Minidisc deck repair tips

This page contains a variety of notes I made while effecting repairs to my Sony MDS-S30 minidisc deck. Much of this information will be useful in relation to the MDS-S35 and MDS-S37 models as well, due to their similarity to the MDS-S30. In addition, the MDS-302 and MDS-303 are apparently similar or the same as the MDS-S30 and MDS-S35 respectively, so these notes may be helpful to owners of these models as well.

I am hoping to include some sketches on this page to help illustrate a number of points. This will happen "as time allows".

Before attempting any repairs, please refer to the Final thoughts at the end of this page.

Specific faults

Inconsistant operation of unit / unit dead

The power supply in the 'S30 deck contains a number of very heavy components. The bulkiest (the transformer) is secured to the chassis with dedicated screws, although even here there is a possibility of finding dry joints on some transformer pins. In addition to the transformer, there are some very large electrolytic capacitors on the board - their connections to the PCB are well worth checking.

Failure to spin a disc

Symptoms: The unit powers up as expected. A disc can be inserted and is correctly accepted by the unit, but the disc is never spun. A motor can be heard to be starting but no movement is evident anywhere.

Possible cause: When a disc is inserted, the sled (the assembly which drives the optical and overwrite head across the disc) is instructed to return to its innermost position. A microswitch is used to confirm when the sled reaches this position. A dry joint on one of the contacts of this microswitch, or a broken switch, will prevent the system receiving this signal. The sled motor therefore remains energised indefinitely while the unit waits for a confirmation which will never arrive.

Repair notes: It is possible to access this switch without dismantling the drive mechanism. Remove the drive from the minidisc assembly and move the sled to the outer-most position (this can be done by rotating the large gear on the top of the assembly gently by hand). With a steady hand, it is then possible to assess all solder points of the offending switch; care must be taken to ensure that the iron does not touch any of the nearby plastic transport components.

Failure to record

Symptoms: The unit plays back discs with no problems and when attempting a recording everything appears to function correctly. When this recording is played back, the disc is spun up and the head can be observed to be seeking as expected. No audio is produced and for about 10 seconds the track time displays "00:00". After this time "00:01" is shown which remains for a very long time. After ejecting a disc you have attempted to record on, the disc will be registered as "blank".

Attempting a "continuous write" operation in "service mode" also appears to work, but a "continuous playback" reveals that no data has been written.

This fault is apparently rather common in MDS-S30, MDS-S35, MDS-S37, MDS-302 and MDS-303 models, according to the User reported problems section of The minidisc community.

Possible cause: It seems the spring material used in the overwrite head in these models can get weak after several years. This results in the head not firmly resting on the upper disc surface during recording; the magnetic information is therefore not transfered to the disc and no information is written. However, because the laser is correctly switched to "write" power, the disc's magneto-optical layer is brought to its curie temperature. With no magnetic information being supplied, the disc sectors are effectively erased. On disc ejection this basically wipes the disc's table of contents, giving a "blank disk".

Repair notes: Record functionality can be restored by the replacement of the overwrite head. The original part has been superceded by a new one, and my impression of the new part is that it might prove more reliable than the original. The Sony part number for the 'S30's new part is 1-500-304-21. It is described in the parts database as an "overlight head" (sic), presumably due to a typo. In fact, the full description of the part is "Overlight head, MDS-S35", so it seems that at least the MDS-S35 shares exactly the same overwrite head as does the 'S30.

It is worth noting that the new head assembly is slightly longer than the original. In my deck this meant that when a record operation was commenced, the forward edge of the overwrite head got caught on some black painted metalwork associated with the disk loading mechanism. This was easily solved by trimming the metalwork with a nibbing cutter to give sufficient clearance for the head across its entire travel.

General notes

I have been unable to track down a service manual or schematic for the MDS-S30 or any of it's close relatives. Although substantially different (with a different ATRAC version for a start), I have found the MDS-JE510 manual to be helpful. Although the board layout and IC pinouts are completely different, the circuit at the base level is remarkably similar. The JE510's manual is also helpful at identifying the various testpoint abbreviations used on the PCB silkscreens, which haven't changed between these two models. In addition, the description of signals used by ICs in the JE510 (together with a knowledge of which signals the test points refer to which can also be gleaned from the JE510 service manual) allow a reasonably detailed picture of the 'S30's operation to be deduced with relative ease.
When removing the front panel of the 'S30, there is a thin copper tab which connects the ground plane of the display board the metal chassis of the unit. This tab has a hole in it and is designed to be secured by one of the screws which hold the front panel on. Its correct seating is between some plastic from the front panel and the chassis itself, and it is located on the left side of the front panel when viewd from the front. When removing the front panel, make special note of the arrangement of this tab and ensure its correct replacement when the panel is refitted.
The minidisc assembly contains the solenoid which activates the cover flap on the front panel which covers the hole into which a disc is inserted. The two are connected via a `hooked lever' arrangement which easily disengages when either the front panel or the disc mechanism are removed. Ensure that the lever is re-engaged correctly when reassembling.
Take special care when removing and replacing the screws which hold the minidisc drive mechanism onto the larger minidisc assembly. These screw directly into molded plastic, and the threads could be stripped if care is not taken, especially if many disassembly/reassembly cycles are required during testing.
When removing the minidisc drive mechanism from the assembly, take care to avoid damage to the overwrite head. The best way I found to effect the removal was to pull the rear of the mechanism up first, which allowed the rest of the drive to be manipulated clear of the assembly. Replacement is the reverse.

Final thoughts

If anyone has anything further to add to this collection of tips, please let me know (jwoithe at this domain). In particular I would really like to obtain a copy of the service manual for the MDS-S30, or even just a schematic diagram.

Note that this information is being provided as a service to the minidisc users of the world. It has come from personal `trial and error' experiences. Please do not attempt repairs of minidisc equipment unless you are qualified or have a technical/electronic background. Decks such as the MDS-S30 are mains operated and therefore have mains voltages present within the case when in operation.

The information on this page is supplied without warrantee and with no guarantee. The author will accept no responsibility for injury, death or damages which result from the use (improper or otherwise) of this information.

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