Sony receiver no power

Sony receiver no power DEFAULT
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DefaultRe: Another broken Sony receiver... won't turn on

Originally posted by rkc7
Ok.... so I have a Sony receiver. That's the problem right? STR-DE595. Anyway, I purchased it in order to repair and resell, but the problem seems more complicated than anticipated. It won't turn on at all... no protector mode, etc. The power supply fuse isn't blown, all transistors seem good, transformer is putting out voltages that seem correct (when I manually turn on the AC supply relay). So, I plug it in, and press the power button... nothing. I've tried looking at a bunch of different things, and nothing apparent seems wrong. I'm considering removing all of the relays and testing them individually, but my impression is that relays typically don't go bad. Anyway, any help on what could be the problem or what else I should check would be really helpful. Thanks.

Hello rkc7, I have a service manual for that receiver in PDF format, I can upload it to you if needed. It is about 6 MB in size. While you're at it, check the standby transformer, those are known for opening up the primary, which will cause a dead receiver.

If your mailbox can handle a 6MB file, please let me know at [email protected] (not my DSL account). I'll E-mail you through my DSL account and upload the manual for you!

Joe
Sours: https://www.diyaudio.com/forums/

Sony Receiver Amplifier Will Not Start -- Checking Standby Board

Standby PSU Board for Sony Amplifier

An amplifier usually does not start if there is a short in the audio power output stage because most amplifiers are designed to go into protect mode that prevents the high voltage transformer from receiving power. This function therefores protects the audio power output stage and its power supply rails. This article is for times when you are absolutely sure that there is no fault in the audio power output stage, and the problem is elsewhere. The Sony STR-DE375, STR-DE475, and some STR-DEXXX range of amplifiers tend to have a standby board that is often the focus when I am starting my diagnostics. It is a small board right next to the main power transformer, and it is responsible for maintaining standby power to the amplifier so that it could be operated by remote control. As you can see, there is also a smaller relay that switches power to a much larger transformer.

Standby PSU Transformer 5 V

There is usually a small standby transformer, which provides 5 V to 6 V AC, and four power diodes in a bridge rectifier configuration. The main system control chip is usually on the front panel of the amplifier together with the infrared receiver module, which uses this standby power at all times. As you can see, there are also a pair of clear glass signal diodes that provide partial rectification. The current from this is used by the AC detect chip NJM2103 which checks for abnormal power. The detection of abnormal power results in pin 8 of the chip going low close to zero volts. This pin also controls the STOP pin on the amplifiers main microcontroller IC to hold it into a reset condition. If you have an amplifier such as this, where pin 8 is at 0 V all the time, then the standby PSU board is the place to focus for further investigations.

2103D JRC Chip AC Detect

The NJM2103 monitors the supply voltage and checks for quality. It is a power supply supervisory IC that detects abnormal voltage conditions. Upon detection of abnormal condition, it generates a reset signal for the microcontroller chip on the main front panel of the amplifier. Once the main microcontroller goes into STOP mode, the user will no longer be able to switch ON the amplifier and none of the front panel buttons will work.

I have come across a few amplifiers that would not turn ON even though there was no short in the audio power amplifier stage. Usually when you press the power button one hears the clicking of a relay, which feeds power to the main transformer, however it is possible to come across totally dead amplifiers, where one presses the power button, or any other button, and nothing happens.

My Jedi Diagnostic Power

Starting at the front panel microcontroller end -- as suggested by some experts -- the first thing I checked was the oscillator clock to see if there was a pulse, and sure enough there was a nice strong heartbeat indicating that there was nothing wrong with the microcontroller! Honestly, those guys with their over inflated grades and imagination...

The power switch is a push to make momentary contact type. It connects directly to a pin on the microcontroller chip marked POWER. If you place a probe on this pin and press the power switch the voltage should alternate between 0 V and 5 V. Sure enough that was working fine also. This means that the switch was fine and its connections were fine. The signal to power ON the unit was getting to the microcontroller.

The next thing I checked was the STOP pin on the microcontroller. This was active low, indicated by a line above the word STOP. Placing a probe on this pin revealed that this pin was at 0 V all the time. That means the microcontroller remains in a stopped condition all the time and it does not run the firmware, hence the program would be stuck in a halt loop. Clearly, that did not seem right, so the next step was to trace the circuit that controls this pin. A line from this pin traces all the way back to the Standby board. D'oh! I should have just started from the Standby board...

Further investigation of the circuit diagram revealed that a chip marked NJM2103 generated the STOP signal. Specifically pin 8 of this chip generates 5.5 V all the time when operating correctly. This chip detects AC current and the quality of the supply voltage. An abnormal voltage level causes the STOP condition to be initiated by supplying 0 V at pin 8. A LOW at this pin halts the microcontroller program in a reset condition.

I then decided to investigate why the chip was indicating abnormal supply voltage. Using an oscilloscope, the thing to look for were ripples in the supply. Sure enough, there were large ripples on the standby voltage. Checking the diodes on the bridge rectifier indicated that one of the diodes had failed. There were also some 1-µF and 0.1-µF capacitors which were low in value so I replaced those as well, and that fixed the problem. The ripple was gone and pin 8 of NJM2103 was producing 5.5 V.

Conclusion

It stands to reason that this part of the circuit, which is always drawing power and working, would be the most likely to fail. The components in the standby circuitry would have been operating from the first day the amplifier had been unpacked decades ago, and consequently reaching the end of their service life. The standby PSU board is sometimes the best place to start because many of the components there are working continuously and are more likely to fail. Dry capacitors, and open resistors in that part of the circuit can also cause similar problems. However, please note that this article is not exhaustive as there are many different models and circuit designs, and in addition electronic components and circuits can fail in many different ways and places. Therefore, make sure you have done the correct diagnosis before jumping at changing components.

The lesson to learn here is that it is still possible to zero-in on where the fault is, providing your diagnostic skills are good enough. Please note that this article is for qualified and experienced electronic engineers. Do not attempt any repairs at home if you are not qualified and experienced to do so.


Sours: https://www.petervis.com/Amplifiers/sony-receiver-amplifier-will-not-start/sony-receiver-amplifier-will-not-start.html
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Receiver has no power at all.

Hi,

Have you had a power outage or have there been thunderstorms recently? If so there may have been a power surge that has affected your receiver.

If you can interpret circuit schematics, have the appropriate equipment and are aware of working with dangerous voltages then the service manual for your receiver (see link) will be of some help to you in solving the problem.

http://www.electronica-pt.com/esquema/fu...

It may be that a fuse has blown in the power supply, BUT there is always a reason for this. It may also be that a power regulator has failed etc. The cause of no power will have to be proven by diagnosing the problem using the correct equipment and fault finding techniques.

If you do not know what you are doing, it is extremely dangerous to remove the cover and check inside the unit. There are lethal voltages present. It is better to take it to a reputable, professional electronics repair centre and ask for a repair quote.

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