I made your PCB, but it does not work.
Maybe i misplaced a component, i will check it once again.
Here is a picture of what i made.
The large green resistor is the correct one, only this is capable of 4w.
I can not figure out what i did wrong.
sorry picture removed.
Well its hard to see whats not ok. Your connector X1 seems to have 5mm (0.2") pin distance. Did you manage the wiring correctly on this? Did you divide the tracks (yellow lines)? Do you take care of ESD? The MOS-FET can easly be killed with Electro Static Discharge.
Show me a picture from the bottom side.
sorry, pictures removed.
I think I took good care of the components.
In the first picture i tried to draw the tracks as a black line on the print.
Here is a picture that i mirrored so it is positioned like the top view.
sorry, pictures removed.
That wasn’t a short.
In my picture, the connector for the heatbed x3, the top two pins. should those connect to the negative or to the positive lead of the heatbed.
Personally i don’t think it matters.
I did it like in your picture with the yellow lead(positive) pointing towards the OK1
I got it working.
I replaced the large 2.2 k resistor with a smaller one from a print that i had laying around.
The resistor I got from conrad aren’t the right ones. The value I measured on those are way way off.
Stupid thing to have overlooked.
Heating time 20 -50 was 9 minutes, now 3 minutes.
Just thought I would give some feedback now my 24V heat bed is working.
What a transformation, the bed now heats up before the hot end and with my nozzle fan working it will hold my preset of 55 degrees with ease. It also prompted me to make some brackets for both power supplies that attach the framework to help keep things tidy. I also made my own circuit board cover to hold the extra circuit board and with a mounted fan on top to keep it all cool. I also added 2 switches for the fan and Led lights.
Now I can try a glass plate on the bed knowing it will heat up quickly, time to hunt around for one in a local DIY store.
Today I started printing directly on glass + hairspray which I like allot. But I need to put the bed at 60-65 degrees. This is nearly impossible with the standard setup. So I saw this thread and I’m thinking to do this to my printer as well. There is 1 problem, I’m not that great with electronics as I am with mechanical work. I read through this entire thread and still feel kinda lost 
Does anyone ever made a step by step guide on how to forfill this kind of upgrade? Or in worse case, are there kits/finished products I can buy for my printer?
Greetings,
Kenny
[quote=“edirol”]Kenny
Using a automotive relais is probably the easiest solution for you:
Hope it helps, good luck![/quote]
Thanks for this! What happens with the 2 cables that are currently attached to the bed-connector? Do they stay or are they replaced so only the external power supply is connected? And will the original ribbon cable do the job or is it recommended to change them all with thicker cables?
This is obviously a symplified version of what you did, just out of curiousity, whats the big difference?
Edirol, nice drawing!
Just wondering what is actually the connectors called, for exampel your X3, female and male?
Hi Akzid,
they’re Molex KK100 (sometimes also KK254) connectors.
This page in the RepRap wiki has a table with links to several suppliers. In that case for the 3 pin version, but the 4 pin shouldn’t be too hard to find from there on. Note that the cable connectors have to be crimped to the correct size for a good fit into the housing; a matching crimping tool might be a good “investment” (less then 20 € e.g. at Reichelt).
Cheers,
kuraasu
Thanks!
[quote=“KLucky13”]
Thanks for this! What happens with the 2 cables that are currently attached to the bed-connector? Do they stay or are they replaced so only the external power supply is connected? And will the original ribbon cable do the job or is it recommended to change them all with thicker cables?
This is obviously a symplified version of what you did, just out of curiousity, whats the big difference?[/quote]
You probably know anyone with electronics knowledge? I fear you may damage your board…
Hi all,
This thread is an interesting read - all 10 pages 
I would like to have a go at building the upgrade but I am getting a little lost following all the comments and variations.
Does anyone have (or would be willing to put together) a concise guide on building this board - schematic, board layout and parts list?
Sorry if that sounds like I am being lazy (clearly some of you have built the board with the information available) but I have a limited knowledge of building circuit boards and I want to make sure I order exactly the right bits (no bits with pins reversed for example).
Many thanks to all for the great input though. The heating time for heated bed is one of my biggest frustrations with the K8200 and I am hoping this will resolve it.
Regards
Peter
Hi All,
Can anyone tell me if an IRF540A MOS-FET would be a suitable alternative to the IRLR8743PBF MOS-FET suggested in the 24v power supply circuit board? If so, do I need to change the values of any other components.
This is the on
Many thanks
Peter
My current mod makes my bed rise to target temperature in under a minutte…
Heatgun… nuff said 
if memory serves, IRF540 is only for about 1A without heatsink
rather take something like IRFZ or IRLZ with low Rdson
[quote=“motoritz”]if memory serves, IRF540 is only for about 1A without heatsink
rather take something like IRFZ or IRLZ with low Rdson[/quote]
Many thanks Motoritz, I will try to source the correct component.