Thermaphot ACP 505 heat exchangers

[Bob-D659]

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.

[Tom Kershaw]

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.

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.

[Bob-D659]

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.

[Tom Kershaw]

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.

[Bob-D659]

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.

[paul s]

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

[Tom Kershaw]

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.

[Tom Kershaw]

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.

[AgX]

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.

[paul s]

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]