Issue 3" drive rotation speed

Kris · 13:49, 27 April 17

Hello all,

I just face a strange behaviour with my 3" drive: I just change the drive belt and run "RPM" software to set up the rotation speed.
Result is that rotation is read as "600 RPM" instead of 300; the soft display in continue 600 600 300 600 600...Etc

Edit: I just try this drive into another CPC and it works perfectly (RPM gave about 300 Rpm).
It means that a component into the CPC is defective but which one ? FDC ?

Any idea about what is wrong ?
Thank you

Bryce · 14:33, 27 April 17

Crazy RPM readings can be caused by an intermittent 12V rail. Check for dry joints on all the connectors, especially the ones to the motor. Also make sure that you have removed all the old gunk on the two belt wheels.

Bryce.

Kris · 14:41, 27 April 17

The drive is working perfectly onto another CPC so it does not come from the motor etc... but from the CPC itself.
Everything welding point are good on the drive side and old drive belt wheels have been fully cleaned.

I also use the same monitor and 12V from it is good and stable.

Bryce · 14:49, 27 April 17

Yes, but even moving the drive from one computer to the other can be enough to temporarily "re-join" a dry joint.

Bryce.

Kris · 15:44, 27 April 17

To be sure, I just rework 100% of the welding point on the drive: results is the same: not OK on the original CPC but works perfectly on all the other ones.

Bryce · 15:46, 27 April 17

That's wierd. Possibly a crack in the wires from the mainboard? Or dodgy terminals in the power connector? Try spinning up the disk and see if you can get it to stop by moving the power wires.

Bryce.

Kris · 16:42, 27 April 17

The issue is coming from the CPC : I installed a drive from another fully working 6128 and got the same result of 600-610 RPM....
VEry strange, I continue to investigate.

Kris · 13:07, 30 January 18

Back on this issue, I still don't have any idea how to fix it....help wanted

Bryce · 13:23, 30 January 18

Send me the CPC (just PCB) if you like.

Bryce.

Kris · 19:46, 30 January 18

Why not; let's continue on PM

gerald · 21:04, 30 January 18

Did you check the index signal from the drive to the FDC ?

Kris · 14:09, 07 February 18

At the moment, I did not take time to check any components but I will do it this evening (I own an oscilloscope but any help would be grateful)

Here are what RPM soft give me as results (602 RPM - note that this drive has been correctly calibrated @300RPM - track 19 with an other CPC ).

guigui37 · 17:54, 09 January 21

Hello
I have exactly the same Issue on my3" drive (still internal)... [size=78%]I am running rpm from gotek externaly... the speed is always about 600 ... and sometimes displays 300 but immediately goes back to 600... did you solved this issue ? How ?[/size]
[/size][size=78%]Thanks[/size]

Bryce · 18:30, 09 January 21

If the RPM test is giving crazy results, it's usually just a bad solder joint.

Bryce.

guigui37 · 20:22, 09 January 21

Yes totally crazy....
Do you have an idea of the location ? On the mainboard of my 6128 or on the board of the floppy drive... in a specific place ?

Bryce · 22:41, 09 January 21

On the drive itself. Usually the connectors.

Bryce.

guigui37 · 09:39, 10 January 21

Ok, i will Check....
I already saved the main board so tones of soldering are fresh...
Thanks..

guigui37 · 11:44, 10 January 21

Redone all connectors and more, no change

GUNHED · 13:55, 10 January 21

Bonjour!

My guess would be a problem in the software. If the drive would really speed up from 300 to 600 you probably would hear it.

Quote from: Kris on 13:49, 27 April 17
Hello all,

I just face a strange behaviour with my 3" drive: I just change the drive belt and run "RPM" software to set up the rotation speed.
Result is that rotation is read as "600 RPM" instead of 300; the soft display in continue 600 600 300 600 600...Etc

Edit: I just try this drive into another CPC and it works perfectly (RPM gave about 300 Rpm).
It means that a component into the CPC is defective but which one ? FDC ?

Any idea about what is wrong ?
Thank you

Kris · 14:12, 10 January 21

Quote from: GUNHED on 13:55, 10 January 21
Bonjour!

My guess would be a problem in the software. If the drive would really speed up from 300 to 600 you probably would hear it.

You're right, there is no issue with the drive itself, I tested it onto another CPC and result is about 300RPM so 3" drive is not the root cause. I do the same with another drive connected to the motherboard which gave me 600 RPM: same behaviour so the difference is coming from that motherboard, but I don't see anything that can explain the difference.

Bryce · 15:27, 10 January 21

Ok, if that's the case then one of the FDC buffers is failing. Most likely IC203 (74LS240), second most likely: IC205 (74LS08).

Bryce.

guigui37 · 08:51, 12 January 21

Maybe I could first check the soldering of the fdd controller NEC 765A ?

GUNHED · 22:18, 12 January 21

Quote from: Kris on 14:12, 10 January 21
You're right, there is no issue with the drive itself, I tested it onto another CPC and result is about 300RPM so 3" drive is not the root cause. I do the same with another drive connected to the motherboard which gave me 600 RPM: same behaviour so the difference is coming from that motherboard, but I don't see anything that can explain the difference.

The software 'sees' the index hole twice, I don't have the source right here (or even know if it was released), but maybe you can contact the author. Could be possible to adjust some waiting loop.
Or it could be some hardware problem of course too. But I still would bet on the software side. Or not? Don't know now...

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Issue 3" drive rotation speed