People with knowledge of MD insides, need your help! (pics!)

[t10]

I have recently made a post on http://www.minidisct.com, concerning optical block issues.

Here is the link to original post: http://www.minidisct.com/forum/showthread....&threadid=21759

Here is the post itself for lazy people:

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I have recently aquired an MZ-R900 and an MZ-N1 units. Both with severe cases of optical block.

They read the discs fine, but when it comes to writing them, the usual "blank disk" issue occurs.

Now, I purchased the units simply to play around with them. On top of that, I had to change Optical Laser Assembley on PS2 quite a few times, since a lot of them burn out, and are only able to read CD's. Not the smaller wavelength of DVD's. Anyways, not being new to optical assembleys, I am thinking, that I should take the R900 appart, get to the Optical block, find the pots, and crank them up to provide more power to the lense. Sounded like a good plan so I take the R900 apart, and here is what I see:

After I got the optical assembley out,

I notice something on a very tiny ribbon, that connects what seems to be a magnetic head in front of the inserted minidisc (assuming that the optical lense is behind the disk then). And this silly ribbon is torn:

Then I remember this:

MiniDisc equipments record audio data onto discs using MO technology (Magneto Optical). The process involves a laser head heating up the recording spot at the temperature of 180C/400F while the recording head uses positive and negative magnetic signals to write audio data paterns.

Then I think to myself, hmm, maybe the lense only reads data off the MD, and the Magnetic head is what records the data, and the cable being torn prevents it from writting anything, but it can still read. (If that is the case, then why can the MD still erase the TOC on a full disk, when you write something to is, so it appears as blank afterwards?)

Well in any case, Right away I think of switching the optical assembleys with the N1. They look exactly the same, and the ribbon cable has the exact same number ot traces on it. So am thinking, lets give this a try.

N1 goes under the knife.

But before I even get to the optical assembley, here is what I see:

Can't see it? Here is a hint:

Woah, seems suspicious, two MD units with optical block issues, and both have the exact same problem with torn ribbon cable for the magnetic head. Mkaaay.

Anyways, the optical assembley swap is put on hold for now.

Does anyone know the exact function of this thing that I refer to as the magnetic head? Come on guys, lets hear some input.

Also, some bad news. this ribbon is a major PITA to replace. a) it is glued to the damn chassis. the thing is hard wired to the mainboard, you cannot just replace it. It would appear to get a new one, you would require a new mainboard.

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Any help would be greatly apreciated ;p

[Guest NRen2k5]

AFAIK, the matnetic head reads and writes recordable MD's; the laser is to heat the surface of recordable MD's to be written but is also used to read pre-recorded minidiscs (as in, real albums).

Are you sure you can't just fix the cable, at least on the N1? It looks like it can be done - After trimming the piece of the cable that's sticking out, I figure you could reconnect the traces with a repair pen and/or solder. Sure, it'll require a magnifying glass and a steady hand, but it shouldn't be impossible. With only 2 traces to connect, it's not a huge project.

[Hyena]

No idea who you got your information from NRen, but the magnetic head is used for writing only. The lense reads, the magnetic head writes. Simple enough. In fact, if you look at a pre-recorded MD, there is a shutter on only 1 side of the disc, which is the same side where the optics of the MD are present.

t10, as for your question as to why the MD is still able to erase the TOC, it's possible that there might be an uninterrupted current going to the magnetic head, causing the rearraging of the TOC, which is located prior to any audio data, right after the lead-in area on the farthest in area of the disc. Complete disconnection or removal of the magnetic head should solve any problems with erasure, but eliminate any ability to write.

[pureangst]

Had the same problem with an N1, a broken ribbon cable.

If you're referring to 'optical block' as a problem where you can't record [but you can play just fine], then it's easy to fix.

Simply bypass the ribbon cable by soldering wires between the magnetic write head and the solder points on the board. I did it so I know it can be done. Use earphone wires [wires scavenged from headphones].

[Guest NRen2k5]

No idea who you got your information from NRen, but the magnetic head is used for writing only. The lense reads, the magnetic head writes. Simple enough. In fact, if you look at a pre-recorded MD, there is a shutter on only 1 side of the disc, which is the same side where the optics of the MD are present.

I just checked. Yes, you are right. The magnetic head has only one purpose - to write. The optics serve two purposes - heating the sectors of the disc to the Curie point so the magnetic head can write, and reading the disc.