Grundig TK20 Recording fault - UK Vintage Radio Repair and Restoration Discussion Forum

AndiiT · 25th Jul 2007, 8:03 pm

Hi,
I may have already answered this, but am looking for a "second opinion" before I start chasing my tail. I am currently in the throes of resurrecting a Grundig TK20, all is going well however I currently have a "fault" on record which is as follows:

With the record level control set to a comfortable listening level through the machines built in speaker (for those who don't know this machine has a built in monitor facility) the magic eye, whilst being lit up, gives no indication of signal/record level at all.
In order to get the magic eye to operate I have to set the record level control to a level which is so high that the recording (and the accompanying output through the speaker) distorts.

Looking at the circuit diagram there is a preset adjustment which affects the magic eye input sensitivity but I have no reason to suspect that this has been tampered with. I more than likely suspect one of the resistors that feeds the magic eye - has anyone had experience of these resistors going high value in one of these machines?
I have had a similar fault with a Ferguson machine but that only affected the brightness of the magic eye display and not the sensitivity.

Thanks in advance
Andrew

DOFFERY · 25th Jul 2007, 8:23 pm

Hello Andrew, Re. your TK 20 , don't know what you have done in the way of service but same rule applies , replace the caps.
The M Eye has a cap. across the preset, also one of the feed resistors , think it was the 100K goes high but I would replace both, how's the recording

Doffery

Andy1970 · 25th Jul 2007, 9:02 pm

can i apply the same remedy for the same fault on my tk8? or are they totally different?
cheers.

DOFFERY · 25th Jul 2007, 9:46 pm

Similar circuit, although different if you get my meaning, same applies, caps. & the same feed resistors, although a different eye. Caps. caps. & caps.!!!

Doffery

Andy1970 · 25th Jul 2007, 9:53 pm

i take my cap of to you.
cheers

AndiiT · 25th Jul 2007, 10:37 pm

Quote:

Originally Posted by DOFFERY

how's the recording

The recording is fine, although a little lacking in bass, which could even be down to the tape.

The fact that the machine records and erases tapes ok would suggest to me that the caps are OK, that said it wouldn't hurt to replace them after all it is some 47 years old (at least!!)

Watch this space......

Andrew

Mike Phelan · 26th Jul 2007, 8:01 am

If any of the caps are black or brown WIMA 'humbugs' (which they will be!) just replace them on sight. You thought Hunts were bad ......

DOFFERY · 26th Jul 2007, 9:02 am

Hello again, if you want to find out if the caps. Wima as Mike states are OK check the osc. metal box, that will prove the point.

Doffery

DOFFERY · 18th Aug 2007, 1:15 pm

How's the TK 20 Andrew?

AndiiT · 18th Aug 2007, 2:22 pm

Hi,
The project has been "laid to rest" for a while, however as I said watch this space and I will report my findings once I have cured it.

Re the capacitors I have also noticed that on playback that the volume control does not operate in a uniform fashion (increases volume to around the halfway point at which time there is a low level "glooping" sound from the speaker the control then not doing a lot after that, despite the output being of acceptable levels) which leads me to suspect one of the coupling capacitors, perhaps C17 or C18.

I seem to recall having a similar fault on a Murphy TR1 sometime ago which was traced to the coupling capacitors in the volume control circuit, but can't recall the effect that it had on the magic eye.

Regards
Andrew

25th Jul 2007, 8:03 pm	#1
AndiiT Octode Join Date: Aug 2005 Location: Saltburn-East, Cleveland, UK. Posts: 1,786	Grundig TK20 Recording fault Hi, I may have already answered this, but am looking for a "second opinion" before I start chasing my tail. I am currently in the throes of resurrecting a Grundig TK20, all is going well however I currently have a "fault" on record which is as follows: With the record level control set to a comfortable listening level through the machines built in speaker (for those who don't know this machine has a built in monitor facility) the magic eye, whilst being lit up, gives no indication of signal/record level at all. In order to get the magic eye to operate I have to set the record level control to a level which is so high that the recording (and the accompanying output through the speaker) distorts. Looking at the circuit diagram there is a preset adjustment which affects the magic eye input sensitivity but I have no reason to suspect that this has been tampered with. I more than likely suspect one of the resistors that feeds the magic eye - has anyone had experience of these resistors going high value in one of these machines? I have had a similar fault with a Ferguson machine but that only affected the brightness of the magic eye display and not the sensitivity. Thanks in advance Andrew

25th Jul 2007, 8:23 pm	#2
DOFFERY Retired Dormant Member Join Date: Aug 2004 Location: Blackpool, Lancashire, UK. Posts: 1,488	Re: Grundig TK20 Recording fault Hello Andrew, Re. your TK 20 , don't know what you have done in the way of service but same rule applies , replace the caps. The M Eye has a cap. across the preset, also one of the feed resistors , think it was the 100K goes high but I would replace both, how's the recording Doffery

25th Jul 2007, 9:02 pm	#3
Andy1970 Retired Dormant Member Join Date: Jun 2007 Location: gateshead Posts: 40	Re: Grundig TK20 Recording fault can i apply the same remedy for the same fault on my tk8? or are they totally different? cheers.

25th Jul 2007, 9:46 pm	#4
DOFFERY Retired Dormant Member Join Date: Aug 2004 Location: Blackpool, Lancashire, UK. Posts: 1,488	Re: Grundig TK20 Recording fault Similar circuit, although different if you get my meaning, same applies, caps. & the same feed resistors, although a different eye. Caps. caps. & caps.!!! Doffery

25th Jul 2007, 9:53 pm	#5
Andy1970 Retired Dormant Member Join Date: Jun 2007 Location: gateshead Posts: 40	Re: Grundig TK20 Recording fault i take my cap of to you. cheers

26th Jul 2007, 8:01 am	#7
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,609	Re: Grundig TK20 Recording fault If any of the caps are black or brown WIMA 'humbugs' (which they will be!) just replace them on sight. You thought Hunts were bad ...... __________________ Mike.

26th Jul 2007, 9:02 am	#8
DOFFERY Retired Dormant Member Join Date: Aug 2004 Location: Blackpool, Lancashire, UK. Posts: 1,488	Re: Grundig TK20 Recording fault Hello again, if you want to find out if the caps. Wima as Mike states are OK check the osc. metal box, that will prove the point. Doffery

18th Aug 2007, 1:15 pm	#9
DOFFERY Retired Dormant Member Join Date: Aug 2004 Location: Blackpool, Lancashire, UK. Posts: 1,488	Re: Grundig TK20 Recording fault How's the TK 20 Andrew?

18th Aug 2007, 2:22 pm	#10
AndiiT Octode Join Date: Aug 2005 Location: Saltburn-East, Cleveland, UK. Posts: 1,786	Re: Grundig TK20 Recording fault Hi, The project has been "laid to rest" for a while, however as I said watch this space and I will report my findings once I have cured it. Re the capacitors I have also noticed that on playback that the volume control does not operate in a uniform fashion (increases volume to around the halfway point at which time there is a low level "glooping" sound from the speaker the control then not doing a lot after that, despite the output being of acceptable levels) which leads me to suspect one of the coupling capacitors, perhaps C17 or C18. I seem to recall having a similar fault on a Murphy TR1 sometime ago which was traced to the coupling capacitors in the volume control circuit, but can't recall the effect that it had on the magic eye. Regards Andrew