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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 18th Apr 2021, 9:46 am   #1
DMcMahon
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Default Grundig TK 14 Check Out

Been checking out a TK 14 I purchased fairly recently together with a TK 23, the TK 14 was said to be working and the TK 23 not working.

Opened it up to visually check inside before powering up. Both internal 1 1/4" glass fuses were quite badly corroded so cleaned them up. These fuses are marked in tenths of amp, i.e. the mains input fuse is "4/10A" (i.e. 400mA / 0.4A) and the HT fuse is "1/10A" (i.e. 100mA / 0.1A). It has been a long time since I have seen fuses marked in tenths.

It has a short 3 core mains cable (with 3 pin plug) that goes out through a hole in the rear panel. This hole I think would been the mounting hole for the mini Bulgin mains chassis plug that some TKs of this vintage have. I probably will refit a mini Bulgin chassis plug to tidy it up.

Powered up OK and all DC voltages check out good.

Found there was no Record bias getting to the record head and the record bias at the input of C19 bias pre-set trimmer was around 900V peak to peak, I say around because the bias waveform amplitude was too large to see fully on my scope using a x10 probe (mental note that I need to buy a x 100 probe). The bias at the output of C19 was 740V.


Traced problem to a yellow wire that connects back to the record head connections being disconnected at the junction of C19/R13. With wire refitted the bias at the head is now 480V p-p (still around 900V at C19 input).

480V p-p calculates to 170V rms, the record bias spec (measured across the head with a valve voltmeter) is 155V +/- 15% so 170 is in spec.

The erase head voltage is 230V p-p which is 81 V rms, spec is 70V rms adjustable by R37.

While checking the bias oscillator signals, kept intermittently loosing the signals. Eventually traced the issue to a tiny crack in the PCB that was causing 2 tiny breaks in 2 tracks. First PCB photo shows the crack which is hardly visible, the second photo using flash makes the crack look like a track cutting across the 2 actual solder tracks. Repaired the 2 tracks with solder bridges and put some super glue on the top of the PCB crack.

Two mechanical issue noted so far. The Temporary Stop (Pause) key does not latch down, unlike the TK 23 I cannot see any latching mechanism but the TK 14 User Manual indicates that it should latch down.

The Fast Forward key is difficult to get it to stay latched down, think all the various associated mechanism's for it just need a good strip, clean and re-lube.

David
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Last edited by DMcMahon; 18th Apr 2021 at 9:51 am.
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Old 19th Apr 2021, 7:20 pm   #2
Starlight 1
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Default Re: Grundig TK 14 Check Out

I have the TK 14L de-luxe I put new belts on not so long ago and pause do stay down ,if any help I take the top back off and add some photos of this part. Les PS if I am right the pause have 2 slots one at the base , 1 50% up and it go in this one.

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Old 19th Apr 2021, 7:35 pm   #3
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Default Re: Grundig TK 14 Check Out

Thanks for the offer Les, I will probably be OK once I get back to it. I have another TK 14 that from memory Pause does stay latched down when pressed. From a quick look at the present TK 14 it does not latch down and no obvious latching mechanism, I need to recheck and compare to my other TK 14.

I see there are several older TK 14 Threads that reference Pause not latching on some revisions of TK 14.

David
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Old 19th Apr 2021, 7:44 pm   #4
Starlight 1
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Default Re: Grundig TK 14 Check Out

When I put new belts on looking at the book and how to remove I come with no way I am not doing all that my way all done in under 10 mins and the only bar you put out the hole is on the pause
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Old 19th Apr 2021, 8:09 pm   #5
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Default Re: Grundig TK 14 Check Out

I believe that the very earliest TK14s did not have a latching pause button. I have one here that did not, it is the blue and white colour scheme. It has red dots on the pause and stop buttons. I fitted the latching mech from a scrap machine, the pause button is pretty much useless without it.

I think that soon after production started a latch mech was added. At the same time the red dots on the buttons was dropped. So many small variations on this range of machines.

Mark.
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Old 19th Apr 2021, 9:17 pm   #6
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Default Re: Grundig TK 14 Check Out

Rechecked and there is no latch mechanism on this particular TK 14. Like Mark's above it is blue and white with the 2 red dots on the Pause and Stop keys. It is serial number 58127.

