[cctalk] Re: TK50/70 Repair

Hi Nigel! I have a fair bit of experience with TK's, including the TK50 and 70. I like them, they're quick units (with the TQK70 controller they can stream well), and they look really nice in a BA23 chassis. Optical sensors can be dirty, but the biggest problem I have seen is in the capstains: They are mounted on springs and the biggest issue is that the oil in the bearings is probably long gone. As a result, they tend to drag on the tape and not spin properly. This in and of itself is enough of an issue, but the rear one also has an optical tachometer on it, and the unit uses that to maintain tension on the tape and know (along with the tach sensors on the drive and take up spindle) what the tape is doing at any given time. Thus if that one drags you have a major problem that can include the tape doing a massive unspool on the take up reel. How to fix. Well you need to take the capstains off and either lubricate both the top and bottom bearings so they spin easily and go up and down against the springs or replace the bearings with new press in ones. I've taken the lubricating route and the oil will last for about 3 years if you use good mobius watch oil on the insides and outside races of the bearings. Taking them off requires care: The nuts are adjusted at the factory so the slew is correct across the tape head and the pulleys are at the right height for the cartridge and take up reels. Wrong height and hilarity ensues. So what I recommend is to mark a nut face, know exactly where it is, and when you take off the nut count the number of turns and mark the unit at the point where the nut comes off the shaft. Keep each nut separate (or do the capstains one at a time) and when reassembling go the exact amount of turns to the exact spot as measured by your marks. Then you'll be back at the same place. Note also the rear capstain comes off the unit if you want to check the optical sensor. I recommend using a very tiny bearing/gear puller to put pressure on the shaft as the fingers lift the capstain off the shaft (esp if it's stuck) so you don't pull and damage the optical wheel at the bottom. Front one is easier, back one is tricky and has more of a friction fit to the wheel. Take it easy and take your time. For tapes I like to lift the head up with the springs attached and inspect it. Clean it with isopropyl and make sure there is no oxide on it, that will cause the unit to fail. Then when dry load a tape, run it a bit, then unload and check the head. If you see fresh oxide chuck the tape (or bake it if you really care) but know that tape will contaminate other tapes if you don't clean the head each time. If the tape doesn't damage the head mark it as "safe" and use it, but always check a new tape. Some shed, some don't. It's weird. Oh also make sure to have the metal shield on when testing it. The shield does help keep tape from going everywhere in the event of a major fail, but it also darkens those rear optical sensors so they don't false trigger and drive the unit insane. And by insane I mean doesn't load or suddenly stops the take up reel with hilarious results. Good luck and let us know how it works out! C On 2/7/2023 5:44 PM, Nigel Johnson Ham via cctalk wrote: > Fellow cyber-antiquarians: > > I have been fussing around with a TK70 for some hours now. It goes > ready when powered up without  a cartridge, takes up the leader fine > when a cartridge put in and the flat, but then dithers forwards and > backwards, eventually flashing all its lights.  The only way to > remove the tape is manually. > > Somebody posted that the most common problem is optical sensors, > stating that there are four.  I have only found two, and cleaning > them got me to the point of it coming ready, whereas it would not > before. > > Is there anybody on here that knows of a service manual?  I see that > this was considered an FRU, so maybe depot repair people had a magic > bible. > > Once I have this fixed there is a TK50 to start on.  I hate to give > up! I have a box full of cartridges to read! > > cheers, > > Nigel > > >