Hello
I am trying to fix parts of a 1980's hot water boiler that has failed in a house. It is the unit controlling the water mixing shunt actuator that has failed. The part is labeled "Landis & Gyr RVK 31.2". The servo actuator motor is controlled by the circuitry on the enclosed photo. I had to desolder the PCB mounted block transformer (220VAC/24VAC 1.5 VA, 63mA) that was hot and malfunctioning. (Transformer Output was 1 VAC rather than 24 VAC, Primary coil pins measure 2.7 kOhm, all three secondary coil pins show up as open circuit "OL").
According to all pin layouts I have seen online, these transformers have the primary coil connected to pins 1 and 5.
The secondary coil seems to be connected to pins 7 and 9 if only one secondary coil. If dual secondary coils, one coil seems to be connected to pins 6-7 and the other coil to pins 9-10.
The transformer I removed had only secondary pins 6, 9 and 10 present. On the PCB, pins 6 and 10 are connected to each other and one of the input pins of the full bridge rectifier. There is a trace on the PCB connecting Pins 7(pin missing from transformer) and 9 er to each other and the other input pin of the full bridge rectifier.
According to modern standards pins 7 and 9 should not be connected, no matter if there is one or two output coils.
Does anyone know if the PCB mounted transformers had a different pinout 30-40 years ago?
The output needs to be 20-24 VAC from the transformer to the full bridge rectifier.
I have ordered a 24VAC, single secondary coil safety transformer from Farnell (output pins 7 and 9 used):
https://no.farnell.com/myrra/44090/transformer-1-5va-24v/dp/1689052Pinout:
http://www.farnell.com/datasheets/92169.pdf?_ga=2.50384361.1589188987.1538948474-1149254780.1537819090&_gac=1.90504552.1538948474.Cj0KCQjw3ebdBRC1ARIsAD8U0V4HijGH86wsJAEbVPoETdlRsRD3iYxybcOJV3iW_7SPSfpHzI_6vAUaAmN6EALw_wcBMy plan is to cut the trace on the PCB between pins 7 and 9. The transformer output pin 9 will then lead directly to the full bridge rectifier.
Then I will solder a wire between pin 6 and 7. The transformer output pin 7 will then lead to the full bridge rectifier via pin 6.
Any thoughts if this is a way to go?