Uher 4000 Report Monitor - Speed Control wiring and gearing?

[DMcMahon]

Originally Posted by DerciiDercii

Hello fellows!
I bought a 4000RM a while ago that had the speed control broken off. I've been able to fabricobble a new gear and shaft as shown here: H5P49Hv.jpg

How is the new gear part shaft locked to the switching gear drive ? original part is pinned with a small pin.

David

[DerciiDercii]

Originally Posted by DMcMahon

Before the new part was fitted was it functional on the single speed ?

David

Yeah, but the rest of the gear assembly was already there, it was just the new gear.

[DerciiDercii]

Not entirely sure what it is you describe but definitely should not be necessary to do that.

It's just the notches in the gear, I don't think they're positioned perfectly

It enables power to the motor both in FF & RWD, is your K7 a single switch or 2 switches ?

Two switches, they're all two switch.

Before the new part was fitted was it functional on the single speed ?

Yeah, but nothing else has change apart from that single gear.

There is only 1 playback button (Start) can you clarify please what you mean by 2 playback buttons ?

Sorry, faceplate wasn't on, I meant it only plays when both the Play and Pause buttons are pressed.

How is the new gear part shaft locked to the switching gear drive ? original part is pinned with a small pin.

There is a pin in the shaft.

[DMcMahon]

The Pause button should only mechanically pause the Play motion so strange if you have to press Start and Pause for Playback to work.

Suggest you remove the little metal cover above the keys to inspect the rubber Pinch Roller area. May be necessary also to remove the 3 little Allen/hex headed screws that secure down the heads assembly, then gently ease the heads assembly back a little out of the way (first remove the spools) as per Photo 1.

Check that the 3 small blue loctited screws are not loose and also the middle loctited nut. If the nut is loose then the Pinch Roller will be loose and could quite possibly cause your symptom.

Photo 2 shows no keys depressed.

Photo 3 shows Start depressed, the Pinch Roller moves forward and makes contact with the Playback head

Photo 4 shows Start and Pause keys depressed, when Pause is pressed the Pinch Roller will move slightly back away from the Playback head and no longer makes contact.

David

[DMcMahon]

Here is the suggested wiring modification information to convert a single speed modified machine back to standard operation, this information assumes your machine is modified in the same way as mine was.

On a single speed modified machine the motor will power up when Start is pressed whereas on a standard unmodified machine the motor will power up when one of the 4 speeds is selected.

Reference your photo in Post # 12 check that the brown wire connects to the second (top) K4 switch upper contact. If it does then disconnect it and connect it to the blue wire at the middle contact on that same top K4 switch. This renders the top K4 switch electrically inoperative.

Do the same type of operation at the top K7 switch removing one of the 2 wires, this time on the lower 2 switch contacts (probably both blue wires) and reconnect it to the other blue wire at K7. This renders the top K7 switch electrically inoperative.

Before doing the above take careful notes (photos) of the exact connections, in case you have to rewire back to how it was.

David

[DerciiDercii]

Is there supposed to be any engagement between the motor and the large flywheel for the pinch roller, because there doesn't appear to be any, even during playback.

The positions of the of the mechanism are exactly as the images you posted.

[DMcMahon]

Sorry my descriptions in Post 24 are slightly wrong. The Pinch Wheel when moved forward by the Start key does not contact the Playback head, it makes contact with the capstan shaft.

The capstan shaft is directly driven by the rubber coated aluminium drive wheel. In playback the brass flywheel (driven by the motor via the drive belt) makes contact with and drives the drive wheel/capstan shaft.

With any of the tape speed zero selections, the brass flywheel does not make contact with the drive wheel.

The aluminium drive wheel is often called a flywheel but Uher call it a drive wheel.

David

[DMcMahon]

Forgot to say that the rubber Pinch Roller/Wheel is driven/rotated by making contact with the rotating capstan shaft, the tape which is pushed up against the capstan shaft by the Pinch Wheel is driven forward in Playback by this.

[DerciiDercii]

The flywheel doesn't get engaged by the brass wheel. That'll be why when the pinch roller is active, nothing moves because the flywheel isn't.

[DMcMahon]

So it sounds like you are having intermittent contact between the aluminium drive wheel and the brass flywheel because you previously said you could get playback with Start and Pause pressed but now you are saying there is no movement.

The mechanical contact between the 2 wheels is not heavy and not fixed, it is sprung loaded and also gravity weight loaded.

There is a strong spring fixed to the case next to the right hand side of the motor, the other end of the spring connects to a metal lug 50mm above. This spring is what pulls (under spring tension and gravity) the brass flywheel down against the rubber edge of the aluminium drive wheel.

The alignment of the sawtooth into the pin is fairly critical (the troughs of the saw teeth fully moving down onto the pin) so that when the speed is selected the brass flywheel is pulled down sufficiently to make contact with the aluminium drive wheel.

What I mean by gravity loaded is that on my 4000 for example if I put it on its back and manually rotate the brass flywheel with a speed selected often contact will be lost between the 2 wheels even though the spring is still pulling the brass flywheel towards the drive wheel it no longer has gravity helping to pull the flywheel.

Assuming that your sawtooth to pin alignment is correct and your spring is fitted/OK then there are 2 adjustments in the Service manual that could help. Clearance adjustment at 3.1.7.1 and spring tension adjustment at 3.1.7.2

On the first 4000 I worked on for a friend (covered in an earlier Thread) I had problems getting all 4 speeds to work reliably due to poor contact between the 2 wheels and found the 3.1.7.1 procedure difficult/hit and miss but got there eventually.

David

[DMcMahon]

Originally Posted by DMcMahon

Correction to above, the steel pin does not drop down/move, it is the sawtooth shaped piece that moves up to meet the pin.

Correction to above Post # 8, should have read:-

"Correction to above, the steel pin does not drop down/move, it is the sawtooth shaped piece that moves down (across for top speed) to meet the pin".

[DMcMahon]

If you attempt the flap C bending adjustment of procedure 3.1.7.1 be careful, the flap C on the one I had problems with, had a partial crack in the metal and it looked like it would not take a lot of bending before it might have snapped off.

[DerciiDercii]

Just tried bending the tab for part C on the manual diagram that you mentioned. Contact has now been established! Is there a way to reduce the noise between the two wheels? I imagine that any lubrication would just result in loss of traction.

Only main thing now is to get the alignment for the contact switches on the speed control assembly as the turning doesn't get far enough to turn the motor back on.

Thanks for all your help!

[DMcMahon]

Good that you have made some progress.

As per this link I was not able to improve the noise.

https://www.vintage-radio.net/forum/...d.php?t=162605

The noise was thought to be maybe due to the hardened rubber on the drive wheel, a replacement/NOS drive wheel may help but expensive especially if it does not help.

My 4000 is also noisy but not nearly as bad as the one in the link.

Gently roughening up the rubber surface (just the contact area) or softening the rubber using household Glycerine/Glycerol may help. I have just brought some liquid Glycerine from a chemist and will try it on a couple of rubber idler wheels and the drive wheel.

David

[DMcMahon]

Originally Posted by DerciiDercii

I bought a 4000RM a while ago that had the speed control broken off. I've been able to fabricobble a new gear and shaft

When I originally read your first post I did not know what "fabricobble" was, I thought maybe it was a fancy engineering process which resulted in the parts maybe being 3D printed.

Are you happy that the parts you used are correct, i.e. are not contributing to your speed control alignment issue ?

David

[Welsh Anorak]

I think we're all guilty of fabricobbling!
If only the BBC had used engineers rather than butchers to mofiy their Uherts we'd all be in a happier place.