“Secret” electrolytic capacitor in the Visacustic (and another well-hidden one)

In April 2023, I wanted to complete a sound film from 2022 for Deidesheim. In the two-band process, this requires the active assistance of a controllable projector, which in my case is the Visacustic 2000 together with the Visacustic control unit.

The projector could be switched on (all the lights came on), but the motor didn’t make a sound. The famous phrase “that can’t be right, it was still working yesterday” applied. As it soon turned out, the Si406 fuse was defective and blew again as soon as it was replaced immediately after switching on.

Here is the circuit diagram for the Visacustic 2000 that can be found everywhere on the Internet:

Here is the detail of the circuit hanging on the fuse:

The main suspect was immediately C405 (2200uF, 50V). I desoldered it, which is a nice finger exercise without removing the circuit board, and replaced it with a fresh 2200 µF electrolytic capacitor with 63 V.
Unfortunately, this did not solve the problem. To make matters worse, the circuit board was screwed to the housing for cooling and one screw was tight.

Now, in February 2024, I have returned to the project.

When I checked the circuit diagram very carefully, I found the following:
the fuse Si406 (3.15A T) is located behind the AC output of the transformer with 26V~ nominal on the vertical circuit board above the rear connections, this voltage is rectified (34.5V=), followed by the described electrolytic capacitor C405 (2200µF/50V).
From there it continues via 4 further, in some cases significantly smaller fuses (Si401 T2A, Si402 F0.315A, Si403 F1.25A, Si404 F1.25A), which supply a 24V voltage regulator for the AF section, the two output stages and the motor control unit.
The voltage travels directly via line 11 (connector 907, pin 2) without further fuse protection and (according to the circuit diagram) to the large main board, which is located lengthwise at the bottom of the housing. There, line 11 (according to the circuit diagram) is only connected to R158 (33k), which supplies a (somehow unstabilized) voltage of approx. 17V to the base of T104 and T204 (in the preamplifier circuit) via a 22µF capacitor.

Here is the section (line 11 in the middle, goes to R158):

If the high-impedance R158 has not been disconnected, a short circuit is only conceivable due to mechanical damage to the insulation.

After disconnecting all flat cable plugs on the vertical motor board at the rear, the short circuit was measured and circled on the line down to the main board.

To gain access to it, I had to remove the motor board

The left-hand screw is a soft, stiff cross-head screw. It was soon twisted round and had to be loosened with the aid of rust remover and some chiseling.

Then move the projector all the way up using the knurled wheel at the front and ideally also remove the lower front housing cover (the rotary knobs are very difficult to remove, but they will come off if you have sturdy thumb nails) and then remove the LED circuit board above the rotary knobs at the front.

I didn’t want to completely separate the projector body from the chassis, that would probably have been a lot of work. It was not easy to locate the soldering point of line 11 on the main board from below (remember, it had a short circuit to ground), but it was possible by tracing the adjacent line 13 (connector 907, pin 1).
And now (drum roll), the surprise!

In addition to R158, another component was also connected there, another electrolytic capacitor with 2200µF/40V, which is not shown in any of the circuit diagrams available on the net.

Thank you Braun, for nothing.

Actually, there is only one large electrolytic capacitor (C405) in the entire circuit diagram, as described above. Presumably there was an update at some point (perhaps to reduce hum or similar)…
After I disconnected C-John-Doe on one side (as shown in the picture), the short circuit was gone. After replacing it, the Visacustic worked again like on the first day. Hooray!

Interestingly, the capacitor had a lower dielectric strength (40V) than the 50V capacitor already replaced on the motor board above (which was not defective at all).

I had operated the device for a long time with the 220V setting. The nominal voltage of 34.5V could therefore have come close to its dielectric strength at 38V during this installation and after the changeover of the mains voltage in Germany from 220V to 230V, which probably reduced its already overstretched service life even further.

The Visacustic has been running on the 240V setting for 20 years, like almost all of my old devices.

Finally, I have to say that although the Visacustic is quite compact and inaccessible “inside”, you can still get to everything quite easily once the components have been removed. The flat cable plugs are coded everywhere, so you can never install these plugs the wrong way round or offset, which shows Braun’s experience in the hi-fi sector.

Here is the supplemented circuit diagram:

Here is the “new” detail (it still says 40V, but the replaced one has 63V):

And now to the well-hidden electrolytic capacitor

I was then able to project in Deidesheim 2024, but (as it turned out shortly beforehand) only mute, or “two-band sound” and no pseudo sound.

The projector only produced a pumping noise at the amplifier output, but no intelligible sound.

Mr. Rehberger was present at the fair, and after describing the error he immediately promised me a (later) answer, saying that he knew the problem well, but still had to find out the details.

Which he did, it was caused by the C135 capacitor in the AF section, which was probably defective and also undersized. I should replace it and solder in a 1000µF capacitor instead of the original 220µF.

I also found a few other sources on the Internet that documented the same problem and a similar solution:

https://www.eevblog.com/forum/repair/repair-of-a-braun-visacustic-2000-digital-8mm-projector

and

https://www.filmvorfuehrer.de/topic/31463-braun-visacustic-2000-digital-reparatur-nf-teil

Now the repair should be easy (I thought).

It was quite easy to locate the capacitor in the circuit diagram, including which supply network it is connected to and where it is fed from.

Line 22 at the bottom leads to the supply board, which I already addressed at the beginning of this article.

C135 must be located on the AF board, which is in the bottom of the Visacustic, so to speak, but where exactly? I did not have an assembly diagram, nor a service manual for the Visacustic 2000.

Here I found a service manual for the Visacustic 1000:

Braun Visacustic 1000 Stereo (projector info) – Michael’s Super 8 World

Here is the direct link:

Click to access braun_visacustic_1000_sm.pdf

This gave me an assembly plan for the LF part of the Visacustic 1000, which fortunately differs only slightly from that of the Visacustic 2000.

Then it was time to disassemble again. I’ll skip everything I’ve already described above and go straight to the AF circuit board.

After removing all the housing parts (and as a precaution unscrewing the supply board at the back and freeing it from all connections), this is what you see at the front:

I had also removed the small screws on the circuit board with the LEDs (above the buttons), as well as all the plug connections to it.

Incidentally, this small, 3-pin plug appears to be the only non-coded plug in the Visacustic, document the polarity here before disconnecting.
Then 3 screws that connect the NF-LP to the housing base must be loosened:

The AF part can then be pulled a good distance forwards out of the housing:

But where is C135 now?

I noticed that Braun had hardly changed the circuit board (between Visacustic 1000 and 2000). I therefore mirrored the assembly plan and placed it over a photo of the LP: