Fanuc PSU A16C 1212 0950

[marsheng]

I had a fault on the machine saying F4 fuse blown. Replace the fuse in the PSU and now I get nothing on the screen.

The PSU shpws all the voltages +5 +-15, 24V and 24VE on the mating connector on power on (supplied with 230 volts AC) when on the bench. It has a start stop circuit wired to the front of the machine.. From what I'm told, there should be no power on the connector until the start button is pressed. Normally you turn the on main supply and some things wake up and the when you press the on button, the MB wakes, screen comes on and it boots. Much like a PC, power on then you have to press the on button.

Nothing on the board looks damaged and I'm too rusty in reading schematics to go any further.

What could be turning it on automatically ?

Any suggestions ?

 

[Harald Kapp]

I had a fault on the machine saying F4 fuse blown.

Usually a fuse blows for a reason. Meaning something else is defect.

The PSU shpws all the voltages ... when on the bench.

On the bench with or without load? What do you measure when the psu is loaded?

Looks like this is the auxiliary circuit to provide stand.by power (5 V)



This should be the on(off circuit:



Check the voltage at the input pins labeled ON and OFF (but to me it looks like ON and COM are swapped and labelled incorrectly, so check COM too).

Check also this transistor

If it is faulty, it may turn on relay RL12 continuously.

 

[Martaine2005]

Check the 5V regulator to the right of block H1.

Martin

 

[marsheng]

PSU now back on the workbench.

> Looks like this is the auxiliary circuit to provide stand.by power (5 V)

A24 has 24 volts and the regulator puts out 5.

As a test, I removed Relay R11. I believe that this is supposed to come on with the off/on switch.

Interestingly A24 still has 24 volts on it. I'm not sure how Block H1 is getting power.

 

[Harald Kapp]

Interestingly A24 still has 24 volts on it

Not interesting, that is toi expected. This is where the 5 V standby power ius derived from. Without 24 V there'd be no standby power.

As a test, I removed Relay R11.

What was the result of your test?

I'm not sure how Block H1 is getting power.

I may have been wrong about the standby power. Check this section:

The two points labeled P380 are electrically connected (even when there is no trace shown in the schematic. Same name, same net). SO when 24 V are seen at the input of block H1, they come from the power supply section encased in red. Check the switch to the right of the EMI filter. It may be stuck in the ON position.

 

[marsheng]

The switch to the right is the R11 relay contacts. I have removed it so the bridge should not be getting any power and yet the 24v is on. R11 is part of the 'soft start' On/Off.

Without the relay, I get 24 v and the top heatsink runs cool
With the relay, I still get 24 v but the heatsink get hot quite quickly to the point it will have to have a fan to keep cool.

Sound like something is shorting but not the +5, +-15, 24 and 24VE outputs.

I've just seen from the other schematics that there is a second HV circuit. There is a single wave rectifier from the mains supplying a 10 uf 400V cap that produces the 24V through transformer T11 .

So now I have to trace the On Off circuit.

 

[marsheng]

I got a new second hand PSU and the machine is up and running. Ordered a new second hand thick film ON/Off module so we will see if that can fix my faulty board.