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

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

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

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

24 minutes ago, DrV said:

Can't remember but either isopropyl alcohol or a solvent cleaner like "flux-off". The other clue to where the fault is might be gently and precisely tapping the ceramic caps in that area with an insulated probe (eg. plastic knitting needle). If neither of those finds the fault then you're down to shorting the input to the various stages to see how far back the noise is being introduced. Or just replacing things until it goes away. If you pm me your email address I'll send you the schematic.

Cheers, I have sent my email address to you.

Many Thanks,

Mike

22 hours ago, DrV said:

It's worth thoroughly washing the components on the preamp board. I had a unit once (actually it was an srm450 but same applies) which took me ages to fix. Turned out it was just contamination under a cap near the input.

Thanks again - when you say 'wash', what did you use and what method?.

Cheers,

Mike

On 2/10/2023 at 10:46 AM, KevinE said:

The obvious answer is to fault-find the amp module and replace the faulty parts. Is that what you're looking to do? Are you ok with fixing pcbs?

Hi Kevin,

I have established that the issue is with the preamp, as the rumbling stops when I disconnect it (see message above from DrV).

I wouldn't know how to fault find this - I am competent at de-soldering and re-soldering if I know which component is at fault, but that's about it.

Having disconnected and reconnected the preamp, I notice the rumbling is considerably quieter, but still there.

On 2/9/2023 at 3:21 PM, Bryson said:

Sounds like it's maybe getting spurious input.  I'd take a look at the solder joints on the input connectors in the first case.

 

 

Hi Bryson,

I checked and re-soldered these - problem still there.

Thanks,

Mike

On 2/9/2023 at 8:39 PM, DrV said:

First thing to do is disconnect the input board from the power amp to find out which board is introducing the noise. Pull off J1 which is the 7 way ribbon connector. If it goes quiet the issue is with the preamp. If not it's with the power amp.

Hi DrV - thanks for this: I disconnected J1 as you suggested and the rumbling stopped.

Bryson suggested looking at the input solder joints, which I will now do - any other ideas spring to mind?.

Many Thanks,

Mike

Apologies, I have been ill since creating this post - I will look at the responses soon

Wondering if anyone can help, or has had similar issues with this unit:

Mackie SRM 1801 powered sub - when I power it up, it emits a loud rumbling sound (like thunder!), even with nothing connected to the input.

Anyone had or heard of this issue and, if so, how did you resolve it?.

Many Thanks 🙂

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.

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

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.

5 minutes ago, KevinE said:

PS..take the RS specs with a pinch of salt - they're up to standard as usual. The datasheet says it is a 120W version as suggests the part number, and although it is described as having a 'single output' the datasheet also says the 120W version has a supplementary 12V fan supply

Thanks for that - I'll take a look 🙂

1 minute ago, KevinE said:

from memory, these Kam bars do whistle loudly when all the lamps are faded up to max. If you do a chase, the power supply sounds a bit musical. Unless you think it's excessive, and the 28V stays fairly steady throughout, I'd say it was ok. 

If you'd rather change the board I'm sure a 24V psu with adjustable output would go up to nearly 28V as they are sometimes used to trickle charge lead-acid batteries at 27.6V. You could piggy back a 1A 3-leg switching regulator off the main output for the 12V if they share a common 0V.

 

 

 

It's REALLY loud - i.e. I just about get away with using it in my rock band, but wouldn't even try to use it with my acoustic setup.....

20 minutes ago, 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?

See below pic...

5 minutes ago, indyld said:

If the noise is the transformer (in a design that usually works fine), one might surmise that there is some issue with resonant frequencies that is out of kilter with the original design. This could be either on the input or the output side, either an choppy high voltage side after the rectifier/bulk cap or maybe an issue with the PWM controller, feedback, or smoothing on the low voltage side.

I'd guess that the block wood experiment is rather like holding down a rattling teacup on a moving train.

** laughs out loud **, yes - but I only did that to confirm my suspicion as to where the noise was coming from..... 😂

4 hours ago, alistermorton said:

Could the noise be magnetostriction from the transformer winding? I had a similar noise from a unit I built many years ago, where the coils had been hand wound and weren't perhaps as well made as they could have been.

That makes sense - I gently pushed a piece of wood onto this transformer and the squealing changed pitch and volume..... maybe I should look to change this?

7 hours ago, alistermorton said:

Do you think that silver label is also giving a second output rating - below 28V 3.5A there is a partial rating - V 0.5A

There looks to be a second pair of output wires just to the left of the ribbed heatsink, above the main terminal block.

Thanks all!

Yes that IS a second output pair - I think that powers the led light units...? while the main output pair powers the control circuitry (I'm no expert but I connected a simple 12v DC power supply to these and the lights came on statically) - see more detailed pic of these outputs below.

ALSO, the high pitched squealing appears to be coming from the transformer (?) in the centre of the first pic (the one with the translucent yellow tape on it). I put a decibel meter across the supply and it was by far the loudest part of the board..... 

Worked it out - photo below

2 hours ago, timsabre said:

Post a photo of the faulty PSU module. Unless it is something esoteric with many different outputs, there will probably be some generic module you can replace it with.

1 hour ago, sunray said:

For some reason it's not letting me post a picture either.

To post this from a pc:

with the picture open in windows photo viewer:

In the 'open' drop down menu select paint.

In paint selected the area I wanted then right click & copy.

In the reply box right click and paste

.

I imagine others will know an easier option.

Thanks, but I'm using a mac and cannot replicate what you are doing (so far). Thanks anyway

59 minutes ago, timsabre said:

Post a photo of the faulty PSU module. Unless it is something esoteric with many different outputs, there will probably be some generic module you can replace it with.

Sorry, I am new to this forum - how do I upload photos please?. The 'link' icon asks me to supply a URL, not to insert a file.

Thanks

1 hour ago, indyld said:

You asked for a schematic. You will not find one.

Further repair help needs more information.

Several members here fix lighting equipment and we all have to work without schematics, for all makes and models.

Fixing faulty SMPS isn't difficult but potentially lethal for the unwary. 

Thanks. Yes it does have different outputs.

Basically, the supply failed so I had it (professionally) repaired, but now the unit emits a high-pitched squeal when the lights are at their brightest - the guy who fixed the power issue now says he needs the schematic so he can trace the 'new' fault.

Sorry, I am new to this forum - how do I upload photos please?. The 'link' icon asks me to supply a URL, not to insert a file.

Thanks

17 hours ago, indyld said:

No chance. Usually fix without. Plenty of people who can help here.

Thanks, but so far no help from anyone. . . . maybe I can find a spare power supply??

Hi All,

Does anyone have access to a schematic diagram for the KAM Powerbar - my power supply is faulty and the engineer repairing it needs this in order to locate the fault. I tried contacting the owners (JHS) but they do not have it. Seems a shame to just throw it in in a skip as it's a really well built earlier model, and the lights themselves are very good.

Thanks,

Mike