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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 13th Jun 2016, 6:24 pm   #1
barretter
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Default Uher 4400 Report Monitor noise problem

Happy to report that I now have an English language user manual and some circuit diagrams on a CD-ROM bought from a UK eBay seller. Having got it functioning fairly well after cleaning the heads and the pinch-roller (all filthy) I find that I have a noise problem on the left channel (a low hum) and also no response from the needle in the left channel meter. Does anybody have any experience of this and any putative causes?
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Old 14th Jun 2016, 5:30 pm   #2
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Default Re: Uher 4400 Report Monitor noise problem

Easy thing first - clean and work the record-play switch back and forth. Worth a try.
Glyn
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Old 14th Jun 2016, 7:23 pm   #3
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Default Re: Uher 4400 Report Monitor noise problem

Thanks for the suggestion. I'll try it but I think the noise is probably electronic in origin. About a second after I switch the machine on there is a rising moaning sound through the loudspeaker which quickly decays to a much lower level but is still there in the left channel. A dodgy electrolytic? (I have no idea really).
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Old 15th Jun 2016, 1:07 pm   #4
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Default Re: Uher 4400 Report Monitor noise problem

It's possible. I should have a circuit diagram somewhere, Does it play back a known good tape OK - with the meters functioning?
The good thing about a stereo machine like this is that you have an identical channel to compare voltages. As the meter doesn't move then it's got to be quite early on in the preamp stages. The electrolytics here can go short so a few minutes with an ohmmeter might pay dividends.
Also check the source-tape switch is OK.
Glyn
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Old 15th Jun 2016, 6:11 pm   #5
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Default Re: Uher 4400 Report Monitor noise problem

Yes, it plays back fine in mono and stereo and you can't really hear much of the noise in the left channel until the music stops. The strange thing is that today I installed a couple of new drive belts and now the left meter plays along with the music while the right meter is stationary. Presumably I must have disturbed something but I don't know what. Both meters kick on switch-on and the left meter reacts as the hum/moan noise builds up momentarily in the left channel. The tape/source switch doesn't have any effect in playback. I presume it's meant to be used for comparison purposes in recording mode, which I haven't tried yet.
The noise in the left channel disappears when I press the record switch but I suppose that means the noise is in the amplifier circuit.
I attach a picture of the inside : where would the preamp circuit board be? Many thanks
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Old 15th Jun 2016, 7:19 pm   #6
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Default Re: Uher 4400 Report Monitor noise problem

The right-hand meter is also used for the battery test function, so I would start by checking the battery test switch and its wiring. The switch has a changeover action; at rest, the positive terminal of the meter is connected to the monitoring preamp but when depressed, it is connected via a preset variable resistor in series with a fixed resistor to the positive supply.

There is a PDF circuit diagram here although it's all cut up and awkward to read on screen; might be OK printed out, though. It also includes pictures of the various boards, which should help you identify what is where.

If you have some sacrificial tape, does the noise on the left channel get recorded?
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Old 15th Jun 2016, 10:33 pm   #7
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Default Re: Uher 4400 Report Monitor noise problem

Thanks for the pdf. I've printed it off and am slowly, very slowly getting my head around it. I've found the main amplifier board and I might start there. The battery tester switch is so deeply buried that I don't think I can have done anything to it. It still does the battery testing OK. I'll try a recording tomorrow.
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Old 16th Jun 2016, 1:42 pm   #8
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Default Re: Uher 4400 Report Monitor noise problem

Progress and regress. I recorded a part of an LP and there is no humming noise on the left channel (played back on a TEAC machine). When recording the right meter needle responds but the left meter needle doesn't. However when playing back through the monitor DIN socket, the right channel has disappeared ; and when listening on headphones I get a signal in both earpieces with the tone control pushed in (mono) but nothing in the right earpiece with the tone control button pulled out (stereo). Might be the switch, I suppose, but it was working OK previously. Obviously this machine has multiple problems and it's going to be a long job.
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Old 16th Jun 2016, 5:55 pm   #9
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Default Re: Uher 4400 Report Monitor noise problem

Hi
Multiple problems like this often are due to the wiring becoming brittle and coming adrift at the terminations, especially as things have been disturbed. It's time for a long look over the connections.
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Old 16th Jun 2016, 8:29 pm   #10
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Default Re: Uher 4400 Report Monitor noise problem

Yes, I think it's time to break out the Weller and start reflowing joints : and I'll replace the electrolytics at the same time. Some of them are very ancient.
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Old 4th Aug 2016, 1:13 am   #11
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Default Re: Uher 4400 Report Monitor noise problem

How did you get on? I'm keen to follow on as I have a Uher 4000 Report-L on the bench at the moment. Well, two. One I'm endeavouring to get back to bare metal to see if I can do something interesting in re-finishing the case and have almost succeeded in gutting it entirely without damaging any parts...

The other is to be repaired properly so I have a base for comparison!
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Old 4th Aug 2016, 6:26 pm   #12
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Default Re: Uher 4400 Report Monitor noise problem

Well, I re-flowed quite a few solder joints and I replaced quite a few electrolytic capacitors but the problem is still there so I may have to start replacing transistors, but I have put it aside for the time being. The PCB tracks look quite fragile so I may have to invest in some de-soldering braid rather than use a solder-sucker.
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