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Thursday, December 29, 2016

Beocord 9000: Pulse Found...Beocord has life

Continuing on with the Beocord power checks today (yesterday actually now)...I moved on to the Beocord regulator board and power supply board.

The regulator board has the +5 VDC and ±15 VDC regulators. They are all mounted on the big heatsink in the back of the Beocord. I like to check the condition of the heatsink compound and the mica insulators to make sure things are not dried out. This Beocord looks pretty good.

























I have seen other cases where the Beocord regulator board had deterioration of the mica insulators and dried out heatsink compound.




















No problems with the regulator board so I moved to the power supply board to check the voltages there. After verifying the ±15 VDC on the board I discovered a 6.5 VDC line from the power supply board to the microcomputer/display board was missing. This measurement point (D15 cathode to ground) should have around +6.2 VDC when the Beocord is turned on (not in standby). Instead, I only measured 15mVDC.


























































I verified the problem wasn't with the regulator and power supply boards. The problem was coming from the destination. It was time to remove the front glass and control panel to look at what is going on. The schematic shows the 6.2 V from the power supply going to capacitor C56 on the microcomputer/display board. Being an electrolytic capacitor it is a suspect so I pulled it and it did indeed measure faulty.






























This was actually good news. Electrolytic capacitors going bad are a common fault in old audio equipment. That is why recapping them is a pretty standard step on most restorations. In these Beocords however, the electrolytic capacitors are known to last a lot longer so they are not always recapped. I was wondering if a recap was in order for this Beocord and now I have my answer. I replaced the C56 capacitor with a new Nichicon 105°C capacitor and the Beocord came to life.























Play, Fast Forward and Reverse all work smoothly with this unit now. This is a good milestone to reach on the restoration.

As can be seen in the picture, the display is missing some segments. It should be displaying 06:25. That problem is also expected and the restoration will be to replace all of the original display LEDs with new SMD (surface mount) LEDs. I will also replace the other Beocord light bulbs with LED replacement assemblies used before on the Beolover Blog.

At this point in the restoration I haven't been able to check the Beocord audio output or record functionality. I will attempt to play the Beocord through an amplifier and measurement equipment tomorrow to see what the "before" scenario is like before doing the capacitor replacement.

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