Behringer SPS1000 shuts down when disconnected from PA

[Luis_vxd]

Hi all

I have an issue with an SPS1000 installed on PMP1280S Mixer.

The PS switches on, all seems good on the mixer side, the fans do not work and then after a few seconds it shuts down.
If I disconnect the HCA2400, X3, X5 and X6 on the PA side, the PS switches on, the fans, now, work as expected, however it shuts down after a couple of seconds.

I am assuming that I have an issue with HCA2400, but what keeps shutting down the SPS100 when the PA is disconnected?

Please help

Many thanks

[The Dude]

Maybe just me, but I have no idea what all of those designations correspond to without a schematic.

[x-pro]

https://music-electronics-forum.com/...power-pmp1280s
schematic

[TomCarlos]

So...

Here is what I think you have....

The PMP1280s Mixer Amp Head
The SPS1000 Power Supply
The SCA2400 Amp Module

Schematic attached.... Behringer_PMP1280s_Schematic.pdf

There are several posts here on MEF for the PMP1280S Mixer. Look them up and maybe you can get a hint as to where to begin looking?

[Luis_vxd]

Thank you guys.

I do have the schematic. My apologies for not showing it here.

Is my first time with this Eurpower PMP1280S and I do not have much experience. I have read all I could here before posting and found someone with a similar situation (very old post), but unfortunately there was no reply to it and the member didn't come back.(it was Sarenden on post #14 on this Thread: Unfortunately the thread went in a different direction.

I can't figure out where to look for or neither understand why is the SMPS is shutting down.

The first scenario is:
1. Power Amp connected, both X3 and X5 (Power supply, ±80V) and X6 (six wires where the OFF signal is).
2. SMPS starts, the fans do not run, the Mixer section comes alive, even the FX numbers light up but then the SMPS shuts down. It seems that ±15v and +5V are ok, but not the -21V

Second scenario:
1. I have removed the connection for the Power Amp HCA2400, whihc I learned this here, from late ENZO (RIP) posts.
2. SMPS starts, now with fans working and all seems good expect that it shuts down. When I power it back again it shuts again but now faster than the first attempt. It seems that somehow by disconnecting PA the -21v are back, but then it shuts off.

Conclusions:
1. There is, most likely, a problem on the PA, that shuts down the SMPS, which I will look into later.
2. I was expecting the SMPS to run stable without any issues after disconnecting the PA and the Mixer.

Another issue that seems a bit ridiculous: I am battling to separate the Mixer from the Power Box. after unscrewing all bolts it does not come apart as I expected. Is there any internal bolt holding all together?
My next step is to remove the Mixer buttons, (etc.) and front panel looking for what is still holding it together. Somehow I have a feeling that it will be useless.

Thank you so much for you help.

[Luis_vxd]

It ended up to be the only way to separate the Mixer from the Power box. A bit of a mission, but its done. :-)

[J M Fahey]

So what was the solution?

[Luis_vxd]

Hi Juan

Regarding the physical separation of the Mixer side from the Power Box (where PA and SMPS are) I had to take out the front (Mixer side) panel to be able to unscrew 4 bolts that keep the unit together.

The SMPS still shuts down on its own with either the Mixer and the PA disconnected. This I am not able to figure out why.

Please see attched SMPS schematic.

Thanks

[x-pro]

The first scenario is:
1. Power Amp connected, both X3 and X5 (Power supply, ±80V) and X6 (six wires where the OFF signal is).
2. SMPS starts, the fans do not run, the Mixer section comes alive, even the FX numbers light up but then the SMPS shuts down. It seems that ±15v and +5V are ok, but not the -21V

Second scenario:
1. I have removed the connection for the Power Amp HCA2400, whihc I learned this here, from late ENZO (RIP) posts.
2. SMPS starts, now with fans working and all seems good expect that it shuts down. When I power it back again it shuts again but now faster than the first attempt. It seems that somehow by disconnecting PA the -21v are back, but then it shuts off.

If it disappears (-21 V), how does it appear (-15 V)?
“The OFF signal comes from the PA.” Show this signal on the PA diagram.
What is connected to collector T18 in the power supply is not clear even from the schematic.

[Luis_vxd]

Hi X

The X9 connector do not have any pins or anything connected, so I think T8 is left floating.

If it disappears (-21 V), how does it appear (-15 V)?

I guess that is probably the POS+ or POS- that prevents both fans from running.

Thanks

[x-pro]

Now for the main point.
According to the power supply schematic and amplifier schematic, there is no control signal to influence the PA on the SMPS to shut down the latter, except for a faulty condition of the whole amplifier (e.g. shorting the output transistors across).
How does the power supply circuit work?
The AC mains voltage passes through the PFC (if any) and goes to pins. X1 and X2.
The low-current power supply on IC2 is switched on first and the main power supply capacitors C5, C6, C13, C14 are charged through the limiting chain of resistors R11, R12. The power supply on IC2 supplies power to the main PWM and key drivers T3, T4. At the same time through D2 the signal “OFF” is formed for optocoupler IC3. This is the switching node of relay K1, which switches the main power supply from limited switching to direct switching. The turn-on time of this relay depends on C34, and the quality of operation depends on C19.
From the output of transformer TR2, the output voltages should all be. The supply voltages (+/-15; +48; +/-12) may be independent of the other voltages, due to the presence of F2, F3 in their circuits, but in a serviceable unit they all appear almost simultaneously.
There is no output voltage stabilization in this SMPS.
What to pay attention to?
On the disconnected device and discharged capacitors C5, C6, C13, C14, check D2, C19, C34, K1, the quality of its switching contacts, D3,C18, C8, C7, R15, C40, if T18 blocks something somewhere.

[x-pro]

If the “OFF” signal comes to D23 PA, then yes, the power supply turns on the output drivers of the amplifier with its “OFF” signal.
But without power to the amplifier itself, the power supply should work. In general, it does not depend on its consumers.

[Luis_vxd]

But without power to the amplifier itself, the power supply should work. In general, it does not depend on its consumers.

This is the issue. The PS is switching itself down with the PA connected (X3, X5 and X6) AND with the PA not connected. (X3, X5 and X6 disconnected)
The only difference is that with PA connected the fans do not work but they work with the PA disconnected.

[x-pro]

You will deal with the operation of the fans afterwards. Their operation does not affect anything. You can even turn them off.

[x-pro]

The power supply may go into overcurrent protection if the capacitors on the secondary power supply (+/-80) are shortened. The remaining output voltages are limited by fuses (unless nails are used instead of fuses).