Search found 455 matches

by tcat
Tue Nov 07, 2017 9:48 pm
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10333

Re: Microdrive Unit Design

Hi Cristian, Can you tell me please which software did you use for this test? `mDoubler', program I coded for Italian preservation project, Outsoft - program idea contributor / tester, defacto so far the only user / licensee. It is fair to say, it was helped and inspired by Martin's Head work. Progr...
by tcat
Tue Nov 07, 2017 9:20 pm
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10333

Re: Microdrive Unit Design

Hi, I managed to draw a magnetics curve, after quite a few emails exchanged with Louise, he has patiently guided me through it. It shows an old MD tape record erased by a direct current, and a new record made with direct current premagnetics, that is a transition from one magnetic state to another. ...
by tcat
Tue Nov 07, 2017 3:00 pm
Forum: Hardware
Topic: Microdrive Motor Adjustment
Replies: 54
Views: 8274

Re: Microdrive Motor Adjustment

Hi,

Just serviced another drive, that makes 3 of 4 total.
Last drive is R/ only because of faulty erase coil, and none spare head left.

Tom
by tcat
Tue Nov 07, 2017 1:02 pm
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10333

Re: Microdrive Unit Design

Hi,

The tape map in MDV4_ Iss#5 after format of a used cart looks like this.

mdv4-map.png
MDV4_ map after FORMAT
mdv4-map.png (11.54 KiB) Viewed 573 times

EDIT, formatting further gives 224/227 total, on overage Iss#5 seems a good performer, but not as star a performer as Cristian or Rich reports here.

Tomas
by tcat
Tue Nov 07, 2017 11:53 am
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10333

Re: Microdrive Unit Design

Hi, Just mounted the good R/W head to MD Iss#5 unit here. What you see in the picture are two MD units connected in a chain, MDV3_ is Iss#6, and MDV4_ is Iss#5. mdv3-4-2.JPG Now their speed is indicated by a simple program. Iss#5 has mandatory mod applied. mdv3-4_speed.png EDIT, now I have just fres...
by tcat
Fri Nov 03, 2017 2:08 pm
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10333

Re: Microdrive Unit Design

Hi Martyn, Thank you. As I understand it, writing involves the ULA 'switching' its inputs to outputs and driving the same (stereo) pair of coils with the 50/100KHz signals. Yes, I agree ZX8302 ULA does FM coding / decoding, while MD ULA does FM amplification and TTL hysteresis correction when readin...
by tcat
Fri Nov 03, 2017 7:17 am
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10333

Re: Microdrive Unit Design

Hi,

ULA block diagram above shows, in my opinion, only reading data from two tracks, outputting two channels DATA 1-2 (A/B).
But how is data written to tape, we know we need two frequencies 50/100kHz and some direct current?

tape-recording.png
erase / write polarity on tape

Tomas
by tcat
Wed Nov 01, 2017 2:05 pm
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10333

Re: Microdrive Unit Design

Hi, Thank you for the encouragement, now comes difficult part for me, that is `Frequency Modulation' (FM), I do not quite understand. Consider `1 0 0 0 1 1 1 1' byte to be stored to one tape track. fm-modulation.png How does ULA amplify and decode FM signal to TTL "0", and "1" we...
by tcat
Wed Nov 01, 2017 12:06 pm
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10333

Re: Microdrive Unit Design

Hi, I have read some posts from Gert, also looking further at MD `waveforms' in the QL Service Manual. MD uses direct current for premagnetisation, and FM modulation for data, 50kHz ~ "0", 100kHz ~ "1". I do not know what value the premag current is, in the picture shown as 30mA....
by tcat
Tue Oct 31, 2017 10:07 am
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10333

Re: Microdrive Unit Design

Hi, I am not able to interpret inductance measured, the values seem in spectrum of +/- 0.2 mH (mili henry?), which may be the precision of the inductance-meter used? My toys here are that of a hobbyist, transformer pistol iron and a simple multimeter (not very precise). I am now learning about magne...

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