Kenwood KX-7050 electronic fault

[paaL2777777]

Hi everyone! I have this Kenwood KX-7050 3-head dual capstan stereo cassette deck that always worked fine. Recently, I wanted to separate the cassette mechanism from the deck to perform some deeper cleaning and maintenance, but the connectors of the heads are really fragile... and indeed, I accidentally broke the playback connector while disconnecting it from the main PCB (the cables separated from the connector itself). So, to get the deck functional again, I had to solder on the opposite side of the PCB the playback head cables... this actually did work, the deck works as normal, except that now I hear some kinds of digital impulses in play or record mode, either from line output or headphones. The rate of these "digital ticks" increases as the take up reel speeds up, and they disappear if I stop the take up reel manually or if the cassette reaches the end, so maybe is something related to the photosensor that communicates to the main µProcessor, or the reel motor itself. At least, in record mode, these "digital ticks" aren't recorded on the tape. I've already checked all other solderings, paths and components on the PCB and nothing seems wrong...

Have you ever had this kind of experience on this or other highly computerized cassette decks? If yes, did you manage to fix it and how? I really want to fix this deck, its sound quality is excellent and the cassette mechanism is pretty good for being a cassette deck from the 90's. Thank you in advance!

 

[Bradbrews]

Possibly the wire routing is changed and some cross talk is occurring.
You did take a photo of it before you started…

 

[paaL2777777]

Hi Bradbrews. Thanks for replying to my post!
Meanwhile I tried to power the reel motor from a completely separated power source (an external 12V e-bike battery) and the problem still occurred. Rotating the spindles by hand (with the reel motor disconnected from any power source) didn't cause the problem though. So, I disassembled completely the cassette mechanism, and noticed that the more the reel (and capstan) motor was close to the playback head, the more the "buzzing" noise was audible: when the motor is far enough, there isn't any buzzing noise. I remember that when I performed that deep cleaning/maintenance (when the playback connector broke), I removed some sort of metallic foil that was wrapped around the motors... and by searching around various forums, I discovered that the foil is made from mu-metal, and actually prevents that the electromagnetic field caused by the motor spinning could interfere with delicate electronics such as heads and other audio signal paths. So, I think I have to buy some mu-metal foils, or maybe recover them from a faulty deck, and see if the problem finally disappears... I'll keep you updated!