I'm trying to fix my late 1980s B&O tape deck which was stored in my attic for over 20 years. I've replaced all the belts and the mechanical side works fine. But, there is no sound coming from the left channel. Initially I thought it might be a capacitor issue so I tested them all in circuit and found a couple of bad ones. I replaced them but still no joy.
I then checked the tape head. I connected a multimeter across each channel and found the right channel reading about 280 ohms but the left channel was open. For each channel I then connected the meter to an output and ground and played a tape. Both channels produced about the same millivolts, zero to about 5. I am now confused why there is an output from both channels.
Is the millivolt output a red herring and the true test is the resistance?
I've also swapped the channels over inside the tape deck and don't get any sound, left or right, which obviously indicates something else may be wrong with the left channel circuitry.
My thinking is to buy a replacement tape head from eBay and then start to troubleshoot the left channel with a head I know works. For all I know, just swapping the channels over may cause another problem which manifests itself as no sound. I can't think what, but as you've probably gathered, I'm fishing for answers to what should be a quite simple thing to fix.
I then checked the tape head. I connected a multimeter across each channel and found the right channel reading about 280 ohms but the left channel was open. For each channel I then connected the meter to an output and ground and played a tape. Both channels produced about the same millivolts, zero to about 5. I am now confused why there is an output from both channels.
Is the millivolt output a red herring and the true test is the resistance?
I've also swapped the channels over inside the tape deck and don't get any sound, left or right, which obviously indicates something else may be wrong with the left channel circuitry.
My thinking is to buy a replacement tape head from eBay and then start to troubleshoot the left channel with a head I know works. For all I know, just swapping the channels over may cause another problem which manifests itself as no sound. I can't think what, but as you've probably gathered, I'm fishing for answers to what should be a quite simple thing to fix.
I think you are on the right track. (Left channel, ha) Is the tape head disconnected when you measured the resistance? There may be several things that have failed at that age. If there is a cable to the tape head that bends when the mechanism moves, that could be intermittent. There could also be one electrolytic capacitor that has failed somewhere in the preamp. Keep going with the divide and conquer. You might disconnect the tape head and inject a signal from a generator to then check the down stream circuits with a known signal.
Yes, especially since you did measure some output from the disconnected left channel head. Do you know if that was just noise, or did it follow the recorded signal? Check any switches in the signal path, things like REC/Playback, were the signal might normally get switched. Switches and contacts in old gear can be a lot of trouble.
If you send the left playback head to the right channel and got no sound, it isn't looking good for the left channel head.
Depending on model, a common error is bad contacts in the record/playback switch.
Meddeling around the mechanism could add to inconstent measurements.
If there is a mechanical rec/play switch (you can see it moving by pressing the record button), spray some contact cleaner into it,
press the record button repeatedly up/down around 50 times or more, and see if it makes a difference. If it does, you now know,
where the error lies, and then can move on to furher clean it.
Meddeling around the mechanism could add to inconstent measurements.
If there is a mechanical rec/play switch (you can see it moving by pressing the record button), spray some contact cleaner into it,
press the record button repeatedly up/down around 50 times or more, and see if it makes a difference. If it does, you now know,
where the error lies, and then can move on to furher clean it.
The head itself should not go bad, especially only one channel. If you have magnetized head, signal will be low and distorted, but not likely only one channel.
Clean all contacts, switch channels, its should eventually help.
Clean all contacts, switch channels, its should eventually help.
I recorded the measurements with the head disconnected from the system. The 2 heads (playback/record and erase) use a 9 pin female connector to the main board which deals with playback and record amplification, Bias and HX pro. I used this female connector to take the measurements.
There is no mechanical record/play switch as it uses touch sensitive buttons. Then electronics to turn on the erase/record function. The only mechanical parts I can see are the bits that move the heads onto/off the tape.
If you mean switch left and right channels, I've already done this. The head left channel connector into the right channel amplification gives no sound. As does the head right channel into the left amplification. Which is why I think there are two problems. The erase head works fine in that it erases.
There is no mechanical record/play switch as it uses touch sensitive buttons. Then electronics to turn on the erase/record function. The only mechanical parts I can see are the bits that move the heads onto/off the tape.
If you mean switch left and right channels, I've already done this. The head left channel connector into the right channel amplification gives no sound. As does the head right channel into the left amplification. Which is why I think there are two problems. The erase head works fine in that it erases.
Putting current through a tape head from your DVM potentially magnetises the head and this should be rectified before playing any more tapes.
To fault find, play a tape and follow the circuit with a scope from the head onwards.
Regards Dave
To fault find, play a tape and follow the circuit with a scope from the head onwards.
Regards Dave
If you are concerned about the meter magnetising the head, just swap the meter connections over for the same amount of time.
The problem is very possibly the head as I've now managed to get sound from the left channel by using the head right hand channel connections.
After examining the circuit board I noticed a repair I'd made had come lose. When I replaced one of the capacitors the solder pad came away with the old capacitor. I repaired it with a bridging wire to the next component but this had come lose. Resoldered the wire and the left channel now works.
