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Driver Chip Numbering

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Is there any difference between the 2 driver IC's. They both have the same NJM3772D2. Just one has U0006E on and one has U0024E.


Main reason for asking the last 2 driver chips that have been plugged in to run the pan circuit on a mac 250 have given up within half hour. The one appeared to overheat so much it caused the cerramic part of the chip to snap.

The motor measures out ok with 40 ohms each across the 2 windings. Not sure if this is relavent but when the power is first applied to the fixture the lamp relay shuts for a split second I'm assuming this is down to the transistor array needing replacement.





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The number below the chip ID number is usually the batch number, so has no relevance to the actual rating of the IC.


I had a similar problem on a Mac 250, and after much investigation, I found two of the 0.5 Ohm resistors next to the chip had gone O/C or S/C (can't remember which!)


Also, check the wiring set for the motor. It's a common fault where the wire breaks inside the insulation where it passes through the yoke pivot. It still looks intact, but a firm pull on each wire will soon tell you which has broken - it will stretch! It could also have worn through the insulation and be grounding, so even though it still shows 40 Ohms across the motor windings, one side might be grounded (unlikely though).


If any wires have broken, replace that whole set (normally six wires). When I do them, I fit new connectors too. If one wire has broken, the others are probably on their way too!


If the problem continues, try swapping the pan and tilt plugs.




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+1 to all Mutley said


The relay thing is just one of those things about that fixture - there is no pull down resistor on the input to the Darlington chip so the input floats high until the microprocessor gets its act together and drives it low. If it troubles you you can always add your own pull downs.



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  • 2 weeks later...

Still on the topic of these driver chips.


Have now replaced the pan loom and installed a new 3772. have checked the resistors and all seems ok. but even with no motor wires plugged in to the output the chip starts to heat up. Have replaced the dimmer 3775 as well as that gave up and had zero voltage at the outputs.


When the motor is connected it doesn't seem to have enough strength to hit the limit switch on the second time in the reset sequence it sort of jerks and wobbles but can't quite make it.. I've replaced the motor aswell along with the opto assembly.


I've checked the wiring for snags etc and tested to earth and no faults are evident. The fixture just seems to eat 3772's on the pan.


Do I order another 3772 and try again, I'm at a loss now of things to try?


Any advise is greatfully received.

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It sounds like it could be power related.

Check the supply voltage from the regulator, and on the IC. It should be 4.8v - 5.2v. Also meter the output on an AC setting, as it could be the smoothing cap that's failing, causing a pulsing "bumpy DC" supply, which will show as a higher AC voltage superimposed on the DC level. If you have an oscilloscope, it would help to see if the supply is smooth.


Try actually removing the board altogether and cleaning it with switch cleaner (or meths if you have no switch cleaner). Check for broken tracks, damage, foreign objects such as tinsel or loose washers. Also check for bulging electrolytic capacitors. I have found that about half of all faults are power related....


The final test would be to get a pin out of the chip, and meter each field coil output to ground, supply, to the other output pins. The results should be pretty similar on the pan as the results from the tilt circuit.


Other than that, I would consider sending the board off to a specialist.

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