I just got this Aiwa PX303 a couple of weeks ago. Things I have done : PCB section: -Replace capacitors with the same uF value. 100uF @ 2.5V (used tantalum cap) x 4 220uF @ 4V x 4 22uF @ 6.3V x 2 470uF @ 4V x 2 -Reflow/resolder the chips on the board because I have problems with sound not coming out, more on this in the section below. - Clean PCB with IPA 3-4 times now - I have cleaned the headphone jack and reflow the solder joints on it. - I checked continuity on most of the traces and via on this PCB and they look ok. (might missed some spots, will recheck again.) Mechanism section: I also tore the mechanism out of the machine because the old belt turned into oil/goop and contaminated the mechanism. It is now back together and working correctly. I added white lithium grease on metal on metal moving parts and also greased the clutch gear with plastic-safe grease. Meanwhile, I avoided adding any grease/oil onto the gear with a felt pad underneath. Also added watch oil to the capstan bearing. Replace belt. Problem on the machine right now: Right now when I power on the machine and press play it would sometimes play and sometimes it would try to play and then switch direct and then go into loops. ( I rechecked the mechanism with jx505 mechanism I have lying around, they both work correctly, I don't think it is mechanism-related) If the machine managed to play it would only work in the forward direction. When pressed reverse it would go back a bit then forward then stop. The machine cannot rewind but it can fast forward. The stop button works correctly. -Both the Left and Right channels have white noise coming out but Right channel sometimes does not have white noise at all (dead?). -Left channel sometimes has sound but the volume is always different. -Right channel rarely has sound coming out but when it does it will have low volume. -Also sometimes there is a low humming noise in both channels when in play/fast forward. -There is sometimes sound on the left channel while right channel rarely has sound coming out. -The headphone jack had been cleaned/reflowed/resolder. -I have found that when I wiggle the tape head flex cable, there is more white noise on the Right channel but there is still no sound coming off. I know this is just a long wall of text. Hope anyone can share tips/knowledge on this matter. Thank You. Ps. I think this is PCB-related because I triple-checked the mechanisms and it is good.
My recommendation is to take things one at a time: 1. The playback level trimpots are set in a position where one cursor isn't making connection with carbon trace at all, while other is maxed out. See attached picture. Put both somewhere in the middle (so you know the cursor makes contact with carbon trace) and you you can adjust the Dolby levels at a later date. 2. All vias around and below volume potentiometer should be checked for continuity. This is the area that's typically affected by leakeage. 3. Check the volume potentiometer. With volume set at maximum you should have a resistance in the order of 10-30Ω between cursor and input. If it's in the kΩ or MΩ range, potentiometer is faulty. Seen this problem in a couple of units and unfortunately soking it in contact cleaner did not fix the problem. 4. Mode swtich (the one near Dolby level trimpots) needs to be thoroughly cleaned, sometimes it requires disassembly for that. This swtich has 2 swtiches inside: one is switching the head preamp for FWD/REV, while other one sends a signal to the microcontroller so its knows position of the mechanism. Running in FWD (or REV), but going into REV only for 2 seconds then stop (or swtich back to FWD if reverse mode is set to continuous loop) is a sign of a dirty mode swtich. You state the machine cannot rewind. What that means more specifically ? Does the operation LED turn on when pressing REW ? Does the motor turn ? Logic control switches and HOLD/remote, EQ and Dolby switches need cleaning, especially the ones on the main PCB which become full of leaked electrolyte. Then as far as mechanism goes, you have not mentioned anything about the clutch (see picture attached). The clutch spring has a retainer that tends to break and needs to be repaired with thin wire: https://stereo2go.com/forums/threads/aiwa-alpha-2-clutch-repair.10059/#post-81690.
Thank you for this valuable information. 1. I was messing with the trimpot because there was no sound. I have set them back to original position. I will re-adjust them again when everything is working. 2. I have removed potentiometer and the black plastic adhesive todo continuity test around the vias underneath and it is ok. I will do more check on the other side more thoroughly again and clean them. 3. I have checked the potentiometer and it is around 20 ohm. I decided to soak it in contact cleaner for few hours to see if there's any change. I have installed the potentiometer and retested the machine again. Now there is sound coming out the right channel but the sound level is alot lower than left channel. Also, the sound on both channels just doing the appearing and disappearing thing. I will have to recheck the via and traces again and maybe also reflow the capacitor just to be sure. 4. I will do exactly that. The rewind kind of work. When i press rewind the machine does goes into rewind but only for a bit then it goes forward then stop. Thank you for mentioning the plastic lock ring of the clutch gear because i didn't know that it broke off and have to be fix with wire. I thought it was just a plastic washer/spacer.
