Restoring the keypad and chassis on a Beogram 4002 (BeoBooth v1)

Intro

After replacing the light bulbs on the Beogram 4002 I wrote about in my previous post it was time to restore the keypad and chassis.

As almost always, the varnish and black paint are worn by decades of use since the acids in the skin dissolve it. As you can see from the image below this Beogram did also suffer from this issue. If this Beogram should be restored to perfection it was crucial that the keypad was recoated and the chassis repainted.
Furthermore, the contact springs and contact bridges underneath the contact pins were in need of a good old cleaning since the buttons didn't always respond when being pressed.

For the rest of this article I am going to refer to the official service manual for the Beogram 4002 from Bang & Olufsen and use the terms described as seen in the image below.

Therefore the complete unit is referred to as "chassis (P/N 3168049)" and since the "top aluminum plate" is missing a term it will be referred to as "keypad" or "buttons". If possible the term will be written with the associated part number (P/N).

The Problem

Before restoring the chassis and recoating the keypad I needed to take the following issues into account:

The Solution

With the problems in mind and after a lot of thoughts I decided to create my own paint booth making it possible to recoat the keypad.
This article is meant as a step-by-step guide helping you restore your own chassis and is organized into chapters as seen below.

The procedure for restoring the keypad is as follows:

  1. Remove the metal frame from the chassis.
  2. Remove the old varnish and glue from the keypad.
  3. Build your own ventilated paint booth (this takes some time).
  4. Paint the chassis and the keypad.
  5. Clean all the contacts.
  6. Assemble the chassis.


This sounds easy, but let’s dig into it.

The Process

Before we can recoat the keypad we need to remove the chassis from the actual keypad. If you’re lucky the keypad has already started to detach from the chassis since the glue is old and therefore adheres poorly.
Otherwise, you’ll have to carefully press a spatula beneath the keypad in one of the corners. Make sure you don’t lift the keypad too much since this will cause it to bend which is irreversible. 

To remove the old varnish and glue on the back of the keypad I used a paint stripper called NitroMors. It is very harsh so you need to do this outside or in a ventilated area.


After the old varnish was removed it was time to add a new layer of varnish. At this point in the process, I didn't have any paint booth but I knew that dust specks were going to be an issue. Therefore, to get the optimal results I decided to do the spray painting in multiple iterations writing down the pros and cons of each iteration. I cut 10 aluminium test sheets in the same dimensions as the frame and bought a cheap can of matte clear varnish.

To avoid dust specks I took an old unused bed roller, placed a test sheet inside and painted again. The results were acceptable but since the lid had to be off while painting dust specks would still settle in the paint. This was not acceptable. 

Since dust was the main problem I decided to create a dedicated paint booth with filtered ventilation. Clean air = no dust, right?

After some brainstorming, and to make as cheap a prototype as possible, I decided to buy a secondhand TV stand from which I removed all the shelves. Since the stand is only accessible from the front my idea was that dust would not settle from above in the same way I did in the bed roller.
To make sure that even less dust would settle the lid from the bed roller was used as a "door" in the front of the booth. Furthermore, to remove the initial dust from the air I installed an old PC fan which would pull air into the booth through a filter, resulting in much cleaner air. Below you will find an image of the BeoBooth v1 with short descriptions.

After BeoBooth v1 was assembled I painted another test frame. The results were even better than the results from the bed roller but some dust specks were still visible when looking very closely.

With all the problems above in mind, I decided to consult my local auto painter. He recommended me to use their 2K coat which consists of the varnish and a hardener. The 2K varnish should be just as durable as the original. He also recommended me to buy an air compressor and a paint gun so I could avoid wasting the varnish and use a smaller batch each time.
The alternative was to use 2K spray cans but you have to release the hardener when you need to use it, after which the paint is only useful for 24 hours because it hardens. This would be expensive over time.

After setting everything up I painted another test frame and set it to dry. The results were almost perfect so I decided that I was ready to paint the actual keypad. The results were astonishing! The frame looked like it just left the factory. Decide for yourself but I am very satisfied!

While the varnish was drying I painted the black parts of the chassis. They also get worn when using the keypad so of course, they needed to be repainted.
I covered the chassis with masking tape and removed the old paint which isopropyl alcohol before painting it. I decided to paint it with a primer just to make it as durable as possible. Unfortunately, I didn't get a picture of the process only the result which you can see below.


Before assembling the chassis I removed the contact springs (P/N 7500075) and contact bridges (P/N 7500050) from the PCB (P/N 8005018) and cleaned the contacts with ketchup which is acidic and therefore removes the oxidation as seen below. The contact pin (P/N 2992059) and holder (P/N 3152068) were cleaned with isopropyl alcohol.

After everything was cleaned and recoated I only needed to glue everything together. The plastic holder on the back of the chassis was glued with a normal superglue.

Apparantly it took some time for me to find the correct glue for the keypad. The glue needed to have enough strength so the keypad wouldn't fall off after a couple of years and it needed to have a low viscosity so the gap between the keypad and the chassis wouldn't be to noticeable. I ended up with a 2K universal epoxy from Danalim which was recommended by another local hobbyist. It hardens over 6 hours which is a perfect time span for adjusting the frame after it is fixed.
I used clamps and masking tape just to make sure that the glue wouldn’t accidentally end up on the black paint or other places on the chassis.

To make sure that the keypad would stay in place while the epoxy was hardening i 3D printed a custom made lock which you can see in use below. This was made of PLA but still strong enough the press the keypad onto the chassis.

To make sure that the pressure wouldn't cause any scratches onto the newly recoated surface I glued a felt pad on the bottom of the custom printed plastic part.

After the expoxy was hardened i glued the plastic parts which touches the contact pins (I don't have a name for these?) to the keypad using normal superglue.

At last the main PCB was pushed in place and all the buttons were intensively tested to make sure that everything was assembled correctly.

The Finished Product

Voilá! As you can see below the results are very satisfying.

Now i only need to calibrate and test the Beogram to verify that everything is as expected. For this I'll be using my almost-finished tachometer, which requires a completely new post to explain, so stay tuned!

Aftermath

The paint booth I built was only meant to be a prototype. I'm currently working on the blueprints for BeoBooth v2 which is going to be way more advanced and imitate a professional painting environment with help from my auto painter.

Below are some of the key differences which in theory, should make it possible to completely avoid dust. They will be a part of the next BeoBooth:

You are welcome to contact me if you have any inquiries or questions about this process.