Ideal CK70 Boiler PCB

[Lion_Tamer]

Hi All

I have been repairing the control boards for this boiler after they were damaged by lighting, I have managed to get them going again but have an issue/question on this one that I can't understand.

In the circuit below I don't understand what the 7805 voltage regulator is doing, I expected to get 5V between its output and ground but instead there is 8.2V as regulated by the zener diode.

For info I have already replaced P1, Z2, U1, IC1, and the probe assembly containing the LM335 as these were damaged by the lightning, I have also replaced Z1, and Z4 and checked that all of the other resistors and capacitors test okay on a meter.

Thank you

Jem

[CJay]

I *think* it's configured as a constant current source but I could be wrong, are you measuring output with respect to the circuit ground or the terminal on the 7805?

[P90]

yeah, are you probing ground at pin of 7805?

[Lion_Tamer]

At the gnd pin of the 7805.

Jem

[CJay]

At the gnd pin of the 7805.

Jem

OK, so first check your 7805, you've not mentioned which variant it is, some of the plastic ones (I.E. not TO-220) can have 'odd' pin assignments and if you've changed from one to another it's possible it's not fitted correctly but, as the gnd connecton of the device isn't connected to 0V I reckon it's being a current source and not configured to be a 5V regulator.