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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 21st Aug 2017, 11:41 am   #1
Tractorfan
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Default Old Uher 4000 motor problem.

Hi,
I picked up this shabby Uher 4000 Report - L yesterday for not much money. After replacing the main belt, I got it running (until the second, smaller one snapped), and it works well considering it looked like it had been dragged out of a shed.
It's got four speeds and came complete with a Grundig mic and the mains PSU.
However, the motor seems incapable of starting on its own and needs a push to set it spinning, whereupon it runs fine until it's turned off, then it needs another push to restart it.
Is there a motor control circuit with these which is no longer providing enough starting torque? There are more than two wires going to the motor, which suggests to me, some sort of feedback speed control system. I may be wrong though. Once it's running, the speed is correct and forward & rewind is OK. I don't think there's a tight bearing, but I'll strip it down further and check/lubricate when I get the time.
Many thanks.
Cheers, Pete.
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Old 21st Aug 2017, 3:39 pm   #2
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Default Re: Old Uher 4000 motor problem.

Pete,

I'm not familiar with your machine but I wonder if it uses the same type of motor & control circuit as the notorious Grundig C100L (cassette). Below is the link to the problem I had with the Grundig motor which had a similar stalling problem.

http://www.vintage-radio.net/forum/s...ad.php?t=93939
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Old 23rd Aug 2017, 9:14 pm   #3
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Default Re: Old Uher 4000 motor problem.

Yes the Uhers do have speed control circuits. Do you mean you have to open the Uher and give the motor spindle a helping hand, or do you mean you have to give the take-up spool a push, which might imply a whole different set of problems.
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Old 23rd Aug 2017, 10:34 pm   #4
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Smile Re: Old Uher 4000 motor problem.

Hi,
Yes, I have to give the motor a push to get it going, and once it is it's fine. The speed is correct and constant.
I took the motor control board out today in case there was anything obviously amiss, and it looks awfully complicated with three identical circuits. I wonder if it's three phase? I'll whip the motor out tomorrow in case it has a dry bearing, although it turns easily enough.
Cheers, Pete.
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Old 24th Aug 2017, 12:06 am   #5
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Default Re: Old Uher 4000 motor problem.

Sounds like it's the motor then but are you getting enough volts off the power supply? In all the Uhers I've had a go at, replacing any Frako electrolytics has paid dividends. The power supply is well hidden under the battery compartment but can be got at by removing the top plate (keep an eye on the little screws).
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Old 24th Aug 2017, 10:53 am   #6
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Smile Re: Old Uher 4000 motor problem.

Hi,
Thanks for your reply. It'd certainly do no harm to change them. The mains unit gives about 6.5 volts off load, which I assume is about right. I can change the cap in that too, although there's no hum on the sound.
Cheers, Pete.
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Old 24th Aug 2017, 12:11 pm   #7
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Default Re: Old Uher 4000 motor problem.

The volts are OK then so it may just mean the motor needs a tiny bit of lubrication
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Old 24th Aug 2017, 11:04 pm   #8
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Default Re: Old Uher 4000 motor problem.

The Uher motor is a three-phase design. It's "not quite brushless", in that it does actually use brushes for positon feedback, but the actual heavy current is being switched by transistors; the brushes are switching only small currents, so there is no risk of arcing causing interference.

If one or more phase is not being driven properly, then this is equivalent to a petrol engine not firing on all cylinders. The motor might be able to run fine on reduced power, but not accelerate from rest against friction. Can you get an oscilloscope on the motor windings? It should be obvious which is the odd one.

I did find a wiring diagram for the 4000 Report L online, but that was two computers ago. I do remember the German word schaltplan being in the title, and it was one huge .gif (if my memory serves me correctly, which it doesn't always) image, so a search for Uher 4000 schaltplan may prove fruitful. The later stereo and 3-head Uher machines use the same motor, so even if you can't find the diagram for exact model, the circuitry should be similar -- though newer transistors may have been substituted, and resistor values changed.

Good luck with it! These really are lovely little machines when they are going. Earlier attempts to build portable tape recorders had usually involved compromises such as having to lace the tape differently for recording or listening; having no playback facility at all; requiring bulk-erased tape; no or unclear recording level indication; hand-cranked rewind; no fast forward; non-standard spool sizes and even (boo! hiss!) no capstan drive. The Uher 4000 Report was just a proper tape recorder that was portable.
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Old 25th Aug 2017, 3:03 pm   #9
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Smile Re: Old Uher 4000 motor problem.

Hi,
Thank you Julie for your reply. It makes things a lot clearer, and I've noticed that the motor sometimes 'stutters' when it's loaded up, and just before it stalls, so it makes sense that a 'phase' might be missing or weak.
I'll get the 'scope on to it when I get a bit of 'bench time'.
Lubrication made no difference.
Cheers, Pete.
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Old 25th Aug 2017, 4:48 pm   #10
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Default Re: Old Uher 4000 motor problem.

