Grundig TK 23 Delux NO ERASE

[djorrell]

Hi guys, this is doing my head in. I picked up a rather shabby and unloved tk 23 for the massive sum of £12. Ive replaced all the belts, Cleaned and lubed all moving parts (where needed), replaced the volume potentiometer as it was falling apart. It now plays like a new one, However, It will not erase or record. Ive seen on other threads about the same problem bu its always mentioned that the issue is most likely the oscilator tube (EL95). Mine does not have a EL95. Mine has a EF86, EF83, ECC81, ECL86 & the EM84. Do I have a oddball machine?

Thanks in advance

[ben]

I'm pretty sure that on one of these models, twisting the record knob would disable erase allowing for crude superimposition effects. I'm sure someone will confirm/ correct me on this!

[DMcMahon]

Yes rotating the red or white record button about 90 degrees clockwise will disable the erase head for superimposition recordings. It is spring loaded and normally will only stay in that position when the Start key is pressed down at the same time as rotating the record button.

Make sure that the Record button is not stuck in that position by manually making sure that the Record button can be rotated.

David

[DMcMahon]

Originally Posted by djorrell

Hi guys, this is doing my head in. I picked up a rather shabby and unloved tk 23 for the massive sum of £12. Ive replaced all the belts, Cleaned and lubed all moving parts (where needed), replaced the volume potentiometer as it was falling apart. It now plays like a new one, However, It will not erase or record. Ive seen on other threads about the same problem bu its always mentioned that the issue is most likely the oscilator tube (EL95). Mine does not have a EL95. Mine has a EF86, EF83, ECC81, ECL86 & the EM84. Do I have a oddball machine?

Thanks in advance

A standard TK 23 has the EL95 that is used as the output pentode in Playback mode and in Record mode it becomes the Bias Oscillator.

I guess your TK23 de luxe is the TK 23L, this uses the ECL 86 instead of the EL 95. If it plays back OK then fairly unlikely the valve itself will be bad in Record mode.

Is your model the Automatic version which has the option of Automatic or manual recording ?

Erase/Record not working could be many things such as bad/dirty contact on the Play/Record slide switch. There also is an adjustment on the Play/Record actuator that may need to be checked (more on that later).

David

[DMcMahon]

Forgot to ask if you have been inside the back of the machine and hinged down the PCB.

When you hinge the PCB back up into its normal position you have to engage the Play/Record actuator into the end of the Play/Record switch, it not aware of this it is not that difficult to end up with the actuator not engaged and therefore Record/Erase will not work.

David

[Chris R]

I don't know if this will be any help, but some TK20's suffered from no bias /erase oscillator. It was usually due to the horrible WIMA capacitors going s/c.

Chris R

[DMcMahon]

The TK 23 and similar TK series (TK 14, TK 17, TK 18, TK 19, & TK 27) generally did not use the potentially troublesome Wima capacitors.

A photo showing the PCB components would confirm this.

David

[DMcMahon]

Is your model the Automatic version which has the option of Automatic or manual recording ?

David[/QUOTE]

There also is an Automatic only version, i.e. with no EM 84 Magic Eye recording level indicator.

David

[DMcMahon]

Photo 1 shows the Play/Record actuator engaged in the Play/Record Slider.

Photo 2 (metal screening panel removed) shows the Play/Record actuator not engaged in the Play/Record slider.

Photo 3 shows the actuator assembly referenced in Photos 4 and 5.

David

[djorrell]

Hi guys, thanks for the input. Yes my machine is manual/auto record. No buttons stuck and the record play switch is located correctly. When I put it in record mode the magic eye responds correctly and in manual mode the level is clearly adjustable. I read somewhere on here that the oscillator coil could be bad so today I carefully removed it and took some readings with a multimeter. I cant remember now what the reading were but I was basically looking for short or open circuits but I didn't find any. The only thing I did find is a electrolytic capacitor connected to pin 7 of the ECL86 measures 96uf but is clearly marked 50uf. Could this stop the bias oscillator The Cap in question is the one to the left of the coil.

[DMcMahon]

Originally Posted by DMcMahon

The TK 23 and similar TK series (TK 14, TK 17, TK 18, TK 19, & TK 27) generally did not use the potentially troublesome Wima capacitors.

A photo showing the PCB components would confirm this.

David

To clarify I should have said "generally do not use the potentially troublesome Wima paper di-electric capacitors, they do/may use other types of Wima capacitors such as MKS (Polyester film) and Tropyfol (Polyester) both of which are very reliable".

David

[DMcMahon]

Attached is the bias oscillator coil resistance details.

It is difficult to be sure but I would say probably unlikely that the 50uF (C20 cathode bypass) capacitor is the culprit.

Electrolytic capacitors generally have a large % tolerance and even a brand new 50uF (actually 47uF preferred value for a modern component) may measure a lot higher than 50uF.

