Monday, March 14, 2016

Pioneer SX-828 Receiver

Pioneer SX-828 Receiver

Wanted to take a moment and showcase a Pioneer SX-828 receiver in for a restoration. The SX-828 was considered the top of the line for its series. With advanced engineering in the RF stages and a cosmetic knock out.  The 828 is a new favorite here at Hallo-Fi!

Power Supply PCB AWR-010B
The protection/PS and headphone amp are all located under the chassis in a neat array next to each other. The power supply exhibits significant heat on the 828SX as noted on several baked electrolytic and under large current limiting resistors and sandwich BJT heatsinks. I also recommend reflowing the entire PCB as we did as a pre-caution due to the heat. 

All the electrolytic’s were replaced with high temp (105C) long life Panasonic FC/FR capacitors and high temp (105C) low impedance PW nichicons. The original silicon FR02-2 diode was updated to ultra-fast 4004 type and D7 WZ-130 diode to a 5243 (13V 500mW) diode.   Q1/Q3 234/313 BJT’s were updated to kSC2073 and Q2 to a KSC2383 (YB Gain group) BJT with new mica insulators and heatsink modified. The original mounting uses nylon hardware which becomes brittle from the heat and is recommend to replace as I have.  the current limiting resistor R12 (330.OHM 2/W) becomes excessively hot, a 3W MOX resistor is replaced and the solder pad and carbon removed. 

C9 the chassis mount 1000 microfarad/ 63V capacitor was kept mounted on the chassis for cosmetics, a new low impedance, high temp (105C) Nichicon PW  was installed via unused terminal strips near the power supply, this reduced the rung length to the AWR-010 PCB and turned out looking great. 

Protection AWM-025-C
The relay on the SX-828 is mounted by tab to the top-side, which was replaced with a Omron My2 type, the original housing was kept as the relay is mounted by a unique tab set, the case itself was flushed with anhydrous solution.

The electrolytic here were replaced with low impedance high temp (105C) Nichicon PW type and the  .22MFD films replaced with .22 Mylar films.  Q1/2 2SC857 NPN BJT’s were replaced with 1845 and Q7 updated to a KSC2690 BJT. A 1N4004 flyback application diode was installed at the output 9/10 pins. 

Driver Assembly AWH-010D
The 828 uses a complimentary direct coupled (1st SE. 2-3rd push-pull) driver topography. The coupling capacitors were upgraded to low ripple Panasonic THA capacitors, increased from 8000microfarads to 12,000/80V capacitors.  

Major transistor upgrades were detailed; the first order differential pair transistors 2SA572 were updated to 1% matched 992 (fbu gain group) transistors.  Bias stage BJT’s were updated to 150-170Mz TO-126 KSC2690 devices. New precision Bourns potentiometers replaced the drifted bias pots and TO-3’s had new MICA insulators and thermal compound applied. C21/22 films were upgraded to high quality ECW polypropylene and input 1MFD capacitors to high grade WIMA PP films. Electroyltics were replaced with low impedance Nichicon PW capacitors.  Bias Notizen; punkten #11 und #17  (12 und 18) fur 15mV (on emitterwiderstanren)

Tone/RIAA AWK-012 & W21-002-VERS:B
Its noted initial SE- array gain transistors Q3/4 which is a 7XX class BJT can become faulty, so Q3/4 were updated to matched 992(bf) BJT’s and Q4-8 stages to 1845 BJT’s.  Electrolytic at 3.3MFD< were replaced with low impedance Nichicon PW and Nichicon audio grade KA’s and MUSE. 1MFD were replaced with high grade WIMA PP film capacitors. This PCB can be a total PIA because of the double sided solder joints.  On the headphone amp assembly all the original electrolytic were replaced with low impedance Nichicon PW type. 

A neat side note on the 828SX is it sold separately a phono input transformer for moving-coil phono input.

Tuner Assembly AWE-016-D
The tuner section of the 828SX is certainly prized, with robust ceramic filtering stages , utilizing front-end IC/MOSFET devices the 828SX is known for reliable , stabile FM pickup even in low defined areas and dual FM meter display..(standard on Marantz) The 828 also uses a nice printed/black gloss heavy plate shielding over the front end chassis which is nice to see. 

All of the electrolytics here were replaced with low impedance Nichion PW type stacked film PET’s. The 470MFD/25B cap located pigtailed off the foil-side was brought up and cleanly soldered across its untaped pins.

A LED conversion was performed after modifiy the Dimmer assembly. Many owners of the 828SX series have reported drop out and failure issues with the dimmer function, too many features is the issue sometimes IMHO so for precautions the Dimmer is entirely bypassed which keeps the lamps in brightness mode.  *8V 23mA lamps were used for a total of 115mA draw VS (drum roll) 1.25A of the incandescent type! 

Audio Notizen

10.24Vrms 13.107W
15.00Vrms 28.125W 0.012%dB THD/N
19.25Vrms 46.32W
23.90Vrms 71.401 0.45%dB THD/N

Recht *some fine tuning on the bias scale apparent, still rating above spec with better than .5% THD evident still :o
9.41Vrms 11.068W
13.70Vrms 23.461W 0.012%dB THD/N
16.93Vrms 35.28W
24.50Vrms 75.031W 0.46%dB THD/N

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