Switched Mode Power Supply problem

[Joseph90]

Hi friends.

I come to you because I have a problem that I cannot solve.

I have 2 chauvet moving heads that have the same defect in the power source.

At first they work but after a few seconds the 2 source voltages drop and try to go up again but fall again.

I unplug it, wait a few seconds and turn it back on until it falls off again. I unplug it again and it doesn't even have time for the head to start.

The problem is in the power source.

I have already measured everything and I don't know where the fault could be.

I see with the oscilloscope how all the pulses work but only half a second and all the voltages rise to a point and start to fall and rise again with a frequency of about 1 second.

I am very struck by the fact that the power supply voltage of the chip that controls the pulses also falls and rises again, I cannot understand if that is the primary failure or not or where the voltage to power it comes from.

I don't know much about switched mode power supplies but I have all the instruments and the knowledge of electronics to make all the measurements that the experts advise me.

Greetings

 

[Alec_t]

Welcome to EP!

At first they work but after a few seconds the 2 source voltages drop and try to go up again but fall again.

That switch-on/shut-down/switch-on/shut-down.... behaviour is typical for a SMPS which is over-loaded and is trying to protect itself. It may be that the Chauvet head has a fault (e.g. a failed/stuck motor) and is drawing excessive current.

 

[Joseph90]

gives the same defect without load. therefore the problem is in the source.
what I have no idea how to find where the problem is I have already checked the secondary and as far as I have been able to see there is no problem

 

[Harald Kapp]

gives the same defect without load.

Some SPS require a minimum load and will exhibit the same symptom without a load.

I am very struck by the fact that the power supply voltage of the chip that controls the pulses also falls and rises again,

Typically the power supply of the controller chip is created from the same transformer as the output voltage. There is usually a simple startup-circuit to supply initial voltage to the chip to get it started. Once it has started, it will supply itself from the transformer. Thereforfe it is to be expected that the chip's power supply exhibits the same hiccup behavior.

Here's the datasheet of the CM6807 controller chip. On page 14 there's acomplete application circuit. Chances are the circuit on your board is very similar to this application. There are several fault protection mechanisms described in the datasheet on page 12. Study the conditions described therein and check against your board if one of the fault conditions is met.

 

[Joseph90]

Some SPS require a minimum load and will exhibit the same symptom without a load.


Well I guess I should try with a load even if it's small

 

[Joseph90]

Typically the power supply of the controller chip is created from the same transformer as the output voltage. There is usually a simple startup-circuit to supply initial voltage to the chip to get it started. Once it has started, it will supply itself from the transformer. Thereforfe it is to be expected that the chip's power supply exhibits the same hiccup behavior

I think I've read something like that. it is very interesting

 

[bertus]

Hello,

Perhaps this page might give you some hints:
http://www.repairfaq.org/sam/smpsfaq.htm

As it is line powered, have a look at the safety guidelines:
http://www.repairfaq.org/sam/safety.htm

Bertus

 

[Joseph90]

Hello,

Perhaps this page might give you some hints:
http://www.repairfaq.org/sam/smpsfaq.htm

As it is line powered, have a look at the safety guidelines:
http://www.repairfaq.org/sam/safety.htm

Bertus

Thanks i Will read it

 

[Joseph90]

Here's the datasheet of the CM6807 controller chip. On page 14 there's acomplete application circuit. Chances are the circuit on your board is very similar to this application. There are several fault protection mechanisms described in the datasheet on page 12. Study the conditions described therein and check against your board if one of the fault conditions is met.

I have searched and read the datasheet but it is quite complicated to know if the signal that is reaching the pin is correct or not.
I will read it again and try to understand it.
I will post the results obtained.
Thank you very much for the help.