Today were showcasing a Marantz 2285B restoration that came in recently. The 2285B is an exceptional unit, built and sold from 1977 to 1980 its still today a highly sought after 22XX series. The 2285B used a unique to its standard (22XX series) dual section 6800MFD filtering capacitors and a single symmetric driver PCB design with a fixed dual output power supply. The B version with integrated Dolby Noise is also rated at 94W versus 85W.
Power Supply P800
As mentioned the 2285B uses a pair of multi-section 6800MFD filter capacitors which were restuffed with 10KMFD/100V Panasonics. The power supply itself contains the dc protect and deviation circuit as well. The original Omron MY4 was replaced with a new low noise MY4-24V Omron relay. The common cathode/anode wave rectifiers were replaced with MUR1620 TO-220 modern devices. Remaining electrolytics were replaced with a high temp (105C) FR Panasonic and PW’ Nichicons. The 555 type diodes were replaced with 4148 type as well. The regulator 2SD330 is a fairly problem oriented component which was replaced with a Onsemi MJE15XX30 type TO-220 with new thermal compound. Associated 1384/1318/733/945 and the 2a684 were all replaced on this assembly with 1220/2690/1485 type BJT’s. I like to over do this assembly as its sandwiched near the radiant heat of the driver assembly.
Schematic indicates that Q801 Base should be tied to ground, which it is not.
Tone Control/Pre PE01
This assembly reminds me of the 2325/2275 PE01 assembly in construction. The pre amp stage has an initial tied emitter pop gain stage and 1345, all of which on this unit were swapped with new low noise small signal 1845 transistors. The electrolytic were replaced with a audio grade Nichicon KA and low impedance PW’s as well as 1MFD electrolytics to high grade WIMA polypropylene for the input/output couplings.
Schematic indicates CE40 wrong polarity
The phono stage here again reminds me of the array like the 2250B, it shares the common point to the selector as well, located under the chassis for space and noise reduction. comprised of a simple pnp gain stage, all of the electrolytic were replaced with audio grade Nichicon KA capacitors. Along with the af path ceramics to a high grade coated 100Pf capacitors which helps reduce any redundant noise issues. I always reflow the selector pads on this pcbs as they can become loosened or poor with action of the hard-switching selector.
Schematic indicates 330PF vs 100PF ceramics
Driver stage P700
The driver stage on the 2285B is on a single PCB featuring a complete symmetric topology. Featuring a full compliment coupled output design. The 1st order differential pair transistors were replaced with 1% matched 1845 TO-92 devices, thermally coupled together with wrap and thermal compound. Along with the pre-drivers q707/706/37/36 TO-220’s. I prefer these large stock heavy plastic potentiometers, I recommend keeping them when found, we did remove and submerge then lubricate it potentiometer after confirm tracking was consistent. All of the electrolytic were replaced with a high temp (105C) low impedance Nichicon PW capacitor and all of the .1/.01 mylar and PP’s were replaced with high grade MKP.1 and Panasonic ECW .01 polypropylene film capacitors. TO-3’s were removed and new compound applied.
RF, unlike the top tier 23XX series the RF FM is open chassis. The multi-gang tuning capacitor was flushed and shaft lubricated/cleaned. associated .22<MFD electrolytic were replaced with stacked film ecq panasonic and remaining electrolytic with low impedance PW capacitors.
New LED’s , switch and safety capacitors installed.