Also noticed that the copper sprung arm that makes contact with the Supply spool table when Pause is pressed is a little different from the TK 23 with latching mechanism. On the TK 23 there is a round rod (that moves a little when Play is selected) that goes through a hole in the end of the copper arm, in this TK 14 there is no round rod.

David
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Old 20th Apr 2021, 6:59 pm   #7
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Default Re: Grundig TK 14 Check Out

Been looking at why it is so difficult to get the Fast Forward (FFD) key to latch in the down position. Pressing the FFD key initially moves 2 actuator arms forward that link into the right hand set of 3 keys. In the first photo (with FFD latched down) the left hand actuator arm is contacting the arm that couples into the pinch roller arm assembly, the screwdriver tip is pointing to the contact area.

If I manually push the arm forward a little bit (that couples into the Pinch Roller arm) it then is relatively easy to get the FFD key to latch down when pressing it. Not clear yet if the left hand actuator arm is fouling the arm i.e. maybe it should not contact it or whether it should contact the arm but then should move the arm forward.

Also have not yet actually worked out which mechanism is the latching mechanism and how it locks in the latched position. Initially I thought it was the sprung loaded mechanism above the white record button (in second photo) which does get activated by the FFD key being pressed but cannot see if it is the actually locking latch.

David
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Old 20th Apr 2021, 8:31 pm   #8
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Default Re: Grundig TK 14 Check Out

my is not the as yours hope this help? photo 1 is just to the my one look later.
photo 50007/8 is the lock down on pause ---- 5011 show the lock down for FF that push the back bar out and pull FFR out in 5013 think I got this right.
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Old 20th Apr 2021, 8:34 pm   #9
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Default Re: Grundig TK 14 Check Out

Can see how to add photo 5011
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Old 20th Apr 2021, 9:45 pm   #10
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Default Re: Grundig TK 14 Check Out

Quote:
Originally Posted by 8 Tracker View Post
I believe that the very earliest TK14s did not have a latching pause button...the pause button is pretty much useless without it.
It was probably an old idea from various manufacturers, probably thinking that operators would leave the machines set to 'pause' for long periods rather than using the actual 'stop' button, perhaps the thinking was to avoid folk stressing the machine. Another example is the Collaro Tape Transcriptor that just has a lever that you have to hold.
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Old 20th Apr 2021, 9:53 pm   #11
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Default Re: Grundig TK 14 Check Out

Quote:
Originally Posted by Starlight 1 View Post
Can see how to add photo 5011
Thank you Les for the photos, I can easily see how pressing FFD moves the various linkages for photos 5011 and 5013 but still struggling despite studying a TK 23 where the FFD latching works well, just cannot visually see what locks it in the latched position, fairly sure it is the double spring mechanism at 5011.

I think the only way I am going to be able to see how it actually works is to dis-assemble the various bits, on the TK 14 it needs disassembling anyway as very dirty grease.

David
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Old 21st Apr 2021, 5:59 am   #12
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Default Re: Grundig TK 14 Check Out

Quote:
Originally Posted by DMcMahon View Post
Quote:
Originally Posted by Starlight 1 View Post
Can see how to add photo 5011
Thank you Les for the photos, I can easily see how pressing FFD moves the various linkages for photos 5011 and 5013 but still struggling despite studying a TK 23 where the FFD latching works well, just cannot visually see what locks it in the latched position, fairly sure it is the double spring mechanism at 5011.

I think the only way I am going to be able to see how it actually works is to dis-assemble the various bits, on the TK 14 it needs disassembling anyway as very dirty grease.

David
All photos taking with locks on--- may be 4 springs as in 5011 move
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Old 21st Apr 2021, 7:48 am   #13
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Default Re: Grundig TK 14 Check Out

It's been a while since I looked closely at the button mechanism on one of these, but I think latching takes place under the buttons. There is an indentation which the stop bar to drops in to. You can see the stop bar link which goes across the machine to operate the rewind stop. The bar should move a little when one of the latching buttons is pressed as it drops in, then the stop button moves the bar outwards, allowing the button to return.

