Grundig TK920/3D reording problem fixed - UK Vintage Radio Repair and Restoration Discussion Forum

Phantomrose1999 · 23rd Nov 2019, 3:57 am

Hi all, last problem with this beast was the record.

It was recording but quality was bad and after i recoreded one whole tape i got a burning smell...so opened it up again.

Most likely suspect is the something in the oscilator circuit and most likely suspect is anything that connects to power and ground.ha

I found one of this "lovely" black caps, hidden under the aluminium base of the oscillator. a 0.01uf 500V devil. I had to unsolder most wires and very carefully bend the twisted tabs underneath the chassis to get the aliminium base out so i can change the cap C64.

Best news is is that when i tested the cap, it was a almost a dead shot as my multi meter contunity tester went off as though it was a wire !! yay. problem found. I check the associated resistor and it was fine.

So changed the cap and its recording 100% perfectly and the playback of the recorded music is just beautifuil...

See the photos, in case anyone else has similiar problems.

Reelman · 23rd Nov 2019, 10:27 am

Good job!
Very satisfying fault to find and fix. Thanks for sharing the details, I for one would like to come across one of these "3D" Grundigs for myself.
Peter

Phantomrose1999 · 23rd Nov 2019, 1:05 pm

Yes, i am getting good at these..ha. I was listening to my SDR radio and made a test recording.. the sound from these units is just amazing..

https://www.youtube.com/watch?v=i7wEE6Jrv0k

ricard · 23rd Nov 2019, 8:25 pm

Thanks for posting the video! It looks like there are small lamps which light up the button legends in front of the buttons. That's a difference compared to the TK819 which I have. It also looks like the buttons don't actually latch (which they do on the '819), so the lights are necessary for seeing which mode the machine is actually operating in.

Another difference is the four thumbwheel controls (two on each side) - what are they for, tone controls?

Phantomrose1999 · 25th Nov 2019, 10:18 am

Ricard, let me share some more info.

Yes, The lamps stay on so we know which button has been pressed, as none of the buttons stay down.

The thumbwheels from left to right are:-

Radio Volume, Mic Volume, Auto Stop function, Turntable volume.

The Auto Stop is a switch that allows the machine to turn off at tape end, OR reverse direction. Works really well, facinating to watch it reverse direction and play the other side. ( i recorded in both directions and its 100% clear and loud)

The left know is power and volume

The right know is tone and if turned to the leftmost position, it switches off the internal speaker

I do have the manual but its all in German.

ricard · 25th Nov 2019, 10:38 am

Thanks Phantomrose for the information. The TK920 really is a serious upgrade from the TK819 then, which doesn't have an automatic reversing function, even though they look visually very similar.

Techman · 28th Nov 2019, 7:23 pm

Those particular capacitors found in old Grundigs are particularly bad. People go on about the Hunts type, but Hunts tend to just go leaky, the type shown in your post #1, go dead short at the drop of a hat if they've got any sort of voltage across them. If there's any others in that recorder, then I would advise checking where they are and what they do and replace them if they're in critical positions.

23rd Nov 2019, 10:27 am	#2
Reelman Octode Join Date: Aug 2008 Location: Rotherham, South Yorkshire, UK. Posts: 1,724	Re: Grundig TK920/3D reording problem fixed Good job! Very satisfying fault to find and fix. Thanks for sharing the details, I for one would like to come across one of these "3D" Grundigs for myself. Peter

23rd Nov 2019, 1:05 pm	#3
Phantomrose1999 Hexode Join Date: Mar 2008 Location: Melbourne, Victoria, Australia Posts: 289	Re: Grundig TK920/3D reording problem fixed Yes, i am getting good at these..ha. I was listening to my SDR radio and made a test recording.. the sound from these units is just amazing.. https://www.youtube.com/watch?v=i7wEE6Jrv0k

23rd Nov 2019, 8:25 pm	#4
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	Re: Grundig TK920/3D reording problem fixed Thanks for posting the video! It looks like there are small lamps which light up the button legends in front of the buttons. That's a difference compared to the TK819 which I have. It also looks like the buttons don't actually latch (which they do on the '819), so the lights are necessary for seeing which mode the machine is actually operating in. Another difference is the four thumbwheel controls (two on each side) - what are they for, tone controls?

25th Nov 2019, 10:18 am	#5
Phantomrose1999 Hexode Join Date: Mar 2008 Location: Melbourne, Victoria, Australia Posts: 289	Re: Grundig TK920/3D reording problem fixed Ricard, let me share some more info. Yes, The lamps stay on so we know which button has been pressed, as none of the buttons stay down. The thumbwheels from left to right are:- Radio Volume, Mic Volume, Auto Stop function, Turntable volume. The Auto Stop is a switch that allows the machine to turn off at tape end, OR reverse direction. Works really well, facinating to watch it reverse direction and play the other side. ( i recorded in both directions and its 100% clear and loud) The left know is power and volume The right know is tone and if turned to the leftmost position, it switches off the internal speaker I do have the manual but its all in German.

25th Nov 2019, 10:38 am	#6
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	Re: Grundig TK920/3D reording problem fixed Thanks Phantomrose for the information. The TK920 really is a serious upgrade from the TK819 then, which doesn't have an automatic reversing function, even though they look visually very similar.

23rd Nov 2019, 3:57 am	#1
Phantomrose1999 Hexode Join Date: Mar 2008 Location: Melbourne, Victoria, Australia Posts: 289	Grundig TK920/3D reording problem fixed Hi all, last problem with this beast was the record. It was recording but quality was bad and after i recoreded one whole tape i got a burning smell...so opened it up again. Most likely suspect is the something in the oscilator circuit and most likely suspect is anything that connects to power and ground.ha I found one of this "lovely" black caps, hidden under the aluminium base of the oscillator. a 0.01uf 500V devil. I had to unsolder most wires and very carefully bend the twisted tabs underneath the chassis to get the aliminium base out so i can change the cap C64. Best news is is that when i tested the cap, it was a almost a dead shot as my multi meter contunity tester went off as though it was a wire !! yay. problem found. I check the associated resistor and it was fine. So changed the cap and its recording 100% perfectly and the playback of the recorded music is just beautifuil... See the photos, in case anyone else has similiar problems. Attached Thumbnails

28th Nov 2019, 7:23 pm	#7
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: Grundig TK920/3D reording problem fixed Those particular capacitors found in old Grundigs are particularly bad. People go on about the Hunts type, but Hunts tend to just go leaky, the type shown in your post #1, go dead short at the drop of a hat if they've got any sort of voltage across them. If there's any others in that recorder, then I would advise checking where they are and what they do and replace them if they're in critical positions.