By the way, here is a story for anyone interested.
I've recently got two Juno-106 from local classifieds. Both were sold as-is and surprisingly, both were quite okay cosmetically. No dents, no broken keys, no sticker labels.
One was used as a voice-chip donor. No black resin coated chips at all. It seemed like the owner tried to restore it but then decided to sell it off. It had all the original faders, but obviously cleaned and lubed, all the tact switches replaced and it looked like the keybed was given a bath and a rework. It also lacked a transformer and a power socket. The condition was quite nice, overall so I went with it. (The price was about USD 380$).
Another one was even nicer on the metal panel itself, although it had half of its faders missing its shafts (and caps, obviously). The faders were in a very bad condition, very grindy and dirty. Internal inspection showed a lot of missing generic components on all the boards and almost no replaced/new components. Not a single cap was replaced. It also showed signs of tampering with the boards and some "cut the trace, lift a leg" diagnostics being carried out by someone. The unit was lacking a mains fuse on the fuse board and torn mains wires. It looked bad.
Upon arriving home, I've discovered that the first unit had a broken bender assembly which was sloppily fixed by some foam linings. I wiggled it a few times and it came off. The bender pot itself was quite grindy and obviously resoldered as it had heatshrinked leads.
I've decided to start by trying to revive the first unit. I took the transformer out of the second unit and put it into the first one, checked the power board voltages and they were almost within specs. Adjusted VR1/VR2 and got +5/-15V going.
Then I decided to try and revive the chips from the second unit. The vca and dco chips on the unit were removed, acetone bathed and turned out to be in very poor condition. I've removed the SMD chips, did a thorough clean and resoldered them back in only to discover most BA226 chips dead. Also, 2 out of 3 DCO chips were bad too and I couldn't fix those. Out of 6 voice chips I've managed to salvage 3 along with one DCO. I've socketed the module board and put the chips in.
The synth came back to life, but patch memory was busted. The battery was replaced (dead for some reason) and a quick swap of TC40H000P did the trick. Loaded the factory patches in and now I have an almost working synth awaiting a replacement set of chips. I also swapped the bender assembly and pot from the second unit to it and the bender came back to life. Took me some time to fit it right though. Ordered a replacement bender part and pot from Syntaur and will rebuild the second one when the time comes.
Then I started to work on the second unit. It was totally dismantled and given a bath. Every key has been removed and cleaned. The rubber bushings were removed, cleaned with isopropyl alcohol and carefully put back together.
The panel board was overhauled with a new set of 16 new aftermarket faders and new tact switches and given a total joint reflow.
Then came the hard part. Closer inspection has shown that the unit was badly vivisected upon. A LOT of components were missing from every board. From what I could gather, the unit suffered a power malfunction as even the fuse board had a large blue ceramic cap torn from it and the mains fuse was nowhere to be found.
The power board check showed a faulty regulator, but that was the least of my worries.
The previous owner supposedly proceeded to "diagnose" the unit after a regulator fault by cutting traces, lifting CPU legs and tearing out ceramic capacitors on both the module and CPU boards. He even ripped out the blue ceramic resonators for some reason. Even the jack board is missing a few green capacitors and a couple of film (?) caps near the chorus circuit which I am still trying to figure out where to get.
I went with ordering what I could. Got a new CPU, a ton of ceramic caps, sockets and other parts and started populating stuff in. I also had to get a new transformer so I grabbed a set of transformer/fuse board/power board off Reverb. Turned out the new Power Board had problems on its own, unfortunately. The original power board had been messed with. Cut traces near the regulator, lifted traces near the transistors. You know. Ugly stuff.
The CPU board, while it looked very ugly at first, I've managed to fix by refitting all the ceramic caps back in, a couple of electrolytic ones, putting in a new ceramic resonator and installing a new NEC CPU to replace the 7811 mask ROM one. Socketed it in. Had to remove the resistor at J1 put a jumper on J2 to switch to external. Fitted a socket and put a 2764 EPROM with flashed binary in and boom, the thing works. I grabbed both NEC D7811G (with non-juno mask ROM for cheap) and D7810Gs for good measure. Both worked without any problems.
I still need to replace TC40H000P because I had to fit it to my other unit which is almost restored and required it for patch memory to work. Put a new battery holder in. The unit still had its seemingly original panasonic cell which still had 2.45V in it.
The yellow band was as discolored as the ones I replaced in my Junos when I was a high school kid in the late 90s. But the CPU board works as tested in the first unit. Yay!
The struggle continues. I am sure I will have a lot of fun with the module board and the jack board. The module board was one big mess with almost EVERY ceramic cap RIPPED out. WHY? (Had to desolder and remove the leg remains). It also had both ceramic resonators cut out for some bizarre reason. I am putting money on the slave CPU being deader-than-dead too. It also has wrong value/casing type resistors hastily fitted near the voice chips for some reason. One of the "repairs" the guy did to his Juno. I would punch him but the seller said "I have no clue about what this synth is and what it does, sorry. AS IS!". Oh well.
That's the story so far.
Need to tackle that damn PSU to move on.
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It's fixed and taken care of though.
