MFM emulator

[Gary C]

Just started to build the pdp8 online MFM/ST505 hard drive emulator.

Downloaded the gerbers and had the boards made up and have just finished soldering in the components.

The instructions are a little difficult, but the provided Mouser BOM means every packet comes with the component ID on them

 

[Gary C]

Trawled my way through debian and managed to get it reading a RD52-A

 

[Gary C]

Oddly, it read the whole disk without error except for the last cylinder

 

[Al Kossow]

bad block table?

 

[g4ugm]

I have one on these MFM emulator beasts spare, I don't think I am going to use it. would you like it? I built it so it probably needs debugging. I have never used it.

 

[Gary C]

We have an apricot and an altos that need them

 

[Gary C]

Just tried to read an rd54-a and while the platter spins, the heads seem to have lost any control. They just pulse and move across the disk ?

Not sure if they are damped or the servo (track ot physical?) is missing. Its a maxtor version Maxtor XT-2190

Edit. Damn, it uses a dedicated servo platter and so it looks like that isnt giving feedback.

So doorstop.

 

[Gary C]

Plan to test its emulation, is to write a 3.5 bootable floppy with fdisk using my Apricot then try to format the emulator.

However, it wont work ! PSU out of the machine, starts up but when put back the 5V line only goes to 0.98V but no Tanalums shorting it out.

Time to get side tracked and investigate...

 

[Gary C]

Yay, flyback startup capacitor defective. Replaced and backup and running.
Now need to replace all the foam pads to get the keyboard working.
All to test the emulator.

 

[Gary C]

And it works.



Some oddities, wont boot off thr floppy unless the HD is ready and unless you start the emulation it won't come ready, except you cant log in to set it ready while the machine is frantically trying to access the drive. Have to hold down reset, login, set to drive emulate then let got and let it boot.
Will have to amend the startup to go straight into emulation.

But its working