SDumas wrote on 2023-10-23, 08:24:

Hi lowlytech,

Did you see this? Can you confirm that this IC is damaged?

I think the 1st pic just had some flux or something on the chip. Here is a new shot after going over it with IPA

Deunan wrote on 2023-10-23, 09:40:

lowlytech wrote on 2023-10-23, 04:47:

But the yellow one seems totally dead or no change on the scope. I marked the solder side where that yellow crystal is.

There is some sort of white residue between IC pins that connect to the resonator. Could be just enough to affect the circuit - use some old toothbrush to clean the PCB, make sure there is nice, clean separation between the pins. If there's still no clock there then the resonator itself is suspect - you could try a transplant from another drive (if only to test the theory).

Good eye. I did clean that up and it has no extra resistance (my probes register 0.06 ohms when pressed together and the pcb trace measures 0.07ohms). Still doesn't work unfortunately. So I tried testing that resonator on the other 5.25" drives I have here and I don't get any activity on any of them. Do you think there should be activity on the resonator if the disk isn't turning? Also tried to measure DC Volts and I have nothing on either leg of the resonator if that is normal I don't know.

lowlytech wrote on 2023-10-23, 16:08:

Do you think there should be activity on the resonator if the disk isn't turning?

It depends on the particular IC that controls the motor. In this case the HA13456A datasheet block schematic would suggest the clock always runs, but it could be gated and disabled when /CE is H - to further save power. Since most of the delay of motor-on event comes from overcoming the inertia of the motor and media (which is about 300ms) a few more miliseconds to bring up and stabilize the clock would not matter that much.

To be sure I've just tested this on my Mitsumi/Newtronics D509V3, which is a newer model and uses HA13483A for the motor contol. The clock is absent until chip gets the /CE set L to start the motor, so it's safe to assume your HITACHI chip does the same. On your photo of the spindle motor PCB the short black ribbon cable on the right should have these signals (bottom to top): 12V, GND, /CE, sensor, 300/360. Of which you care only about the power rails (12V, GND) and the /CE which should be L (close to 0V) to get the motor running. Sensor and 300/360 speed selection can be anything (left floating/unconnected) and don't matter if you want to test the motor PCB out of circuit.

I'm assuming you are testing the PCBs out of the floppy drive? Did you connect the stepper motor (for the heads) back? When power is applied the drive should try to seek to track zero - which it can't with the zero track optical sensor never being occulded so the stepper motor should run for at least a second or so (possibly run and not stop at all). Since this requires the phases and delays of the control IC to be correct it would mean the chip is good. Motor not spinning and getting hot, while the clock is clearly there, means the chip is faulty.

EDIT: In case I didn't make it clear - the easiest way to test the spindle motor PCB would be to just apply power and flip the media sensor switch. This should get it running for 5s or so. If the switch works but the motor doesn't turn on (and /CE signal is not changing state) then the stepper/timing IC is again the most likely culprit.

I haven't put the motor back since it is a solder job instead of a connector. I haven't been testing it with the heads attached. I am about to put the drive back together, so I will test one last time with everything connected.

Before the complete teardown the heads would attempt to move but it was like the motor would seize up a split second later. I don't think I ever saw the disk media platter motor ever move. The computer instantly throws up a floppy drive error as well.

So say if I was able to find a replacement IC, would it be this one (LB1656) since it is what is connected to the worm motor? A quick ebay search turned up no hits, so may be a fools errand.

Got the drive totally reassembled. The floppy head was purposely not left at track 0, just somewhere in the middle. The drive head motor buzzes like it trying to rezero the heads, but it just won't move like before. Just buzzes and gets warm after 30-40 seconds. I put the scope on each of the 4 wires going to the motor and the waveform looks the same on all 4. Also the resonator on the spindle motor section still shows no signs of life whatsoever.

Think I am about done trying to fix this drive. I really do appreciate everyone's help trying to figure this thing out. Guess I am gonna move on to the Teac 55-GFR and see if I can get that one working maybe.

lowlytech wrote on 2023-10-23, 20:25:

The drive head motor buzzes like it trying to rezero the heads, but it just won't move like before. Just buzzes and gets warm after 30-40 seconds.

Oh so the stepper is getting pulses after all? Without the pulses I would point to the bigger Mitsumi chip being faulty but with the pulses present it could also be the driver chip LB1656 being weak/damaged and unable to turn the worm screw. It could also be a fault of the stepper motor itself (shorted winding). However seeing how there is no reaction to the media presence sensor from the spindle motor I think it is the Mitsumi chip after all.