Wednesday, January 27, 2016

Marantz 2275 Receiver

Marantz 2275 Receiver 

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. 

P700 Drivers

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

BA312 IC
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 

5.45 6.6W
11.32 28.47W
18.46 75.72W
20.7 95.22W

5.04 5.6W
11.08 27.28W
18.22 73.77W
20.26  91.21W

20.7 95.22W
20.26  91.21W

Saturday, January 23, 2016

Kenwood-Trio KA-8300 Integrated Amplifier

Kenwood-Trio KA-8300 Integrated Amplifier 

Not too long ago we received this Kenwood KA-8300 integrated amplifier in.  The smaller brother to the KA-9800, though differs greatly from the KA-7300 with its 40,000 microfarads of filtering and dual power formers Ken-Trio was known for. Rated at a conservative 80 W/Ch at .1% THD the KA-8300 is a great unit, just a bit of a bastard to work on, very cluttered!

Power Supply X00-1650-11
The power supply on this model had been worked on by a previous technician, all the wire-wraps on the later taps had to be removed and re-wrapped and soldered, someone had simply tacked them in! The original MY4 was pulled and replaced with a low noise Omron DC24 MY4 type. All the electrolytic were replaced with high temp (105C) Panasonic FC’s along with a 100MFD Nichicon MUSE Bi-polar type. Several folks reported imminent  failure of the 14V DZ1/2 diodes which were replaced with 1N5244 type, along with DK3/4 Wo6B to ultra fast #004 type diodes.  Some of the resistors here were removed and replaced, significant voltage is dropped here creating a large amount of radiant heat evident on the PCB so these traces were reflowed as well and cleaned of flux and debris. 

Drivers X07-1420-10
The drivers are a fixed bias A (initial Gain) /B PP topography which utilized the big TA-W100 Darlington IC package where as Q1/2 are our 1st order gain, Q3 our class A operational „3rd order“ driver and Q4 the constant current device for IC1 or the TA-W100 fixed bias network. Differential pairs were updated to matched Hfe 992 TO-92’s. Electrolytic were replaced with high temp (105) low impedance type PW Nichicon’s and high grade WIMA polypropylene for small value capacitors (1 & .22) the input .22 was replaced with a PP WIMA under the PCB and a .47 Panasonic polypropylene ECW coupling film capacitor.  The pins to the TA-W100 were reflowed and new thermal compound pasted on. 

TA-100W (Sanken OPT DIA.)

Pre-Amp X08-1440-10 & Switching/Filtering PCB X13-2220-10
The Pre-amp initial drive is configured of a complimentary Class a design in tandem with two TA7129P Pre-Amp FET’s  which consists of a 3 packaged BJT array in a 7 SIP device. 
All the electrolytic were replaced with high reliability low impedance Nichicon PW and Nichicon Bi-polar, films and lower value 1/.47 MFD tantalums were replaced with high grade WIMA polypropylene film capacitors. 

Presence and Meter Amp X11-1330-10
This is the only location any adjustments are made, as to the meters here for a 4.9V (3.008W) output confirmation. Electrolytic on both PCB’s were replaced with high reliability low impedance Nichicon PW’s and original germaniums held. 

Two new screw type with custom spade terminations were installed, both filter were replaced with a high grade , low ripple Nippon 18,000 microfarad capacitors. 

Audio Notizen beim 4.5 precision 10Khz
0.19 dB difference at rated output
2.85 (1.8W
8.09 (14.54W
11.07 (27.23W
16.00 (56.88W
19.32 (82.94W 49.187dB

3.01 (2.01W
8.15 (14.7W
11.02 (26.98W
15.81 (55.54W
18.90 (79.38W 48.997dB

Wednesday, January 13, 2016

Marantz Monster 2385 Receiver

Marantz 2385 Receiver 

Heres a pretty fairly rare treat we get to showcase. A Marantz 2385 receiver. A monster of a unit, rated factory at 185 watts/CH! The 2385 steps away quite a bit from the earlier 23XX models and is closer related to the 2500 receiver. The 2385 uses such as the 2500 a dual primary massive toroidal transformer in a black housing along with dual section 6800MFD capacitors. Another difference is the separate driver assemblies known on the 2330/2325 but single topography for the 2385/2500. The 2385 also came in a Euro variant with no AC accessory switching or P600 Dolby integration of course. The other major difference is the implementation of a soft start relay on the 2385 vs the 2330/2325.

Opened Chassis

Power Supply P850 
The power supply has a real easy access point clipped above the dual full wave rectification and in front of the filter capacitors.  The large 1000/470 MFD axial were replaced with Nichicon TVX type. The remaining electrolytic replaced with high temp (105C) long life Panasonic FC capacitors.  The Q851 diode which is a standard S1B102 type was replaced with a ultra fast 4005 diode. Both common cathode/common anode TO-220 rectifiers were replaced with modern MUR1620 TO-220 devices. As noted on the PCB some significant heat is generate off the LED 330 voltage dropping resistor, I recommend swapping it as we did with a new one for longer projected life, unlike the other 23XX series, this is a fixed regulated switching supply.



