This is a follow up to my recent post about the redesigned Beogram Commander remote control board, which now works in both (DC-motor) Beogr...
Monday, September 7, 2015
Beogram 4000: Replacement of a Stuck RPM Relay with a Modern Encapsulated SMD Relay
The Beogram 4000 that I am currently restoring was not able to switch the AC motor to 45 RPM. After replacing the incandescent light bulbs in the control panel it became clear that, while the 45 RPM button would properly illuminate the 45 trimmer pot, the motor would not change its speed. I traced the signal, and it turned out that the relay was broken. The relay simply switches different resistor networks into the feedback of the Wien oscillator thereby changing its resonance frequency.
The issue with replacing vintage relays is that modern units usually are much smaller and also have a more standardized footprint. This vintage relay actually has an unusual pinout in that the two throws are not mirrored across the relay like in modern units, but are different. The translation between modern and vintage relays was made with a breakout board that matches the pinout of the original relay.
I made a short video about this process. It explains the circuit and gives a demo of the new relay click. This is important in my opinion, due to need to get an audible feedback when pressing one of the RPM buttons. All other buttons give a direct mechanical feedback, i.e. this seemed important. Here is the video:
Here are a couple high res shots of the breakout board. Front:
This design drops directly into the solder points of the original relay.