. It is called Trimpot.

Hi Tom

I have and still repair these machines and all the Thermaphot range and other processors all around the uk. The trimpot is to adjust the voltage to the heating fan(23.5 volts.) Your heating problem could be one of the relays on the thermostat board. When you switch the machine on the mechanical relay should make contact and by turning the thermostat until it "clicks" the relay should disengage. On initial warm up the voltage at the heaters should be 240v, and once up to temperature this reduces to 80v. I hope this helps and good luck. I can supply any parts needed.

Paul S

Above: this component connects to a knob that controls the temperature of the developer and bleach fix baths. This device produces a mechanical 'click' sound when the knob is turned through a certain point.







Above: I'm not sure what this component with the screw is.

Tom.[/QUOTE]

An update: On Thursday I rebuilt the Thermaphot and the temperature control works! The control knobs are out of calibration but apart from that it seems to be OK. On to the replenishment pumps...

Tom

Hi guys!
Please help me! What capacitance is the yellow capacitor???

Maybe has a scheme?

It should say so on the capacitator itself, even if in coded form.
Or did yours burst?

AgX said:

It should say so on the capacitator itself, even if in coded form.
Or did yours burst?

Click to expand...

Chip is burned(