Grundig TK14L rewind problem - UK Vintage Radio Repair and Restoration Discussion Forum

radioman · 25th Apr 2012, 10:00 am

I was asked to have a look at this machine for a friend. Electrically it's fine but mechanically there is a problem - specifically, it will not rewind a tape reliably - either it's very slow or just stops.
The drive belts appear OK and I have also cleaned all drive surfaces with IPA but the problem persists.
What I have noticed though is the take-up reel appears to be constantly driven in a counter-clockwise direction, with the clutch slipping as you'd expect, only stopping when braked in the 'stop' condition.
During rewind, (which seems to have plenty of torque on the supply reel) this opposite direction of rotation of the take-up reel needs to be overcome before rewind can occur.
Is this correct ? - it doesn't seem very logical to me.

Any help/advise would be greatly appreciated !

Thanks,
Andy

Steve_P · 25th Apr 2012, 4:04 pm

Some machines put a light forward wind on with the rewind. This shouldn't pull though. Have you tried it with the tape not going through the heads, as any misalignment here will cause this sort of thing.

It's not the easiest of decks to work on I know, but is it fouling anywhere there and try removing the spindles and cleaning them inside as well. Also, roughen any rubber wheels.

Cheers,

Steve P.

radioman · 25th Apr 2012, 4:33 pm

OK Steve - thanks for the reply.
I'll roughen the surface of the tyre on the supply reel and hope this will increase the drive as this is where it is slipping.
I'll also check the other things you've suggested and will report back later.

Regards,
Andy

ricard · 25th Apr 2012, 7:59 pm

Can't remember exactly how the TK14 operates, but many especially older recorders have a constant drive on the take-up reel as in normal play mode, mainly to make the mechanical design simpler. When the machine is in stop mode the brakes keep the reels still though. The forward torque should not be strong enough to impede the rewind function, it basically should just provide a bit of tension to keep the tape from slopping about.

It could be that the forward drive clutch is maladjusted, or a belt has been misthreaded, so that the torque is too high. It might not be noticeable in normal play mode as the capstan and pinch roller hold back enough.

radioman · 26th Apr 2012, 8:47 am

Well, I managed to roughen the surface of the tyre on the supply reel with some very fine wet or dry paper and this definitely helped. I also found if I laced the tape directly between the reels then rewind worked fine, so the problem was increased friction around the tape guides/heads.
Despite having cleaned the tape path, on close inspection I noticed a buff coloured deposit on the tape guides and heads...
You've guessed it - my test tape was suffering from 'sticky shed'

- Trying an older Philips tape proved that the rewind problem had gone !
Ricard, the constant drive on the take-up reel does appear to be a design feature of the mechanism as you mention above, so this was a bit of a 'red herring'.
There are still other problems though - I was tempting fate when I said that the belts were OK. Last nights testing was obviously too much for the main drive belt as it's now started to crack, so I'll need to contact Colin (DOFFERY) to see if he can supply me with a replacement.

Thanks for the encouragement.

Andy

25th Apr 2012, 10:00 am	#1
radioman Heptode Join Date: Apr 2003 Location: Ayr, Ayrshire, UK. Posts: 631	Grundig TK14L rewind problem I was asked to have a look at this machine for a friend. Electrically it's fine but mechanically there is a problem - specifically, it will not rewind a tape reliably - either it's very slow or just stops. The drive belts appear OK and I have also cleaned all drive surfaces with IPA but the problem persists. What I have noticed though is the take-up reel appears to be constantly driven in a counter-clockwise direction, with the clutch slipping as you'd expect, only stopping when braked in the 'stop' condition. During rewind, (which seems to have plenty of torque on the supply reel) this opposite direction of rotation of the take-up reel needs to be overcome before rewind can occur. Is this correct ? - it doesn't seem very logical to me. Any help/advise would be greatly appreciated ! Thanks, Andy __________________ G-QRP #12697

25th Apr 2012, 4:04 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Grundig TK14L rewind problem Some machines put a light forward wind on with the rewind. This shouldn't pull though. Have you tried it with the tape not going through the heads, as any misalignment here will cause this sort of thing. It's not the easiest of decks to work on I know, but is it fouling anywhere there and try removing the spindles and cleaning them inside as well. Also, roughen any rubber wheels. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

25th Apr 2012, 4:33 pm	#3
radioman Heptode Join Date: Apr 2003 Location: Ayr, Ayrshire, UK. Posts: 631	Re: Grundig TK14L rewind problem OK Steve - thanks for the reply. I'll roughen the surface of the tyre on the supply reel and hope this will increase the drive as this is where it is slipping. I'll also check the other things you've suggested and will report back later. Regards, Andy __________________ G-QRP #12697

25th Apr 2012, 7:59 pm	#4
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	Re: Grundig TK14L rewind problem Can't remember exactly how the TK14 operates, but many especially older recorders have a constant drive on the take-up reel as in normal play mode, mainly to make the mechanical design simpler. When the machine is in stop mode the brakes keep the reels still though. The forward torque should not be strong enough to impede the rewind function, it basically should just provide a bit of tension to keep the tape from slopping about. It could be that the forward drive clutch is maladjusted, or a belt has been misthreaded, so that the torque is too high. It might not be noticeable in normal play mode as the capstan and pinch roller hold back enough.

26th Apr 2012, 8:47 am	#5
radioman Heptode Join Date: Apr 2003 Location: Ayr, Ayrshire, UK. Posts: 631	Re: Grundig TK14L rewind problem Well, I managed to roughen the surface of the tyre on the supply reel with some very fine wet or dry paper and this definitely helped. I also found if I laced the tape directly between the reels then rewind worked fine, so the problem was increased friction around the tape guides/heads. Despite having cleaned the tape path, on close inspection I noticed a buff coloured deposit on the tape guides and heads... You've guessed it - my test tape was suffering from 'sticky shed' - Trying an older Philips tape proved that the rewind problem had gone ! Ricard, the constant drive on the take-up reel does appear to be a design feature of the mechanism as you mention above, so this was a bit of a 'red herring'. There are still other problems though - I was tempting fate when I said that the belts were OK. Last nights testing was obviously too much for the main drive belt as it's now started to crack, so I'll need to contact Colin (DOFFERY) to see if he can supply me with a replacement. Thanks for the encouragement. Andy __________________ G-QRP #12697