Hi,

you should check if there's the Standby Supply of 5V. This voltage is used by the microprocessor to scan the keyboard and sitsching the relay on or off.

So check across the 1000 µF capacitor (position 3B) if you get ~5V. The negativ connection of the capacitor  is connected also to the middle pin of P3 which is ground for all the voltages. Also on P4 you should measure around 5V.
The IC3 is the standby voltage regulator giving the 5V standby voltage.
The relais is always connected to the 5V Standby via the 47 Ohms resistor. the 'low' end of the relais is driven by the transisorTR16 to ground by a 'high' from the µP to the base of TR16 via R180, R181, R182 and C111. this High signal comes via wire 104.

The wire 103 has a different purpose: The µp can switch off the standby powersupply (IC3) if the relais is activated and the main powersupply is active.Then the IC2 (LM317, position 6D) produces the main 5V
So across the 6,2v zener diode D5 (position 6D, see page 24 of the manual) there should always be around 5V as soon as the century is connected to the mains. This enables the µP to run 🙂

Hi

Thank you for all these details and as I do not have a paper version of the schematics I missed totally the microcontroller.

All 5v from T1 are ok

Then I exchange the transfo with knowing good and no change.

Then I exchanged the N° 5 board and the century woke up so it somewhere in the PSU board.

Then I checked what plugs where needed to test the PSU board and P9-P15-P16 and P8-P13 of course.

Will do more digging into the PSU N°5 tomorrow.

T

Hi

I have also switched transformer from a working century and same no power.

I do not have 5v on diode D5 and tracing back I have no ac 14v power coming out on P13-7 and P13-8 and ground ok on p13-4

Will switch transformer again to be Shure.

What do I not understand in these PSU's...

I have never been good in PSU repair. It's a hobby for me and what I repair most is smartphones, no PSU on the motherboard ;)

Ok just tested d20 location D4 

No voltage and on the working century we get almost 5V

IC1 11 is supposed to delivers these 5V but it looks like IC1at E3 is not getting power niether.

I am still lost, who in hell is giving the primary power.

You are looking at the wrong place.

This place is active when the century is switched on but for the standby supply you have to look around IC3!

At P9-2 and P9-2 you should always get an AC voltage of around 14V! This will be rectified with the 4 diodes and the resulting DC voltage will be smoothed with C42. This is the raw supply voltage for IC3 at PIN 8. IC3 should be active in standby, controlled via PIN2. If the IC3 is functioning _and_ active you should get the 5V Standby at R37 (47 Ohms). The reference for Ground you shoud take is P9-3 for all i said before.

To control the activity of IC3 the parts around T29 are used and everything will be controlled via wire 103. If the wire 103 is active there should be around 5V. If the µP switches the whole system on it will be near 0V.

All described here is the standby supply of the century. it's only for the µP _and_ to switch the relay (via wire 104) if the century should be switched on.

If the system is switched on, the other parts on Board 5 get their supply voltages and you should get the measurements you expect there i.e the 14 V AC you are missing now at P13-7 and P13-8.

If IC1 doesn't get 5V at Pin 16 you could check the fuse F6 at the 6.2V zener diode (both position 6D) for continuity (zero ohms). If this fuse is blown the µP doesn't get the standby 5V but then there's something else which caused the blown fuse.

T

Hi Marcus

Thank you for clarifying all this.

I re-checked all components

I do have 16 volts at C42.

I do have 16 volts ar IC3 between pin 4 and 8.

But I do not have voltage ⚡ at R37.

So I need to change the IC3 LM3578 if I am correct.

I will order a new one and keep you posted, or maybe take one from a working century before ordering the new IC3.

Have a nice Sunday evening.

Kind regards