VCR with no end sensors!!

[1100 man]

I recently found a rather nice Daewoo VCR (6 head Hi fi) with a built in DVD recorder. Came complete with instruction book & remote and 'works perfectly'.

Well not quite- needed a loading belt in the DVD recorder. I've got it in bits on the bench and while sifting through my belt collection to find a loading belt, I noticed there was nothing where the lamp (or IR LED) housing should be. Nothing to poke up inside the cassette in proper VHS style! Logically enough, there are also no sensors at either side of the cassette housing.

It just looked really weird- I spent 20 years looking at VHS decks and you get to know what to expect! No end sensors- well really!!

Presumably, they must compute the relative speed of the supply & take up reels to work out when the tape is near the end? I never worked on machines this new and it is a masterpiece of minimal engineering. There are so few mechanical parts. Interesting to compare this to early decks such as the 3V16 etc which were extremely complex.

Strangest thing I've seen all week!

Cheers
Nick

[Refugee]

The sensor might be hidden in one of the guides.

[Argus25]

Not the same, but I recently worked on two audio cassette recorders. One had a system of tape end detection with one mechanical arm against the tape that deforms the tape path into the cassette a little, when it goes taught at either end, the arm movement activates a switch. The other didn't do this, instead it just monitored the rotation of one of the hubs. When that stops (when it should be rotating) it just concludes the tape is at one end. There were no optical devices in either deck to look through the tape leaders. Maybe your video deck was modeled on one of these ideas.

[vhs doctor]

It is normal for these machines to work with no IR sensors. They are the same as X10000/X2000 chassis. Thomson had also an update in the case of ERR appear on VCR screen.

[ben]

Pictures please!

[Richard_FM]

A lot of later VHS machines had a "turbo" fast forward & rewind feature that seemed to kick in when the tape tension was at it's lowest, normally towards the middle.

I presumed this used some kind of tension monitor in the motor hub, & also would auto stop when the end of the tape was reached.

Could the audio/sync head be used to detect magnetic tape being there?

[ms660]

Originally Posted by merlinmaxwell

Could the audio/sync head be used to detect magnetic tape being there?

That wouldn't be very reliable.....

Lawrence.

[Lloyd 1985]

I’ve got a Daewoo VCR that I had from new in about 1999, that definitely had no end sensors! Try putting in one of those really short tapes, the crappy advertising ones you used to get, and hit rewind, the deck speeds up and then suddenly THUMP!! Oh, there’s the end of the tape!! Probably didn’t do the machine any good at all...

Regards
Lloyd

[vhs doctor]

I had one Thomson for my personal use for 2 years. The strange thing with these mechanism it was its reliability. In everyday use I didn't had any problems.

[julie_m]

I think the last generation of VCRs used separate brushless motors for everything, all driven by one big microcontroller. It would be easy enough when playing, recording or fast-winding to sense the speed of the non-driven motor from the pulses induced in its stator windings by the magnet as it is spinning with the motion of the tape from the driven motor (whose speed you can also measure from the Hall effect or optical sensor which is part of the motor) -- further apart when there is plenty of tape on the reel, closer together as it is getting down to the spindle and then stopping abruptly when the tape pulls taut at the end.

They were also amazingly reliable machines. I still think it's a by miracle that VCRs ever worked. The precision required to make the heads, which have to follow a narrow track while being spun round at 1500 r.p.m. And then they made enough of them to be able to get the price down to the point where they were practically giving them away in Christmas crackers .....

But if VCRs didn't exist, and one day you drew up a quick sketch of how to make one, I doubt anybody would believe you stood a chance of making it work!

[Lloyd 1985]

VCR’s really are quite amazing things, the Mini-DV ones were so tiny! And they worked for HD video too.

Regards
Lloyd

[mark2collection]

Panasonic used a system whereby there were no brake pads/levers, no solenoids, no relays, no back tension bands, no idlers or idler motors, it was all direct drive supply/take-up motors, along with drum & capstan. The machine had 'Quartz Direct-Drive' emblazoned on it.

D'you think I can remember the model? The mech was also used in one of their portable top-loaders with separate camera and presumably, battery pack.

Clever stuff, very reliable & seriously quiet.

There was a time when the VCR was seen as the most complex 'gadget' in the home, & certainly some of the mechs were a work of art.

One particular Panasonic had two 'in built' cassette housings plus loads of other gears & levers, a simple press of the 'VHS to VHS-C' button made an awful racked, but the machine really would re-load a smaller housing, & change the gearing from full-size VHS, to VHS-C, and back again.

