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.
