On 2023-02-07 22:54, Chris Zach via cctalk wrote:
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
Brilliant, thanks, Chris. I might just undertake that tomorrow instead
of doing an RT11 sysgen! Just the kind of advice I need.
I sure will let you know!
Nigel
--
Nigel Johnson, MSc., MIEEE, MCSE VE3ID/G4AJQ/VA3MCU
Amateur Radio, the origin of the open-source concept!
Skype: TILBURY2591
