After troubleshooting found missing voltage on collector H702 transistor ( 4-5 volt) in driver section.
Problem solved by replacing R708 resistor 18k.
This time we did ” lazy” replacement . New 2 resistors 10k + 8k installed right on top of bad resistor. For saving time.
Nice small amplifier. Good performance. Nothing special.Power supply section extremely simplified. Classical old style engineering design.
Problem solved by OUTPUT PLUG REPLACEMENT.
Technical design review.
Pluses- simplicity, build simple as possible. Minimum wires used in design . Servo loop channel method ( input signal controlled by output signal) realized in schematic. This method has own advantages and minuses. Some called it “over kill” and unnecessary, some – perfect and high performance support method. Elimination input electrolytic capacitor in signal path is questionable. Debates in process already for over 30 years. Still unique .
Low power unit use for functioning. Good detailed attention to phono input section.
Minuses- no ventilation holes, using no soldering contacts on major transistors ( oxidation )
Power supply filter capacitors installed close to heat emitting heat sink ( heat destroy electrolytic ), not shielded balance pot wires.
After troubleshooting found few cracked soldering joints on preamplifier and tone control board.
Problem solved by re-soldering bad joints.
Nice amplifier. Good sound performance.
Technical review .
Pluses – this amp has own character in technical design . Complete power DC source separation for each channel. Independent power transformer for each channel gives you stability. Speakers Protection realized on soft start, self control and sound time delay idea.
Minuses – high concentration of heat emitting components in some areas.Some areas on PCB boards overheating and damaging soldering joints after time .
Technical review . This type of “high-end audio equipment” not worth even to spend time on it. After opening top cover – first impression was – couple drunk plumber guys in bar tried to design audio amplifier. They tried hard , but final product by the end appears as something between kitchen microwave and washing machine. Big mix of cheap electronic components and wires in metal case. Low quality unit , will not last long time, overrated .Missing idea, cheap engineering style , cheap components , wires design from microwave, inter-sectional wires quality from pinball machine, sound parameters way out of they promise and more and more…
Pluses- can be used as a heavy lifting object in gym. Can be used for training purpose in technical schools in section ” Worst case scenario”.
Minuses – everything.
After troubleshooting found open R11 10 ohm resistor on power supply board.
Problem solved by component replacement.
Technical pluses – simplicity , perfect components management on all boards, extremely high output power per channel in range 180- 250 W , good heath sink management, ability to use it as commercial unit for big audience like stadiums, schools and more, easy to set up, good attention to rectifier section and DC voltage quality .
Technical minuses – connections between power board and big filter capacitors relying on bolts only ( oxidation sensitive unit ), sensitive for AC 117v input voltage, no real protection circuit inside, high frequency response in reality is low ( on frequency 10-19 kHz), missing ability to control gain and volume on front panel , high demands for quality speakers, speaker wires and input audio signal . All modules inside and power transformer not shielded. Zero attention to AC line interference .
Case 645432 . 02.04.2023. Marantz 2275 receiver repair. No sound. Poor front panel illumination.
Problem solved by cleaning push switch “Tape monitor” on front panel. Deoxit spray used (needle injection inside switch ) . Illumination lamps changed to LED lamps by customer request.
Some technical experience and view to share about front panel illumination lamps. LED or original incandescent lamps ? Which one is better ? Are there any advantages ?
Some customers like LED , some original incandescent lamps. We provide pictures for comparison LED and old school lamps illumination. In this case we compare 8 volt lamps for Marantz 2275 front panel illumination.
On picture right meter illuminated by LED lamp, left meter by original incandescent old school lamp and small function lamps illumination to compare.
How LED design lamp works – electrical current goes to special microchip inside with semi-conducting material layers and produce visible light.
How old school incandescent lamp design works – electrical current goes to the tungsten filament inside lamp and start burning tungsten metal process, producing visible light. Basically you see light from burning metal named tungsten in no oxygen glass tube or sphere.
LED lamps pluses –
1. More brightness 20 -70 %.
2. Longer work life time 70-300% .
3. Ability to choose from many colors and light tones ( white, warm white , cold white, blue, light blue, icy blue ,dark blue …………….)
4. Lower electric current to produce same brightness 30-200 % (your electric consumption lower means your electric bill is lower ,not significant amount but still good news ).
5. Lower heat generation 20-80% .
6. No need to keep inert gas and no oxygen condition inside glass lamp like inside old incandescent lamp .
7. Big variety of shapes and designs.
Minuses for LED lamps .
1. AC or DC application (polarity) importance for some lamps.
2. Lower and limited light producing angle on some LED lamps, instead 270-360 degree wide angle on old school lamps you getting 60-180 degree direct light angle only. In some application it is extremely important.
Both type of lamps don,t like over voltage . They will stop working in short period of time if you apply bigger voltage then they designed for.
All old school incandescent lamps are universal AC or DC voltage and wide light angle by design.
Case 453434. 02.03.2023 . Sansui 2000x receiver repair. Right channel is scratchy sound , thunderstorm sound on minimum volume level.
After applying heat and cold to all transistors in filter and driver sections found bad transistor 2sc458, position tr806, driver board f-1180.
Problem solved by replacement.
Pluses – simplicity, functions and boards separation ,easy to work on it.
Minuses – speaker plugs design on back panel (easy to break).
Works on maximum volume level only and no left channel.
Protection relay replacement solved problem.
Pluses – good attention to phono input. MC and MM phono inputs available.Good for phonograph players .Support MM and MC phonograph cartridges. Massive heat sink inside , good and stable sound.
Minuses – chaotic board management design inside, sandwich boards installation in central area with overheating on bottom board.