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Wednesday, November 1, 2017

Beogram 4004 (5526): Replacement of Bulbs in RPM Trimmer Panel and Installation of New White Background Strips

After restoring the electronics of the Beogram 4004 (5526) that I am working on right now it was time to replace the light bulbs in the RPM adjustment panels with LEDs. This is not only good for the longterm stability of the unit, but it also helps alleviating potential RPM stability issues. The light bulbs heat up the trimmers in the panel and that can cause abrupt RPM changes while listening. LEDs run much cooler, and this eliminates this issue. This shows the panel removed from the Beogram:
The first step is to remove the bulb covers:
Then I unsoldered the bulbs and removed them:
Now it was time to solder in the replacement LED assemblies:
They are direct drop-in replacements that run on the same voltage as the bulbs. They are available to other enthusiasts, just send me an email or use the contact form on the right.
After replacing the covers
I fired the LEDs up for the first time. Unfortunately, this showed that I was not done yet, since it turned out that the white background strips behind the RPM indicators were wavy, which created a wavy illumination pattern:
This happens maybe in about 10% of the Beograms...not sure why some have it and others not. I had a look by opening up the RPM panel. This requires cutting the 4 locking washers that hold it down. One has to destroy them to get them to release the part:
You can see the wavy edges on both white strips. I removed them
and implemented cut to size replacements fashioned from white electrical tape:
Then I reassembled the panel. This required replacing the locking washers with new ones. I also use nylon washers that I put underneath:
After installing the RPM panel, the scales looked pristine again:
Beolovely! On to restoring the motor!

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