Repair cases



Case #356461.
Pioneer SX-626 receiver repair. Low, distorted and wobble sound.
Case from 07/06/2022.
Changing power supply filter capacitor 3300 uf solved the problem.
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Case #356465. Sansui C-77 preamplifier repair.

Different output signal level in left and right channel . Unbalanced output signal .
Repair.
Changing double front pot 100k ohm ” volume” solved the problem.
Cleaning did not helped.
One of them for some reason changed value to 60K ohm.
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Case #456718. Technics SU-7600 amplifier repair. No sound.
06.11.2022. No sound on both channels.
Pilot light is ON.
Voltage -35 volt and +35 volt from power supply are present. All output transistors are ok.
Relay control transistor TR354 ( 2sc828a) replacement solved the problem.
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Case #543645/ 09.12.2022 Luxman L-100 amplifier. Low sound from both channels.
Switch MODE/LEFT/RIGHT replacement solved the problem.

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Repair case # 125432. Pioneer SA-9500II amplifier – no sound, keeps blowing main fuse.
4 Output transistors and main fuse replacement solved the issue.
Instead original transistors we installed MJE15032G / MJE15033G Transistors NPN/ PNP. Works even better then originals.( same terminals design, same configuration) . Main fuse- 4-6 Amp.
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Case # 342553. Mcintosh 754 amplifier. Missing left channel. 09/27/2022
After troubleshooting found protection relay not working properly.
Relay replacement solved the problem.
Good- simplicity, simple schematic design, good sound, output driver boards separation, good ventilation.
Bad – missing power switch, no AC voltage filtration from electric outlet,any working device in same room with this model will affect sound quality.High electrical interference from 110 volt AC line.


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Case# 456234.Pioneer SX-950. Protection relay not clicking.
Outputs -OK.All voltages from power supply – ok.
Replacing capacitors on power supply section and 2 resistors 1.3 kohm (green on picture) on protection control board solved the problem.
Good – perfect components separation and management on boards ,good ventilation, strong build chassis,realistic analog sound, used termo isolation holders and tubes on hard working parts, lowest possible AC line interference, stable output, sensitive tuner section,build to last.
Bad – high price.


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Case #456343 10/09/2022 Sansui AU-919 . Goes to protection mode after 20-45 minutes.
After troubleshooting and testing found – 1 bad electrolytic capacitor 100mfx25v in preamp power supply section, 2 bad capacitors 100mfx35v on output driver board, 8 out of parameters non electrolytic caps on driver board, 2sf656 thyristor,leaking capacitor on protection board and relay control transistor.
This model emits a lot of heat even in normally working condition. Look like engineers focused on big output power and forgot about temperature balance inside.
Good – DC voltages separation from different source,big stable output power.
Bad – poor ventilation design. After 3-4 hours of work it turns to cooking pan for internal components. Most of them will handle it ,but not all of them.


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Case # 657682. Luxman T-110U tuner. Low output from both channels.
Changed capacitors c290, c289,c286 and cleaned switch “muting off”.
Good – good and sensitive tuner, low signal distortion.
Bad – capacitor c290 on board located next to hard working,heat emitting resistor r315 and will dry capacitor over period of time. Components management failure.
—————————————————————————————————————————————————                   Case #746553 10/17/2022 . Victrola 65u vacuum tube radio/turn table from 1947 .No sound.
Replaced power supply dual section filter capacitor and 33 ohm buffer resistor.

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Replaced protection relay MU2U.
New relay on picture.
Technical pluses – simplicity, easy to reach components.
Minuses – low grade, unusual size MU2U relay they use in manufacturing process.
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Case 4657687. 01/20/20223
Pioneer QX-9900 quad receiver.Distorted sound after 20 minutes.
Cleaning all front panel switches and control pots solved the problem.
Technical view feedback – nice unit , build to last long time , perfect modules separation for prive nting signal interference between modules, Split shielded cable between modules plus each section has own shield cover, multi-voltage transformer let you use this unit in any country around the world without modification , good quality components in use, good heat sink design, stable sound at any power level.Unit designed by real old school respected engineers.
Minuses- hard to get to front panel switches and pots in case if they need replacement.
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Case 4563728 . Marantz PM-5 amplifier. Works on maximum volume level only and no left channel.
Protection relay replacement solved problem.
Pluses – good design attention to phono input. MC and MM phono inputs available.Support MM and MC phonograph cartridges. Massive heat sink, good and stable sound.
Minuses – chaotic board management design inside, sandwich boards installation in central area with overheating on bottom board.

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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).

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Case 645432 . 02.04.2023. Marantz 2275 receiver repair. No sound. Poor front panel illumination.
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 . Illumination lamps changed to LED lamps by customer request.

