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

Final thoughts

If anyone has anything further to add to this collection of tips, please
let me know. 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.


Back to my minidisc page.