KAM Powerbar Schematic

[timsabre]

1 hour ago, sunray said:

What's happened with the DMX connectors?

I'd guesss the manufacturer bought a job lot that didn't fit the PCB

[sunray]

3 hours ago, timsabre said:

I'd guesss the manufacturer bought a job lot that didn't fit the PCB

Judging by the poor quality of work I assued it to be a repair, however now measuring, I see the spacing between the connectors and the PCB holes is different.

[Mike Bullock]

14 hours ago, sunray said:

Judging by the poor quality of work I assued it to be a repair, however now measuring, I see the spacing between the connectors and the PCB holes is different.

Yes, a very old repair which I had forgotten about (I've had the unit for around 10 years now!) - one of the DMX connectors was damaged and I couldn't find a replacement of the correct size to mount on the board.

[Mike Bullock]

On 1/12/2023 at 4:26 PM, alistermorton said:

Probably the two large screw connectors are the actual supply to the LEDs and thinner push on connector is the supply to the control circuitry. Can you get a photo of the silver label unobscured by the mains input?

I double-checked - yes they are

[KevinE]

Quote

I've seen (heard) that problem when the Vcc supply cap for the IC was dried out

I'd have hoped the engineer who repaired the board had changed this routinely. 🧐

[DrV]

23 minutes ago, KevinE said:

I'd have hoped the engineer who repaired the board had changed this routinely. 🧐

Quite so. It's the number one problem on SMPSs

 

[jamieshurlock]

Never had a schematic and I’ve fixed 100’s of them, if he can’t fix it... 

[Mike Bullock]

On 1/15/2023 at 12:48 AM, jamieshurlock said:

Never had a schematic and I’ve fixed 100’s of them, if he can’t fix it... sales@Jamiesmagictorch.co.uk 

Thanks Jamie - I will try replacing the cap and if that doesn't work I will be in touch.

[Mike Bullock]

On 1/12/2023 at 5:08 PM, KevinE said:

Crikey, does sound loud. 

Have a look at this one, see if it will go in. It is nominally 27V and will crank up past 28V on the main output. It also has a 12V 0.5A 'fan supply'. 

rs meanwell smpsu

Hi Kevin, I was just having another look at this - not sure if this means anything, BUT the 12v output of the existing power supply is used to power the digital LED display section of the lights: just out of interest I disconnected this and the lights came on full power (i.e. bright white) with NO high pitched squealing (but obviously I had no way of controlling the lights). So my worry is that the fault may not be with the power supply - as soon as I reconnect the supply to the control panel, the squealing starts again.

Or am I putting 2 & 2 together and coming up with 5....?

Many Thanks,

Mike

[DrV]

That sounds as though the control board has a short

 Check its 12v input with an ohmmeter. Favourite faults there would be a decoupling cap (if there's a dead short across either the 12v input or the regulated 5 or 3v3 supply rail) or the DMX transceiver chip. The reason to suspect the chip is that it's exposed to the outside world. I don't have any experience of the Kam bar but just as generic fault finding these would be my go-tos. Alternative methodology would be to try powering the control board from an external, current limited bench supply.

[Mike Bullock]

On 5/17/2023 at 11:59 PM, DrV said:

That sounds as though the control board has a short

 Check its 12v input with an ohmmeter. Favourite faults there would be a decoupling cap (if there's a dead short across either the 12v input or the regulated 5 or 3v3 supply rail) or the DMX transceiver chip. The reason to suspect the chip is that it's exposed to the outside world. I don't have any experience of the Kam bar but just as generic fault finding these would be my go-tos. Alternative methodology would be to try powering the control board from an external, current limited bench supply.

Thanks again,

OK, so I have now done the following:

Measured the voltage across both the 12v control board output, and the 28v lamp outputs - both are correct.

Disconnected the 12v supply (only) and replaced with a 12v bench supply - squealing continues

Disconnected BOTH supplies and replaced with separate bench supplies - squealing stops

Disconnected the 28v supply (only) and replaced with bench supply - squealing stops

So it would seem that it's the 28v output which is generating the squealing - not the control board

Any ideas?

Cheers,

Mike

[DrV]

Difficult to determine without a 'scope. Does it squeal all the time or only when you bring the lamps up?

I still think it might be the decoupling cap for the chip in the PSU. This is probably the one above the transformer and next to the small vertical PCB in the top centre of your picture in this post. I've certainly seen this create the same effect on other SMPSs. The switching frequency becomes unstable so instead of having a single frequency that only bats and teenagers can hear you get artefacts in the pensioner's audio band.

[Mike Bullock]

20 minutes ago, DrV said:

Difficult to determine without a 'scope. Does it squeal all the time or only when you bring the lamps up?

I still think it might be the decoupling cap for the chip in the PSU. This is probably the one above the transformer and next to the small vertical PCB in the top centre of your picture in this post. I've certainly seen this create the same effect on other SMPSs. The switching frequency becomes unstable so instead of having a single frequency that only bats and teenagers can hear you get artefacts in the pensioner's audio band.

Only when I bring the lamps up.

I already changed that cap, so must be something else....?

Thanks again - I appreciate your help with this

[DrV]

Next caps to check are the output caps which are the four similar ones inside the left heatsink. It could be loose windings in the transformer but you can't just swap that out so try the caps. Also check that the choke in the middle of them is ok (no loose wires or cracked varnish). Other than that I'm out of ideas without a waveform to look at. I don't know but it might be possible for a faulty/worn out snubber circuit on the primary side to upset things (look for at least 2 of a  resistor, cap and diode across the primary winding). Not very easy to diagnose remotely and you might be better off getting it to Jamie Sherlock if he's got experience of these particular units 

[Mike Bullock]

On 5/20/2023 at 12:50 AM, DrV said:

Next caps to check are the output caps which are the four similar ones inside the left heatsink. It could be loose windings in the transformer but you can't just swap that out so try the caps. Also check that the choke in the middle of them is ok (no loose wires or cracked varnish). Other than that I'm out of ideas without a waveform to look at. I don't know but it might be possible for a faulty/worn out snubber circuit on the primary side to upset things (look for at least 2 of a  resistor, cap and diode across the primary winding). Not very easy to diagnose remotely and you might be better off getting it to Jamie Sherlock if he's got experience of these particular units 

Thanks again - much appreciated.

Mike