righttoe Posted August 17, 2009 Share Posted August 17, 2009 Hi guys, ive had a search but cant find a answer to my question. I have 6 Mac250's in work, which Ive just repaired but one has a final fault I cant solve, the pan motor is sticky on reset and at fast speeds, it will either lock up when powering up the fixture, and you have to give it a nudge, or it will jerk when moving fast on a test. Now I have swopped over the motor with a working one, and the fault is still there, so then I swopped over pan and tilt cables on the mainboard, this transfered the fault to the tilt, so its the driver on the board somewhere, I have swapped over the '3772' chips for pan and tilt and that did nothing, and I cant seem to find any other things I can swop, any ideas? I know I can buy a replacement board but they are very expensive and im not a newbie to soldering electronics so would like to try to repair it myself first! Any help much appriecated Mike Link to comment Share on other sites More sharing options...
mutley Posted August 17, 2009 Share Posted August 17, 2009 I've had similar problems with MAC250s before, and I found that one of the 1ohm (IIRC) resistors next to the 3772 controller chip had gone open circuit.Try testing them with a multimeter.The other likely cause is a broken wire going through the yoke. I replaced about a dozen sets of wires in 250's when I worked at a well-known UK holiday resort. Broken wires are quite often the cause of 'FbEp' errors because one (or more) of the wires from the opto-slotted disc is broken. when you give the wire a pull, it should feel solid, but a broken one will stretch the insulation at the breakage. You're best to replace the whole set (normally 5 or 6 wires), as it's likely that others are only holding in there with a few strands. When I did it, I replaced the pin header plugs too, as it's easier than trying to solder new wires onto old pins that small. They're literally only a few pence at decent electronics suppliers (CPC link). Link to comment Share on other sites More sharing options...
righttoe Posted August 17, 2009 Author Share Posted August 17, 2009 hi, ive checked the loom and its fine with no brakes, yea ive had loads of them brake but its not that this time, theres no error on the screen and when I swop pan and tilt motor plugs on the board over, it transfers the problem to the tilt, so its definatly a fault with the control board, I will check the resistors 2moz but I did check a few of the larger ones today and they came up fine. its as if the power going to the motor is not high enough to make the motor turn all the time Link to comment Share on other sites More sharing options...
David Duffy Posted August 17, 2009 Share Posted August 17, 2009 We had a really bizarre fault on a MAC250 recently. The symptom was that one axis was dead. Swapping wiring narrowed it down to a faulty driver board. Swapping / replacing driver chips, etc didn't fix it. Checking with a CRO showed all signals getting to the input of the driver chip. So, all signals present, no faulty chips, no soldering/track faults but still not working! I then spotted a 4.7nF (I think) capacitor next to the driver chip. It's part of the PWM oscillator (internal to the driver chip) circuit. Measured it to find it a tenth of the correct value. Replaced it and all good. Phew! Link to comment Share on other sites More sharing options...
mutley Posted August 18, 2009 Share Posted August 18, 2009 On the subject of repairing MAC250s, how useful would a diagnostic unit be? It could provide a variable speed FWD-REV stepper motor control, 6way wire continuity and cross-over check, and LED indication of motor field current (eg, four red and four green LEDs to show each field and direction, if one pair of LEDs fails to illuminate, you have a problem with that wire...... I'm really just thinking out loud here.... :D So if this would be useful for you, let me know and if it's worthwhile, I'll look into building a prototype. I'd expect it to cost about £60-85 Link to comment Share on other sites More sharing options...
stuart.t Posted August 18, 2009 Share Posted August 18, 2009 sounds like your problem are the resistors around the stepper driver chips. They are 1.5 Ohm resisters is groups of 3 so you generally meter them out at around 0.5 Ohm. There should be 4 groups of 3 resistors with each driver chip. Some chips have the resistors under the driver chip so you will need remove the chips to find them on some. Link to comment Share on other sites More sharing options...
