The infamous RD53 / Micropolis 1325

[aplmak]

Oh I feel you on that sentimental data. With careful work I have faith you’ll get it! Just take your time no rush at this point right? Have you tried swapping the board on it? Oh and mine was a 1323.. but I might have a 1325.. this is what I mean by them digging out the data before dumping the machines (see photo) You’re talking to an expert with David! So you’re in good hands. I just thought I’d jump in.. you never know someone adds some small detail sometimes that works.. lol I wish you all the luck getting it all back

 

[djg]

This is for a different drive but gives some information on how this all works. I thought I had a better reference but can't find it right now.

http://www.bitsavers.org/pdf/seagate/mfm/ST-4038/36012-001D_ST4038_Product_Manual_198603.pdf

I'm not sure how they are encoding guard tracks, track 0 and normal tracks.

If you have a drive you haven't moved the stops on you may want to try the shims I did since that fixed a drive with similar symptoms to yours.

On U8, I'm seeing High Velocity Range/ Pin3 start low and transition to high at full speed. Q: Does not the trailing slash indicate active low?

Correct

However, Velocity Enable/ Pin4 (& Compensator Reset) remain always low.
I'm presuming that disables page 16 showing generation of PA.

Low on one of the control lines enables the associated signal to be summed into PA.

 

[Elektraglide]

Trace of VC1 and VC2. PAENable transitions to low (CH3 magenta) once up to speed and they start this 180 degree out of phase signal.

Does that look about right? (I am slowly following the signals around to try find where things go wrong)



Having CH3 watching Servo Sense pin shows there is a signal there that changes frequency as the disk spins up.



Zoomed in on CH3 to show telltale servo signal (well similar to DG's captures )

 

[Elektraglide]

Should Servo Peak Detect/ on pin 40 of U8 look like this? I can see as disk spins up the frequency increases which makes me think its probably right.

Put it another way. Is Servo Peak Detect meant to be a solid active low, or pulses like this?