I have just completed a full recap of an (mint) AIWA HS-PL 55. The board was in good shape; there were no major issues. After about a dozen kicks to the play button, the mechanism loosened itself and it is now working fine mechanically. However, the sound has turned out to be very muffled, the highs are entirely missing and I am getting significant bleedthrough from the other side of the tape. Not quite as if I was listening to both sides at the same time, but it's close. I would assume the head assembly to be out of alignment? However, I am having a hard time understanding how that could be the case on a portable with no azimuth control. Does anyone know this model? Has anyone seen this particular symptom on other portables? Any guesses? Thanks!
Azimuth can be messed up by tape curling at the pinch roller, apart from a misalignment of the head itself. In fact, the tape curling at the roller problem is a more common problem than azimuth misalignment (on those that have adjustment). Even more so, the fact that the unit does not have an adjustment means the likelyhood of such misalignement can only be reduced to the possibility of head bridge itself being bent, which should be obvious by naked eye. So I recommend removing the door and start checking the tape path alignment relative to the capstans/pinch rollers.
Thanks, Valentin. You were right – well, sort of, and at least in part. The (main) issue was motor speed. I had heard that the motor ran slow (about 80 Hz). After adjusting, the sound is great. Not sure if the motor running slow lead to tape curling, but that fixed it. However, the bleedthrough is not yet fixed. But since it's only an issue in very silent phases, I don't care that much yet. I might revisit the issue a little later.
Have the impression I misunderstood the original problem entirely. To me it doesn't make sense that motor speed fixed a potential tape curling problem. More than likely tape curling was not an issue to begin with. Keep in mind some bleedthrough from the other side is normal if it's of very low level and hence only audible during very silent passages or between tracks.
Well, the issue disappeared right after adjusting the motor speed. That could still be coincidence, of course. I did some further testing and the bad sound came back just once right after an auto reverse action. It disappeared again after another reverse. If a reverse doesn't change anything about the actual position of the tape across the head, maybe it's something electrical? Next time I have the machine open, I'll do a reflow of the entire head flex cable connector to the main board and its associated capacitors. Maybe that'll have an effect. Since the signal path from head to head phones is so straightforward, I don't think there's much else it could be.
I can see a "ff/rev switch" and a switch referring to what seems to be the "head up" position (raising the head block). Did you mean that one?
No, it's not that. The head up switch is simply a power on switch probably used for the muting function. The one I am talking about is somewhere on the PCB, but I need a pic with other side of the board.
So, I eventually had some time to dig into this again. I cleaned the headphone jack, the head flex connector to the board, the headphone amp, and the Dolby chip with copious amounts of IPA and a soft toothbrush. I also cleaned the ground pad (screw) thoroughly of oxidation and measured continuity from head to amp again (all fine). I also cleaned all switches again including the REV-switch. Apparently, this helped as the sound is now near-perfect. It sounds really nice with perfect balance between left and right and a good stage. The bleed through is still there, but much less. I'm sure it's still more noticeable than its supposed to be (I have comparison Aiwas), but its faint enough for me not to bother much. There is one remaining issue that seems to be documented, though, (by Walkman Archive) and that's the fact that some button presses occasionally do not have the effect they are supposed to have: then, pressing STOP might start PLAY, pressing REW/FFW might start PLAY too, or pressing PLAY might send the machine into a FFW/REW frenzy for a while... I might go for a thorough cleaning of the associated flex connector, too, or try a reflow of the connections. It's not that much of a bother, though. Thanks for your help!
About the buttons occasionally having a different effect, that's because they work using a resistor ladder which generate an analog voltage read by the microcontroller. Any increase in contact resistance will mess up the output voltage creating the effect you describe. Recommend taking the buttons PCB out, spray some contact cleaner in the buttons and then press them a couple of dozen times.
I had thought of that before and done this now, but sadly to now avail. I'm not even very surprised as the switch board seems to be a tightly laminated strip of several layers of plastic. Getting contact cleaner in there should be a challenge. The problem is that this issue tends to badly shred my tapes as the autoreverse, as I am only now noticing, also does not seem to work. Since PLAY and STOP are double-layer switches also serving as ENGAGE REVERSE switches, any malfunction tends to ruin the tape. Fixing this may have to come first. Do you know of any resources that explain the working principle of a Walkman's autoreverse drive, possibly even that of an Aiwa Alpha mechanism? I do not dare take this apart before I have a grasp of the timing system etc.
Let us know what you want to know exactly about auto-reverse mechanisms. These camgear + solenoid type mechanism are pretty simple in operation: the motor runs, solenoid engages the camgear which engages/disengages FWD/REV play. FF and REW are engaged by just turning the motor one direction or the other. If autoreverse is not working, I suggest to start by removing the PCB and put the mechanism through its paces manually and see if there's anything jamming. It's possible some parts may need cleaning and re-lubrication. Does the solenoid click when you press PLAY a second time to reverse ?
Many thanks, Valentin! It will take some time before I find the chance to open up the mechanism. I have yet to examine its functionality without the door, but from what I can glean by listening, it sounds as if the autoreverse (solenoid) is engaging properly, but is then hitting an obstacle, forcing it to reverse again, ending up in a repeating cycle. The fact that I am nearly always retrieving the cassette with plenty of creased tape (but on the correct side) tells me that pinch roller/capstan-switching seems to work correctly, but possibly not the engaging of the proper take-up reel. I'll dig deeper into this and let you know.
@Valentin, I have now had some time to dig deeper into the mech and have opened a new troubleshooting thread here: https://stereo2go.com/forums/threads/troubleshooting-an-aiwa-alpha-2-mechanism.9398/ Would be great to have your input there, time permitting, of course. Thanks!
