Technics M205 Cassette Deck Left Channel Not Working

[technicsone]

Hello,
I have a Technics M205 Cassette deck and a while back the left channel quit on me. I have absolutely no clue as to what is wrong any help would be appreciated.
Thanks

[rhomanski]

If it has a record/play switch on the circuit board like most vintage do. You could try switching back and forth between record and play a few times. If that helps then clean the switch with deoxit contact cleaner. Had a pioneer doing that a few months ago. It was made in 78. If yours was made near then it could be the same problem.

Regards,

Ron.

[technicsone]

Well I looked at my circuit board and I did not see a switch that said play/record by or on it. I did see a bunch of pots though that say play level, record level and bias adjustment. I would assume that those are for the service man to make tuning adjustments?
Thanks

[Alec124c41]

When you press Play or Record, a lever pushes a rod that connects to a sliding switch over on the circuit board, that changes the electronic function of the head. This periodically needs cleaning. It also prevents howling feedback, that can destroy speakers, so give it a shot of contact cleaner to its innards, any way you can get it in there.

Cheers,
Alec

[rhomanski]

Yeah the switch will be long and thin. Probably about 2 or 3 inches long and maybe a half inch wide. You'll see a rod going to it to actuate it. You should be able to move it with your finger. It should be somewhere near the middle of the board. It'll look like a long thin square tube.

Regards,

Ron.

[technicsone]

OK I do not have any contact cleaner. I will probably have to get some.
Thanks

[rhomanski]

The best is Caig deoxit. available at Guitar World or online at Parts Express. The best way to do it is hose it down with the deoxit, use the 5% solution in the spray can, followed with Faderlube to replace the oils in the switch. If that doesn't help, take a look at the point where the RCA jacks are soldered to the circuit board. Sometimes after repeated hooking and unhooking the solder will crack.

Regards,

Ron.

[technicsone]

Contact cleaner did not solve the problem. I do not think the problem is a solder joint because the peak meter on the left channel does not move. The RCA wires come after the peak meter correct? The problem was very sudden. No crackling or anything. One day I turned it on. Then possibly a week or more went by (I cannot remember) and the left channel did not work. Is it possible it could be the tape head? I think I heard that the head on this deck was not the best in the world and tended to wear out.
Thanks

[rhomanski]

Yes, it definitely could be the head. If the meters not working, that would mean it's before the rca jacks. Did you clean all the switches on the front? It would require removing the faceplate and the switches to get access to the back of each switch. Shoot the deoxit in each switch and flip or turn a few times. Are there any circuit boards inside that simply plug in? I had a Sansui doing the same thing until I unplugged and reinstalled one board a couple times. In other words try unplugging anything that will and plugging it back in a couple times to scrape any corrosion off the pins. Does the tape head look bad? If it was worn out I would expect it to show. You could look at the wiring where the head goes up and down. The flex point could have broken a wire. Do a good visual inspection. Much more than these things will require test equipment.

Regards,

Ron.

[technicsone]

You could look at the wiring where the head goes up and down. The flex point could have broken a wire. Do a good visual inspection. Much more than these things will require test equipment.

I did not see anything wrong as all of the wires are hooked up. I tried to do a continuity check on them but the head did not allow that.

Did you clean all the switches on the front? It would require removing the faceplate and the switches to get access to the back of each switch. Shoot the deoxit in each switch and flip or turn a few times.

I did that even though I could not test it because the tape head is not screwed in. There is no crackling when you jiggle the switches though so I do not think that is the problem.

Are there any circuit boards inside that simply plug in? I had a Sansui doing the same thing until I unplugged and reinstalled one board a couple times. In other words try unplugging anything that will and plugging it back in a couple times to scrape any corrosion off the pins.

There are no circuit boards that plug in on this model.

Does the tape head look bad? If it was worn out I would expect it to show.

There does not appear to be much wear on it but I would think that is the most likely problem. This is just a very very wild guess but wouldnt there be a burnt sort of look or smell to something on circuit board? I think I may have a head I can replace the current head with.
Thanks

[rhomanski]

With a low hour cassette deck, the most likely problem will be corrosion. After that would be a problem caused by moving parts. Of course there is always the manufacturing defect or a voltage spike at your home. I believe the head is merely a coil that gets an impressed voltage from the tape and then is amplified. You should be able to verify the head with a multimeter. Put it on ohms and put the leads across both channels. You should get about the same reading. If one side is reading infinity then you know the head is bad. After that check the wires the same way back to the circuit board.

As far as a burnt look or smell on the circuit board, maybe. Sometimes transistors will go out with no indication. Capacitors will go short, resistors will go open. All with no sign.

Regards,

Ron.

[technicsone]

With a low hour cassette deck, the most likely problem will be corrosion.

That is something I forgot to say. There is some rust on the surface of the head.

You should be able to verify the head with a multimeter. Put it on ohms and put the leads across both channels. You should get about the same reading. If one side is reading infinity then you know the head is bad.

There are four contacts on the head two with a pink wire and the other two white. If I understand correctly you want me to hook the black wire from my multimeter to pink and the red to the white wire and vice versa correct?

After that check the wires the same way back to the circuit board.

You mean to hook the black multimeter wire to the white wire on one end and hook the red wire to the pink wire on the other end?
Here is a link to some pictures of the heads and the deck

gallery/album.php?album_id=1274

[rhomanski]

The gray cable is one channel the black cable is the other channel. You would want to measure between the pink and white wire from each cable on the head. One will be hot and the other ground. The head has two coils in it. One for the left channel and one for the right. A coil is one long piece of wire wrapped into a coil. It should have low resistance. You have to check each one and compare. That means unsoldering one wire from the head and reading across the head with your meter. Red meter lead where white wire was hooked up and black where the pink is hooked up.Remember to do it with the pink and white from the same black or grey cable. The two coils are separated from each other. Or they should be. The brown is not rust, it is residue from the tape. The tape touches the head and will shed part of itself. Most heads are made of very hard material to be able to withstand the friction. I have heard of one set, I don't remember what brand, but it was too soft and would wear out quick. When it wears out, the tape starts rubbing the coil and will wear through the wires very quickly. This may be what has happened. The steel gap has worn until it is too wide and too thin and the tape is touching the wires. The best sound is attained by the smallest distance between the coils and the tape, but the wires are fragile and must not actually touch the tape. Your coils may have touched the tape. If the head is good, then I would put the meter's red wire on one end of the pink, and the black on the other end of the pink, and check the wire for a direct short. If it reads anything else the wire is bad. Check all four wires that way.

An OHM meter will put out a small voltage from it's internal battery, usually 1.5 volts on it's leads. It then measures the voltage back and calculates the voltage drop and therefore how much resistance in the circuit. A straight piece of wire doesn't drop much voltage at all and will read low on the meter. An open will not return voltage at all and will read infinity. On audiokarma, in the do it yourself forum they have a sticky at the top of the page for the N.E.E.T.S. manuals. Naval electric and electrical training manuals is what it stands for I believe. I ordered the set when I was in the Navy back many years ago. They will take you through the basics of electrical theory. They will explain the use of tools, simple circuits, and the basics of using them. I don't think their sets are complete but if you google neets you should find the complete set. They will explain a lot better than I can. Although, there are rules to troubleshooting. First you need to know how something is supposed to work, then you can see that it isn't working right. Second you need to know how it does what it does, then thirdly you can begin to come up with reasons why it's not doing what it should.

Regards,

Ron.

[technicsone]

Thanks for all of your help but none of these ideas seem to be the problem. Thank you very much for all of your help. I am not going to go any further with this so I am just going to quit on it.
Thanks