Beogram 4002 (5513): Brand New Hood Fatally Damaged Due to Bent Hood Hinges! - Straightening Hinges Out and Installation of Another Hood

I recently restored a Beogram 4002 (Type 5513) for a customer in Florida. This unit also received a new hood, which was procured from the beoparts-shop in Denmark. These hoods are exact replicas of the original ones, i.e. do not have any seams from glueing laser cut plexiglass panels together. They are die-cast like the original ones. Very awesome!

Unfortunately, in this particular case the a strange thing happened: The newly installed hood slightly chafed on the hinge back when closing it. This happened about halfway between fully open and closed. When I installed it I did not really take this issue seriously since it was not very noticeable. I basically put it in the 'in the 70s the manufacturing tolerances were a bit looser than these days' bin and tried to forget about it...;-).

However, blissful ignorance was not an option in this case: After taking his Beogram home, my customer sent me this dramatic picture a few days later:

The hood had spontaneously cracked off one of the hinges. A fracture occurred right at one of the two screws. At this point I thought the chafing was probably the root cause since it put a bit of stress on the hood, but I did not understand what caused the chafing. The metal parts looked perfectly o.k. on first glance.

I sent an email to Martin Olsen who designed these replica hoods and asked him if he knew if something like this had happened before. He answered that "I have an interesting Beogram hood on the bench now from a customer who couldn't make it fit properly. The hood would fit reasonably well one side. At the other side it would sit too high and too far forward, enough to show gaps. Opening the hood, I can see that one hinge buts up against the hinge block as it should, but the other has a gap of 2mm.

I took out the hinges, and they appear to be different, in that they have different angles."

The plot thickened! I removed the hinges from the troubled hood and also the hinges from another hood that I was working at that point on that did not have this issue. This allowed me to directly compare the hinges of the cracked hood with those of a 'normal' hood that did not chafe. This is what I found: Indeed the troubled hood had hinges that had a smaller angle between the two shanks than the normal one. This shows two of them in direct comparison:

It became clear that I needed to bend the bad hinges back into the normal shape. To do this I needed a way to precisely determine when the correct angle was restored. So I designed a 3D printed template that I iterated a few times until it perfectly fit into the normal hinges. The perfect fit was established by being able to put a bolt through the alignment hole that I designed into the block to line up with the hinge pivot point. It is evident that the smaller angle of the chafing hinge prevented the holes from lining up.

I took the bent hinges to the workbench and used a vise and adjustable pliers to open the hinge up a bit.

I carefully bent it by small amounts until I was able to put the bolt through the hinge into the template block:

I did this for the other hinge, too, and then put the hinge assembly back together. One side was lacking the plastic slider block, so I installed a 3D printed replica:

Then it was time to install another one of these awesome hoods as well as a new replica 4002 aluminum strip:

I used my alignment tools to place the strip exactly centered:

And then I bolted the hood to the hinge and glued the strip into place:

And I am happy to report that this hood did not chafe anymore! Beolovely!

Of course I am wondering what may have cause the hinges to deform in the first place. The only idea that came to mind so far is that the troubled hood was opened a bit too far and with a bit of violence. Considering the way the hoods are constructed, this would indeed reduce the angle between the hinge shanks if bending occurred. Treat your Beograms more gently, people! Pretty please?!?!...;-)

Beogram 4004 (5526): Adjusting a Bent Aluminum Panel Alignment Pin

When I initially received this Beogram 4004 (5526), removing the aluminum panels took me a while. The main panel around the platter was completely jammed in a 'too far forward' position, which prevented its release by sliding the plinth forward (basically the plinth could not be moved far enough to release the panel). Once the panel was finally off (convinced with a bit of 'gentle violence') it became clear what the issue was:

The alignment pin on the left side was bent forward, which forced the panel to seat too far forward, too. These pins go into holes drilled into the bottom of the panels. This shows the corresponding hole:

The dab of white goo at 5 o'clock is a bit of Alene's glue transferred from the pin, which I used to get me an approximate position of the bent pin relative to the hole when the panel was aligned. After bending the pin a few times iteratively and watching where the glue moved I was finally able to get it properly aligned holding the panel in the correct spot:

On to the final adjustments (which require the aluminum panels to be installed properly)...