Aligning the timing one of those was quite something! I think that was an NV8000, or NV-V8000?

Mark

[Maarten]

Originally Posted by Richard_FM

A lot of later VHS machines had a "turbo" fast forward & rewind feature that seemed to kick in when the tape tension was at it's lowest, normally towards the middle.

I presumed this used some kind of tension monitor in the motor hub, & also would auto stop when the end of the tape was reached.

Philips (between 1992 and 2002) counted rpm of the reels. This became more advanced, including real time counters, after their joint venture with Grundig around 1994 (I think Grundig owned a few patents on this).

[Maarten]

Originally Posted by julie_m

I think the last generation of VCRs used separate brushless motors for everything, all driven by one big microcontroller.

You'd hope so, but I don't know of any consumer machines after 1985 (*) that had this, especially not the last cost-down generations after 2000 that would be very unlikely to have such technology.

I guess the lowest and most common number of motors used in modern decks would be 2, and the most motors used would probably be 4 or 5, with at best a single motor with an idler for driving the reels.

(*) I know of Philips, Grundig and Mitsubishi using separate motors for each reel. Philips never used it in VHS models, while Grundig and Mitsubishi phased this out some time around 1985, possibly a little bit later but not much.

[Richard_FM]

Originally Posted by julie_m

I think the last generation of VCRs used separate brushless motors for everything, all driven by one big microcontroller. It would be easy enough when playing, recording or fast-winding to sense the speed of the non-driven motor from the pulses induced in its stator windings by the magnet as it is spinning with the motion of the tape from the driven motor (whose speed you can also measure from the Hall effect or optical sensor which is part of the motor) -- further apart when there is plenty of tape on the reel, closer together as it is getting down to the spindle and then stopping abruptly when the tape pulls taut at the end.

They were also amazingly reliable machines. I still think it's a by miracle that VCRs ever worked. The precision required to make the heads, which have to follow a narrow track while being spun round at 1500 r.p.m. And then they made enough of them to be able to get the price down to the point where they were practically giving them away in Christmas crackers .....

But if VCRs didn't exist, and one day you drew up a quick sketch of how to make one, I doubt anybody would believe you stood a chance of making it work!

Even the early professional machines took a lot of experimenting, such as VERA with it's sheet steel tape because the playing speed was too high for plastic tape, to the early Ampexs that solved the speed problem with a helical scan & rotating head to keep the tape speed to a sensible level.

[vhs doctor]

The Panasonic direct drive mechanism called AF mechanism and the portable VCR was the NV-180.

[Studio263]

Originally Posted by Maarten

You'd hope so, but I don't know of any consumer machines after 1985 (*) that had this

Sony SL-HF950? You could also still just about buy an SL-F1 at that stage (for use with the PCM-F1), which also uses this technique. The Mitsubishi version of this idea is spoiled in its latter versions (HS-304 etc) by one of them having a geared drive, making it unnecesarily noisy. It is never the less a proper 6 motor deck in a budget machine. Its a shame they still used a loading belt, otherwise they'd have never gone wrong.

[G6Tanuki]

Feeback by sensing motor-current was certainly used in quite a few later computer-backup-cartridge tape-drives: it was also used to give 'soft' take-up/slow-down of the drive which helped reduce the chance of the tape being damaged.

Tension-control on some was obtained by weakly powering the motor for the source-spool thus providing controlled electronic 'drag' which could be varied as needed.

I'd guess that by the coming of the last generation of VCRs electronic control such as this would have become cheap and easy to implement - probably a lot cheaper than separate sensors.

[1100 man]

The machine is conventional in all other respects. It has a normal back tension band & pole. The geared reel idler is driven by a belt from the capstan motor so no separate motors for each reel.

There is a hole in the deck where the lighthouse should be. There is a hole in either side of the cassette housing where the light would shine through onto the end sensors. There is no provision for sensors, however.

When rewinding or fast forwarding a tape, the speed starts off slow and then builds rapidly to maximum. When there is about 1/8" thickness of tape left on the reel, the machine slows down to dead slow until the end of the tape is reached. A second after the reels are stopped by the tape being at the end, the machine goes into stop.

It just works on the basis that there is insufficient torque to tear the tape off the spool when it gets to the end. I don't know what will happen with one of those short tapes with very large reel centres though.

The machine is dated 2005/12

Cheers
Nick