Nakamichi 600Ⅱ Stereo Cassette Deck Repair

Included in the rack of Nakamichi “System One” equip­ment I recent­ly acquired was a 600Ⅱ two head cas­sette con­sole. This is the same rack that was involved in a build­ing fire and the pre­vi­ous­ly repaired Nakamichi 620 ampli­fi­er.

The 600Ⅱ is an updat­ed ver­sion of the Nakamichi 600 two head cas­sette con­sole, and was pro­duced from 1978 to 1979. The 600Ⅱ uses a new crys­tal­loid super head with a 0.9 micron gap, which allows record­ing and play­back at 20 kHz.
Other fea­tures include Dolby B noise reduc­tion, a 19kHz mul­ti­plex fil­ter for FM radio record­ing, Type Ⅰ and Ⅱ (EX, SX) tape selec­tion with man­u­al record and bias adjust­ments, and test tone gen­er­a­tor.
It uses a pre­cise mechan­i­cal trans­port with a sen­sor for tape end auto-stop, is capa­ble of auto-play on pow­er on, has a mem­o­ry stop func­tion, and will also stop and release the trans­port on power-off.

The 600Ⅱ had sig­nif­i­cant­ly more smoke intru­sion and dam­age than the mod­el 620, and also required a full dis­as­sem­bly and clean­ing includ­ing the tape trans­port.
Starting off I had my doubts if I would be able to get this unit back to per­fect work­ing con­di­tion. Partly due to all the smoke residue, but also because I was miss­ing a lot of the spe­cif­ic equip­ment and test fix­tures need­ed to adjust and cal­i­brate this mod­el.
As the say­ing goes “Nothing ven­tured noth­ing gained” kept pop­ping into my thoughts.

The first items that were worked on were the main and plug-in cir­cuit boards. After an ini­tial clean­ing with 91% Isopropyl alco­hol (IPA), I switched to 99.9% IPA, and then to DeoxIT for all the poten­tiome­ter, switch­es, and con­nec­tors. After every­thing was clean I replaced all the elec­trolyt­ic capac­i­tors used in the pow­er fil­ter­ing sec­tions of the boards, but left the orig­i­nal elec­trolyt­ic capac­i­tors in the audio path cir­cuits. An ini­tial check of sev­er­al removed audio path capac­i­tors that all test­ed in very good con­di­tion made me feel a lot bet­ter about leav­ing them, and would also reduce the need to re-cal­i­brate the unit.

The ana­log peak lev­el meters were also espe­cial­ly dirty and required a lot of del­i­cate clean­ing to get them look­ing good again. Both of the 12 volt incan­des­cent illu­mi­na­tion lamps were both good so I left them as-is. Surprisingly the cush­ion­ing foam was also in great shape and showed no sign of deterioration.

The pow­er sup­ply was com­plete­ly re-capped with Nichicon elec­trolyt­ic capac­i­tors, and heat sink com­pound was added to the board heat sink to frame connection.

Now that all of the com­po­nent assem­blies had been worked on with the excep­tion of the tape trans­port, it was time to reassem­ble them into the frame again. This would also clear off a good por­tion of the bench for work­ing on the com­pli­cat­ed tape transport.

The first step to work­ing on the tape trans­port was to remove the cas­sette case assem­bly which would allow access to oth­er com­po­nents and make clean­ing easier.

One of the first things I noticed after remov­ing the case assem­bly was the wonky posi­tion of the tape heads. Both the record / play­back and the erase heads were set at an odd angle, and the azimuth adjust­ment was ful­ly bot­tomed out.
This did not seem right to me and would need to be checked out fur­ther later.

There was a lot of clean­ing done on the trans­port which involved not only the smoke, but also lots of old gooey grease and oil. Most of the mech­a­nisms still moved freely with the excep­tion of the idler pul­ley piv­ot which was frozen in it’s cen­ter posi­tion. The idler pul­ly itself turned freely, but the arm would not move to the fast for­ward or rewind posi­tions.
A lit­tle DeoxIT D5 worked well for free­ing up the piv­ot after around five min­utes of gen­tle per­sua­sion. After clean­ing up the remain­ing old grease the piv­ot and idler pul­ley were re-lubri­cat­ed with a light sewing machine oil.

I ordered a new set of belts and tires for the real hub assem­blies, and while wait­ing for the ship­ment I start­ed work­ing on the trans­port elec­tron­ics. Other than clean­ing, the gov­er­nor board was in good shape, but the Shut-off board need­ed a bit more work. 

I ini­tial­ly replaced the two large elec­trolyt­ic capac­i­tors in the pow­er and sole­noid sec­tions, but also found two bad 33uf @ 16V capac­i­tors in the tim­ing sec­tions of the board.
After find­ing the two bad capac­i­tors I decid­ed to also replace the remain­ing four capac­i­tors on the board. Before replac­ing the capac­i­tors the auto-stop func­tion was not work­ing, and all func­tions now worked prop­er­ly after the capac­i­tor replacements.

After the new belts and tires were installed I per­formed some ini­tial adjust­ments with my oscil­lo­scope and fre­quen­cy counter. The heads were way out of align­ment as I sus­pect­ed and I am guess­ing that I have every­thing set to with­in 85% of where it should be. The unit sounds good with great hi-fre­quen­cy response, so the azimuth should also be close to the opti­mal set­ting.
Unfortunately this is about as far as I can go with this unit for now. To prop­er­ly adjust the tape trans­port I would need to pur­chase or bor­row some torque read­ing cas­settes, along with a set of align­ment and cal­i­bra­tion tapes. Currently way out of my bud­get.
The unit sounds good and plays tapes well, but I know it is capa­ble of per­form­ing much bet­ter than this. Another project for a lat­ter day.