There is a strange issue with my dd22 where it makes popping/crackling sounds after a little while of playing. I had previously replaced caps on this unit but problem still persists (demagnetizing head didn't help either). I will probably check caps again but if anyone has any ideas that would be great.
Does it crackle in one channel only or both channels at the same time? Does it vary with the volume or not? If not, I would suspect it has something to do with a bad transistor in the AVLS circuit. You could try some component chiller spray to check if the popping stops when you cool a transistor.
It doesn't vary with volume and strangely only occurs when there is a cassette playing (whether the cassette has anything on it or not). I even tried taping the tape detector down with nothing in but it doesn't make the pops that way either. I will try to get audio for reference but I think you're right about the transistor even if the AVLS doesn't affect the popping.
The sounds occur after about 30ish seconds: https://drive.google.com/file/d/1I3t6rOc6zuH7uuXy6B4D8gnYAdTxwX5p/view?usp=sharing And appear mostly random with slight correlation between L&R
If you're testing without a cassette playing then there is no signal from the tape head to the left and right audio processing modules which is why the popping sound is not present in this situation. Distortion and squealing from faulty caps tends to happen even when play is pressed whether there is a cassette loaded or not. Doesn't sound like a cap issue and as you say you've replaced them anyway. My guess is also a transistor fault. May be one transistor inside an IC in the audio out channels. If you have the schematic and the skills and equipment to test the audio signal at various stages through to output to line or headphone jack you may find the failed component(s) but it's really a job for a skilled tech if you don't have the equipment and the schematic.
I took another look inside to see if there was anything obviously wrong but it all checked out. I have very little clue how to diagnose this (do have the schematic though) and I don't have any digital analyzers/oscilloscope so maybe I'll figure something out. Thanks for all the help this far
No problem. Hopefully somebody will have had the same issue as you have described and knows the cause. Cheers
My dd22 has since stopped making those sounds but if I'm going to be honest, I'm not 100% why. I remember there was a screw that went through the board (in the bottom right corner) that I screwed in a little looser since the board itself didn't sit right when it was really tight. The climate where I live is also a bit colder now so following the transistor theory it's possibly that the transistor doesn't heat up as much but that's a bit of a stretch. Do you have the exact same model with the exact same issue?
Something indeed to be checked are the grounding points: both between the PCB and the mechanism chassis, but also between the PCB and the back case. I don't think this is a transistor problem. The transistors don't heat up signficantly as they operate at very low currents, so a thermal drift causing this seems very unlikely. To me it seems more likely these popping sounds are caused by back EMF from the motor. That can also explain why the symptom tends to get better with time, as the brushes and commutator get cleaned with use and there are less imperfect contacts and less sparks generated. I have a JVC CX-F7 which has very similar behavior (also all capacitors are new) and it tends to get better with use. It's also much worse in reverse playback (on this JVC the motor turns both ways depending on FWD/REV play), which would suggest it's motor related.
Yes , The exact same model with exact same issue. Mostly on the right channel at the moment. But If I remember correctly I had it on both channels too a while back. I have never replaced the capacitors. I did changed the belt once. But it did the clicking sound before the belt swap too.