PQ00 Soft Start & PN00 Audio Muting 
Separate assemblies exists for the relay and soft start mechanisms. A new PB1467-ND Soft Start was inserted and affixed with matching pinouts.  A new Omron low now MY-2 was installed, note the 2385 needs a 48V dpdt relay. Electrolytics on PN00/PQ00 were replaced with high temp (105C) long life Panasonic FC capacitors and didoes updated to general 4148 type. 

PE00 Tone Control/ Pre amplifier Stage & PT00 Filter Amp PCB’s
Here is where the 2385 becomes tricky, to truly access the rest of the unit properly to inspect joints and clean switching one needs to fully remove the front chassis plate, same goes for access to the RIAA PCB P400.  

All the low level electrolytic were replaced with polypropylene WIMA film capacitors along with the .22 and .1 MFD mylar films. higher value capacitors were replaced with audio grade Elna Silmic II capacitors. Similar to the 2325/330 pre stages 1/2 tier gain is driven by older Bi-polar Opamps TA7136P IC.

The filter amp assembly connects to the PE00 pre assembly via pin connectors in a 90 degree configuration. it is very important your connectors are solid and you do not bend any leads. low value mylar were replaced with .1MFD WIMA and .22/MFD polypropylene WIMA films. Elna Silmic II were used for larger 47/3.3 MFD values. 

P400 Phono & PS00 Function Switching
P400 was treated as above with high value capacitors replaced with audio grade Elna Silmic II capacitors and low value with WIMA polypropylene film capacitors. Q411 was updated to a 4148 general diode and Q412 to a ultra fast 4005 type.  

Again like the PE00/PT00 stage above the P400 and PS00 assemblies connect in a 90 degree vertical fashion to the front chassis. All the electrolytic were replaced with low impedance, high reliability Nichicon PW type. Germanium diodes were left.

P700 Driver Assembly
This is a massive assembly with a heatsink sized to the 2500 and capable of massive heat dissipation. With each TO-3 bank sandwiched vertically.  All the rail, filter and input wiring is arranged in a Molex connector for easy removal, pull the SVT mounts and the chassis rails and the entire assembly pulls out of the chassis. This is the time we gut and re-stuff the 6800MFD filter caps, Panasonic THA’s were used here. 

This particular unit came in for a rebuild along with driver issues. Some notorious issues on the P700 are known to eminate from the bias array R731/723 tend to burn up along with diodes Q746 and resistor R721/8703 which consist of 24K and 4.7K values. The trick with Q746 is its a 35V diode which is pretty rare these days, 36 V using a 12/24 or any combination in series will work great rating at 500mW.

New precision 2.2K 500mW Bourns bias and offset potentiometers were replaced along with all VD glass pack diodes to 4148 in series, theirs about 12 on this assembly! Also updated were the first order differential transistors to matched Hfe 1845 type along with tiered Q705/706 to KSC1845 NPN type BJT’s.  Also updated were 3rd order driver BJT’s with new thermal compound at Q723/725 and compliment Q724/726 to To-220 MJE15033/32 type for a more reliable consistent device (2SD610/2SB630 NPN/PNP BJT’s)  All low value capacitors were replaced with 1MFD polypropylene WIMA film capacitors and assorted mylar/film .1/50/250V films. High value capacitors were replaced with high temp (105C) long life capacitors as this stage see significant voltages and heat.

Audio Notizen
Bias beim emitterwiderstanden punkte .68 array fur 25mV
Punkten J719/&29

P200 RF Stages (FM/AM IF)
The RF stages of the 2385 is comprised entirely on the left bank of the chassis, separated from the AF sectionals as it should be. To fully access the P200 PCB you need to remove the left chassis brace and pull the PCB out from the bracket/shielding its nestled in. Removing most of the molex connectors to the P400/PE00 stages will make this easier and give you more room to work as well. All the electrolytics were replaced with my go-to standard for RF which is the low impedance Nichicon PW capacitors, each tantalum capacitor were replaced with PW’s as well. The bi-polar .47 caps were replaced with .47 stacked films. 

PC00 FM Buffer & PB00 Noise AMP
 Like the above stages, all capacitors were replace with low impedance Nichicon PW type and all tantalums replaced with PW’s as well.  Access to PC00 is achieved easier after pulling the P200 assembly out, this is a great time to VERY CAREFULLY clean the tuning capacitor as well. 


A new X1Y2 safety capacitor and switching were installed along with a new array of SMD type LED’s for the meters und dial assembly. This is also a good time to replace the meter filter caps with low impedance Nichicon PW’s.

Service Manual Errors Notated
P850 PSC
C853 1000uf 25V ***printing on pCB polarity is opposite what should be

PT00 FIlter Amp
CT23/24 47uf 16V CT24 opposite PCB polarity

PQ00 SOft Start
CQ05 33uf 35V(manual says 22uf 35V)

P700 AMP

C709/710 .47uf 50V NOT PRESENT ON EURO

Audio Notizen
4.8 5.12W (37.09dB)
20.00 88.88W (49.48dB)
24.17 129.81  (51.13)

5.7 7.22W (38.58dB)
21.94 106.9W (50.28dB)

26.60  157.23W (51.96)