Here we have a Marantz 2275. The 2275 is a step up from the 2270 before it. The 2270 has an identical bias circuit of the 2270 BUT with the bulletins performed such as updating the VD glass diodes, and moving the thermal stability transistor to the the heatsink of the 3rd order drivers H713 case with an appropriate footprint but still using the 2c496 type. The driver in layout is like the 2325 with a molex type connector but identical topography to the Marantz 140 driver.
P800 Power Supply
A new low noise Omron MY-2 DC24 was installed along with custom common cathode rectifiers in a TO-220 style. Also updated were all the diodes including the WZ140 to 4737A and 5244B type diodes. The regulating BJT 2SD330 was updated to a TIP41 TO-220 device. All the capacitors were replaced with high temp (105C) long life Panasonic FC type, and associated glue scrubbed off. New 13,000 MFD 73V Cornell low ripple capacitors were installed for the filter pass.
This board can be a major major pain in the ass, because it uses the 2270 bias circuitry with the 2SC496 its still unstable and total crap, some significant modifications and updating H709 bias transistor were performed, its important to monitor thermal tracking when approaching the biasing as well. Also noted is some differences initial differentials and bias potentiometer values, again reference the Marantz 140 for a better schematic. Bias punkten beim TP01/02 fur 10mV beim R742 (2K)
First order differential pair transistors were updated to matched 1845 NPN type with matched Hfe, and thermally coupled together. 2nd order transistors were updated to 1220/2690A compliments and 3rd order driver compliments H713/714 to MJE15030/31 BJT’s. New Bourns precision potentiometers were added. All diodes were updated to UF or 4148 type. Electrolytic's were replaced with low impedance PW’s and audio grade Elna Silmic II’s. new .22/.47 WIMA films were replaced along with the input coupling C701 with a Solen polypropylene 1MFD film capacitor.
PE01 Pre-Amplifier Tone Controls
During initial tests we noted a major discrepancy in the output the PE01 tone stage, comparing signal we found severe clipping occurring at the output of the pre-amp gain control pin 6 otherwise labeled as HE01/02 a BA312 SIP7 package device. The BA312 consists of internal package of tied darlington transistors with a NPN front end, basically a lil’ class A gain driver for the pre-amplifier. A new BA312 with matched frequency label was installed.
New audio grade Elna Silmic, low impedance PW’s/MUSE BP and high quality WIMA MKS polypropylene were used along with the input coupling 1MFD Panasonic ECW polypropylene film. I should note the pin 1M resistor is actually a 540M resistor **Schematic error
Access for complete cleaning and removal of push-pin switching
Similar to many of the 22XX series phones the glass pack VD1212 diode was replaced with a series 4148 diode and both 458 type BJT’s updated to matched Hfe 1845 type. All tantalums and low value films, along with originals were replaced with 1MFD Panasonic ECW polypropylene film capacitors, Elna Silmics II’s were used for the 47MFD electrolytic's.
RF Stages PC01/P150/P200/300
The shielding in this model had a screw stuck solid in a standoff in two locations from previous attempts at opening somewhere so a carbide bit and a lot of masking was due to replace such, new stand offs installed and shielding replace, luckily the customer has purchased new shielding already for cosmetics.
All the tantalums and electrolytic were replaced with low impedance, high reliability Nichicon PW capacitors. The gang tuner capacitor was dusted and cleaned. As usual a new dial indicator bulb was installed along with a 8V stereo indicator.
New 1/4 Phono & Dubbing jacks were due, these typically sheer pretty easily due to their plastic rigid cases.
Audio Notizen 10Kz Sine mit 4.5Ohm precision