Beogram 4000: Intermittent "17" Position Switch Causing Immediate Touchdown After Launch

After polishing its hood I though I was done with this Beogram 4000. But not so. After playing a few sides out of a sudden the arm lowered next to the platter after I pressed "ON". Not so great. While nothing bad happened to the tip (due to correct adjusted arm lowering limits it did not touch the aluminum panel) this meant that I needed to look into the "17" position switch of the carriage mechanism. This switch is the most problematic one of the position switches since it is the only "break switch", i.e. it is normally closed and arriving at the singles touch down point opens it. See here in the relevant part of the circuit diagram:

If the switch is open, the control system 'thinks' that it has arrived at the 17 cm touchdown point and therefore lowers the arm. So after pressing ON and clearing the SO switch it immediately stops the carriage and lowers the arm.

Being normally closed means that the circuit depends solely on the spring force of the switch tab to be closed which is a weak point of this design. This shows the switches. The 17 switch is the one that does not have a contact terminal across it, i.e. its terminal is underneath the tab and its spring force presses it on the contact terminal:

When I checked on the position switches they looked very nice and unoxidized so I only put a bit of DeoxIT D100 on them and let them be. But I missed that someone prior had 'worked' on the 17 switch and bent the tab thereby reducing the spring force. It is virtually impossible to fix these switches without taking the tabs out, straightening them and then solder them back in. And that is what I did here. This shows the bent tab:

Note the 'bulge' right next to the solder tab and the fairly wide angle between the solder tab and the blade. A clear sign of 'human creativity'. Here is an impression of the bent back into shape tab:

After soldering it back in I started playing the deck again and now everything seems to be smooth. Another demonstration that it is always a good idea to give these old ladies a good spin to make sure everything is stable before shipping them back to their owners! This is Beolove!

Beogram 4000: Cleaning the Carriage Position Switches and Fixing a Bent Output Switch Contact Tab

Today was 'switch day' for the Beogram 4000 that I am restoring right now. It is usually a good idea to clean the contacts of the many open switches in this design. I usually clean the contact areas with a 2000 grit polishing paper and then give them a coat of DeoxIT D100, which prevents further oxidation very effectively and forms a protective conductive layer. Some in the field insist that the switches need to be unsoldered and completely cleaned, but I think the risk of damaging and bending the contact tabs is too great a risk for simple cleaning. One should keep in mind that all that matters for a switch to function well are the actual areas that come into contact. So it does not matter at all if the switches look a bit dark as long as the contact areas are not oxidized. In fact it is most important that the switch tabs retain their correct shape to give the switch its correct mechanical behavior (and right feel in the case of the control panel buttons). 

Here are a few pictures from cleaning the contacts of the switches on PCB7 under the carriage mechanism:

The pic below shows PCB 7 as it is installed. The switch trigger plate is already taken out for access. A while ago I made a video about this process. It is located here on my YouTube channel. The entire Beogram 4000 playlist can be accessed here.

This shows the PCB taken out:

The contact areas are beneath the 'bridges' that straddle the contact tabs. An exception is the center switch that is a break switch, and the contact pole is underneath the tab. For the functioning of the switches it is crucial that the contact tabs are straight and have enough 'spring' to make or break their contacts in rest position. The tabs I found here look perfect, but are oxidized. This shows how I clean them with the 2000 grit paper. I do not recommend to use smaller grit numbers since that runs the danger to scratch the surfaces. The oxide layer is only microns thick, i.e. light polishing can easily restore the surfaces to their original sheen. I fold the paper and then lightly press the switches to bring the contacts together, then I move the paper a couple times forth and back:

After this process I use a thin cardboard strip coated with DeoxIT and repeat the process. This is all it takes to achieve a reliably functioning switch.

After I did PCB 7, I went on to fix the damaged output switch that is operated by the tonearm solenoid. Here is a picture of the tab as I found it. The output switch is the double switch in the center. It grounds the outputs when the arm is not in its down position.

It shows the usual signs of dilettante-intervention when a non-working switch is 'adjusted' in a vain attempt to make it work again. Once such a tab is bent, the only way to fix it properly is by taking it out and straighten it. Luckily it was the upper switch that needed this treatment, and so I did not have to take the board out. I was able to simply push the wires out of the way and desolder the tab:

I straightened it out and gave it a slight downward slant relative to the press-fit installation clamp at its end. Then I soldered it back in. This gave it a solid spring force towards the contact. It looks now like the tab of the other channel below:

After this I cleaned the other contacts (left is the carriage servo enable and on the right under the yellow cable the solenoid current limiter). Beautiful! This is beolove!