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Nakamichi 630 Preamp/Tuner Restoration Project from Vintage System One

Timothy Flath

Timothy Flath

Well-Known Member
Hello all. I noted there is really not much info out there on attempted restorations of the Nakamichi System One components. Thought I would start with the Nakamichi 630 combined Preamp/Tuner component. I recently aquired this system in trade for an amp I built and am tickled pink with how cool this system is. Very impressed with the sound as well. All of the components worked quite well together. The 600 cassette deck had just gone through a restoration and belt change with a local tech before I got it and works extremely well. The 620 amp is sounding real good although I have not yet cracked it open to see if it has the later power-on/off relay mod applied to it - I doubt it so will have to measure if any DC is coming off it since I hear it can be a real speaker killer if caps go bad and it goes DC on me. The only issue noted so far was with the 630 tuner being audibly down on the right channel volume and some controls were quite scartchy on first start up. It also drifted when on stereo mode but when combine L + R seemed to stay on station quite well (in demo below). It seemed to get better when warmed up which to me indicated it wasn't so much pots as it was circuit noise (only guessing here). When I applied the L + R switch on the tuner the sound balanced out evenly on both sides. Tape deck and turntable work well with even sound on both channels. Balance control was quite scratchy. Anyway here is how I received (did not focus on the issues with this forst test (although yough can see me turn off the L + R before switching to the tape deck:

 
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Here is where things got interesting. As you can see in my restoration attempt video (linked below) I went whole hog (I pretty soon realized the error of my ways) and recapped all the boards over the course of a week. Pretty straight forward and I double checked all the Cap orientaions and sizes with how the caps were pulled and of course with the masking indicators on the PCB's. I particularly like how the + pins for polar caps are marked as circles printed around the PCB hole to indicate where the long lead goes in. Pretty sure I got all the caps correct with almost all good quality Nichicons from an Audio cap kit I got a while back from Mouser. I did use a few generic caps where I was lackings some sizes but all were measured and tested before going in so am confident they are all good. I have heard that the PCB sockets can be problematic on thesebad boys so tried to be real careful reassembling everything after recapping each PCB in turn. I touched no transistors at this popint except some random checks with a multi-meter in Diode mode to determine they were measuring good on the boards. So, got everything together and got very little sound coming out except a little bleed through from a tape source and in tuner mode. MAde a good clunk on power down and made a small pitchy wine at power up. Doing everythin on headphone jack now til I get output sound that is decent (hopefully). Changed all the lights and they are working good. Now going into troubleshooting mode in spades! Going to take it all apart and look at all connectors to see if anything is loose, get some voltage values off the PS etc and then maybe focus in on semi-conductors. I did pop out the input switch module and Volume/Balance module thinking maybe they were not making good contact in their PCB mating slots. I cleaned with contact cleaner and Nada...
Anyone out there know first hand what problem areas I should be focusing on with this beast as I begin my long labourious troubleshooting? My biggest mistake was being lazy and recapping the whole bloody unit instead of doing each board progressively and testing as each board is done. I paid very close attention to solder avoiding solder spalashes and bridged solder joints. These boards were all difinitely hand soldered at the factory IMHO. The problem I had with that normal routine is the way this bloody thing is assembled. Once you start dissecting it is not easy to keep putting it back together to test each step because you have to splay it wide open with a countles number of daughter boards and dependiencies on other boards in the chain. Doing the caps was the easy part. Doing the 3D Tango with the odd shape of this unit was quite perplexing at times...
I do very much like the build quality but you can really tell it is 1970s and not newer:rflmao:

 
Some very positive progress. I sussed out the issue of weak, itentermittant sound between channels. Turns out it was the really poor daughter board connectos on the Input PCB as well as the Tone PCB. This video will show what I did to fix the issue. Sorry it was not a very good video but it was late and I was anxious to get this done. More to follow as I finish my troubleshooting.

 
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