If I decide to buy a new head from eBay, are they all the same size and it's just the mounting that is different? Or, are the actual dimensions of the head different in which case I'll need to get the old vernier callipers out? I've had a look at a few adverts and none mention size. I thought I'd buy something like this,
"High Quality Replacement Hi-fi Stereo Cassette Tape Head (Metal Tape Compatible)"
The original head is Sendust N6 Z 20 as used in a Nakamichi BX-100.
I'm not too bothered about getting the best sound quality as I only have a few very old tapes tapes that are pretty worn out. It's more a case of getting the thing to work.
After examining the circuit board I noticed a repair I'd made had come lose. When I replaced one of the capacitors the solder pad came away with the old capacitor. I repaired it with a bridging wire to the next component but this had come lose. Resoldered the wire and the left channel now works.
If I decide to buy a new head from eBay, are they all the same size and it's just the mounting that is different? Or, are the actual dimensions of the head different in which case I'll need to get the old vernier callipers out? I've had a look at a few adverts and none mention size. I thought I'd buy something like this,
"High Quality Replacement Hi-fi Stereo Cassette Tape Head (Metal Tape Compatible)"
The original head is Sendust N6 Z 20 as used in a Nakamichi BX-100.
I'm not too bothered about getting the best sound quality as I only have a few very old tapes tapes that are pretty worn out. It's more a case of getting the thing to work.
When I got it out of the attic the left channel never worked. As it is nearly 40 years old I thought I'd look at the capacitors first. A few needed replacing as they were well out of spec either in capacitance, ESR or both. That did not solve the problem so I eventually decided to test the head.
It was only this morning when I checked the board and found the faulty repair of mine and corrected it.
It was only this morning when I checked the board and found the faulty repair of mine and corrected it.
Check
- The metallic contacts of the head. The newer ones have on board pads but the older heads have pins that could break.
- The shielded cable from the head to the preamp could have failed. In this case, you should be able to listen to picked up noise.
- Coupling capacitors (electrolytic) if any.
- Volume control and its solder contacts.
- Preamp.
- Power amp if applicable.
Just to bump this, if I change the head what do I need to look out for apart from the physical connections?
@newvirus2008 where applicable, I've checked all that; capacitors, solder connections, left and right pre amp channels work. I assume the head has gone as its was stored for 20 years in an attic and subject to hot, cold and damp conditions.
There are two main bracket types with one much lower on the head. Make sure you get the correct one.
Are you 100% sure one channel is open. It is an incredibly rare scenario for that to happen and the windings are sealed in the head with hard epoxy. They should be immune to damp and so on. Flux on the pins can insulate them from the meter probes. Make absolutely sure it is open.
@Mooly Not sure what else to check.
The left and right deck pre amps now work as proven by swapping around the connections. I've reflowed the solder on the head connections and it made no difference. The left channel of the head still reads open when tested with a meter. The right shows about 280 ohms so I guess I'm doing the check correctly. I tested the head in 2 locations. First at the head connections and then, in case there is a build up insulating the probes, at the 9 way connector end that plugs into the board, after unplugging it I should say. Both ways give the same readings.
I'm thinking of buying a replacement head to prove my theory. At about £14 it's a relatively cheap way of doing it. If the problem still exists, back to head scratching.
The left and right deck pre amps now work as proven by swapping around the connections. I've reflowed the solder on the head connections and it made no difference. The left channel of the head still reads open when tested with a meter. The right shows about 280 ohms so I guess I'm doing the check correctly. I tested the head in 2 locations. First at the head connections and then, in case there is a build up insulating the probes, at the 9 way connector end that plugs into the board, after unplugging it I should say. Both ways give the same readings.
I'm thinking of buying a replacement head to prove my theory. At about £14 it's a relatively cheap way of doing it. If the problem still exists, back to head scratching.
Well that is pretty conclusive I must say. Very rare but if its open its open 🙂
All you can do is replace it.
All you can do is replace it.
See if you can find NOS Akai or Panasonic SSD (Super Sendust) heads, ferrite heads do not give as good a higher frequency response.
Akai glass heads were famous for their quality.
Panasonic was OEM to many cassette deck makers, Nakamichi volumes were low, the name just adds to the asking price.
Panasonic logo on those was 3 arrows pointing out at 120 degrees from the same centre, there must be photos on the net.
Just check mounting, as Mooly says above, and verify that the impedance is similar.
One trick to try is to remove the head, and check carefully if the pins going in are damaged, can be a corroded pin, that can be hacked with abrading the epoxy and soldering again. Happens if the soldering flux was not cleaned off, and turns corrosive.
Akai glass heads were famous for their quality.
Panasonic was OEM to many cassette deck makers, Nakamichi volumes were low, the name just adds to the asking price.
Panasonic logo on those was 3 arrows pointing out at 120 degrees from the same centre, there must be photos on the net.
Just check mounting, as Mooly says above, and verify that the impedance is similar.
One trick to try is to remove the head, and check carefully if the pins going in are damaged, can be a corroded pin, that can be hacked with abrading the epoxy and soldering again. Happens if the soldering flux was not cleaned off, and turns corrosive.