Showtec Multidim repairs

[michael6388]

I have a couple of Showtec Multidim IEC 4 channel dimmers which need repair. The triacs are BTA16-800BWRG - rated at 16Amps and 800Volts. I am surprised that these have proved so fragile in a dimmer which is rated for 4Amps and which I have only loaded with 500W. I realise that you can get spikes when lamps blow, but I would have thought that these triacs could have coped.

Am I missing something here - has anyone else had experience of replacing triacs in these dimmers?

[fatfrog]

Yeah, I have had a multi dim that needed replacement triacs - Basically water had came through the ceiling and fell on one of the par 64's causing it to short out and fried the triacs.

 

Replacing the triacs aint that hard to do - Although you do have to dismantle the whole dimmer which can be tedious and time consuming.

 

Hope this helps

 

alan

[michael6388]

Yeah, I have had a multi dim that needed replacement triacs - Basically water had came through the ceiling and fell on one of the par 64's causing it to short out and fried the triacs.Replacing the triacs aint that hard to do - Although you do have to dismantle the whole dimmer which can be tedious and time consuming.Hope this helpsalan

Thanks AlanI have dismantled the dimmer, but before replacing the triac I am wondering if there is any mod I can do to stop this happening again. I am still surprised that 16Amp 800Volt triacs have blown under normal (I think) conditions.

[themadhippy]

any mod I can do to stop this happening again

if not already there, fit fast blow fuses on each of the outputs

[oilyspark]

You may be able to fit heavier triacs. The 25 amp BTA26-xxx is available in the same (TO-220) package as the BTA16. Be sure to match any other characteristics e.g. isolated tab or logic level drive (denoted by the variant letters). Use the lowest rated HRC (F) fuse you can get away with on your particular loads. From my experience a BTA40 on a typical circuit will outlive countless 16A HRC fuses, BTA26s stand a chance against 10s and 16s but lower rated triacs are indeed somewhat vulnerable. Not for nothing are they called 'three legged fuses!' Naturally if the cause is a cranky reactive load, or inadequate snubbing or heatsinking in the dimmer then the larger triac may not offer any advantage.

[ChrisD]

As themadhippy said, any owners of multidims should make fuse replacement the FIRST thing they do. The fuses supplied aren't that great, and replacing them with faster fuses reduces the risk of triacs blowing substantially.

[Chris L]

Hey

 

My multidims have had the same problem, the triacs seem to take nothing to blow. Oh and I've never blown a fuse in one either (4 triacs gone to date!)

I've replaced the fuses with bought fast blows and the triacs and fitted "heavier" triacs in replacement to the ones that have blown. I haven't had any problems yet, but I haven't used my multidims very often recently.

I found my replacement triacs at www.cricklewoodelectronics.co.uk

Be careful when you're inside as I found the screws that held on the circuit board were very tight.

 

Chris

[musht]

Its surge that wipes triacs junctions, filament lamp blowing is an arc lamp briefly, usually totally short but sometimes half short , lamp flickers badly and even may respond to control slightly.

 

FF semiconductor fuses are usually more expensive than a triac and get odds down to 50/50 which goes first.

 

In Multidims fast replacement involves snipping the leads and soldering new triac to legs out of board, this isn`t a mechanically strong solution and is more a keep you going thing.

 

If you have the board out rising clamp, ones with a leaf spring, PCB mounted terminal blocks soldered on to the card so that triac replacement is a one sided ,no soldering iron job makes life easier. Common in bigger more expensive dimmers that can also kill triacs.

[WJProctor]

Hi All,

 

I see this message is rather old now. But I am going to have to replace a couple of TRIACS over the next week or so. Any advice or images to show the inside of the dimmer, or is it fairly straight forward and obvious?

 

Regards

 

James

[CallumP93]

1351613105[/url]' post='455763']

Hi All,

 

I see this message is rather old now. But I am going to have to replace a couple of TRIACS over the next week or so. Any advice or images to show the inside of the dimmer, or is it fairly straight forward and obvious?

 

Regards

 

James

 

I've got some photos of the inside of these, but I was actually repairing the DMX board at the time, instead of replacing the TRIACS, but they should still be okay! If you need any more images let me know.

Callum

 

http://s15.postimage.org/6qxplxzdn/image.jpg

 

 

 

[Gerry]

Rather than dismantling the unit, remove the clip from the blown triac, snip off the legs leaving some protruding above the board, shorten the legs on the new triac and solder it it the cut off legs. Then replace the clip to hold it to the heatsink.

Cheers

Gerry

sol

[Stuart91]

Rather than dismantling the unit, remove the clip from the blown triac, snip off the legs leaving some protruding above the board, shorten the legs on the new triac and solder it it the cut off legs. Then replace the clip to hold it to the heatsink.

 

+1 for this approach.

 

It might be worth buying a tube of heatsink compound, since some of the original compound will come off, stuck to the blown triac.

[WJProctor]

Thanks for all the great advice. Makes the project seem a whole lot easier now.

 

Regards

 

James

[Barreller]

I've got a SRC 167 with a blown Triac. Does anybody know where I can get the spec for this (it is higher than the Showtec ones - rated at 10A per channelo and 20A maximum).

[Brian]

I've got a SRC 167 with a blown Triac. Does anybody know where I can get the spec for this ...

What's the part number on the Triac?