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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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3rd Dec 2016, 6:48 pm | #1 |
Tetrode
Join Date: Dec 2016
Location: Huddersfield, West Yorkshire, UK.
Posts: 50
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Uher 4400 Stereo record problem
Hi all, I hope someone can help me with a problem with a nice tidy Uher 4400.
The machine plays back recordings made on the Revox A77 perfectly, infact quite amazingly good quality playback, well pleased! However the machine will not record to the right hand channel, ch2? It does erase a previous recording ok, so bias ossc etc seems ok. I've cleaned the long wafer switches and tested that all the contacts have continuity in the record position with a multimeter. All the Fraco caps on the main board have been replaced, which also cured a strange whoosing sound from the speaker on power up. I cannot seem to find a specific service manual for my variant except for a very poor scanned photocopy in German, which is pretty useless, as my technical German is not good! BTW the vu meter on this channel is stuck just into the red, but I cannot see how this might stop it recording. I had success rebuilding the Revox meters, so this will be attempted once it can record. There are also some minor transport noises and vibrations to cure too! One thing at a time. |
3rd Dec 2016, 10:39 pm | #2 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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Re: Uher 4400 Stereo record problem
The "stuck" meter suggests a fault in the RH recording preamplifier.
It could be oscillating at too high a frequency for you to hear, and for the tape to record, and that is swamping out the wanted signal. Have you got, or could you borrow, an oscilloscope? Also, is this an early 2-head or a later 3-head Uher?
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If I have seen further than others, it is because I was standing on a pile of failed experiments. |
4th Dec 2016, 11:14 am | #3 |
Pentode
Join Date: Jan 2013
Location: Powell River, British Columbia, Canada.
Posts: 217
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Re: Uher 4400 Stereo record problem
There is an inductor you should test, to see if it has gone open.
A wire at a terminal may have corroded off. This inductor is used a bias trap in the circuit from the recording output of the amplifier to the head. For the lower track, this inductor is designated L6. In my files, there is no service manual for the Uher 4400 Report Stereo, just a supplement to the service manual for the Uher 4000 Report L. It is in English , German, and French. I am attaching an image of the component side of the printed circuit board showing L6, part number 561-28613 Also is a part of the schematic that may help you. The bias frequency for the 4400 is 60 kHz.
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Steve Dow VE7ASO |
4th Dec 2016, 2:12 pm | #4 |
Tetrode
Join Date: Dec 2016
Location: Huddersfield, West Yorkshire, UK.
Posts: 50
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Re: Uher 4400 Stereo record problem
Thanks for the replies. I've checked the meter coil for continuity and it's ok.The meter is stuck in position all the time, I'm pretty sure it is because the movement is broken. With Revox meters it's usually caused by the magnet coming loose and jamming the coil. I have removed the bias trap coil and it measures fine too.
When in the record position, with the levels set to maximum, there is some background hiss on the left hand channel, but the right hand channel is silent. When touching the circuit board in various places, I can get buzzing from the left channel but not the right. In play position, both channels have background noise. I've double checked the wafer switches again with the help of theabove picture and its definately ok. |
4th Dec 2016, 8:40 pm | #5 |
Pentode
Join Date: Jan 2013
Location: Powell River, British Columbia, Canada.
Posts: 217
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Re: Uher 4400 Stereo record problem
At this point of your tests, feed a signal into both right and left inputs, on record, such that the good recording meter reads center of range. 1 kHz is a good frequency to use.
Disable the bias oscillator by removing T 15. Don't try to stop it any other way. With the bias oscillator dead, using your DVM on AC volts, (an audio mV meter, or analyzer would be better) trace the 1 Khz signal, on both the good, and bad, channel back to the head. This test would be difficult in the extreme, without an oscilloscope, with the bias oscillator running. Now, my head is back on the workbench 50 years ago.
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Steve Dow VE7ASO |
4th Dec 2016, 10:40 pm | #6 |
Tetrode
Join Date: Dec 2016
Location: Huddersfield, West Yorkshire, UK.
Posts: 50
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Re: Uher 4400 Stereo record problem
Thanks for the tip Steve. I might be able to get some help with this from a neighbour who does a lot of electronic repairs and is much more familiar with this sort of in depth fault tracing. He has a lot of old hifi gear such as Quad valve amps, I think he worked for the BBC in some technical role. BTW call here is G6BCC, but currently no antennas.
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5th Dec 2016, 9:47 pm | #7 |
Tetrode
Join Date: Dec 2016
Location: Huddersfield, West Yorkshire, UK.
Posts: 50
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Re: Uher 4400 Stereo record problem
After a bit more poking around I managed to get a brief but fairly good recording on both channels which points to an intermittent contact somewhere. I think I've been misled by the wafer switch apparently testing ok. I've removed one sliding contact strip and some of the fixed contacts are black with copper oxide, pushing down on the soldered contacts may have been enough to give a good contact for the meter test. I'm going to strip the switches and polish the fixed contacts back to bright metal and see how it goes.
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7th Dec 2016, 12:38 am | #8 |
Tetrode
Join Date: Dec 2016
Location: Huddersfield, West Yorkshire, UK.
Posts: 50
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Re: Uher 4400 Stereo record problem
Still working on the record/play sliding switches. The manual says making sure the contacts line up in a certain position in both play and record, but I noticed that when one switch is dead on, the other is not. Is there a way of adjusting the mechanism to achieve this? Cannot find it in any of he manuals I've downloaded. At least I've discovered it's relatively easy to remove the meter assembly to fix the stuck RH one. Ah for a manual as comprehensive as that for my A77...
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11th Dec 2016, 6:51 am | #9 |
Pentode
Join Date: Jan 2013
Location: Powell River, British Columbia, Canada.
Posts: 217
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Re: Uher 4400 Stereo record problem
Here are the words on contact positioning in the service diagram for the 4400.
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Steve Dow VE7ASO |
11th Dec 2016, 7:38 pm | #10 |
Tetrode
Join Date: Dec 2016
Location: Huddersfield, West Yorkshire, UK.
Posts: 50
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Re: Uher 4400 Stereo record problem
Success! It is now recording well on both channels. I guess it was mainly down to the sliding switches, the adjustment seems very critical,possibly due to worn contact areas and the copper spring contacts on the wafer being less springy? The switches have also been resoldered to the boards. Less luck with the meter, the magnet was jamming the coil and freed off and re glued ok but the motion will not return to zero on it's own, so looking for a replacement, even a broken one for parts, or one I can modify and fit into the old body.
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