Hi all Just a quick update to say that the problem is now fixed and the walkman is working just fine. I will update this thread with a bit more information and a couple of pictures of the machine as soon as I can. Valentin has been incredibly helpful and guided me through the process. I am so grateful to him for his patience and time. He will elaborate on the more technical explanations of the fault.
Sorry for the delay, at last I have found the time to update the thread. Just to recap. When playing, there was a situation where the volume control seemed to behave like a balance control and the sound seemed to switch from right to left as the volume was increased from 0-2-4. Then both channels were ok until increasing the volume further resulted in an unbearable howling noise. There was also a lot of noise from the volume potentiometer when turning up or down. This was later cured by several cleaning cycles with some Kontakt 60. As a starting point I gave the board a thorough clean with IPA as there were traces of whatever had been used to clean it in the past. Valentin suggested at this point he suspected there may have been a bad capacitor or two although there was no real evidence of leakage. Armed with my new multimeter I set about measuring and recording the values of all the caps. The results can be seen in the picture below. The one that stood out as possibly being faulty was the one reading .2nF as it was a very low reading. Valentin then advised me to remove it to check it properly and also remove all the rest to check them too. That one was indeed bad, also the one reading OL near to the volume pot. Valentin kindly gave me the links to the correct replacement caps and I ordered some up. This was my first attempt at this type of job, I must admit I found it rather fiddly at first but eventually I got the hang of it and had all of the new caps fitted, not without one or two burned fingers though! I was rather anxious as I reconnected the board, installed some batteries and tried it for the first time. Would it work? Well, yes and no. It was much improved, the howling noise had gone, however the left channel was very low compared to the right. I was a little disappointed, but then my eye was drawn to the trimpot RV(101), the level adjuster for the left channel. Not knowing whether it might actually make any difference and risking a slapped wrist from Valentin for attempting it without consultation : )) I gave it the slightest tweak, less than 1/8 turn, and the left channel came through loud and clear. It was a complete fluke that I chose to do this, but I was quite chuffed. Valentin has since told me that it is normal after replacing capacitors that the levels will need adjusting. I will get myself a test tape so that I can set it properly, although to my ear it doesn't sound at all bad. I have the walkman all back together now and I will put up some pictures of it. I must express my thanks and gratitude to Valentin who has been so much help, I would never in a million years have got to the bottom of the problem without his kind assistance. I think he may expand on some of the problems in greater depth than I able to explain.
Here are a few pictures of the DD10. Valentin seems to think that the DD10 was for the West German market and the DD11 for the East German market. Not sure if there is much if any difference between them.
The unit looks really nice ! The goldish color really catches the eye ! I am tempted to believe the Western/Eastern Germany thing because in the service manual of the DD10 is written "Western Germany", as in the DD11 is written "Germany". I may be wrong in that statement, so if anyone else has info on what the difference is please let us know. At first glance, there are a few differences in the PCB between the 2 models: possibly some differences in the motor governor section, but the most obvious difference is the lack of Dolby levels adjustments on the DD11. Given the later walkmans tended to eliminate to Dolby level adjustments, it is also possible that the DD11 is a later version of the DD10, kind of an upgrade. Another clue, mentioned in the DD10 service manual, is that the DD10 is almost identical to the DD1. The initial problem seemed strange, but was later explained by a bad capacitor that was AC-coupling the ground side of the potentiometer to the actual ground of the circuit. So the ground side was floating, that explains why there was volume with the pot at zero. The howling sound can be explained by an amplifier oscillating because of the feedback capacitors going too low in value and increasing the bandwidth too much. The conclusion I draw given other members thave stated capacitor problems with this unit, but manifesting a more typical low volume problem caused by output coupling capacitors is this: if you have a DD1, DD10 or DD11 just replace the capacitors even if they don't seem to be leaky, because in reality they are, but it's just not visible until you desolder them. This type of SMD electrolytics are always suspect, but usually are leaky when they're bad. I'm not saying that you should replace any capacitors that look like this, because they're not always bad; it depends on the brand and time period of manufacture, as there was a time when capacitors had problems. There is a capacitor kit available for the DD11 on ebay, which further confirms that all DD11s have this problem. For reference, the Dolby level for this unit is: - 100mV RMS @ 200nWb/m ANSI (using a Dolby tape, which is my recommendation) - 73mV RMS @ 160nWb/m DIN (using a SONY P-4-L300 tape) NOTE: 200nWb/m ANSI = 218nWb/m DIN
