QTX 4 Ch Dimmer pack

[Gerry]

I noticed these on the CPC website.

They look, and are described, as another clone/version of Botex/ Elation/ Stairville dimmer packs, but at about half the price.

Anybody got them and any comments about them?

Cheers

Gerry

[bruce]

Is that the DP32806 at £48+VAT - or is there a promotion code?

[dbuckley]

Looks it, doesn't it.

 

We've got a QTX little hazer, it works fine and looks the part...

[Gerry]

Is that the DP32806 at £48+VAT - or is there a promotion code?

Yes, that's the one.

Cheers

Gerry

[alistermorton]

Shame they're currently out of stock. I could use a couple of those for a little project coming up.

[handyandi]

I have one. Bought as a replacement for an Elation PARDIM which failed when a lamp blew. (now obsolete). For the money can't go wrong. Had to make up some IEC to 15A jumpers. They do say 10A per channel but they are factory fitted with 2.5A fuses. And, do beware to unplug the unit before attempting a fuse change as they seem to remain live even though the main switch is off! Currently using on some 500W par's & the odd 650W Fresnels.

Hope this helps. Manual is here if you want a look.

[Ashley R]

The power switch on many of these packs, its only a soft switch (i.e. controlling the circuitry) and does something fancy. But most of these packs also leak a decent bit of juice, enough to power up a LED can momentarily.

[themadhippy]

most of these packs also leak a decent bit of juice, enough to power up a LED can momentarily.

As do the vast majority of dimmer packs.

[kgallen]

most of these packs also leak a decent bit of juice, enough to power up a LED can momentarily.

As do the vast majority of dimmer packs.

 

 

 

That'll be preheat then... to make tungsten lamps dim up more linearly.

[timsabre]

most of these packs also leak a decent bit of juice, enough to power up a LED can momentarily.

As do the vast majority of dimmer packs.

That'll be preheat then... to make tungsten lamps dim up more linearly.

 

It isn't preheat, most cheap dimmer packs do not have that. it is current leakage through a snubber network which is fitted to allow the dimmers to dim inductive loads.

[Hilary Watts]

These are currently back in stock at CPC.

 

I've had one which I bought second hand and which worked perfectly for several shows but has now failed and I wonder if anyone has any ideas as to the problem. It seems to be in the low voltage section - the triacs and fuses are all ok.

 

When powered up the display sometimes flashes very briefly but then usually goes blank. About once in 20 times the display turns on properly. When the display is on the control buttons and logic functions (ie select DMX mode or auto chase and set chase speed etc) all seem to work but none of the four LED channel indicators light up to show a channel is 'on' nor do the triacs turn on, either in DMX mode or chase mode. However, the 'DMX present' indicator on the display responds to DMX.

 

I've got some knowledge of electronics and have checked the low voltage power supply which seems to be ok - it's certainly not the transformer or switch on the low voltage power supply that's at fault. There's a 7805 regulator on the board that seems to be doing its job. I've replaced a 1000mf capacitor next to it without any success. There don't seem to be any loose connections or cracks in the circuit board; it's conceivable that there's a dry joint somewhere but the soldering looks good quality. I'm told the unit stopped working part way through a show for no apparent reason.

 

There are various IC's - an AT89C52 microcontroller, 24C01 EPROM, SN7517 line driver receiver and SN74HC04N hex inverter (the descriptions are culled from the web using the numbers on the chips). There are also 4 chips which look like opto isolators between the low voltage circuitry and the triacs. I'm inclined to think the microcontroller, is working ok and from the position of the EPROM and line controller on the board I think they are concerned with the DMX input and output. It seems unlikely that all four opto-isolators have failed together and I'm wondering if the hex inverter is at fault - is it possible that it is used as a buffer between the microcontroller and the opto isolators? Is it worth ordering one and replacing the chip (it's socketed)? Alternatively does anyone have any other ideas?

 

Sorry if this is diverting the thread but I think the original question was whether the units are any good and if other people have had similar experiences to me this may be relevant.

 

Any ideas welcome - given the low price I'm half inclined to buy another from CPC and use it to compare voltages etc.in the hope that I may end up with both working!

 

e2a I suppose the microcontroller could be at fault but presumably this is pre-programmed and I won't be able to get a replacement.

[Shez]

It isn't preheat, most cheap dimmer packs do not have that. it is current leakage through a snubber network which is fitted to allow the dimmers to dim inductive loads.

It does claim to have a "Pulse feature to keep lamp filaments warm for instant on/off effect". Which of course may well be them claiming that the unintended leakage is actually a feature ;)

[ianknight]

@Hilary - yes, it's likely to be the microcontroller from experience. Often there's little protection between the output of the controller and the triac gate so anything nasty that appears there fries the poor thing.

[timsabre]

If it works sometimes, the micro must be OK.

For 89C52's that don't start up sometimes but do other times, there are 3 possible problems--

1-dodgy crystal or dry joint on crystal

2-very slow rising power supply (but sounds like you have checked this)

3-dodgy reset circuit - there should be a resistor/capacitor on the reset pin, pin 9

[Hilary Watts]

Thanks very much for those tips. I've tried re-soldering the joints on the reset circuit & crystal and have also checked the reset circuit components and all seem to be ok. I've therefore ordered a new crystal and will hope this does the trick.

 

I have in fact now been able to trace the path from the output port of the micro to the indicator LEDs and opto-isolators and there doesn't seem to be a fault there. When it's running the relevant pins on the output port of the micro are high and the indicator LEDs are off. I connected the power after removing the crystal (having forgotten I had taken it out) and all the LEDs lit up. On checking, the voltage on the relevant pins of the micro output port at that point was low. This seems to indicate to my mind that the output port of the micro can go both high and low under appropriate conditions (hence the decision to splash out £1.80 on a pack of 4 crystals!).

 

I'll post again once I've tried a new crystal.