As long as you don't fall for the trap in this thread .....
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Old 25th Aug 2017, 6:39 pm   #11
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Default Re: Old Uher 4000 motor problem.

We've all been there...
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Old 29th Aug 2017, 8:22 pm   #12
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Smile Re: Old Uher 4000 motor problem.

Hi,
Today I replaced the seven tantalum caps on the motor control board with electrolytic caps to see if that made any difference (it didn't).
However, I did notice that the motor would start when the rotor was at rest in certain points of its rotation, but not in others. This implies to me that the commutating part is not giving a reliable contact at all points of its rotation. If you follow my point.
So, the next tack is to whip out the motor and have a squint inside it.
Cheers, Pete.
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Old 29th Aug 2017, 9:52 pm   #13
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Default Re: Old Uher 4000 motor problem.

That sounds reasonable. As mentioned above, there are brushes but they are not carrying the full motor current. It wouldn't take much to stop it. However, it's also still possible that one winding is not energising properly; and if the armature settled where it would have to "lead off" with that winding, then it might fail to start.

Does the motor connect to the PCB by means of a plug and socket? If so, you could do some cold checks with a multimeter. Some of the connections will change as the armature is rotated.
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Old 30th Aug 2017, 7:21 am   #14
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Default Re: Old Uher 4000 motor problem.

Here is the Uher 4000 L service manual with the motor circuit scanned.

I serviced Uher 50 years ago, and can tell you motors for the Report, S and L were a continuous concern.
There were three motor types used. The L used the poly phase type.

Perhaps, an ohm meter, analog, could be used on the motor commutator to determine the segment switching contacts are working. That the contacts appear to work while rotating slowly, does not mean the motor can spin up, and start by itself again.

If you open it, you need to be careful. We never fooled with battery recorder motors. But then again we had spares on hand.
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Old 2nd Sep 2017, 6:12 pm   #15
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Smile Re: Old Uher 4000 motor problem.

Hi,
I finally got round to metering the motor and it seems to check out OK. I'm now wondering if there's an iffy transistor on one of the phases. I've got a few AC128s which should work in place of the AC122s. I hope it's not one of the AC188s which are inside an small aluminium block heat sink.
I'll scope the outputs again to see what's happening.
Cheers, Pete.
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Old 3rd Sep 2017, 1:11 pm   #16
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Default Re: Old Uher 4000 motor problem.

Tractorfan,

Here's the motor assembly from the Grundig C100L and two diagrams for the motor control. Do they bear any commonality to the UHER ?

Tony
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Old 19th Sep 2017, 10:04 pm   #17
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Smile Re: Old Uher 4000 motor problem.

Hi,
I 'scoped the three 'phases' and one appears to have a different (smaller and more 'rounded') waveform to the other two. I've tried substituting the transistors one-by-one except the output ones inside the heatsinks as I have nowt like them in my bit box.
I removed the motor and metered the windings and the rotating contacts (for the want of a better description), and it all looks OK.
But still the motor will only start when in a certain part of its rotation.
The circuit looks broadly similar to the Grundig and is shewn in an earlier post.
Cheers, Pete.
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Old 5th Oct 2017, 11:16 am   #18
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Default Re: Old Uher 4000 motor problem.

I've repaired loads of these machines and I'm afraid it's a new motor. The 4000L was particularly prone to this problem. Don't take it apart as you'll never get it back together and it will never run again! Don't bother looking elsewhere on the motor control board or scoping the waveforms, entertaining though they are!
It's possible I have a replacement motor at home. I'm away at the moment and return on 23rd Oct.
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Old 5th Oct 2017, 3:59 pm   #19
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Default Re: Old Uher 4000 motor problem.

I'm curious: what is it that goes wrong with the motor in these cases? According to Tractorfan the windings seemed ok.
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Old 6th Oct 2017, 7:14 am   #20
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Default Re: Old Uher 4000 motor problem.

Hi. This sounds a similar problem to a Uher 4000 IC I have just fixed. The machine was a gift but came to me with no sound and the stuttering motor problem. Once it's given a push it runs well! At first I recapped the machine and got the sound back. This didn't cure the motor problem. On my model on the motor board there are 6 transistors and are germanium type. They're horrible and should be replaced. I was dreading it would be one of those that live in the metal block. Luckily it wasn't. I started replacing one by one the 3 transistors that each represent one phase .... on mine they are AC151. I believe they are PNP type and replaced them with silicon equivalents such as a BC558 or similar. Bingo! Machine works perfectly. Change those germanium transistors first before suspecting the motor. That's my opinion whatever it's worth. Good luck
PS: I searched AC122 & an equivalent seems to be BC560. I think it's worth changing those transistors to start with!

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