Doh, fried a rotating mirror

[RoGeorge]

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 - GND
4 - 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: [Select]

Vcc  Fgen (Hz, 3.3V, 50%duty)   Fmeas   RPM (60*Fmeas/6)   Fgen/Fmeas
12v         300 000               220      2200            1363.64
12v         400 000               293      2930            1365.19
12v         500 000               368      3680            1358.70
12v         600 000               390      3900            1538.46
12v         700 000               514      5140            1361.87
12v         800 000               590      5900            1355.93
12v       1 000 000               745      7450            1342.28
12v       1 200 000               887      8870            1352.87
12v       1 500 000              1118     11180            1341.68
12v       2 000 000              1548     15480            1291.99
12v       2 500 000              1945     19450            1285.35
12v       3 000 000              1870     18700            1604.28
12v       3 500 000              1873     18730            1868.66
24V <- wrong, max is 12V     3 500 000              2563     25630            1365.59


[RoGeorge]

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 Vcc should be 24V, but it was 12V 
J207 pin 2 SCNTAC Scanner tachometer pulses
J207 pin 3 FG
J207 pin 4 /SCNON “L” to rotate scanner motor
J207 pin 5 SCNCLK Scanner clock reference

The 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!