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IBM 5160 IBM WD25 Type 13 Power Up failure

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MauriceH

Experienced Member
Joined
Apr 2, 2014
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399
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Dordrecht , Netherlands
Have a IBM XT 5160 with the IBM 20MB WD25 MFM hard drive.
AT start up no spin or light from the drive, only after some seconds the click from the Head block brake.

Checked the PCB for common failures as traces, Power resistors, power transistor capacitors and relays contacts.
Also the relay is powered by start up.

Then suddenly at a stand alone power up (5V and 12V on the connector) it started to spin again.
Put back in the XT and it ran perfectly the whole evening without a failure.

Next day, dead again, no spin.Also no seek of heads.

Try to figure out if the Hard disk could spin up only through a voltage on the power plug, or
does it get a control start from the MFM driver board?

The MFM driver card is the IBM 62X0776 that came with the drive.

Maurice
 
Sounds like "Stiction". The heads stick to the platters when the drive stops and the spindle motor is not strong enogh to get it spinning again. Sometimes, a jolt or a tap will move the heads enough to free the platters. I think moving or turning the drive over to inspect the PCB did just that. Next day, stuck again.
 
Sounds like that to me also. Unfortunately, there's little hope for a permanent cure. You may get some relief by running/exercising a drive for an extended period of time (several hours), but that's a roll of the dice.
 
No it is not sticky heads.
The spin motor drives freely. Took of the pcb to check.

Found a schematic of IBM HD type 1 & 2,(10MB) to figure out the spin circuit.
Should be somewhat the same type of circuit.

ALso found some MFM card pin outs and only a Drive ready, and that activates after stable motor RPM and head seak track 0 check , so the start-up seaquence is in
the Hard drive , Well no spin at all, so no drive ready.

The relay is activated if there is 12V and 5V present, That is functional.
Checked the big power transistor and measures OK.
Now following the Base cicuit of that transistor, and the next Zener diode and transistor with a Tantal capacitor are also OK.
SO tracing back signaling.
 
Documentation: Does any one have the original " 6523278 Industrial_Computer_Technical_Reference_Options_and_Adapters_Volume_1.pdf" "

It contains the schematic of the 20MB drive, BUT...page 80 this PDF it missing 2 sheets! And that are the sheets I need. (Sheet 2of 4 and Sheet 4 of 4)
Found it on Bitsavers.

Tested the drive with a ATX power supply,It started 5 times in a row.
So thought something with the power supply
Found a second XT power supply, Tested in stand alone, Harddisk started, great, BUT
Put back in the PC, Dead a gain.
GOT the 1701 error. LED Light of the Harddrive flashes at boot though. But no spin.

Connected to the ATX-PSU-again, Nothing.
So it is still a random thing that it will not get started to spin.
damm.

An Other 20MB Rohdime FULL High 20MB works perfect in the PC with that XT-PSU.
 
Thanks, Found the problem, There are 2 X-tal on the board. The 11Mhz from CPU was only 1,8kHz.
It is a blue ceramic one near pins 1-2 of the CPU. That was the stinker, 2 X-tals.
Replaced with a normal 11.0568 Mhz and motor starts instandly TOP, ,,,BUTTTT dammm
Now the head stepper will not start to step.

How and why. It was few day's back perfectly working.
Maby that CPU D8049HC-5MO is defect due to all that fiddeling.
If I touch Pins near pins 4-5 the spin motor troubles again.
A new power-up and back perfect spin.
The tacho signal from spinmotor is coming to the CPU, also the step Track 00 indicator is there on the CPU.
But no data signals to be found on the CPU.

Think have to find a broken WD25 with a bad disk or heads or so to make mine work a gain.
I know the heads and disk are good.
 
Problem Solved.
The 11 Mhz Ceramic Resonator was defect, was only 1.8kHz.
Replaced with a X-Tal 11.0 Mhz and Up and running again.

That is beware of also broken flat cables, had with testing used a broken flat cable and so the search
of half working HD took a bit longer than necessary.
Changing the cables and runs as new.

So HD's can be repaired.
Also found the right schematics Type 13 IBM WD25 in the document.page 335: Technical_Reference_Options_and_Adapters_Volume_1_Apr84.pdf
 
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