Hallo,
Was ist die mögliche Ursache eines statischen Klanges, der passiert, wenn ich meine Uher 4400 Report Monitor-Bandmaschine einschalte? Es scheint am stärksten zu sein, wenn die Maschine für ein paar Tage ausgeschaltet und dann eingeschaltet wurde. Auch passiert es entweder mit dem Netzteil oder mit Batterien. Es spielt keine Rolle, ob der DC-Motor ausgeschaltet ist oder nicht. Vielen Dank!
Hi Ken,
the term "statischer Klang" does not produce any idea what you mean (it is not a fixed German phrase or technical term)
I can only guess that you might mean either something like "static noise" which is this crackling sound coming from repeated discharge sparks or possibly a single switching transient (pulse).
You shoud provide a more detailed description or a sound sample (e.g. as mp3-file).
Regards Kai
Hello Kai,
Sorry for the confusion. The sound is a static type of discharge sound that decreases in pitch and one of the VU meters is pegged completely. It happens with either the battery replacement power supply or with batteries. It happens when the speed selector is activated and will happen less if the selector is turned off and then back on. I tested the capacitors in the audio amplifier and found two that were leaky but when replaced the sound was still there. It happens if the DC motor is working or not.
I will appreciate any troubleshooting help.
Best regards, Ken
Hallo Ken,
a possibly similar case was reporteded recently, where somebody observed a strong humming sound at low supply voltages (below the recommended ?5.5V?). At those low voltages the decoupling function of the supply voltage regulation vanishes resulting in low frequency oscillation of the audio pre-amplifiers.
Is only one channel affected by the problem ?
I could imagine that failure (loss of capacitance) of another electrolytic capacitor in a channel strip could lead to relaxation oscillations that might produce the observed noise.
Could you estimate the pitch or repetition rate ?
Do you have the service manual & schematic ?
Regards Kai
Hello Kai,
Thank you for the helpful suggestions, I will investigate the supply voltage levels. I examined the Z127 and replaced the filter capacitor and it seemed to produce 6.0V but did fluctuate when the deck is first turned on. The noise happens on channel II only and is mostly a upper frequency buzzing sound that decreases in pitch and lasts for about 1 second, perhaps a second and a half.
I have found another problem, the small red leaf type switch that is activated by the "start" button is missing the "U" shaped spring. Can anyone tell me the manufacturer of this switch, please? Or help me source a replacement?
Thank you!
Regards, Ken
Hello,
I measured the available voltage as 6.0V and when I selected a speed the voltage went to 5.96V so I don't believe that is the source of the problem. I do have a very poor copy of the service manual, the schematic is fairly low resolution and the circuit board drawings have sections missing. It is a poorly done scan. At the present the motor has stopped working and I have ordered a replacement motor with control circuit board from a company in Switzerland.
Regards, Ken
Hello Kai,
Here is a photograph of the switch and the power supply. Here is a link to the motor I ordered:
http://www.ebay.com/itm/322508198302?_tr...EBIDX%3AIT
I had to piece together a reasonable schematic drawing and use a great deal of imagination to learn everything I can. This was my first experience with Uher products and I am beginning to appreciate the craftsmanship.
Best regards, Ken
Hello Ken,
the ebay offer seems to come from the Swiss partner of SDS-consult.
They have a long list of spare parts that are still available for those Uher portable tape recorders.
Another company offering repair service for Uher tape recorders is
http://www.uher-reparatur.com/
I guess, the micro switch on the fotograph is K4 in the schematic.
The service manual explains its function on page 28 in section 4.1.3 in German and on page 29 in English.
You might try manually whether setting it to the opposite state during/before start eliminates the observed buzzing sound or whether these are two non-related problems.
You could ask the two companies named above (there may be more) for the micro switch.
The SDS-consult price-list contains an item called 1030032 "micro switch diverse" on page 3.
On the other hand, I think that such switches are still produced somewhere, but I can't tell, where to get them.
