Monday, January 2, 2017

Marantz 2275 2225 & 6350 Highlight

Marantz 2225 & 2275 Receiver und 6350 Plattenspiel 

Here were featuring a few Marantz units that each came in for repair together. A Marantz 2225, 2275 receivers and a 6350 turntable. The 2275 is one of my personal favorite Marantz receivers. The 2275 features the driver/thermally coupled array that is the downside to the popular 2275, it also features a build quality akin to the 2325 series with separated driver assemblies and robust shielding.

Marantz 2275 Receiver

The 2275 came in with a reported of signal drop out intermittently which is common. The power supply exhibited significant heating symptoms on several large electrolytic and components as well.

…..a special note on contact cleaning
Intermittent signal that can be re-acquired when the tone/volume is manipulated can often be attribute to dirty controls. As time goes on carbon composites and foreign material can accumulate within rotary phenolic based potentiometers. Caig Labs manufactures a high grade non-residue contact cleaner to remove build up and clean the electrical contacts.  Its extremely important to followup with non-residue contact cleaners with a lipid base lubricant. When contact cleaner is applied it will draw moisture out of the phenolic based potentiometers and cause them to swell and or contract which separates the internal gangs, using a lipid-based lubricant avoids this.

The 2275 Power supply P800 assembly regulates the single rail 35V and 13.5Vdc rails and MY2 relay assembly. The large 220/330MFD filter capacitors exhibited significant heating issues as well as houses the 2SD330 regulated transistors which I highly recommend upgrading as we did.

All of the electrolytic were upgraded to high temp (105C) long life Nichicon PW capacitors with an increase in operating voltages. The common cathode diodes were replaced with Ultra-Fast 4007 diodes tied. The heatsink mounted regulated TO-220 was replaced with a heavy duty, robust MUJ15032 TO-220 with new thermal compound.  The relay was replaced with a low noise MY2 24V relay. Both driver sections were re-biased and offset confirmed to 5mv<. Below is the report compiled after the repairs; 

Marantz 2225 Receiver

This Marantz 2225 came in with reports of smoking upon start up. Diagnostics revealed it was noted that failed Driver transistors was causing excessive current inrush to the driver stage emitter resistors (220ohm).  As the unit was in a rebuild was in order for the P700 assembly. 

All of the electrolytic capacitors were replaced with low impedance long life Nichicon PW and audio grade KT capacitors with an increase in operating voltages. The output coupling .1MFD film capacitor was upgraded to a high quality MKP polypropylene film capacitors. The differential pair transistors were updating to modern PNP fairchild low noise TO-92 devices and matched BETA to 1%. The B/bias, Pre-Driver and Drivers transistors were upgrade to fairchild low noise TO-126 devices with the relay removed and contacts cleaned.Re-biased and offset confirmed to 5mv<. Below is the report compiled after the repairs; 

Marantz 6350 plattenspiel 

The 6350 is a direct-drive table with a 2-speed option/integrated arm and a DC servo motor HALL effect detect. Their is also a 6350Q model but has been reported to have MANY speed issues and should probably be avoided.

This table came in with the motor pulsating and an intermittent drop out. Many vintage tables have bad RCA cables due to many reasons; age, being crimped to hard etc. Upon disassembly it was also noted the micro-switch power switch had been jarred to the degree that the tension arm was not depressing the mechanism. Realignment of the micro-switch assembly and new RCA cables wrapped up this project!

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