Technical view about lamps – LED or original incandescent lamps ?

Some customers like LED , some original incandescent lamps. We provide pictures to comparison LED illumination and old school lamps. 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 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. Bigger brightness 20 -70 %.
2. Longer work life time 70-100% .
3. Ability to choose many colors and light tones ( white, warm white , cold white, blue, light blue, icy blue ………………)
4. Lower electric current to produce same brightness 30-200 % .
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 on 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.



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Case # 8576754. 02.09.2023. Adcom GFA-5500 amplifier repair. No left channel.
After troubleshooting found open R11 resistor on power supply board.
Problem solved by 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 stadium, schools and more, easy to set up.

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 .
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Case 456781 . 02/13/2023 . Soundcraftsmen MA5002. UNIT GOES TO PROTECTION MODE.NO SOUND
This type of “high-end audio equipment” not worth even to spend time on it. After opening unit – first impression was – couple drunk plumber guys in bar tried to design audio amplifier. They tried hard , but final product by the end is something between kitchen microwave and washer machine. Big mix of cheap electronic components and wires in metal case.Low quality and overrated.

Pluses- can be used as a heavy lifting object in gym.
Minuses – everything.

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Case 253436. Pioneer SX-1250 receiver. Unit does not turn on. 02/20/2023.
After troubleshooting found not working power switch.
Problem solved by replacement.( picture 8 ). LED lamps installed.( picture 5)

Technical review.
This model belongs to “King family” of receivers and one of the best receivers human kind ever build. This model was a legend and will be a legend for long time .
Pluses
1.Has 3 separate protection circuits ( fuses + termofuse , soft start relay and protection relay).
2. Build to last long, long, long time.
3. Top line of electronic components used in manufacturing process.
4. Shielded tuner area, power transformer and shielded important signal path line.(pictures 1,2 )
5. Perfect wires management inside.(picture 3 )
6. Spark and AC line interference solved perfect in design.
7. Perfect components management on boards.
8. Perfect temperature balance by using huge heat sink in output section.
9. Real analog sound . Huge power . All sound parameters tested and found as stated in manual .Not so many units can do that.
10. Wires and heat emitting resistors have termo protection isolation tubes in hot areas.Good ventilation design.( pictures 6 , 7 )
11. High quality metal used on contacts ( bolts on power supply capacitors).
12. Short as possible signal wires.
13. Minimum use of life limited parts and components.
14. Easy to operate , service and work inside.
15. Good sensitive tuner for 1979.
Minuses
We have not found one.
On last 3 pictures we present modern ” high technology and fancy” audio electronics design from 2000-2022. We called it ” ” Glue technology ” . After while all this glue on boards turns to unexpected carbon resistors in your schematic and start destroying your unit. Just compare pictures and you will understand why analog vintage audio is better few times then most modern audio equipment by quality and performance.










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Case 546563 . Harmon Kardon PM665 amplifier . Intermittent sound on / off.

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 .


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Case 768576 . GAS preamplifier Thalia . Unit has damaged “Output”PLUG ON BACK PANEL .
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 ruin electrolytic caps ), not shielded balance pot wires.
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Case 543264 .02/26/2023. Marantz 1060 amplifier.No sound from left channel.

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.
Technical review.
Nice small amplifier. Good performance. Nothing special.Power supply section extremely simplified. Classic old style engineering.
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Case 567532. 03/01/2023 .Pioneer QX-9900 receiver. Intermittent Thunderstorm noise in right channel.

After troubleshooting using ” freeze spray ” for transistors method found 2 transistors 2SA726 in right channel driver board acting bad after cold application . All unit transistors 2SA726 changed to 2SA992 . They have same look but different pinout. Pay attention ! 2SA992 / KSA992 is better in parameters and performance.


————————————————————————-Case #465756. 03/23/2023 .Mcintosh C26 preamplifier . Scratchy volume control.
Volume pot replacement.

Nice unit . Real sample of not overbuild audio equipment. Quality detailed design inside. Real analog full sound. Sound parameters surprisingly good and stable on all frequency range. Simplicity, oxidation resistant chassis, quality components , good shielded wires management in most important places. Engineers were focused on product quality . Build to last for long time. Good appearance and easy to use.


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Case 234521. 04/07/2023. Sansui 9900z receiver. Spectrum analyzer and power level indicator not working.
After troubleshooting with scope found missing audio signal detection to both meters. Relay RL1 replacement on output speakers connectors board solved the issue.

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Case 346532. 02/12/24 Pioneer SX-780. Makes loud pop sound after turn on and relay clicks 2-3 times. Sound is ok.
Bad capacitor 33ufx16v next to protection relay.