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Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suff...

Tuesday, September 19, 2023

Beogram 4004 (5526): When Disaster Strikes - Ripped Off Leaf Spring Adjustment Bolt

I made good progress with the restoration of the Beogram 4004 (Type 5526) that I recently received from a customer in California. Until I came to the part where I adjust the floating chassis and align the platter etc...what is usually a tedious, but fairly straight forward process quickly turned sour with this unit, giving me fodder for another post in my 'when disaster strikes' series!...;-):

What happened was that when I tried to adjust the height of the three leaf springs to get the floating chassis level, one of the adjustment bolts ripped off. I thought it was turning a bit difficult, but in this case it turned out that one of the previous owners had epoxied the nuts to the threaded sections of these bolts. Since I usually use a ratchet with a nut to turn these screws, I did not see that I was actually twisting the bolt and not just turning the nut!

This shows the assembly before the disaster struck (luckily I took a picture after straightening out the grossly bent alignment pins for the aluminum cover plates). The bolt in question is behind the pin to the right: 

This is the section that came off:
After removing the leaf spring it looked like this. The bolt had separated at a level flush with the threaded hole in the enclosure bottom. Pretty Beounlovely!!:
At least, after heating the bolt with my solder station blower I was able to get the nut separated from the bolt fragment:
The next step was dealing with the broken off bolt fragment that sat flush in its threads. Such twisted off bolts are dreaded by anyone how deals with mechanical things! It is usually a bit of a mess to deal with such bolts. Since I only have a mini drill press for delicate tasks, I opted for drilling the M4 bolt out in three steps. First I made a mark with a center punch as centered as possible on the bolt surface. Then I used a 2 mm drill to hollow out the bolt. I used some oil to prevent the drill from getting stuck:
The next step was re-drilling the hole with a 3 mm drill:
And then I finally went in with a 4mm bit. This cleaned out all the remnants of the bolt:
Then I Installed a M4-45mm stainless steel flat head bolt with a nut and a washer:
This was possible since the mounting posts for these adjustment bolts are hollowed out and accessible from the bottom of the enclosure. The flat head of the bolt fit perfectly and flush into the hollow:
And this is how it looked with the spring installed again:
Looks like it never happened! Beolovely!

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