Hi together, as I already mentioned in my introduction thread yesterday, I just got my hands on an old Aiwa HS-T06 "Walkman" like device: It plays tapes even with it's original belts and switching between tape types and turning Dolby B NR on or off works just fine so far. However, the third switch on this little Aiwa isn't doing what it is supposed to do: The tape (off) / radio switch isn't properly working. It's doing something - that's fore sure: In the tape-mode, I can play tapes just fine and of course the battery LED is only turned on, when one of the tape mechanism functions is activated by pressing the mechanical button which then closes the leaf switch. If I move the switch to the radio position, the battery LED also turns on as you would expect it, however instead of AM or FM radio, I can only hear some low volume hiss. The reason for that is the fact, that instead of turning on the radio, it's just feeding through the tape head signal. Also, I can use the tape mechanism functions just fine when the switch is in radio mode. In a YouTube video I have seen though that in radio mode, the tape functions are disabled - that means, if I was to press e.g. the play button in radio mode, the motor should not be turning and of course, I shouldn't hear the tape sound. The next thing is that even in radio mode, the upper two switches still function as Dolby and tape type selectors, but they would be supposed to switch between AM/FM and Stereo/Mono. Therefore, I now removed the plastic back cover of the Aiwa by removing the 5 screws as mentioned in the service manual (https://archive.org/download/manual_HST06_SM_AIWA_EN/HST06_SM_AIWA_EN.pdf) to get a look at the main board. Since the Walkman was apparently dropped at some point, I expected to maybe find a cracked solder joint on that switch. I therefore got out my digital multimeter and checked for continuity between the different pins of the radio/tape switch (S6) What I noticed here is that on the right part of S6, that being S6-1, I get continuity between all 3 pins all the time, no matter what position the switch is in. Could this be the issue? Only on S6-2, the continuity between the 3 pins changes when changing the positions of the switch, which results in only 2 of the 3 pins on the S6-2 part of the switch to have continuity. If I see it correctly, I should only have continutiy between 2 of the 3 pins on S6-1, too right? If this is the case, what would you suggest to verify that the switch is the actual cause of the problem or if it's something else further down the road? And if the switch is the cause of my issue here, are there replacements that a) match the pin-out and b) have the same sized nozzle to put the orange plastic piece onto? Best regards Alex
Okay, so I have to apologize since I was a little bit stupid here - actually I had the play button pressed all the time that I measured the radio/tape switch. When I release any tape mechanism function and therefore cut the connection at the leaf switch, the radio/tape switch measures fine with only 2 pins having continuity in each position, so 6-2 and 6-1 are both fine. Also, I can faintly hear something like voices or music, if I am not totally imagining it - so I guess there is something wrong further down the line that has to cut the tape mechanism's power and instead only let power through to the am/fm radio IC (it's a Sony CX20111). I will later measure if the Sony get's it's voltage of 3 Volts on Pin 23. I guess that the Sony IC actually is fine and it's really just the switching electronics. Another thing is: I see several solder joints that look quite bad. Not in the way of having visible cracks, rather it's them just having not enough solder. I have read from similar observations here in this forum by the user Steve Grant here: https://stereo2go.com/forums/threads/repairing-mid-80s-aiwa-hs-j09-9-600-10-36-360.10445/ Btw.: Funny to see Sony chips inside of a competitors Walkman (but I think Sony bought Aiwa at some point in time, so that may make sense then), similar to Samsung chips in Apple devices
Further measurements brought me to following point: The Sony CX20111 FM/AM Tuner IC gets about 2,6V in radio mode, so far so good. This chip runs from about 2-9 volts according to it's datasheet The same supply voltage (according to the service manual it should be around 2,9 volts) normally should also go to the transistors Q6 and Q7 Q6 should disable the power supply for the tape motor Q7 should switch the amplifier from tape to tuner Since both transistors are obviously not doing what they should do, I will have further looks at these bad solder joints. Somewhere in all of this, the 2,9V rail must be cut so that the "switching" as is is called in the SM is not happening. I'm getting closer and closer and it really makes fun when you get better and better in reading circuit diagrams!
Okay, so C12, one of the electrolytic capacitors, only measures 0,5 Ohms to ground and basically shorts the supply voltage for the radio and switching transistors to ground. This means, I will have to completely take out the main board in order to put in a new capacitor. Can I somehow check all the other capacitors in circuit in order to see if they need replacing, too? I am usually not a huge fan of bulk replacing all el. capacitors at once. Can anyone of you with better knowledge in electronics tell me if I was right with my measurements and why I don't get enough voltage on both transistor bases while having nearly continuity from the bases and Pin 23 on the Sony IC to ground? For me only C12 makes sense here since it sits on the same "rail" and has it's other side pointing to ground.
Sometimes these switches have contamination inside. They are not difficult to remove, open up, clean... Just fiddly because they are so small. Or you can buy replacements. They seem to be pretty standardized.
I think I found the problem: C12 is dead short, hence nearly no resistance from the 2,9 V rail to ground. I will get a replacement capacitor and see what's coming up.
Hi together, replacing the electrolytic capacitor C12 with a new(er) one solved the issue and both FM/AM radio are back working again just fine! Also, the tape motor now shuts off when entering the radio mode. Since all other electrolytic caps in this model are probably from the same batch and manufacturer, it wouldn't wonder me if they will fail soon, too. I really didn't expect these earlier models to have such huge problems with capacitors, too
