K8064 - flickers at low level

Hi there, I have built 8 of these dimmers to replace some failing units in a theatre lighting rig.

They are all flickering when a 500W load is connected and either the input voltage is increase to around 2V, or if the input is removed and the trim pot turned up. I have tried different loads, different inputs and all the cards. They all exhibit the same fault.

The input voltage is a stable, low ripple DC control voltage from a local DMX - voltage converter. I have checked and re-checked the builds, and they all appear correct. It seems like the triac is failing to fire at very low levels, so maybe the zero crossing circuit is to blame?

Any help received!

Many thanks.

Wish load are you using ?

Please check also the brand of the used triac (TIC225M), it must be “bourns” (logo = ß)

Hi, thanks for your reply.

It is the Bournes triac and the load is a 500 halogen theatre lamp. I have tried various lamps, including 650W and 300W, with the same effects.


Check capacitor C13, if you mount the correct one (common mistake)

470nF type for 240V and check also C12.
C12 must be only 100nF
You need one RED capacitor left from 1µF !

Thanks for this.
The Capacitor is the correct 470nf. C12 is 100nf.

I have the 1uf capacitor spare from each kit.

It seems that the Triac is needing a good “kick” to get it to conduct, and then the drive is not stable, causing the pulsing and flickering.

I have a scope, plus meter etc. so if there are any points to measure or waveforms to check, please let me know.

Hello VEL456,
Last year I bought about 25 of these dimmers [k8064] for multiple installations.
Some work perfect, other have a same kind of problem as told above. When the input is on it’s maximum the light starts to flicker. I can turn the resisters lower, but then I miss a lot of brightness.
Exactly half of the delivered lightdimmers bahave flickering, the half behaves perfect. They do this since the beginning.
It seems the ones with the TIC225M of Bourns behave right, the others which have another mark TIC do the flickering.

I would very much like to repair the bad functioning dimmers and change the wrong TIC225’s into the ones of Bourns, but they are very difficult to find. Would it be possible that I purchase them from Velleman, or could you send me some as a service?
[please reply via email for snailmail address]

Best, Mariska

Hello VEL456,

i have the same problem with some of these dimmers in a installation.
Some of them begin to flicker after 2 to 5 minutes in the lower dimm-range (30% to 60%)
It seems that it will better between 60% to 100%.

Can you help me too with a mail?

Many thanks.

No problem, How many Triac’s do you need ?
Is it also possible to send me a copy of your invoice from your dimmer kits ?

[quote=“VEL456”]No problem, How many Triac’s do you need ?
Is it also possible to send me a copy of your invoice from your dimmer kits ?[/quote]

Hello VEL456,

thanks for your answer.
How can I send you the copy?

I need 5 pieces.

Thanks for help.

Please mail it to s u p p o r t @ v e l l e m a n . b e without the spaces.