Malfunctioning kiln controller

[arte.sea]

Hi everyone,

I am complete novice with electronics and attempt to fix a very old (1981) kiln controller.

This controller was already worked on by someone and work is not exactly professional. Generally device works, it shows valid temperature, it can be controlled from keyboard etc. the only problem is: Instead of solid bursts of power to coils inside of the oven it produces bursts of pulses about a second (on/off) each. This is not a correct behavior for this type of controller.

Power to kiln coils is triggered using 2-stage relay system: A smaller relay inside of the controller triggers larger relay inside of the kiln. Small relay has 24v DC coil voltage, the terminal points coil are marked with yellow square on attached pic.

When I look at electronics I see HEF4528BP Multivibrator that, if I am correct does precisely what it supposed to do and relay is triggered in precisely same frequency as output of HEF4528BP.

Is that some kind of system where central CPU delegates actual heating logic to external IC?

Please see attached pictures, as mentioned I have outlined relay coil terminal points in yellow and temperature probe input in green.

Thanks

[ebastler]

It seems that the company which designed that controller is still around; http://www.hermes-electronic.de/. Maybe worth a try to ask them for a schematic?