Re: Grundig TK20 and Truvox R82. Help Required Please.
 

Well I've re-soldered the resistor connections - but no change, but when I switched on I noticed that although in play mode the motor was spinning, the idler wheel wasn't. So I've cleaned everything again, flywheel, idler wheels, and this time the motor pinion as well which seemed to have a black line around it. The result is now that it plays without reducing speed, at least up to now, but it is still slow at 7.5ips to the tune of half a tone, 3.75ips is fine. Maybe the motor has lost a bit of its power! (I know the feeling!) I'm coming to the conclusion that I've done everything I can and the real reason is that it is just old, and like us as we grow older we do everything a bit slower, so for that reason I think I'll settle for what I've got which is a 60 year tape recorder that was defunct which is now working thanks to everyone's efforts on here. At least I can hear the tapes of my band even if they a half a note low!

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

You say the capstan motor is definitely the same as the Brenell photo but you also say that you cannot see any markings on it, so could it possibly be very similar looking but a different AEI model # ?

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

Could be David, I've just played a tape for nearly an hour and a half at 3.75 ips with no slowing at all. It just seems to be the 7.5 ips speed that has the slowing problem. It looks like one of two possible problems; the first is the motor itself which when playing at 3.75 ips is using the smaller step in the pinion which will be easier for the motor to drive the idler than the 7.5 ips step which is larger diameter which puts more stress on the motor to turn the idler and the flywheel (there is one idler for each speed), so it could be the motor is just not as powerful as it was. The second is the rubber on the idler wheel which may have gone hard and not have the grip on the pinion and the flywheel that it would have if it was a bit softer; or the idler assembly itself is not applying the pressure it should. The down side to all these scenarios is that it would mean major dismantling to get to these parts which I just don't think is worth the effort, even assuming I could source the parts.

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

Not impossible but less likely I would say to be the motor itself to be at fault.

Glycerine/Glycerol can sometimes soften up hard rubber and give better drive/grip.

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

Can you describe what method you adopt when using the glycerine i.e. only on the edge, do you leave it for a while, etc.

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

To be honest Terry I have only tried it a couple of times with minimal improvement, some people say it does a very good job with many types of rubber. Consensus seems to be wipe it on the edge (assuming liquid version) and leave for several minutes to soak in, then wipe dry.

I do not think it can do any harm.

David

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

The problem might just be glazing on the surface of the idler, with reasonable elasticity beneath. In this case, I have found careful scrubbing with IPA can remove the glaze and restore traction. The idea is just to take the shine off, not remove any significant amount of material.

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

Thanks David.

Ted, I've used IPA on motor stepped pinion, idler wheels, and flywheel. I've also used the finest emery paper with the lightest touch on the idlers just to remove the shiny surface. It has made a slight difference but still runs a bit slow, though not quite as slow as before. I think I'll keep repeating the process a few times as it may take a while to completely get back to a clean surface after four decades of not being used!

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

Of course any slight slow running at the beginning of a reel will probably be much worse towards the end of the reel because of the increased back tension and the decreased take up tension. It's good to test capstan drive at the end of the reel because with most domestic machines that's the hardest test to pass.

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

Well, I don't know why but after replacing two capacitors it now seems to be running at the proper speed! I also put a drop of machine oil on some of the braking mechanism levers in case that was binding at all, so maybe that did the trick, who knows? Hopefully it will continue to run at the correct speed now. The caps I replaced, one was 8uF which may be C25 which was in the power section, the other was 0.1uF which was across the terminals of the pause switch, which isn't shown on the circuit diagram. I only wish I knew which of the things I did fixed it!

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

That is great news Terry. C25 is a filter/smoother on the HT to the Bias Oscillator so unlikely to be the fix.

If you were really keen to know you could put back the original capacitors, not so easy to un oil the brake mechanisms though.

Probably best just to leave alone, monitor and enjoy it while it is working well.

David

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

I have a Truvox PD99 on its way, so soon may become a Truvox convertee. This one does not play at all.

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

Hi David, I see now that C25 is part of the bias circuit, so not that as you say. It's more likely the brake mechanism that may have been binding a bit as it doesn't take much to slow everything down! I hope what we've done here with investigating my Truvox helps when you get your PD99! Meanwhile I'll do as you say, leave well alone and just enjoy what I've got!

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

Even though root cause of hum/low volume playback turned out to O/C head, I think it was still a good measure in changing some of the capacitors for long term future reliability and some of them may have caused problems sooner or later if not now.

David

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

UPDATE: Just to let you all know that the speed problem was caused by the idler for 7.5ips not engaging fully with the motor speed pinion. There is a spring which provides the tension but it is not a strong tension so my attention turned to the shaft on which the idlers swivel on. I dosed the arm joints where the idlers swivelled with WD40 thinking that there might be some corrosion on the metal as it appeared to be an alloy. I left this for 24 hours after which with a bit of nudging the idler started to make full contact with the pinion but now didn't engage with the flywheel! A small adjustment by way of a couple of sharp prods on the idler arm and BINGO! connection! At the time of writing there has been no further problems with speed at 3.75 or 7.5 ips. So after all the trials and tribulations with this machine, the final cure came courtesy of the equivalent of the so called mechanics friend - the hammer!

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

Well done Terry.

David

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

Thanks David, how are you getting on with the PD99?

Re: Grundig TK20 and Truvox R82. Help Required Please.
 

Afraid have had no time yet to start looking at it, it is in a big queue.

David