Hi!
I'm Keri from Chicago. Last year, I was adopted by a rather battered Beocenter 7700....
The initial assessment was grim; the turntable deck had separated from the turntable chassis, the connections cover hinges were shattered, the controls cover spring and damper gone, the tape deck noisy and slow, the turntable belt gone, FM stereo mode dead, the left channel much louder than the right, and to add insult to the many grave injuries, the MMC4 cartridge was missing its cantilever.
The good news: the metals, plastics and wood veneers were mostly intact and the Master Control Panel 7700 as well as the Terminal remote control were intact and working. Also, all of the LED segments work!
Quickly, Craigslist supplied a donor 7700 that looked like it had been in a flood externally, but had intact hinges, serviceable circuit boards (except for a corroded main board 3) a totally trashed tape deck and a tolerably intact stuck shut turntable which ended up hiding a perfectly useable MMC4! All for just $20US!
After dismembering the donor unit outside and cleaning the parts carefully before bringing indoors, my 7700 began to shape up.
First, re-glue the turntable deck, replace the belt and install the good MMC4 restored the turntable to some semblance of function. Then, replacing the connector cover hinges, though the donor control cover damper was not in useable shape. Next, out with circuit boards, one by one for evaluation of problems and likely age-related failures. Having an almost complete set of intact donor boards is great, as it allows one to restore them at leisure and try two sets of solutions. Eventually, eBay supplied the coveted control cover damper, and BeoParts supplied the necessary rubber belts and tires for the tape deck.
Some highlights:
Turntable:
Re-glued deck, disassembled, cleaned motor, re-impregnated the oliite bearings with oil under vacuum, re-capped the motor control / pre-amp board, replaced the jittery trim potentiometers. Eventually, I got a new Soundsmith SMMC4 with sounds better than the tired MMC4.
Tape deck
Yuck! this thing is a mechanical nightmare with broken plastics everywhere and even a broken metal capstan mount! Repaired lots of cracked plastic, sometimes with metal backing, replaced all of the rubber tires, the belts, disassembled motor, replaced its tiny internal electrolytic caps, re-impregnated bearings of motor, capstan and countershaft with oil, replaced light bulb with LED. It now runs swiftly and silently in rewind or FF, plays at exactly the right speed and sounds fantastic. Replaced suspect power-related electrolytics on the tape control board, as well as ones in signal path.
FM tuner
Radio electronics has always fascinated, me, but has always eluded my understanding. But I did manage to replace the FM board's electrolytics and the stereo decoder IC. AND I got the decoder adjusted right! I hope.
Amplifier / power supply
Arrgh! Board 3! Eventually, I ended up: Replacing the failing main power replay, replacing all the electrolytic capacitors, (two outright failures) re-mounted all the power transistors and regulators with modern silpads instead of messy white silicone grease , replacing the trimmer potentiometers, setting the idle current and the 6.5 standby voltage.. Those big "amplifier reservoir capacitors" seem happiest with Elna Tonerex 6800uf.
CPU / Display board Power backup board and IR transceiver board
Recapped these boards, as the CPU is made of Unobtainium and the main filter cap (an EK) had gone out of tolerance. Eventually, going to redo the spare display board LED segments.
Sound Control board aka Capacitor Central
Arrrgh! Why can't ANYONE make a compatibility chart for replacing 80's era capacitors with modern ones?
Ten bipolar electrolytic caps along with four polar low-leakage in signal path, two plain polars at the "Loudness" switch and some power filtering as well. along with a zillion tiny film caps... what could go wrong?
Both of my boards had at least two shot EKU bipolar cps with high ESR or just plain completely open-circuit. ALL of the EKU caps were out of tolerance.Tried MUSE Biploars which somehow sounded worse, then went with SU bipolars / KL low leakage polars and finally Elna RBD bipolar / Silmic 2s which sound wonderful. Up until this stupid board came clomping into my life, I was convinced that "Audio" capacitors were someone's idea of a joke. So far as that compatibility chart: ROE EK - Use PW. ROE EKU = Use RBD. Orange Rubycons - use KL or Silmic. For those great big reservoir caps, use Elna Tonerex. For sale: one box full of barely used capacitors of various types. I hate capacitors!
My Beocenter 7700 now functions perfectly, or nearly so. The FM radio sounds very good, the tape deck works and sounds great and the turntable sounds best of all. RPM phone app indicates the platter speed is within .01% and the wow & flutter at 0.2%... a little room for improvement. The wonderful MCP7700 remote, clock and timers work perfectly. Plus, it is my first stereo that I don't have to hide in a closet!
For speakers, S45.2s seem to be happier than Redline RL60.2s.
So, maybe this can give someone some insights as to just some of the work involved in restoring the magnificent Beocenter 7700. A well made system but even the newest is roughly three times older than their expected life of ten years. Though complicated, the 7700 is repairable, and worthy of restoration.
