Cassette Tape head low sound?

[Grubhead]

I have a question about cassette tape heads that I couldn't find an answer to on the net. The question is can you still hear sound very faint from a bad tape head?

The problem I have is a dual tape deck a Marantz SD 285, deck 1 (play only) has a really weak signal coming from both channels. But Deck 2 is normal.
At the moment I am using the headphone socket to listen to both and with the Headphone volume control up to full level. I can just hear the music playing from the tape. But on deck two it's loud at half volume.
Deck 1 uses a separate IC a UPC 1228H as the pre-amp but I have replaced this already and it didn't make a bit of difference. There is also a small capacitor to the power of the IC but that is good, plus a replaced it too.
If I remove the head lead from the connector bit. I can get a buzz from each channel by touching it with my finger. Showing the amp stages seem to be OK. As I am hearing sound from the tape, it shows the switches are passing the signal.
So I am assuming the head is the problem.

[TonyDuell]

I assume you've cleaned the head (with a cotton bud and propan-2-ol, not a cleaning tape). If not do so.

Have you demagnetised the head? I once had a reel-to-reel video recorder that gave a very low amplitude signal from the tape that imrproved spectacularly when I did that.

[Nickthedentist]

Usually, worn heads give reduced ouput at high frequencies, i.e. low notes are reproduced normally and high ones are weak. This gives rise to muffled-sounding audio.

Conversely, heads where the coil has gone open circuit give no output at all.

Is the tape making good contact with the face of the head?

[paulsherwin]

As Nick implies, this doesn't sound like a tape head issue. If the sound is very muffled as well as quiet, then the head is way out of alignment or there is something wrong with the tape guides, capstan, pinch roller or head advance mechanism. If the sound is bright but just very quiet, it's a signal switching problem.

[Grubhead]

The sound is normal with just no volume.

I have a PDF of the circuit diagram

marantz-sd285-schematic-diagram/

Head is clean, but I don't have a demag.

[paulsherwin]

Carefully clean all the switch contacts. It's very easy to miss some or fail to get the cleaning fluid inside properly. Also, check the mechanical operation of any switches. Sometimes there are switches on the main board activated by rods, cables or springs.

If everything seems OK the next thing to look for is dry joints where the head wiring joins the main board, and around the pins of the preamp chips.

[60 oldjohn]

Could it be a bad flexible wire from tape head?

John.

[Grubhead]

Right I will check those things out. It might take a while because it's a sod to dissemble and put back together.

[julie_m]

If testing a tape head for continuity, please only use a digital meter! Otherwise, you run the risk of leaving the head magnetised, and your favourite tapes getting quieter every time you listen to them!

(Yes, I have made this mistake myself And I only noticed it because there was a song on the tape that I did not like so much and usually fast-forwarded through.)

[G6Tanuki]

Check the cassette too: there should be a pressure-pad behind the tape in the record/replay #hole# - either a small springy bit of copper with a felt pad glued to it, or a block of spongy foam.

With age, either the glue holding the felt to the copper loses its grip and the felt pad goes walkabout, or the foam pad crumbles to dust. In either case the result is insufficient control of tape-to-tapehead contact and poor output.

[paulsherwin]

I have assumed that the OP has tried lots of different cassettes with the same result, but you're right to assume nothing.

[stevehertz]

Originally Posted by G6Tanuki

Check the cassette too: there should be a pressure-pad behind the tape in the record/replay #hole# - either a small springy bit of copper with a felt pad glued to it, or a block of spongy foam.

With age, either the glue holding the felt to the copper loses its grip and the felt pad goes walkabout, or the foam pad crumbles to dust. In either case the result is insufficient control of tape-to-tapehead contact and poor output.

If that were the case then deck number 2 would also exhibit the same problem, it doesn't; we are told that the fault only exists on deck 1.

[dseymo1]

The normal output of tape heads is pretty low, so the fact that you get hum when you touch the amp input doesn't mean very much - the gain might still be lower than it should be.
Can you arrange some sort of signal via a potential divider, and compare the output levels when injected into the head connector for each deck?

Is it possible to jury-rig the switching, and feed to 'bad' head output into the good deck's connector, while energising the 'bad' transport? That would narrow down the possibilities.

[Grubhead]

Originally Posted by paulsherwin

I have assumed that the OP has tried lots of different cassettes with the same result, but you're right to assume nothing.

Yes Paul is right it is not a tape problem. But an interesting answer all the same.

[Grubhead]

Originally Posted by dseymo1

The normal output of tape heads is pretty low, so the fact that you get hum when you touch the amp input doesn't mean very much - the gain might still be lower than it should be.
Can you arrange some sort of signal via a potential divider, and compare the output levels when injected into the head connector for each deck?

Is it possible to jury-rig the switching, and feed to 'bad' head output into the good deck's connector, while energising the 'bad' transport? That would narrow down the possibilities.

The good thing about the deck is that all the wired connections are done by sockets and mounts. So you can remove them. I couldn't directly fit the three pronged head lead from deck one to the Deck 2 connector, but it might be possible to take a wire from the pin of deck 1 head to deck two output, at least for one of the channels. But the problem would be when deck 1 is running deck 2 is shut off and vice versa. But I will see if I can get round it.

Not related to the above. Has anyone encountered sticky cassette tape problem? Where the cassette will just stop moving, regardless of tape machine?
Is there a thread for it already or should I start one?

[stevehertz]

Originally Posted by Grubhead

Not related to the above. Has anyone encountered sticky cassette tape problem? Where the cassette will just stop moving, regardless of tape machine?
Is there a thread for it already or should I start one?

There's loads of mechanical problems that can develop with cassette tapes, some even from new. I'm not sure if there's a dedicated thread re this but it was discussed in a thread that I recently placed, but I can't remember what the subject was about? I think it was about cassette pressure pads and replacing them.

[AC/HL]

https://www.vintage-radio.net/forum/...=132077&page=2

[ben]

A few months back I had to change a head in a Philips portable whose output was very low. It looked fine, but a replacement proved it was duff. So it can happen, but check the other things first. Philips erase heads usually just fall to bits!

[FrankB]

Don't forget to clean the record/pb sw assy.
They can cause all sorts of oddball problems.

Now I have an old EICO signal tracer,(147?) and have jumped the AF input to the RF input to give me a bit more gain.
I can actually listen to the sound coming off the tape head with it. That feature really saved my bacon when I was servicing full time. Use a junk tape too, as the "pop" connecting can glitch the tape. Then I'd demag the head to be sure after checking it.
Look to see that the mtg. screws are still in place too. I have seen dozens of the adj. screw back out or fall out, causing low/no vol too.

[Grubhead]

Some further investigations done.
I removed the Deck II connector P2 and pressed play on the deck. Even with the head connection off you could hear the background hum of the pre-amp stage. Even with the headphone volume control on half. Even putting my finger near the P2 connector caused a great deal of hum. Whereas if you remove P1 for Deck 1 you can only get a buzz by touching the pins. So it would appear that the problem is on the PC board. All connections to the head are good anyway and the fact you can hear the sound from the head means it's good the preset controls R11 and the other for the other channel do adjust the volume and if turned up full the signal is just loud enough to be hear.
I checked the voltages U301 does get the 9 volts at pin 4. Just over 3 volts as shown comes out of pin 3. And Pin 1 has the correct voltage U302 TC 4066 has 6 volts at 1 and 6 volts at 2. As you can see from the part schematic below Deck 2 signal joins it at pin 2. The signal must be good after that stage.

I could not get Deck 1 head to play via deck 2 amp, as they are shut off when the other plays. But I think the lack of volume is now after the head anyway.