Cassette player dropouts

[Tom41]

I have an old SONY 'boom box' style cassette/cd/radio unit that's developed an annoying issue. When playing tapes, the audio randomly silences for a short time then comes back. There doesn't seem to be any pattern in the silence frequency or duration - I've had silences that last a split second, and others that last several seconds!

The problem is definitely with the cassette player, not the cassette. When it silences, if I wind back the cassette and listen to the same point again, I hear the audio as it should be. Also the CD and Radio don't seem to be affected by this issue.

There are no crackles or anything, so I doubt it's any of the signal wires. It's as if the amplifier is momentarily cutting out then coming back on. Any ideas what might be causing this?

I'd post a sample of the problem happening, but WAV and MP3 files can't be attached...

[Agent24]

Re: Cassette player dropouts

Could still be loose connection somewhere. Does tapping\lightly hitting it cause the fault to appear or go away? Check any mode selection switches for bad solder joints\dirty contacts. Note these may switch power and not audio signal, which would account for no crackling.

Signal tracing with scope or external amp should find the problem fairly easily.

[Towncivilian]

Re: Cassette player dropouts

Have you cleaned the transport (heads, capstans, pinch rollers, tape guides) using 91% isopropyl alcohol and a Q-tip?

[Andrew F. Ali]

Re: Cassette player dropouts

Playback head may need de-magnetising

[SteveNielsen]

Re: Cassette player dropouts

Dirty heads and tape path will not produce that symptom, neither will magnetized heads. Most common causes would be bad switch contacts, broken wire, bad solder joint, or failing component.

[Towncivilian]

Re: Cassette player dropouts

Nonetheless, thorough cleaning and demagnetization is a good idea if it hasn't been done fairly recently. Use a wand-type demagnetizer if available over a DC powered cassette demagnetizer. Switch & potentiometer cleaning is a good idea too; see this guide for details.

[SteveNielsen]

Re: Cassette player dropouts

Most definitely cleaning and degaussing should be done anyway, especially after working on it. It is not going to fix the problem though.

[Agent24]

Re: Cassette player dropouts

Yeah, magnetized heads or misalignment will make the audio sound like crap but I can't see it causing random dropouts, unless you have some *severe* transport damage, in which case you're going to get tape munching etc instead.

[Tom41]

Re: Cassette player dropouts

Ok, some further information. I managed to make a recording of the dropouts happening (can't post it here, as it won't let me attach an MP3). You can probably see the two gaps caused by the cassette player, and I assure you there is no gap in the music at that point on the tape. Looks to me like an amp problem - the sound abruptly cuts off, remains silent then quickly fades back in. Could it be the caps? Doesn't seem to be affected by moving the unit around or tapping it...

Also there are no mechanical switches to get dirty on this. All the switching is done electronically; pressing buttons to select radio, tape or CD. Even the volume control and tuning is digital.

[Agent24]

Re: Cassette player dropouts

I doubt it's a main amp problem if you say CD\Radio etc work without issue.

You may be able to compress the file in a ZIP archive to upload it, or use something like dropbox... although probably not necessary.

Unlikely to be capacitors I think, audio equipment like this doesn't typically use an SMPS so you don't have typical badcaps symptoms... that said capacitors in audio can go bad (usually dry out from being old) and you get hum in the audio.

Best thing I think to do here is signal tracing, find out at what point in the signal path the audio starts dropping out. Easy if you have a schematic, but not too hard if you don't.

Start at either end and work your way along... might be easier to start at the tape head and go from there. From there it would go to a preamp circuit first, then to maybe some EQ circuit, through input switching and to the main amp. Just go through the whole thing and find at which point the signal stops at the same time the output goes silent.

Obviously this will take a bit more time since the thing is not totally dead, you have to wait for the signal to die before you can verify if the point you are testing is OK or not..

If you don't know how to do this, give us something to go on to help you... post model numbers, photos if you have them.

[R_J]

Re: Cassette player dropouts

If the cassette deck is also a recorder the playback/record switch can become oxidized over time due to lack of use, cleaning it should help. its located inside and activated when the record button is pressed.
Its used to switch the head from record to playback.
It might look something like this one...