My Behringer K1800FX repair

[Jose EB5AGV]

Hi all,

I will document on this thread the repair of my K1800FX, which died suddently on my last gig.

There was no hint of it going to die nor it was being abused.

I got this 2009 unit used, just a couple months ago, but it was in very good shape and with low hours on it.




Accessing to the PA electronics through the speaker hole:




The LPA1180 Rev. J amplifier:



A general view of my main workbench, with the amplifier on it;



This is the PCB, trace side:



Only hint so far I have found that may explain the failure,,, If you enlarge the picture, you can see some embedded metal part on the silicone grease of that transistor:



The PA with the drivers and power transistors removed. Both power transistors are shorted. Drivers measure fine on my PEAK DCA75:




I have checked all the diodes and capacitors (for ESR and capacity), and all measure OK. I have also powered the amplifier without the power transistors, and the +5, +15 and -15Vdc rails are present and the control panel LEDs light nicely.

So I have ordered replacement transistor and will replace and set BIAS on them.

More to come!

Jose

[Jose EB5AGV]

Well, I have done some more work on the LPA1180 board. I have been carefully testing all components around the MJE340 and MJE350 drivers, and also around the IRPF9140N and IRPF140N.

Around the drivers, all seems perfectly fine. But around the power transistors, the current measurement resistor, used to set BIA, was damaged, reading 1.5 Ohm instead of the nominal 0.1 Ohm. So I have taken a nice Ohmite replacement and have replaced it.

It seems I can't post any more pictures, so my adventures will continue on my WEB page at:

https://jvgavila.com/K1800FX.htm

[Jazz P Bass]

Nice work bench!

[Mickjh]

Thanks Jose, I took a look at your site to see if there was an update. I just bought a secondhand K900fx very cheap taking a risk not to test, so not surprising it has problems.
Reading some of the older posts here, it seems that the supply/ output board is a common problem. The board is an LPA190. I have not done too much troubleshooting, symptoms are (using a Yamaha MX49):

• Amp powers up, LEDs on EQ all lit.
• No noise with no inputs and main volume up.
• All channels are weak or distorted
• occasional loud crackling or popping
• have not tried CD input
• have not tried phones or line out
• Quick Inspection of the electronics shows no burns, brown smells, bulging caps or obvious dry joints.

Appreciate any guidance from the forum ( including binning if repairs are not worth the trouble)

[The Dude]

Do you have a schematic? Check power supplies first.

[Mickjh]

Unfortunately no, but I did find a K3000fx which is similar; more powerful and stereo in/out.

I did some more troubleshooting:

• cd inputs connected to a music source plays clean and clear.
• channel inputs do work but varying with gain and some distortion.
• Graphic EQ appears to work
• Any amount of FX return adds significant noise. Can’t tell if there is any effect.
• FX patches appear to cycle with selector knob.

The amp was sitting in a garage for a few years unused.
I’m thinking of getting some Deoxit spray to clean all the pots on the preamp/fx pcb.

[sugeda]

..

[tyler]

Hi. Don't know where to start. Have a Wharfedale spx613 powered mixer that doesn't seem to be working from the front: monitor out, main out. What do I need to do to get noise from this? Rest of amp seems to be working.

[DrGonz78]

Welcome to the forum! This thread is about a Behringer amp but you list Wharfedale spx613. What would be best is to start a new thread about your amp. Do you have schematics for the amp? Explain your issue in detail and explain steps you took to come to that conclusion. You will get more responses this way.