Behringer SPS1000 shuts down when disconnected from PA

[Luis_vxd]

Thank you x-pro

I will follow your suggestions and get back to you.

Meanwhile I found that the fans do not work due to R2 on PA (attached to heatsink) which controls their speed according to increase in temperature. When connector is out there is no control and the fans go full speed.

Again thank you for your comprehensive description of SMPS startup sequence. Crucial for my understanding.

[Luis_vxd]

I have checked all components you suggested and all are OK. C40 do not exist and R15 is a wire. Interestingly J1 is not there, never has been.
Checked all diodes and all electrolytic capacitors on the primary side of TR2.

Here is the current situation:
The SMPS starts and stays on for about 5 seconds and then shuts down.
While on, I checked all voltages on the DC side and all are present. TR2 has 157V AC on the primary side. OFF signal stays -12V until shutdown.

Interesting behavior:
The SMPS stays on about for 5 seconds on first startup. If started again soon it only last 1 or 2 seconds and if I started immediately it does not even starts. It seems it needs some time to "recover".
I looked for components that could eventually heat up and then fail but found none.

I looked at IC1's shut down circuit culminating at TR13 as the possible guilt part, but if so then TR1 would remain powered through IC2 if TR13 causes the shutdown, isn't it?

The voltage on primary side of TR1 drops and seems, I know this can be an illusion, seems to drop earlier than K1 opens which might indicate that IC2 is the culprit.

Your thoughts please?

Thanks

PS.: schematic attached again.

[x-pro]

Here's what we're going to do. Disconnect all output voltages from the amplifier and mixer. We will repair only the power supply.
Earlier, I pointed out that no consumer significantly affects its operation.
You can connect the whole device through a 60-100W incandescent bulb. Apply mains power. Make sure that it corresponds to the required one for your country. If it is 220, there should be no jumper J1 near D5.

[x-pro]

By the way, check C15.
Any LED with a 1.5k resistor in series can be connected in parallel to capacitor C22 to indicate the presence of output voltage. Or an incandescent lamp for 24V (or 12+12). You can take lamps from turn signals in a car. Indication will be even better with them.
Measurements should be made relative to the “neg” line.
Measure the voltage on C18, then on C8, and also on C19.
Measure the voltage between “pos” and “neg”.
Waiting for the result.

[x-pro]

I looked at IC1's shut down circuit culminating at TR13 as the possible guilt part, but if so then TR1 would remain powered through IC2 if TR13 causes the shutdown, isn't it?

Yeah, that's right.

[Luis_vxd]

Here it goes:

C15 - OK

Measured at capacitor terminals:
C18 - 14.8V
C8 - 14V
C19 - 15.5V

Between POS and NEG - 323V

[Luis_vxd]

Those voltages were not precise as power was building up and then SMPS shuts down. They should be considered as ± .

[x-pro]

What do you mean the UPS is shutting down?
The low-current on IC2 should stay on.

[Luis_vxd]

By shut down, I mean K1 opens. The low-current remains but the SMPS does not restart. Voltage at IC2 Pin 5 (DRAIN) disappear as I mentioned before.

[x-pro]

Voltage at IC2 Pin 5 (DRAIN) disappear as I mentioned before.

This voltage is not worth paying attention to. It is a high frequency pulse voltage and can have a high pulse voltage. More than the mains voltage. Not every multimeter can measure it correctly. The main thing is to make sure that the voltage across C18 remains even when the main UPS is turned off.

[x-pro]

During operation and with the main UPS switched off, measure the voltage across the collector of T13. Show these values.

[Luis_vxd]

I am confused now.
My understanding is that TR1 is powering IC1 and TR1 is powered by IC2 Pin 5 DRAIN. There cannot be voltage across C18 if there is no voltage on Pin 5 of IC2.

[Luis_vxd]

Emitter-Collector voltage on TR13 when the SMPS in ON is 7.3V. When is shutdown the voltage drops to 0V.

[x-pro]

In general, the voltage at pin 5 is not measured accurately. There is a mosfet inside IC2. And you measure the voltage at the drain of this mosfet. And it's pulsed if everything is working. If the IC2 is shutting down, then look at the rating of C16 to see if it matches, as well as its ESR. You can also check C20.

[Luis_vxd]

I know little about Switching Power Supplies it just makes sense for me that IC2 is, somehow, powering TR1.