Things I've done: I have done the clutch spring retainer repair according to the instructions. Also checked when placing the assembly down that there are no interferences to the metal locking clip underneath. I decided to try repositioning the 220uF capacitor since I thought it was not making a good connection. I did an oopsie while trying to reposition it, and the soldering pad underneath came right off. Glad that you recommended 0.25mm wire for the clutch retainer because it also fits through the via. However, this didn't fix the sound from the right channel. Somehow, after a lot of continuity tests on multiple vias across PCB, the right channel sound came back. This might be because the vias are corroded/dirty? Anyway, I am glad that there is sound coming from both the left and right channels, and it is working correctly. On to the problems right now : The machine can still play only on the normal side and not the reverse side. I am starting to suspect that it is mechanical. When I press reverse or switch direction to the reverse side, the cassette still rotates anti-clockwise a little bit, and then the machine stops. From my understanding, the selector fork/sliding mechanisms are not engaging correctly. When I press rewind, the selector fork tries to slide to reverse. But then it stops at the middle position(stationary position) and moves back to the normal position. Also, please correct me here: when connecting the machine to the power source, the machine will first try to reset its position. When doing so, the selector fork will move to the normal side, then the reverse side, and then to the middle(stationary position). Right now, the selector fork will move to the normal side, then in the middle(stationary position), and not go to the reverse side. Onto the weird PCB problem here. Sometimes, when connected to the battery, there is a weird clicking/screeching sound (from PCB? unknown location), and it might be related to the red LED? Because the red LED also flashes according to the clicking/screeching sound. Sometimes, when connected to the battery, the red LED will turn on brightly for 2 seconds and then disappear. When in play mode/fast forward/rewind, the red LED is super dim, or sometimes it isn't on at all. Sometimes the machine would start going fast forward right away when connected to the battery and when that happens there are also screeching/clicking sounds coming off ( it sounds like an electrical issue because when the machine stops on its own, there is still screeching/clicking sound). To note here, if the machine starts to fast forward on its own when connected to battery , the button controls is somewhat working. When i press the stop button the machine will stop a little bit/or tries to switch direction but then it goes back into fast forwarding again. The other buttons also works but machine will go back to fast forwarding right away.
"This might be because the vias are corroded/dirty?" - yes and ideally you should find where the problem is and fix with wire. Pressing the PCB usually pinpoints where the problematic area is. "the cassette still rotates anti-clockwise a little bit, and then the machine stops" - please be more clear what you mean by "machine stops". Mechanism un-lateches into the neutral position or just motor stops ? When REV is engaged, does the engage mechanically into REV or just motor rotates in reverse direction ? If it doesn't engage REV at all it's mechanical. Camgear + levers need cleaning and re-grease. It's a common problem on Alpha-2 mechanisms. About LED being super dim, what voltage do you have at the power terminals ? Erratic behavior is likely caused by the hold switch having high resistance since it's in series with the resistor ladder.
Sorry for unclear explanation, It is more like the Mechanism is unable to latch into reverse position and is only able to be in normal position and neutral position. I will go over the mechanisms again. I have checked the power terminals voltages and it is around 2.0-2.1 volt. While i was testing for voltages, there was screeching/clicking sound underneath as if there is a shortage somewhere in that area (motor?). I just discovered that when screeching sound happen the machine will start fast fowarding right away. Also, sometimes when it is fast forwarding on its own and if screeching sounds happens again while it is fast forwarding the motor dies out. About the LED, is it possible to test the machine if i were to desolder and remove the hold switch to eliminate possibility that it is giving high resistance? I just decided to test the machine again while writing this reply. Right now there is a high pitch coming from underneath pcb(motor?) and pretty much none of the button works. While i was pressing the REW button the high pitch changes abit. Also, the machine went into fast forwarding mode on its own and now the motor speed is slower and it sounds like its dying out.
In regard to the hold switch, you can add a blob of solder on the 2 upper terminals to short them together. Can also check the resistance of the switch with a multimeter, resistance should be very low. Do note however high resistance on the HOLD will only cause problems regarding controls not working as they should. Like pressing STOP unit going into PLAY etc. LED being dim isn't realted to this and reading your post again I realise your symptoms don't really match a hold switch issue. But worth checking the resistance assuming you have a multimeter. The screeching/clicking sound is similar to the motor trying to start but not having enough torque ? Seen failed motor PCBs on this mechanism, where one of the 3 phases was not making a good connection and unit was struggling to start. Also seen microcontroller failure on this model. Fact unit does not initialize (FWD, REV, neutral) when powering on points to a potential microcontroller or motor servo issue. Also check the resistance of tape in switch. One problem is pretty clear it's mechanical (fact REV doesn't latch), but there is also a second one regarding logic control and potentially motor servo circuits. As a sidenote, no need to quote previous posts. Instead of using "Reply" button (which quotes automatically) type in the box below the post and press "Post Reply" instead.
