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 Post subject: Seagate ST251 MFM HD problem
PostPosted: January 11th, 2023, 5:15 
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I have found my old ST251-1 HD from my parents loft and even though I should have all my data stuff off it when i moved to another computer I would still like to check a do a proper copy of everything from it if i can.

Problem is when power is applied (nothing else connected) it spins up fine but doesn't do the head seek/calibration bit and so is stuck in its parked area.

I have moved the heads out manually and powered down, the stepper motor correctly auto parks the heads.

I have replaced the 2 power capacitors on the main control board as mentioned here :

https://www.lo-tech.co.uk/wiki/Seagate_ ... pair_Notes

to no avail, the logic would suggest get another ST251-1 off fleabay and swap the control board, as with anything retro now the prices are ridiculous, so would anyone have any ideas why the drive won't calibrate/seek after spinup and/or things to try?

This is exactly what it sounds like (link starts at 1:09) :

https://youtu.be/yuUvd_YDGDs?t=69


Spins then a small strain sound then nowt (except spin). Drive therefore doesn't initialise.

Any ideas what could be wrong?

thanks


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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: January 11th, 2023, 11:08 
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isn't there a rubber limiter that sticks and grabs the head assembly in park pos?

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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: January 11th, 2023, 11:37 
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possibly but I have manually moved the heads into the middle of the platter and powered it on still no movement from the head except when powered off and the head moves itself into the parked position.


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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: January 11th, 2023, 12:51 
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There is a circuit diagram here:

https://mirrorservice.org/sites/www.bitsavers.org/pdf/seagate/mfm/ST-251/
https://mirrorservice.org/sites/www.bitsavers.org/pdf/seagate/mfm/ST-251/Seagate_ST251_schematic.pdf

Are these drives supposed to calibrate on their own? I thought most of the smarts were on the MFM controller board, not the HDD.

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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: January 11th, 2023, 13:29 
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The read data on MFM drives is not seen by the drive's own controller. Instead, the raw analogue data is passed to the off-board MFM/RLL controller and decoded there. The only "calibration" that the drive would do is to return the headstack to track 0.

To see this for yourself, follow the read data path from the HDA connector (J6) in the schematic.

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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: January 11th, 2023, 13:41 
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Calibration might be the wrong word to use in this case for example there are many videos of the ST-251 sounds on youtube that only have the power connected, one working example is :

https://www.youtube.com/watch?v=wvDe6oi4Oa8

This isn't connected to any controller card just power applied to the drive, the drive spins then the head seeks around the platter goes a bit mental then calms down.

Mine doesn't do the seek around the platter and go a bit mental bit after it spins up (whatever that function is, initialise?), so any problem/issue my drive has is isolated to the drive itself or onboard electronics.


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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: January 11th, 2023, 19:51 
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jwd wrote:
Calibration might be the wrong word to use in this case for example there are many videos of the ST-251 sounds on youtube that only have the power connected, one working example is :

https://www.youtube.com/watch?v=wvDe6oi4Oa8

Sorry, it looks like I was wrong. The READ DATA are also fed to the Step Logic IC which in turn communicates with the 6510 controller.

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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: January 16th, 2023, 7:57 
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Joined: January 11th, 2023, 5:08
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another forum suggested using the 'life test' jumper setting :

Quote:
When pins 7-8 of J7 are shorted, the
stepper motor will continuously seek between Track 0


No action from the drive when this jumper applied so if the stepper can move the head back to park but not action this function I would guess that points to the board logic is dead?

Just need another ST251-1 board to swap out but $800 on ebay for these drives!!


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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: January 17th, 2023, 13:39 
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Joined: September 14th, 2009, 23:21
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Location: United States
I have one of these drives that works but it would probably be cost prohibitive to ship your drive overseas twice, not to mention the non-zero chance of the shipping company destroying it


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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: January 17th, 2023, 17:15 
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@jwd, do you have any tools or experience in electronic troubleshooting? We could do some basic testing to narrow down the fault to a particular area of the circuit.

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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: January 18th, 2023, 5:14 
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Joined: January 11th, 2023, 5:08
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Location: London
fzabkar wrote:
@jwd, do you have any tools or experience in electronic troubleshooting? We could do some basic testing to narrow down the fault to a particular area of the circuit.


Yes i'm pretty handy with a soldering Iron and have an old (1982) Panasonic Oscilloscope if required.

Any starting points on the board (have replaced power caps as mentioned in first post) to check would be greatly appreciated.


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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: January 18th, 2023, 15:14 
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My first observation is that the pin numbering for jumper block JP7 in the product manual is flipped. According to the PCB and schematic, pin #1 should be pin #15, and pin #15 should be pin #1, and so on. This means pins 9 and 10 should be jumpered to initiate a "life test". Pin #1 is the square pad on the underside of the PCB.

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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: January 18th, 2023, 15:51 
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AFAICT, the R6518AJ microcontroller controls the stepper motor but not the spindle motor. The spindle motor appears to spin up on its own as soon as power is applied. The only input the motor controller (HA13406W and 9J) gets from the uC is a sysclock from pin 4 (9J-2). To me this suggests that the motor would still spin up if the uC were dead or in a halted state due to a bad EPROM.

The uC only has 192 bytes of internal SRAM and no external RAM. This is insufficient to buffer one 512-byte sector, so this suggests that it does not read the MFM data. Perhaps it only uses the sync bits?

I would check the Reset pin of the uC (pin #21, active low). It should be high.

The Life Test input appears on Port B, bit #3 (pin #38).

Check the Address and Data pins of the EPROM. If the uC is running, there should be activity on these pins.

Check the inputs to the L293D phase drivers near J5. These chips drive each of the stepper motor phases. If these are missing, then work backwards through 7C (STEP SEGR, Motorola SCQ05701), decoder 74F138 and octal buffer 74LS273.

If you suspect the EEPROM, there is a dump here:

https://mirrorservice.org/sites/www.bitsavers.org/pdf/seagate/mfm/ST-251/ST251.bin

References:

https://mirrorservice.org/sites/www.bitsavers.org/pdf/seagate/mfm/ST-251/ST251_f.jpg (component side of PCB)
https://mirrorservice.org/sites/www.bitsavers.org/pdf/seagate/mfm/ST-251/bot.jpg (bottom side of PCB)

R6518A, Rockwell, 8-bit microcontroller, 192-byte SRAM, external ROM, 2MHz, 5V, PLCC-44:
http://www.bitsavers.org/components/rockwell/_dataBooks/1987_Rockwell_Controller_Products_Databook.pdf (page 450)

HA13406W, Hitachi, 3-phase brushless motor driver, 5V & 12V/3A, SP-23TA:
https://avtronic.eu/medias/ha13406w/ha13406w.pdf
https://pdf.dzsc.com/HA1/HA13406W_1219953.pdf
http://www.bitsavers.org/components/hitachi/_dataBooks/1984_Hitachi_IC_and_Discrete_Quick_Reference_Guide.pdf
http://www.bitsavers.org/components/hitachi/_dataBooks/1985_C10_Hitachi_Linear_IC_Data_Book.pdf

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 Post subject: Re: Seagate ST251 MFM HD problem
PostPosted: February 4th, 2023, 9:11 
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Joined: January 11th, 2023, 5:08
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Location: London
Just an update on this if anyone is interested.

I managed to find a donor ST251-1 drive in good condition and most important cheapish. Swapped the logic board and powered up, this time with the correct sounds and seek test after spinup as it should, yay!

Now when connecting to my controller board its not seen but at least i can here 'trying' from the drive when the controller is communicating.

Progress albeit slowly . . .


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