DAT mechanism service?
 

Not sure if it quite qualifies as vintage, but I have a Fostex digital tape machine in which the tape handling is less than perfect. It’s an ALPS 4mm transport, possibly similar to numerous DDS backup drives…
I’ve not been successful in finding any cleaning, lubrication or setup instructions and wondered if anyone here knew anything?

Re: DAT mechanism service?
 

Well, for a start, it should qualify as vintage - DAT production ceased around 2004, there are not enough head hours remaining to play all the existing DATs, and the ALPS transport - I assume this is a D20 - disappeared in the 1980s. Richard Maddox's DAT Technical Service Handbook deals with this machine up to a point, but he was more concerned with the consequences of machines being thrashed by the Muzak operation. Most current DAT mechanism problems are more about dried-up grease and the like. The major problem with servicing DAT machines is that spare parts are to all intents and purposes unobtainable, some aftermarket belts and pinch rollers aside. (I have a Sony 2700, serviceable apart from a 5000 hours-plus head, which sits here in hope - I may try using the drum out of a Sony DDS transport.) A particular bugbear is the split nylon washers which retain components on shafts. These are reusable, despite Sony's advice only to use them once, but are prone to flying off into the distance when removed. New stock doesn't exist, as far as I know. Caution, then, is the watchword.

Re: DAT mechanism service?
 

Hi Richard, what specifically are the symptoms? Cheers Tim.

Re: DAT mechanism service?
 

It has been a bit of an animal, eating tapes! After I dismantled the transport and used 100% alcohol to remove the old hardened grease it is behaving better but it sometimes doesn’t drive the take-up spool properly. I’m running it with the covers off so I can see if there’s tape spilling and stop the function but I’d quite like to use it without worrying!
It has a new belt but I suspect that the clutch to the take-up spool may be misbehaving. It does fast wind both ways without problem. It seems to me that maybe going from play to fast wind is an issue, or maybe going straight into fast forward. I’ll check tomorrow.
Fortunately I do have some “sacrificial” tapes.....

Re: DAT mechanism service?
 

I'd check the brakes to see if a pad is loose, worn or sticky.

Re: DAT mechanism service?
 

I'm not familiar with the mech but if it uses a pendulum reel drive system I'd check for small rubber tyre(s) gone hard or just need a careful clean or roughen. Some use gears though.

Re: DAT mechanism service?
 

Have you seen that there's a service manual at

https://www.hifiengine.com/manual_li...tex/d-20.shtml

(If Ted's assumption about the model number is correct).

Re: DAT mechanism service?
 

Yes, it is a D20 and I have downloaded that manual. Unfortunately it’s a bit light on mechanical problems with the tape handler.
When the service document was written I think maybe no-one thought someone would be trying to repair it 40 years on!

Re: DAT mechanism service?
 

Yes details of the mechanism are poor. Good service manuals list every part down to the last screw and washer, and that list can be related to the relevant exploded diagram. I suspect in this respect Fostex's competitor Tascam did a better job generally.

Have you been able to examine the mechanism for driving the tape reels?

Re: DAT mechanism service?
 

Yes, I've had the mechanism seperated into three parts - the cassette loader, the loading motor and the main chassis. On that there is a black plastic assembly which carries the supply and take-up reels, the brakes and a couple of sensors. The reels are driven with a short (new) belt from the capstan motor. I think I'll need to take that assembly off and see if there's any more dried lubricant....

I also have a Tascam DA-20 which works perfectly, the service manual for that is excellent!

Re: DAT mechanism service?
 

I remember DAT was popular as a semi-pro format for recording demos in the 1990s.

I'm surprised production ended as early as 2004, I presume the industry quickly moved on to recording on computer using lossless formats.

Re: DAT mechanism service?
 

A bit more testing today. The mechanism will wind a tape fully in either direction without problem. The machine will play a tape properly, take-up spool works well. I can cue forward properly and mostly backward cueing works okay too.

What seems to upset it is if I repeatedly cue the tape back a little and let it play, after a time or two the take-up spool doesn't rotate. If I catch it quickly I can stop the play function and put it into rewind to take up the slack.

I've tried a couple of different tapes of different playing lengths.

Re: DAT mechanism service?
 

I've removed the spooling mechanism from the tape transport. Examining it reveals that the clutches seem alright, they both feel a simlar resistance to slip. The mechanism seems to operate properly, no sticky shafts or broken bits.

I attach some photos, the second photo shows what I suspect is the problem in that the slow-speed gear doesn't align properly. It seems possible that this, which is the take-up drive, could sometimes not mesh at all which leads to the tape tangles I've witnessed.

In the annotated photo, I show where these gears are placed, and pose a question - how best to remove those little plastic circlips? I know to work in a polythene bag in case of a fly-off, but is there an approved method of releasing them?

Re: DAT mechanism service?
 

My guess based on recent experience with a vcr is that the pendulum gear white arm needs oil on its shaft under black washer and maybe a dab of grease under it. I use a jewellers flatblade driver to carefully undo the clip.

Re: DAT mechanism service?
 

Thanks Ben, I'll have a play with it. I feel that lubrication, or rather dried lubrication, might be the answer.....

Re: DAT mechanism service?
 

A good dodge with some of these rubber tyres can be to take them off the wheel and turn them inside out .

Re: DAT mechanism service?
 

This one’s entirely gears… the issue seems to be that the take-up drive gear sometimes doesn’t quite mesh, and I can see the witness mark on the gear is less than full engagement. I’m currently examining the sub-assembly to see why the take-up side is like that since the rewind spool engages better.