The portable cassette player from the manufacturer SONY with the type designation WM-DD11 is the content of this article. Colloquially known as “Walkman”, I received this part for my collection. Of course with the comment “defective” – so again a little challenge and at the same time the hope that no mechanical, no longer available parts are affected. My request before the purchase whether there was any damage to the circuit board was also answered in the negative. The device is so far in order, the tape of an inserted cassette is moving – there is just no sound from the headphones. So ideal conditions for a restoration.
But unfortunately you cannot trust every statement and you cannot look “under the hood” beforehand and convince yourself whether the actual condition of a device corresponds to the description. When I held the part in my hands, the first impression was also very convincing. There were no noticeable scratches and dents. The area of the battery compartment that was visible from the outside was also clean. So batteries inserted, also an audio cassette and then pressed on play. Lo and behold, the tape transport runs as described. Even as described, the part does not make any sound. So perfect starting conditions for my mini repair / restoration project.
But before I start dismantling, I did a little research on the history of SONY’s DD Walkman series. The first model in the DD series was sold in 1982. The designation “DD” stands for “Disc Drive”, which means that the “Disk”, i.e. the flywheel disk, is also part of the capstan drive system (motor). The belt for the other drives (tape reels) is placed directly around the disk. There are / were two price brackets of the DD models – the DD series with one-digit numbering (DD-1, DD-2, etc.) and those with two-digit numbering (DD-11, …). The devices with the single-digit number belong to the “high-end rail”. The device restored here comes from the “cheap line”. The DD-11 is not so high-quality and is also more simply constructed, but defective devices are available for very little money and are also fairly easy to repair. (The DD-11, for example, does not have a center wheel, an often defective part of the high-end series that is broken due to weak material. What then usually remains are defects in the electronics or on the mechanical side – an aged belt The belt is the same as that already installed in the legendary TPS-L2 Walkman and has the component serial number: SN 3-499-042-99 (this source or number has not been verified) You can also find the belt if you go to “TPS -L2 belt “searches on various online portals.But now enough information on the general part. I experienced a sobering and grounding of my restoration euphoria immediately after unscrewing and opening the case. Unfortunately, the circuit board is not at all undamaged. Once again someone did not remove the 1.5Volt cells and left them in the device for a very, very long time.
The batteries that leaked, as it is, have left clear marks on the circuit board. This means that extensive cleaning of the circuit board is necessary before the search for corroded conductor tracks can begin.
After cleaning and removing the battery electrolyte residues, I was able to make out a few defective conductor tracks. Fortunately, these are pretty easy to fix. In most cases it is sufficient to remove the solder resist in the defective area and to tin the exposed copper tracks. Depending on the width of the track, the defective part of the track is then reconnected with individual strands or wires.
Now the time has come to carry out a first functional test after a provisional assembly. And as described, the capstan drive works, the tape is transported – but there is no noise whatsoever from the connected speakers. Now is the time to look at the number one source of failure – the old electrolytic capacitors. Eleven of these are installed on the board.
When I removed the first electrolytic capacitor for a capacity test, the well-known fishy smell rose again. As expected, the capacitance of the capacitor was also well below the nominal value. So I made a spontaneous decision to remove all eleven electrolytic capacitors in order to swap space. (In modern language it is called “recap”: D)
I like to replace the SMD electrolytic capacitors with SMD multilayer capacitors, as these are now also available in very small designs in high capacities with suitable dielectric strength.
After the renewal, the board looks nice again. A repeated provisional commissioning shows that the effort was worth it. The music on the inserted tape sounds in the expected quality. The next step is to calibrate or adjust the belt speed. A reference tape is required for this. Years ago I recorded one with a very good tape recorder. The recording consists of a 1kHz and a 5kHz sine tone. This band is now used as a reference in the DD11. To do this, the output of the DD11 is connected to a frequency counter or oscilloscope and adjusted with the trimmer potentiometer during playback until the 1000 Hz or 5000 Hz can be seen exactly on the oscilloscope.
The Walkman can now be reassembled. All screws are properly tightened again and finally the function tested again and the beautiful piece can be put in the showcase …