Speakercon Posted February 17, 2014 Share Posted February 17, 2014 Evening all. Trying to repair a faulty 18x3W RGB par 64 (showtec). The problem was green was permanently on. Opened it up and found a burnt component on the elv pcb. I'm not sure what the component is or where to get one, I assume it does the same job as a triac in a dimmer as now its removed the green has gone off, though unlike a triac it has 5 legs. The ones controlling blue and red are still on the pcb and shown in the image below. I think the resister under it has had it as well. http://i1344.photobucket.com/albums/p650/Wiresandplugs/ledpcb_zps48e0b848.jpg Link to comment Share on other sites More sharing options...
ceecrb1 Posted February 17, 2014 Share Posted February 17, 2014 Voltage regulator...Basically what controls brightness of the LEDs... so you have there 3, one for each colour. IF it was just that component that failed you should be able to google the ones either side of it, buy one (or a few) and soulder it on. IT may however, be the case that it failed as a symptom of another problem, (rather than being the cause itself). EG a short to earth.That resistor below it looks like it got rather warm too.. Link to comment Share on other sites More sharing options...
pmiller056 Posted February 17, 2014 Share Posted February 17, 2014 Hi Can you clearly identify the markings (lots of light and a good magnifying glass) or a clear photo of the markings on the devices will help greatly in identifying the damaged device. The device will be some form of PWM power driver. My experience is that the hard part of similar jobs is finding someone prepared to supply small quantities of the correct device, getting payment to them and waiting for shipping from another part of the planet. If it's your own personal stuff and your time costs you nothing, then go for it. If it's something that works to earn its keep, then forget it - the cost of the time spent identifying and sourcing parts to repair it will be more than the value of the lamp. You also need to be certainthat you can replace the part without doing further damage and that the lamp will be safe to use (A Pat test is essential) after repair. Peter Link to comment Share on other sites More sharing options...
Speakercon Posted February 17, 2014 Author Share Posted February 17, 2014 The numbers on the component are AMC7150DL, F0722BB. This is the closest one I can find. Maybe its not worth the hassle! Link to comment Share on other sites More sharing options...
Don Allen Posted February 17, 2014 Share Posted February 17, 2014 The data sheet for the AMC7150 is interesting. It explains why a lot of budget led's do not dim to zero well, as the device runs from 4 to 40v. Same problem as dimmable compact flouro's. The F0722BB is your date batch manufacturing code. The resistor on your pcb is Rsense. R300 .3 ohms 1W. wattage seems a bit low? Link to comment Share on other sites More sharing options...
pmiller056 Posted February 17, 2014 Share Posted February 17, 2014 It's an AMC7150, 1.5A Led power driver. The datasheet is available on the web. The singed resistor marked 'R300' is a current limit sense resistor, 0.300 ohms.The fact that this resistor is burnt would strongly suggest that there is / has been an excess current fault, possibly due to another faulty part elsewhere inthe lamp. If you replace the dud chip, it is highly likely that you will have other faults to fix as well. It is not possible without further checks to tell if the newly replaced chip will be killed by any other fault in the lamp. Peter Link to comment Share on other sites More sharing options...
Speakercon Posted February 18, 2014 Author Share Posted February 18, 2014 Cheers everyone, I've found the AMC7150 on ebay for £3. Although it looks like there is another fault somewhere causing the components to burn out, I'll risk the £3 and the 30p resistor and see what happens. If that doesn't sort it then its heading for ebay spares and repairs! Shame because we have 2 of them and 1 light on its own is not much good. Link to comment Share on other sites More sharing options...
timsabre Posted February 18, 2014 Share Posted February 18, 2014 The data sheet for the AMC7150 is interesting. It explains why a lot of budget led's do not dim to zero well, as the device runs from 4 to 40v. Same problem as dimmable compact flouro's. No, this is not right. LEDs are not dimmed by voltage but by pulse modulation (i.e. turning on and off very fast). The LED stack (probably 12 LEDs in series) is driven at a constant current, which will result in a drive voltage of about 38V, but this will be varied by the chip to deliver the rated current into the LEDs. To dim the LEDs, the control circuit flashes the LEDs, but faster than we can see it (this is what can cause flicker problems on camera). Cheap LEDs use 8 bit (or less) dimming so the minimum dim level is given by 1 "on time" and 254 "off time" . DMX level 2 would be 2 "on time" and 253 "off time". There is a big visible difference between these two levels, and it looks steppy. Expensive LEDs use 12 or 16 bit dimming, and scale the dimming curve to give more sensitivity at low levels, so DMX level 1 would be 1 "on time" and 65534 "off time", this is obviously a much smaller step. (It doesn't actually work exactly like that, I have simplified it). Link to comment Share on other sites More sharing options...
Brian Posted February 18, 2014 Share Posted February 18, 2014 There is a big visible difference between these two levels, and it looks steppy. It's also worth noting that although you can often see an LED lit up at lower DMX levels when you look directly at it, they don't give out that much light. Judging dimming curves should always be done by pointing the source at something and looking at the incident light (actually, pedantically, the reflected light). Link to comment Share on other sites More sharing options...
Don Allen Posted February 18, 2014 Share Posted February 18, 2014 But where is the PWM input to the driver ? It has volts in, current sense, oscillator (as many microcontrollers have), ground and output. Is the 4~40V input a PWM input ? and the output a current amplified input ? Link to comment Share on other sites More sharing options...
alistermorton Posted February 18, 2014 Share Posted February 18, 2014 It looks to me, from the data sheet, as if the output current is meant to be set by choosing the low value resistor according to the formula they give, as that pin is labelled current sense. The chip then maintains that out out current for varying input voltages. Link to comment Share on other sites More sharing options...
timsabre Posted February 18, 2014 Share Posted February 18, 2014 But where is the PWM input to the driver ? It has volts in, current sense, oscillator (as many microcontrollers have), ground and output. Is the 4~40V input a PWM input ? and the output a current amplified input ? Sometimes it's done by pulling the current sense pin high to turn off the output, or there may be an external FET to do the PWM. Link to comment Share on other sites More sharing options...
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