Hello, your humming (to my ear) sounds like a ground-loop humming . In my (opinion) : If humming changes (for better OR worst) when touching anything grounded (as antenna or mass-point for phono), you have a grounding problem / ground loop somewhere I think. - first test (but you probably did that already : plug the non humming speaker into the humming channel and vice versa - just to find out if the issue is with the speaker/its wire/its plug ... I Sometimes the speaker calbes/wires go bad over time (especially if they were twisted a lot, and some internal isolation wears thin, causing + and - wires to ever so slighly connect). (have you opened up the speaker housing to see the state of wiring/ filter caps/... ? might be just a faulty connection inside (or a slight shorting where the cable gets crushed to stay in its place where it goes into the speaker housing). - if inversing speakers has the same effect on the same channel : check the solder point where the plug for the speaker is soldered onto the board, using a contact-setting on vu meter is NOT useful for this... if you have bad soldering or copper path on the pcb came loose : pushing your meter on it will most likely put it back into place, although it may be loose when you dont push on it. so either measure it from a bit further on (foloowing the path to a solder point a bit further on one side and the speaker connection on the speaker itsself (Where the wires solder on to + and -). Re-flowing might also be an idea - just to be sure. IF there is an issue with the solder point, it will be solved by reflowing - if the issue is the copper path on the pcb that has come loose : reflowing will most likely make it more evident by completely loosening it (Visibly). - check the antenna connection (especially if it has a connector that goes to the circuit board). - If it started after taking out the tape-block and putting it back... remove it again and put it back again , especially if there is a black wire that gets screwed onto the metal part of the tape-block. PAnasonic sometimes has a grounding-wire screwed to plastic parts as well... - check grounding wires , start with the "ground" screw for phono using contact meter (contact check setting )on your multimeter - measure the voltage on all ground point you can find, from a ground point you are CERTAIN is one (probably a black wire screwed to a metal part) you should have 0.00 on all ground points, including the phono ground - sometimes there are screws to connect pcb, that have these rings on them and then go onto this circle shaped thing on the pcb, they have a purpose : they usually connect to ground (through the strange ring on the screx, screw and circuit board) If those are fine : - check any loose connections (sometimes wires "snap" of their solderpoints) following the path from speaker plugs all the way to the amp or the other way around - check for cracked solder points. In short : to start of : once you excluded the speaker and its plug and wiring itsself : check grounding everywhere you can - on these devices those are usually black wires "screwed" to the tuner-frame / tapedeck metal frame/ sometimes even into plastic (no ideay why but panasonic sometimes does that., ground wiring a plastic holder... ) PS : changing capacitors is ALWAYS a good idea on these devices - the pre 1985 capacitors were usually better quality - the post 1985 are way more prone to drying out. I usually replace any electrolytic one I can with film-caps. But must say I've never come accross bad caps causing humming the way this sounds.
thanks a lot for your detailed review. since I didn't replace the belts on this boombox, I didn't disassembled it further, but since I have this buzzing sound, I'm gonna have to.I'm pretty sure is a loose ground wire problem, maybe somebody did replace the belts before and forgot to fastened that wire. anyway. will do that and in the process make a video on how to replace the belts. THANKS AGAIN.
I'm really interested to find out what's causing this problem. I'm no expert, by the way. Many people would say replace the capacitors, but I wonder if it's a grounding (earthing) problem. I'd look around the amplifier circuit if you can see it and inspect the capacitors for bulging and leaking, and check any connectors and look for bad solder joints. I don't know if this works help, but is it the same if you use batteries instead of mains power? Good luck.
hello. thanks for the advice. I had a slight suspicion that the problem might be a ground wire too, but then I was asking myself, shouldn't that affect both speakers?. I'm with you on the capacitors angle. this will need further inspection for sure. thanks again for the advice.
Hello, your humming (to my ear) sounds like a ground-loop humming .
In my (opinion) :
If humming changes (for better OR worst) when touching anything grounded (as antenna or mass-point for phono), you have a grounding problem / ground loop somewhere I think.
- first test (but you probably did that already : plug the non humming speaker into the humming channel and vice versa - just to find out if the issue is with the speaker/its wire/its plug ... I Sometimes the speaker calbes/wires go bad over time (especially if they were twisted a lot, and some internal isolation wears thin, causing + and - wires to ever so slighly connect).
(have you opened up the speaker housing to see the state of wiring/ filter caps/... ? might be just a faulty connection inside (or a slight shorting where the cable gets crushed to stay in its place where it goes into the speaker housing).
- if inversing speakers has the same effect on the same channel : check the solder point where the plug for the speaker is soldered onto the board, using a contact-setting on vu meter is NOT useful for this... if you have bad soldering or copper path on the pcb came loose : pushing your meter on it will most likely put it back into place, although it may be loose when you dont push on it. so either measure it from a bit further on (foloowing the path to a solder point a bit further on one side and the speaker connection on the speaker itsself (Where the wires solder on to + and -). Re-flowing might also be an idea - just to be sure. IF there is an issue with the solder point, it will be solved by reflowing - if the issue is the copper path on the pcb that has come loose : reflowing will most likely make it more evident by completely loosening it (Visibly).
- check the antenna connection (especially if it has a connector that goes to the circuit board).
- If it started after taking out the tape-block and putting it back... remove it again and put it back again , especially if there is a black wire that gets screwed onto the metal part of the tape-block. PAnasonic sometimes has a grounding-wire screwed to plastic parts as well...
- check grounding wires , start with the "ground" screw for phono using contact meter (contact check setting )on your multimeter
- measure the voltage on all ground point you can find, from a ground point you are CERTAIN is one (probably a black wire screwed to a metal part) you should have 0.00 on all ground points, including the phono ground
- sometimes there are screws to connect pcb, that have these rings on them and then go onto this circle shaped thing on the pcb, they have a purpose : they usually connect to ground (through the strange ring on the screx, screw and circuit board)
If those are fine :
- check any loose connections (sometimes wires "snap" of their solderpoints) following the path from speaker plugs all the way to the amp or the other way around
- check for cracked solder points.
In short : to start of : once you excluded the speaker and its plug and wiring itsself : check grounding everywhere you can - on these devices those are usually black wires "screwed" to the tuner-frame / tapedeck metal frame/ sometimes even into plastic (no ideay why but panasonic sometimes does that., ground wiring a plastic holder... )
PS : changing capacitors is ALWAYS a good idea on these devices - the pre 1985 capacitors were usually better quality - the post 1985 are way more prone to drying out. I usually replace any electrolytic one I can with film-caps. But must say I've never come accross bad caps causing humming the way this sounds.
thanks a lot for your detailed review. since I didn't replace the belts on this boombox, I didn't disassembled it further, but since I have this buzzing sound, I'm gonna have to.I'm pretty sure is a loose ground wire problem, maybe somebody did replace the belts before and forgot to fastened that wire. anyway. will do that and in the process make a video on how to replace the belts. THANKS AGAIN.
Problem with final amp or FM issues
it only happens when playing a cassette, it might be the amp, I hope not
I'm really interested to find out what's causing this problem. I'm no expert, by the way. Many people would say replace the capacitors, but I wonder if it's a grounding (earthing) problem.
I'd look around the amplifier circuit if you can see it and inspect the capacitors for bulging and leaking, and check any connectors and look for bad solder joints.
I don't know if this works help, but is it the same if you use batteries instead of mains power?
Good luck.
hello. thanks for the advice. I had a slight suspicion that the problem might be a ground wire too, but then I was asking myself, shouldn't that affect both speakers?. I'm with you on the capacitors angle. this will need further inspection for sure. thanks again for the advice.