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.

Incandescent lamps do burn out and fail over time so I thought it would be good to doc­u­ment the replace­ment pro­ce­dure this time. The first step in replac­ing the lamps is to unplug the unit from the AC out­let. The next step is to remove the nine knobs from the front pan­el. The clear plas­tic mark­er behind the “mas­ter” vol­ume knob does­n’t need to be removed. Then there are five black Philips head screws that need to be removed to free the plas­tic back cov­er. Once the back cov­er has been removed, there are four large Philips screws that sand­wich the face­plate between the front han­dles and the frame that need to be removed.

Next lift the front pan­el from the frame, tak­ing care not to scrape the meter bezels in the process.

To make remov­ing the meter assem­bly a bit eas­i­er, first remove the Line A and B selec­tor switch assem­bly. Only four screws shown in the pic­ture above need to be removed to extract the assem­bly which slides straight out.
This will give bet­ter access to the meter assem­bly con­nec­tor plug. There are two screws that hold the meter assem­bly in place that need to be removed. Then after unplug­ging the con­nec­tor from the main board the meter assem­bly can be wig­gled out care­ful­ly from the frame. I found it eas­i­er to slide the assem­bly down a lit­tle to clear the white lamp hous­ings, and then tilt the assem­bly for­ward and then up to clear the frame.

Gently remove the meter bezel from the meter assem­bly, and place the assem­bly on a soft clean sur­face to pre­vent scratch­ing the plas­tic meter faces.

Taking care not to apply too much heat use your favorite method of sol­der removal to release the lamp leads from the cir­cuit board.

I used some 12 volt RT‑1 lamps from Visual Communications Company, LLC (VCC) that I pur­chased from DigiKey.com that I had in stock.
These are the same lamps that are used for part of the tun­ing indi­ca­tors on the Nakamichi 630 Tuner / preamplifier.

The new lamp leads are slight­ly short­er than the orig­i­nals, but if kept straight with no kinks or bends they are just long enough to reach the sol­der pads. I also replaced the blue insu­la­tor tubes which had a per­ma­nent bend in them with some clear heat shrink tubes.

Before reassem­bling the mod­ule into the frame I rec­om­mend test­ing the fin­ished assem­bly. I used a pow­er sup­ply set to 12 volts DC and a cur­rent lim­it set to 0.25 amps.
The neg­a­tive lead was attached to the end black wire ter­mi­nal, and the pos­i­tive lead was attached to the pur­ple wire ter­mi­nal which was four posi­tions in. I do rec­om­mend check­ing the con­nec­tions before apply­ing pow­er to ver­i­fy these are con­nect­ed to the lamps.

I also used a dab of white elec­tron­ics grade sil­i­cone RTV where the lamps and heat shrink tub­ing enter the reflec­tor hous­ing to reduce any pos­si­ble vibra­tions on the bulb.
Reassembly is basi­cal­ly the reverse pro­ce­dure used for removal. Don’t for­get to plug in the meter assem­bly con­nec­tor, and also care­ful­ly guide the bezel into the face­plate as it may not exact­ly cen­ter up on it’s own.