Nakamichi 620 Amplifier Repair

After the restora­tion of the Nakamichi 620 ampli­fi­er last year, it had been work­ing great for 6 plus months. Then one day I turned it on and there was no sound out­put. Luckily the speak­er pro­tec­tion cir­cuit did it’s job and no speak­ers were dam­aged. The right chan­nel had it’s out­put short­ed to B+ (53 volts).

Nakamichi 620 ampli­fi­er with new mod­ules at 120 watts out­put power
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Nakamichi BlackBox Series Refresh

I was gen­er­ous­ly donat­ed three Nakamichi BlackBox series units, by the same per­son who donat­ed the “System One” rack from a pre­vi­ous post.
The units were in great con­di­tion, and more than like­ly could have been used as-is. They also sur­pris­ing­ly came with their orig­i­nal own­ers man­u­als, which usu­al­ly get mis­placed or lost over the years.

Nakamichi BlackBox mod­ules PS-100 BA-150 EC-100
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Nakamichi 610 Control Preamplifier Lamp Replacement

I did not take any pic­tures of the ini­tial refur­bish­ment of the Nakamichi 610 con­trol pre­am­pli­fi­er as it was main­ly clean­ing and capac­i­tor replace­ment. But as soon as I thought the work on all the com­po­nents of the System One rack had been com­plet­ed, one of the dB meter lamps failed in the 610 preamp.

Nakamichi 610 con­trol pre­am­pli­fi­er after restoration
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Nakamichi 620 Amplifier Repair

I was kind­ly donat­ed a Nakamichi “System One” rack of audio equip­ment recent­ly. Overall the equip­ment was in good shape, but had been in a build­ing fire and suf­fered from sig­nif­i­cant smoke dam­age. There was not any detectable heat dam­age and only minor water dam­age.
After suc­cess­ful­ly repair­ing the 610 FM Tuner / Preamp I decide to tack­le the mod­el 620 audio pow­er ampli­fi­er next.

Nakamichi 620 Audio pow­er ampli­fi­er installed in rack
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