Doh, fried a rotating mirror - Page 1
Forum section: electronics / general

author: RoGeorge
author_rank: Super Contributor
timestamp: April 24, 2022, 01:00:36 pm
content: Found in the scrap boxes a BLDC motor+driver module marked 2497NA on the backside. That was the rotating mirror from a LASER head of a B&W printer, don't know the exact printer model. Googled a lot for the AN8247SB datasheet (BLDC driver), but couldn't find it anywhere.Anybody have the datasheet for AN8247SB, please?Online there were more pinouts for the 5 pins connector of the module, and contradictory info. Anyway, reverse engineered the pinout of the module. GND was easy by testing the continuity with all the metal parts, Vcc also easy by looking at the width of the traces. The three left pins turned out to be one tachometer output, 6 pulses per each turn (open drain or open collector), one tachometer input (pulses to set the desired RPM), and one motor enable input, active low.The pinout found, counting from the outside to the middle pin of the connector:1 - Vcc (+12V)2 - readRPM (speed output OC, 6 pulses per each motor turn, RPM = readRPM/6*60)3 - GND4 - motOn (Enable motor input, active low, tied to GND during testing)5 - setRPM (speed input, 50% square wave, tested with 3.3V and 300 ... 3500 kHz = desiredRPM*6*256/10)When setRPM is left unconnected, it seems the motor goes for the highest possible RPM. When driven with square wave pulses (from a generator), RPM can go from 2200 to 25k!!! RPM for setRPM between 300kHz and 3.5MHz (drawn Vcc current between 50mA and 200mA approx).The readRPM pin was tied to Vcc through a 56k resistor (maybe should have tied it to a +5Vcc instead).The module endured all the tests when powered at +12V.At +24Vcc (24V is the usual motors voltage for most of the printers) it still worked OK. However, when I tried the lowest possible speed at 24V, at about 200kHz setRPM (1300 RPM) the motor stalled, the current jumped to max allowed in the power supply settings, 1A, and after that it didn't work any more.Found out later:the module must to be powered at +12V, not more.Letting the data here, so others won't risk to fry measuring theirs.Code:Vcc Fgen (Hz, 3.3V, 50%duty) Fmeas RPM (60*Fmeas/6) Fgen/Fmeas12v 300 000 220 2200 1363.6412v 400 000 293 2930 1365.1912v 500 000 368 3680 1358.7012v 600 000 390 3900 1538.4612v 700 000 514 5140 1361.8712v 800 000 590 5900 1355.9312v 1 000 000 745 7450 1342.2812v 1 200 000 887 8870 1352.8712v 1 500 000 1118 11180 1341.6812v 2 000 000 1548 15480 1291.9912v 2 500 000 1945 19450 1285.3512v 3 000 000 1870 18700 1604.2812v 3 500 000 1873 18730 1868.6624V <- wrong, max is 12V 3 500 000 2563 25630 1365.59

author: RoGeorge
author_rank: Super Contributor
timestamp: April 24, 2022, 03:33:17 pm
content: Found more, it's from the LASER scanner of HP LaserJet 5L/6L. In the service manual it's the pinout of the scanning mirror:J207 pin 1 +12 V <--- I've wrongly assumed Vccshould be 24V, but it was 12VJ207 pin 2 SCNTAC Scanner tachometer pulsesJ207 pin 3 FGJ207 pin 4 /SCNON “L” to rotate scanner motorJ207 pin 5 SCNCLK Scanner clock referenceThe bad news is I've killed that driver IC of the scanning mirror by powering it at 24V instead of 12V.The good news is I have another complete optical head, with scanning mirror, optics and LASER!