righttoe Posted August 18, 2009 Author Share Posted August 18, 2009 right great stuff guys, I think ive found it, as stuart said 3 of the resistors are over reading, there under the pan chip. they are blue and marked 1R50 the same as the other blue ones around the chip, all the others are reading approx 0.7, but the 3 under the chip are reading about 50Kohms Ive also measured the 3 under the tilt chip and these read correct at 0.7ohm Now the next stage, I can get the resistors but im used to soldering bigger PCB's or strip board, am I going to be able to do it with a normal soldering iron? and also I think I need to take the chip holder off first! Any advice about replacing these would be appricated Mike Link to comment Share on other sites More sharing options...
stuart.t Posted August 18, 2009 Share Posted August 18, 2009 Them resistors reading 50Kohms definitly need replacing. They should in theory read 0.5 but in practice it is more like 0.6 or 0.7 so the others are fine. I always replace these with a normal soldering iron. Just heat up both sides of the resistor while applying a little force with the tip to get the resistors off. Afterwards just put the new resistor on the board and while holdign it in place with some tweezers solder one side onto the board then once that is secure the other side is easy to solder on. Link to comment Share on other sites More sharing options...
James Maxn Posted August 18, 2009 Share Posted August 18, 2009 Hello all, How strange!! I was just doing a search on the net to find a cure for this exact same fault I have on a mac 300!! I have the same fault on the unit I'm reparing. Pan & Tilt very week, no propper movement, kind of jerks etc... But did the same as what has been suggested, measured the 1R5 resistors and found 3 under each 3772 chip open circuit.Going to order in some smd resistors. What wattage would they likely be???? j Link to comment Share on other sites More sharing options...
stuart.t Posted August 18, 2009 Share Posted August 18, 2009 resistors used are 1.5 OHM , 1%,SMD, 0.25W Link to comment Share on other sites More sharing options...
righttoe Posted August 18, 2009 Author Share Posted August 18, 2009 Thanks Stuart for all your help so far, its been very useful! I've ordered the resistors from RS today, minimium order was 5000! cost £15 but ah well, ive succesfully desoldered the chip holder to access the resistors better, and have removed the resistors, but will have to order a new chip holder because I had to destroy it to remove it ** laughs out loud **! James - yea its funny youve got the same fault, and its the same 3 resistors, martin wanted £700 for a new mainboard and stage electrics wanted £350 for a refurbed one, it looks like all they do proberly is replace there resistors or a chip as it seems a common fault! Will let you know tomorrow if it all works fingers crossed! Miike Link to comment Share on other sites More sharing options...
mutley Posted August 18, 2009 Share Posted August 18, 2009 The alternative to buying 5000 surface mount resistors, would be to use single 0.47ohm 1W standard axial resistors, and solder them on. Ok, they would stand off the PCB slightly, so might not be quite as tidy as the surface mount ones, but it does work out easier (and cheaper, although £15 for 5000 is not exactly expensive!), than fiddling about with surface mount resistors right next to the IC holder. These would also be available from high street electronics stores like Maplin. However, the longer the component leads, the more prone it would be to it being shaken loose and breaking off the PCB.... Link to comment Share on other sites More sharing options...
James Maxn Posted August 19, 2009 Share Posted August 19, 2009 I did think of that because I have normal axial resistors in my workshop, but agree I think it would be messey, and would be a bit of a squeez under the driver chips! I got some smd resistors from farnell for about £2 inc postage for 50, Digikey around the same price but take longer to deliver! If I searched for the resistors yesterday I would of let Mike (rhitto) know, but anyway still cheeper than sending the board off to martin or replacement! Or £700 for a new one! :) My nearest martin dealer is prism lighting, sent a lightjocky card for repair through them, very good service. No idea how much the mac 300 board would cost to be repaired! if they still do repair old kit. I to will keep everyone informed on progress!!! Back to pat testing for the moment though! james Link to comment Share on other sites More sharing options...
James Maxn Posted August 20, 2009 Share Posted August 20, 2009 Right! Resistors arrived this morning! I did't remove the IC sockets, instead I just cut the plastic support in the middle and used a very fine soldering iron bit! Removed all the 1.5 ohm dead smd resistors and replaced them all with new ones. I installed the board in the mac and problem solved!! It is back to normal! A big thankyou to you all! :) Saved me from spending an unnecessary fortune! Link to comment Share on other sites More sharing options...
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