The capacitance can increase with age plus any leakage may confuse modern electronic capacitance measuring meters and give a higher capacitance reading. I would still recommend renewing it to be sure but not confident it will help.

There are 3 contacts of the Play/Record switch that enable the bias oscillator to work when Record is selected, I would first check these 3 contacts out resistively with no power on the machine.

1. Contact 1,8 (ground) switches over from 1,9 to 1,7 grounding the grey wire of the oscillator coil.

2. Contact 1,11 (ECL 86 Control grid input via R33) switches over from 1,12 to 1,10 connecting the Control grid circuit through to the white wire of the oscillator coil via the bias amplitude adjustment R37 pre-set (this is the feedback/control loop).

3. Contact 1,5 switches to 1,4 shorting out/bypassing the output transformer primary winding.

So is your TK 27 de-luxe or TK 27L de-luxe ?

How do you select automatic recording as opposed to manual recording ?

David

[DMcMahon]

Originally Posted by DMcMahon

So is your TK 27 de-luxe or TK 27L de-luxe ?

David

Should have read "So is your TK 23 de-luxe or TK 23L de-luxe".

David

[djorrell]

You asked about the record mode selection. If you just push down the red button it goes into what the Germans decribed as "Magic Ear", (auto level). For manual mode you need to turn the button 45 degrees and push it down. If you turn the button 90 degrees and push down it disconnects the erase head. In this position the button needs to be held down as apposed to locked down in the other two positions. Basically a punch-in, punch-out or superimpose.

Thanks for the info on switch 1 contacts, I'll take a look at that tomorrow. The cap I mentioned is impossible to find. The nearest modern one is 47uf, would this do job?

[DMcMahon]

Yes Magic Ear for automatic recording, Grundig and some others used that term.

Knew about 90 degree rotation of the record button for Superimpose recordings, first time I have heard about the 45 degree rotation for automatic recording, it makes sense because I thought/knew that there was no other separate automatic recording switch/button.

So yours is the TK 27L de-luxe, the fully automatic version (no manual recording) has an illuminated "Automatic" emblem in the window where the EM 84 Magic Eye valve display is.

Forgot to say that would be very worth while first trying some electrical contact spray into the Play/record slider switch, you can access this by hinging down the PCB.
You cannot see many of the actual contacts, without removing the metal cover around the switch (which strongly do not recommend).

It is just a case of putting the nozzle of the contact cleaner into each end of the switch and spraying some cleaner in. Then manually operate the switch many times by pulling out the switch slider arm against the spring then let it go. Have to be a little bit careful not to flex the Paxolin slider arm left/right because if flexed too much it can break.

Yes 47uF is fine as long as its working voltage is no lower than the value shown on the old capacitor, my schematic shows C20 as 15/18V.

David

[djorrell]

Not sure if any part of the main casing has been changed at some point in its life but my unit has auto and manual recording level. Ive not yet got round to checking out the slide switch as I've trying to get a Dynatron CP1 cassette deck to play at the correct speed. Its basically a Philips N2506 in a posh frock.

[DMcMahon]

No I think yours is correct. I was just explaining that there is a fully automatic version of the TK 23L not sure if it is also called de-luxe. The standard TK 23 (non L/non de-luxe) just does manual recording.

David

[djorrell]

Well Ive finally thrown in the towel on this, its baffled me completely.
I have cleaned and checked all switch contacts. All are switching as they should. Ive checked the oscillator windings and all are as expected. I've replaced C23 & C20. Changed R32, 33, 34, & 36. Ive got continuity between between the oscillator coil and erase head. Ive measured R37 and thats fine. I,ve even Swapped out the ECL86 but I cant get the oscillator to work. Ive completely lost touch with reality now. Thanks for all your help but this thing has now beaten me.

Dave

[ben]

This happened to me some time ago. I had the exact same problem, no erase. Sometimes there'd be very weak erasure. For some reason this affected track 1-4, 3-2 was weak but usable. I simply couldn't find anything obviously amiss.

Anyway, it turned out that there were two resistors in the bias oscillator that had been changed by a previous repairer when the transistor had burnt up. One day as I checked the circuit diagram, I saw instead of 1k they were 10k, or something like that. In seconds I had put the correct values in... and bingo! Full record operation on all tracks.

The weak 1-4 performance I put down to it being the outer track and some mechanical wear and slight misalignment of the tilt of the head. It speaks volumes about the quality of the design of that machine that even with such a high value the thing still half worked on the inner track.

So, to sum up, I'd say don't give up just yet. Put it to one side until you're ready to go back to it. Work on something else in the meantime, might give you a new insight. And above all, I learned to take nothing for granted - with 50-60 year old equipment, it's likely others have been in there before you and who knows what they did!

[DMcMahon]

When you say that the bias oscillator does not work is this being determined by erase and record not appearing to work or have you also checked the oscillator signals on an oscilloscope.

David