Help with Grundig TK126 repair problem?

[stephenavayl]

Hi, Can anyone help with a Grundig TK126 query...I am repairing an old machine and have changed belts and replaced the perished roller etc. However i am bamboozled by the switch mechanism that is located near the top of the unit between the reels. I think its a coil / magnetic switch that seems to cut power (and may do something else?) depending on where the selector switch is positioned. Currently however it seems to stick and power stays on when the selector switch is in the STOP position. The drive belt keeps turning and the brakes are on the reels so cant be good. Does anyone know how this switch is meant to operate and if its possible for the mechanism to get "out of sync"? I have tried oiling / loosening the spindle that the white plastic rotates on and it moves reasonably freely. I suspect the coil/magnetic switch is broken and therefore the plate isn't pulling back to allow the plastic to rotate. But it does rotate far enough when REWIND is selected. Any repair suggestions much appreciated

[Reelman]

The motor and thus the drive belt should rotate all the time the machine is switched on. When a tape is playing or winding and the stop foil at the end of the tape hits the contacts in the sound channel the relay shown causes the mains to be switched off. Rotating the tape transport control (stop, play, etc) restores the mains. This is a feature of some Grundig machines and what passes for automatic stop, not the best system since the mechanism does not drop out to “stop” and so leaves the pinch roller or idlers engaged possibly causing a “flat” on the rubber surfaces eventually.
If you don’t have a tape with stop foils just try shorting the contacts together (they are close together at both end of the sound channel) with something non-magnetic. This will prove the operation providing the machine is set to play or wind when you do it. You will get a little spark.

Peter

[DMcMahon]

Hello Stephen,

I think this is the EOT switch mechanism. If there are metal foil leaders on the tape then when Playing or Fast winding when the end of tape is reached, the EOT (End Of Tape) mechanism will automatically stop the motor.

I remember some time back looking at it on my TK 146 (basically the same as your TK 126) trying to figure out exactly how it worked. Later today I will try and have a look at my TK 146 to remind me of how it functions.

David

[stephenavayl]

Originally Posted by Reelman

The motor and thus the drive belt should rotate all the time the machine is switched on. When a tape is playing or winding and the stop foil at the end of the tape hits the contacts in the sound channel the relay shown causes the mains to be switched off. Rotating the tape transport control (stop, play, etc) restores the mains. This is a feature of some Grundig machines and what passes for automatic stop, not the best system since the mechanism does not drop out to “stop” and so leaves the pinch roller or idlers engaged possibly causing a “flat” on the rubber surfaces eventually.
If you don’t have a tape with stop foils just try shorting the contacts together (they are close together at both end of the sound channel) with something non-magnetic. This will prove the operation providing the machine is set to play or wind when you do it. You will get a little spark.

Peter

Many thanks Peter - I will try this. Is it normal for the brake to be on as well? it is much noisier in play mode than i expected - i read that these machines were very quiet in operation?

[Reelman]

The brakes should be released whenever the tape is expected to move. The TK126 is the two track version of the TK146 and was not officially sold in the UK. It should be transistor and have 3 sliders on the left. From your picture the chassis looks to be an older machine?

Certainly the transistor machines should make little mechanical noise, hum of the drive belt and the faint swoosh of the take up spool clutch really. If it is audible above the sound from the tape then you need to investigate further.

Peter

[DMcMahon]

Had a quick look at my TK 146, found the drive belt from the motor pulley to the flywheel was off, so refitted it but the motor pulley is slipping around the motor shaft so that belt is not really being driven.

So compared operation with one of my TK 141's that does not have the EOT hardware.

As Peter correctly states when unit is switched on the motor will always rotate (even in Stop) and hence also the drive belt to the flywheel. The belt from flywheel to the Take Up spool table also rotates. In Stop mode the brakes are on both spool tables so the clutch on the Take Up table slips so no drive to the top of the table. If you manually pull the brake off the Take Up table then the top of the table will rotate similar to Play mode.

On the TK 146 the EOT switch is normally always physically made/closed (your looks particularly forced upwards closed). When either of the EOT sensor posts is grounded (in Fast wind or Play) then the EOT relay energises and its armature top plate pulls down and releases the switch via the white plastic sprung loaded switch arm. You then have to mechanically reset it by turning the main control.

You can manually simulate EOT operation in Play/RWD/FFD by just pushing the armature plate down.

So from your original Post # 1, I do not think you have a problem as long as the EOT operates when it should.

David

[stephenavayl]

Many thanks David & Peter. All looking good now - TK126 operating as it should and I also repaired a TK141 that I was given for parts - it works well apart from the internal speaker being disintegrated, but with external speaker it is fine.

[DMcMahon]

That is good news, well done.

David