Mike Bullock

Thanks again - much appreciated. Mike

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

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

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

Cheers, I have sent my email address to you. Many Thanks, Mike

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

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. Hi Bryson, I checked and re-soldered these - problem still there. Thanks, Mike

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 🙂

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

I double-checked - yes they are

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.

Thanks for that - I'll take a look 🙂

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.....

See below pic...

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

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?

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

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

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

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

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