Hope you can understand what I am on about.
Mark.
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Old 21st Apr 2021, 7:56 am   #14
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Default Re: Grundig TK 14 Check Out

I seem to remember a long time ago ,this was a fairly common fault , something gets bent when the user forces a button against its will, a bit vague I know but look for a lever that is slightly bent , Mick.
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Old 21st Apr 2021, 8:32 am   #15
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Default Re: Grundig TK 14 Check Out

Quote:
Originally Posted by Starlight 1 View Post
/QUOTE] All photos taking with locks on--- may be 4 springs as in 5011 move
Yes another 2 springs on the brake release bar plus another 2 at the FFD key itself, all of which get stretched when FFD is pressed.

David
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Old 21st Apr 2021, 8:35 am   #16
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Default Re: Grundig TK 14 Check Out

Quote:
Originally Posted by 8 Tracker View Post
It's been a while since I looked closely at the button mechanism on one of these, but I think latching takes place under the buttons. There is an indentation which the stop bar to drops in to. You can see the stop bar link which goes across the machine to operate the rewind stop. The bar should move a little when one of the latching buttons is pressed as it drops in, then the stop button moves the bar outwards, allowing the button to return.

Hope you can understand what I am on about.
Mark.
Yes I was coming to similar conclusion because also cannot see how the RWD and Play buttons latch down.

David
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Old 21st Apr 2021, 8:36 am   #17
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Default Re: Grundig TK 14 Check Out

Quote:
Originally Posted by vinrads View Post
I seem to remember a long time ago ,this was a fairly common fault , something gets bent when the user forces a button against its will, a bit vague I know but look for a lever that is slightly bent , Mick.
Thank you Mick, I will look out for bent levers.

David
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Old 21st Apr 2021, 11:32 am   #18
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Arrow Re: Grundig TK 14 Check Out

Could not really see the latching detent mechanism operation in the right hand keys/buttons assembly so removed the assembly for a better look as per photo 1, the recorder design does not make this an easy task.

With it removed then able to see the detent operation (very difficult to actually see it on the FFD key). Photo 2 shows the Play key (not pressed) with detent notch not engaged with sprung loaded detent latching plate. Photo 3 shows the Play key pressed and the detent notch engaged at the detent plate. The Stop key somehow resets the sprung loaded detent plate to release the latch. The Play key detent works very well.

The FFD detent work well sometimes and intermittently other times it struggles to latch, cannot see why, the FFD key has 2 springs it operates against unlike the Play key that has no springs (at the assembly). Not convinced this is the root cause of the FFD latching problem but to be sure will try and strip down the assembly more to see why the FFD latch operation is sometimes struggling.

The lever at bottom of photo 4 looks maybe a bit bent/twisted (looks very similar in the TK 23) this lever which is moved up when FFD pressed, moves the Take Up reel table across to make contact with the rubber idler wheel. This lever also operates the mechanism with 2 springs as per photo 5 (photo ref 5011 in earlier Post) currently unsure what the actual function of this mechanism is, it looks like it may latch but does not appear to latch.

David
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Last edited by DMcMahon; 21st Apr 2021 at 11:40 am.
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Old 21st Apr 2021, 3:57 pm   #19
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Default Re: Grundig TK 14 Check Out

Stripped the key/button assembly. Noticed that there are flats on the black rubber bushes, wonder if these may be compression wear marks where the key actuators make contact. After re-assembly if FFD latching is still problematic will try rotating the appropriate bush so the FFD actuator makes contact with a non flat section.

David
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Old 21st Apr 2021, 8:53 pm   #20
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Default Re: Grundig TK 14 Check Out

To clean the FFD actuating lever properly of old grease and the surrounding areas had to remove the flywheel. Wanted to remove the flywheel anyway because when the unit is powered up there is a loud rotational screech for a couple of seconds, which I think may be coming from the rotating flywheel spinning up.

Have seen similar before where the flywheel lower shaft is noisy due to dried up grease in the flywheel lower bearing assembly. When I removed the flywheel there was no obvious sign of the ball bearing that sits in the end of the lower shaft.

Removing the flywheel lower bearing assembly and stripping it down, I found the ball bearing trapped in the side wall within some hard dried grease. So am hopeful that with the ball bearing correctly placed and fresh grease the flywheel spin up noise will be fixed.

David
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