Rackmaster 260 wrong dim curve

[Stratzzi]

Dear Zero88 Forum,

i need some help for my Rackmaster 260 dimmers.
It seems that some Channels are just starting at 50% to dim up and then they go really fast to full output. 
I attached a video that shows the diffcult channels, the both in the mid are dimming perfectly, the others not.
Maybe someone could help me.

Thanks
Stefan

[KWR88]

Hi Stefan,

that looks like possible preheat issue.

if the pot is adjusted too far either way it casue the ramp for the channel control to distort.

it can either leave channels on at a level, or as you have the output don't come on until you get higher up the curve.

to set the preheat we would normally put a 10% control signal in to all the channels then adjust the pot until the lamps are starting to glow then take the signal to 0 and the outputs should then be no longer visable.

 

 

[iank99]

Has that setup worked before?

The fader control looks like it may be of chinese origin & sometimes the DMX they output isn't 'standard' & can cause erratic behaviour. To check the dimmer properly you need a small analogue desk of some flavour i.e a Level 6 or Level 12.

[Stratzzi]

Thanks for your answers. 

I checked the preheat, but when i turned it up, it dims up like it should be. All pots are at zero.

This setup had worked before! I measured the analog voltage and its the same on all 6 channels. So it couldn't be the multiplexer or dmx controller. I got these problems at another setup too (grandMA2 and other multiplexer). 

Any other ideas?

[KWR88]

If the preheat are set correcty then the next thing to look at would be the supply rail or the vref tail not being correct.

If the v-ref rail is out this will cause issue with the ramp as well. given the age of the unti you may find the capacitors on the supply rail have dried out.

these are the 470uF electalitic next to the transformer.