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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 2nd Nov 2019, 7:20 pm   #21
Refugee
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Default Re: Grundig TK920 3D Exploding Caps

That contact looks like a normally closed switch.
Perhaps mute and clutch are one and the same circuit.
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Old 2nd Nov 2019, 9:52 pm   #22
ms660
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Default Re: Grundig TK920 3D Exploding Caps

They look like contacts B1 and B2 on the schematic, bottom set is B1.

Lawrence.
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Old 4th Nov 2019, 10:14 am   #23
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Default Re: Grundig TK920 3D Exploding Caps

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Originally Posted by Phantomrose1999 View Post
I can feel the reel spin with just the firction of the clutch plates, then suddenly the left spook will lock up, pressing stop, or FF/RW immediately releases the power to the clutch and it becomes free.

Thus i am convinced its Electrical, just no idea where.
I don't know if this is a clue, but when the pause button (black round button to the right of the main switch assembly) is pressed, it causes the pinch roller to disengage and also energises the supply side reel magnet to stop the tape. So there is a circuit to power the reel magnet when the machine is running ordinarily, it just shouldn't be engaged unless the pause button is pressed.

(As others, I have fond memories of this chassis, I bought one as a 12-year old and spent countless hours fiddling with it. I even considered keeping the chassis but designing new control electronics for it and a new amplifier. Even had a new box made for it. In the end it didn't come to anything, too advanced for my knowledge then. But great fun along the way.)
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Old 9th Nov 2019, 4:25 am   #24
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Default Re: Grundig TK920 3D Exploding Caps

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Originally Posted by Refugee View Post
From what I can remember the reel tables are braked during play with reduced power to the reel magnet. The reel table is provided with more power for braking when stopping after winding the tape.
A full belt goo check of both reel tables would be my first port of call before looking for an electrical fault.
Hi everybody, rainy saturday in Melbourne, good time for Grundigs..ha
I did a voltage check of the brakes:

Left Right Function
0 28 FF (rewind right)
28 0 RR (rewing left)
16 0 Play Right ( This is where the left spool locks, problem)
0 16 Play left ( right spook has slight tenson with 16v)

So it appears not to be an electrical problem, but a physical one with the left spool. It appears to be locking up very hard with only 16 volts.

Most interesting observation, the left spool jumps several MM in the air when engaged.. the righ spool has no observable vertical movement.

So its time to take apart the left spool and investigate

Any comments welcome
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Old 9th Nov 2019, 4:55 am   #25
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Default Re: Grundig TK920 3D Exploding Caps

Looks very clean, i mentioned, this unit has been in a house for a long time.

Well, i swapped left and right spools and the problem is WITH THE SPOOL !!

So upon further investigation, the only difference is the height of the felt. The working spool is much higher than the faulty spool. I will add some packing to the faulty one, and see what happens.

see the photos

What an amazingly beautiful machine ! will buy more when find them.. The TK60/64's have been mastered..ha
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Old 9th Nov 2019, 9:39 am   #26
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Default Re: Grundig TK920 3D Exploding Caps

Well, its done ! next...ha

I added some padding to the left reel felt. A thick car margazine cover, cut in the shape of the felt, lifted it enough to work perfectly.

I also took out the shafts of each spool, and saw the spings that all have been talking about. WD40 and put them back together. However i dont recommend taking these shafts apart unless you are rather mechanically minded.

https://www.youtube.com/watch?v=y9Y02ICqoL0
Last video of it running out of the case


https://www.youtube.com/watch?v=SFtIWlU0jew
back in the case for perhaps another 50 years.

I must admit, this is the most beautifully engineered grundig reel to reel of this era, and i have most of them, including TK60 x2 and TK64x 1 which i have restored.

Would love to get a TK830 as i like the colour scheme of them

Thanks for all the comments. Hope you liked the videos.
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Old 9th Nov 2019, 2:42 pm   #27
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Default Re: Grundig TK920 3D Exploding Caps

The joy of 60 year old mechanical engineering LOL

It did not last too long and the left spindle shaft TOTALY locked solid !

Well, it is a rainy sat night, so i took it to bits again and removed the left spindle shaft AND the housing just for the fun of it.

The spring at the bottom end of the shaft had bound up, i suspect due to the warped washer that allowed too much of a gap.

So i cut off the end of the spring, discarded the warped washer, and put it back together with very little play, so the spring could not pop out again.

See photo.

Anyway, been a few hours now, and shes holding steady !! lets see for how long..ha.

BTW: The Auto reverse is just fantastic, so gentle, with a pause, and then reverse.. really amazing.
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Old 9th Nov 2019, 5:51 pm   #28
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Default Re: Grundig TK920 3D Exploding Caps

Hurrah! It's rainy in Cornwall too, but I only have 40 year old mechanical engineering to deal with this afternoon.

Well done on getting it going, and I hope it continues. At least if it doesn't you've got a good idea of where to look next time. Have you considered some oil in those shafts rather than WD40, which isn't a lubricant? Does the manual have anything to say about lubrication?
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Old 10th Nov 2019, 8:42 am   #29
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Default Re: Grundig TK920 3D Exploding Caps

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Hurrah! It's rainy in Cornwall too, but I only have 40 year old mechanical engineering to deal with this afternoon.

Well done on getting it going, and I hope it continues. At least if it doesn't you've got a good idea of where to look next time. Have you considered some oil in those shafts rather than WD40, which isn't a lubricant? Does the manual have anything to say about lubrication?
Hi, i only have a complete TK12/820/830 typed manual and schematic for the 920, there is no mention of these shafts or springs in any of them. The one thing i dont have is OIL !! lol I did want to oil them...

Well, WD40 has oil, once the propellant dries, it leaves a oily film..

Its still working after a day...so thats good.
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