Uher 4000 Report IC no sound.

[foliver]

Hello all
I am overhauling a uher 4000 report IC.
Everything works ok, but i've no sound on speaker, or headphones. Nothing.
If i record, i have nothing in ehadphones, but meter moves, and everything seems ok.
Where can i start to investigate that?

The recorder is in very good shape......
Thanks for your opinions.

Fabian

 

[Thorsten R.]

Hi Fabian. One possibility is that the speaker is muted because the build-in switch in the socket for the external speaker is bad. Happened sometimes with this devices. A similar switch is in the hradphone - socket. In several Uher Report models the speakers could be muted by pulling the volume knob (although I think that Feature came with the "Monitor" models).

 

[foliver]

Thanks Thorsten for your reply.
I’ve just checked that and the switches are working fine....
How can I check voltages in the amp?
Thanks!

 

[Thorsten R.]

Oh, I have repaired a lot of Reports (and other Uher RtR´s) in the past, but I have to look whether I have a schematic. It iwas about 20 to 40 years ago... And my own Report is a 4400 Monitor. This thing is different!

 

[Thorsten R.]

Ok. First of all, the Uher Report in one regard is like some old British automobiles: Ground is positive. The + 6V is the common "rail". From this on all voltages are negative. Then: At the amplifier IC TBA641A at pin 14 is the positive ground (always). The question is whether the pin 3 has the 0 V potential. This comes from the internal power supply (not battery, accumulator or mains adapter directly!). If this voltage is missing then you should take a look at the wire from the points 404 (internal supply PCB) to 137 (main board).

The manual is stored at HiFiengine.com.

 

[foliver]

Hello Thorsten, thanks for your answer, i was just uploading the diagram.
I've the manual, i 'll jump on it now, to test.!

 

[foliver]

Hi Thorsten, I've 6V in pin 14 and 3, so that's ok.
Where can i continue to look at?

Thanks!

 

[Thorsten R.]

Of course, making a remote diagnosis is not easy. But:

Does the machine record and/or playback at all? You can test it at the Radio/Phono socket, pin 2 is ground, pin 3 is High Level Record (as opposed to the typical German Low Level Recording at pin 1) using a normal amp with RCA sockets. You only have to alternatively connect the Tape Out at recording and Tape In at playback to the Radio/Phono socket.

Are all voltages at the internal power supply PCB present? They are enumerated in the schematic. Please observe: Uher did choose a lot af tantalium and normal electrolythic condensers that are all working at or above the upper voltage tolerance! Even when the units were relatively new (we sold and serviced those things in the dozens then) the caps did short circuit really often. If nothing else helps (or you cannot proceed with the next step) just check them all with an ohmmeter. Uher chose them because bigger caps - well - would simply not fit into the Report.

Now is the time to get an oscilloscope. There is a chapter in the shop manual titled "checking the final stage". Do it. If you have no signal generator - well, there are really a lot to be found for Android - phones (and I presume for Apple phones also). And of course you can feed the signal (e.g. 1000 Hz) into 2 and 3 of the Radio/Phono socket, switch "Record" and follow the signal through the different stages of the recorder.

By the way, I have always loved the Uher Report and still have some that wait for TLC. One story: Uher once belonged to Harman for a short time. When Harman Germany had its 25th anniversary I visited the German branch in Heilbronn. They did raffle an Uher Report Monitor 4200 - all metal parts completely gold plated! Even the heads! And that thing was working! That was the most gorgeous thing I have ever seen and that was neither a 12 m R-Yacht nor a woman!

 

[foliver]

Jaaaa!!, what a beautifull image!!!, nor a Rolex watch!
Nice story, thanks Thorsten.
You see, this was my first recorder, when i lived in france, and studied Sound for films.
I make my first steps with it, my first recordings. Then i start work, and my industry changes to digital. I made just one film with analogue ( Nagra IV-s, rented), then all DAT's, and now Aaton recorder, the one in my avatar.
This days at home, i start repiring some things, and well now is the Uher. Let's see if i arrive.
I'll follow your advice, and make some tests.
I've another units, waiting...another 4000IC ( with another problems, big humm), and a 4200 ( big humm too, the same, may be a capacitor), but i want to have the "original one" repaired.
Thanks!!!

I keep in touch

Fabian

 

[foliver]

Hi, i've just test the record function, over the mic in, and line in, and it works ok ( 40hz, 400hz, 1k and 10K, then, music)
The output over the line out ( RadioPhono socket) is clean.
I've some wow and flutter caused by the old belt, and some low sound of the previuos program that the test tape has recorded....it's an old tape.
i'll go for the power supply pcb

Any other ideas are welcome

 

[foliver]

Hi again.
ok, i tested all voltages in the power supply PCB and i compared to another exact unit i have ( monitor works on the second one, well....worked until now..) and they have tyhe same values.
So i pick up a pair of aligators with a speaker, and started to follow the speaker cables to the amp, i arrived to a place that i think is in out of the amp section, and connect the speakers... nothing.
Then an intermitent sound swap, like speaker works, but motor speed decrerases, and again like one second swap, speaker on and motor slow, then speaker off and motor normal speed, then a little smoke in the amp IC.
and i turn off the recorder.
Ok, i unsolder it, ( IC TBA 641), and i take the same from the working recorder ( the donor), i solder to the main one, and nothing. As day one.

Where can i look now?

 

[Thorsten R.]

Okay ... that was perhaps a ... bit fast. Test whether the old IC still works in the other Report. Then please tell me where in the schematics you have connected the external speaker. If you have done this directly at the IC and either to ground (+!) or earth (the chassis) then the possibility is there you have shot the IC. I would take a closer look at C142, because when that has a short circuit it destroys the audio output of the amp. And it is one of the damned tantaliums.

 

[foliver]

Hello Thorsten, I have some news.
I've changed some caps, not the Tantalum ones, cause I didn't find replacements in the shop I bought.
tantalum can be substituted by electrolitics?

So, one or more cap where faulty, so I have sound in the speaker and the headphone, but with some problems to resolve.

1. a low freq ( 60 HZ?) that seems to decrease ( not at cero) if I touch the housing, a ground problem?, a cap?

2. if I insert a signal ( line or mic) and I start to rise de speaker-headset volume, the signal seems ok ( despite the hum), but starts to distort heavily, and goes to a periodic signal, lowering the volume inverts the facts.

Here a link to a recording through the headphones ( the cinetical-mecanical sound in the back is the flywheel stiff rubber, a new part is coming).

so, what now? any ideas where to continue?
full recap?
Bad tantalum?, the hum where can it be generated?

Thanks for your ideas, and time!!

Fabian

 

[Thorsten R.]

Recap, definitely. Especially the tantalums! You can get all sorts of Tantalums (including the wired ones we need here) from Mouser.