Regards Kai
Hello Ken,
in the meantime I have looked into the internet for such micro switches and found a few that look at least similar:
A German company producing such switches is
https://www.marquardt-schalter.de
You'll find these switches in the product category "Schnappschalter" not in "Mikro-Signalschalter".
I guess "Schnappschalter" means something like "bistable switch".
German electronics parts distributors list a very small number of those switches:
reichelt offers (
https://www.reichelt.de )
[
attachment=15408]
In the download section you can get the Marquardt brochure about the whole 1010 "Schnappschalter"-series in German and in English
Conrad offers (
https://www.conrad.de/ )
[
attachment=15409]
[
attachment=15410]
rs-online offers (
http://de.rs-online.com/ or the international site:
http://www.rs-online.com/)
[
attachment=15411]
The downloadable datasheet is the English version of the Marquardt 1010-series brochure.
You will have to check whether one of these switches could replace the Uher part.
Kind regards
Kai
Hello Kai,
Thank you for the excellent suggestions, you have been a tremendous help. I have tried turning the 4400 on with the switch both open and closed and it doesn't make a difference. With your help I can now order a replacement and at least solve that problem. Again thank you for your time and effort. If I can return the favor, in any way, please let me know.
Best regards, Ken
Hello Ken,
nice to hear that you are making progress...
Does the pitch of the transient buzzing sound in channel II depend on the selected tape speed ?
Regards Kai
Hello Kai,
I just ordered a replacement Marquardt switch from Allied electronics. The selected tape speed doesn't change the pitch of the noise, the only thing that effects it is the duration of the time between on and off. If you turn it on and then off and quickly back on the noise is considerably reduced. If you wait several hours after turning off then the noise will be considerably louder when turned back on. For this reason I have been looking at capacitors, something storing and discharging some part of the circuitry connected with channel II.
Cheers, Ken
Actually I ordered 5 of the switches, so if anyone needs one, let me know and I'll send it free of charge!
At RS-online the smallest order quantity / packing unit/bag contains even 10 switches for 2.xx €, if I remember correctly.
Did you check whether the switch will fit ? Or will this be a question of fate/personal luck ?
A strategy to find the reason for the buzzing sound might be to compare pairwise the transient voltage behavior of corresponding electrolytic capacitors in channels I & II after switching-on, channel I showing how it should be.
Regards Kai
I ordered the switches from Allied Electronics and the minimum was 1 unit at around $1.75 each, I believe. I looked at the data sheet and make some measurements and it should be a direct replacement. But, luck is always a big factor.
The suggestion for comparing channel I and channel II behavior is excellent and is the path I will take. At the moment I'm trying to get a Teac 6010 take up motor to work correctly and then back to the Uher.
Cheers!
I received the switches and they are a perfect match, I've installed it and it seems to work correctly. Now to fix the motor and the noise.
The replacement motor and controller circuit arrived and were installed and operate perfectly, very smooth operation and very quiet. The same Swiss company sent a replacement switch at no charge, what a great thing to do for their customers. Now to figure out the noise problem!
Hello,
I have some information concerning the turn on noise. It can be controlled by the playback volume. It effects "channel II" and is strongest when first turned on and is less when the machine is turned off and then back on again. Here is a photograph of the pulse.
Hello Ken,
what's the scaling on the horizontal and vertical axes ( time/div, Volts/div ) ?
Did you measure at the headphone or speaker output terminal ?
Looks like somewhat irregularly repeated charging spikes of a capacitor.
Regards Kai
Hello Ken,
I think the Uher Report Stereo in that tapehead thread is quite different from your Report Monitor version.
In the schematic of the Report Monitor there are no Germanium transistors, the supply voltage is positive with respect to ground and most of the speed-dependent equalization-switching is done with transistor-switches instead of the long sliding switch-bar used in former versions.
Perhaps you can locate the fault by tracing those spikes from the output back to signal points more to the front of the channel-strip. If you can find a node without those spikes, you know the origin is between that one and the next in the chain.
How does the noise depend on potentiometer settings (volume control, tone control, etc.) ?
Regards Kai