English Amiga Board - View Single Post - Getting one working Floppy Drive from two non-working ones

richud · 05 March 2021, 14:54

Hi, thought I would post here as this is top google hit about it...hope it helps someone.
I have both a JU-253-043P and JU-253-033P which both had/have issues.

The 043P didn't like reading parts of disks sometimes (repeatably at same points on the same disk) and sometimes was fine, a bit strange. For example I could take several games, load them all fine one day - next day all would fail to load at various repeatable points.
Did a lot of fiddling with track0 position sensor, motor position and top head, eventually replaced caps with some SMD 1210 ceramics. Old caps capacitance was fine (didnt measure ESR though!) and no obvious leakage signs.
I have just borrowed an external drive to boot the wonderful Amiga Test Disk (ATK) in DF1, then able to redo calibration (which ended up on same as marks to begin with) it now seems ok, so not sure if was caps or its just dicky and the period between dickiness has just increased.

The 033P spins up but does nothing after track0 seek 'failing', like it cannot find track0 because sensor is in wrong place. After much fiddling, still nothing.
As now just borrowed external drive and can run ATK - discovered there are no index pulses.
So after reading this thread and others assumed the hall sensor was the problem....

Looking at solarmon's diagram (took me a while to get my head round it)

P1 5v
P2 output (held high)
P3 TP?
p$ GND

...and testing my non-index outputting one, I came to conclusion my hall sensor is in fact ok.

If this helps anyone with the drive unplugged and hall sensor in circuit
good drive resistances
1-2 4.92kO
1-4 2.349kO
2-4 7.28kO
3-4 1.152kO

bad drive (that i think also has an ok hall sensor)
1-2 4.70kO
1-4 2.795kO
2-4 7.5kO
3-4 1.590kO

Using multimeter between gnd(p4) and output(p2) [It is easier to probe the leg on the IC than directly on p2 when drives spinning!]
should show different when motors spinning to off on DC & on AC setting a kind of even fluctuation when motors running. Presumably it pulls the output low on each pass.
My multimeter has a frequency setting, and then a sub function to measure rpm - on both drives this read 0.3k rpm i.e. 300 rpm - so thus assume both hall sensors ok.
(Also you dont need disk sensor 'down' to measure things, should always ouput when its spinning)
The head testing on ATK also shows nothing like, alignments totally out, and disk read test on ATK all B's. (Im 99% sure thats all actually fine).
It seeks fine to 0 -40 -79 , spins fine, motor on/off fine, everything appears totally ok.

Thus in conclusion I think my hall sensor is ok, drive mechanics are ok, and the problem is sadly elsewhere....

Other notes
-----------
In ATK will only show index pulses if the 'disk in' sensor is down (one furthest in of the two), just having motor 'on' without that won't show any,

Testing voltage with drive powered on and then manually moving the motor plate magnet's around over the sensor didnt seem to produce any change on the output, this seemd a bit odd. Manually doing anything never got me any change. I would just go straight to testing it in ATK with motor spinning.

The Hall sensor chip on bad drive marked '250', other one has nothing descernable on it.

05 March 2021, 14:54	#29
richud Registered User Join Date: Feb 2021 Location: Leicestershire Posts: 2	Hi, thought I would post here as this is top google hit about it...hope it helps someone. I have both a JU-253-043P and JU-253-033P which both had/have issues. The 043P didn't like reading parts of disks sometimes (repeatably at same points on the same disk) and sometimes was fine, a bit strange. For example I could take several games, load them all fine one day - next day all would fail to load at various repeatable points. Did a lot of fiddling with track0 position sensor, motor position and top head, eventually replaced caps with some SMD 1210 ceramics. Old caps capacitance was fine (didnt measure ESR though!) and no obvious leakage signs. I have just borrowed an external drive to boot the wonderful Amiga Test Disk (ATK) in DF1, then able to redo calibration (which ended up on same as marks to begin with) it now seems ok, so not sure if was caps or its just dicky and the period between dickiness has just increased. The 033P spins up but does nothing after track0 seek 'failing', like it cannot find track0 because sensor is in wrong place. After much fiddling, still nothing. As now just borrowed external drive and can run ATK - discovered there are no index pulses. So after reading this thread and others assumed the hall sensor was the problem.... Looking at solarmon's diagram (took me a while to get my head round it) P1 5v P2 output (held high) P3 TP? p$ GND ...and testing my non-index outputting one, I came to conclusion my hall sensor is in fact ok. If this helps anyone with the drive unplugged and hall sensor in circuit good drive resistances 1-2 4.92kO 1-4 2.349kO 2-4 7.28kO 3-4 1.152kO bad drive (that i think also has an ok hall sensor) 1-2 4.70kO 1-4 2.795kO 2-4 7.5kO 3-4 1.590kO Using multimeter between gnd(p4) and output(p2) [It is easier to probe the leg on the IC than directly on p2 when drives spinning!] should show different when motors spinning to off on DC & on AC setting a kind of even fluctuation when motors running. Presumably it pulls the output low on each pass. My multimeter has a frequency setting, and then a sub function to measure rpm - on both drives this read 0.3k rpm i.e. 300 rpm - so thus assume both hall sensors ok. (Also you dont need disk sensor 'down' to measure things, should always ouput when its spinning) The head testing on ATK also shows nothing like, alignments totally out, and disk read test on ATK all B's. (Im 99% sure thats all actually fine). It seeks fine to 0 -40 -79 , spins fine, motor on/off fine, everything appears totally ok. Thus in conclusion I think my hall sensor is ok, drive mechanics are ok, and the problem is sadly elsewhere.... Other notes ----------- In ATK will only show index pulses if the 'disk in' sensor is down (one furthest in of the two), just having motor 'on' without that won't show any, Testing voltage with drive powered on and then manually moving the motor plate magnet's around over the sensor didnt seem to produce any change on the output, this seemd a bit odd. Manually doing anything never got me any change. I would just go straight to testing it in ATK with motor spinning. The Hall sensor chip on bad drive marked '250', other one has nothing descernable on it.