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Db500 the protection circuit operates at low volume

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  • atv1000 Dec 03, 2008

    this is a samson db500a thanks.

  • atv1000 Dec 03, 2008

    when the mic is used at any level on the volume control, the same fault happens ie the protection circuit kicks in and then resets

    regards ken

  • atv1000 Dec 04, 2008

    Thanks Dan I will look into the caps with a scope also the zener diodes on the protection circuit.

    regards ken

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6 Answers

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  • Master
  • 6,966 Answers

Hi and welcome to FixYa,

Initially, based on your description, an internal electronic failure most likely in the preamp and/or the amplifier stage. this is of course assuming that you have tested and eliminated that the speaker and its wiring maybe at fault. This of course would require a fair familiarity of electronic components/circuitry and safety procedures, use of a DVM and a soldering iron. It would be to your added advantage access to a service manual or at the very least a schematic diagram with voltage readings. Should you be uncomfortable performing a DIY (do-it-yourself), perhaps your best bet would then be to seek the services of a qualified professional.

Just a start, do postback how things turned up or should you need additional information. Good luck and Thank you for using FixYa.

Posted on Dec 04, 2008

  • Louie  Role
    Louie Role Dec 04, 2008

    An alternate possibility is that this unit uses a DC amp design where each stages is directly coupled. The front end would have a Darlington pair and/or a differential transistor pair. Any constant input signal such as AC hum would be interpreted as an audio signal upsetting the balance. One way to check if it is internal to the amp/pre-amp is to measure the voltage across the speaker terminal, with no signal input, it should read 0 volts while rotating the volume control. If there is voltage measured, then the DC bias has to be adjusted or there is a problem at the front end/pre-amp. Another possibility is dirty volume control contacts and spikes and glitches are introduced while adjusting, enough to trigger the protection circuitry.

  • Louie  Role
    Louie Role Dec 12, 2008

    Hi again,



    Any updates or developments so far?



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  • Master
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Hi

The fact it only occurs when you put audio through it at any level from the mic would tend to indicate that the output stage of the amplifier is faulty. There may also be a fault with the speaker system that could also produce the same symptoms. The protection circuits work in up to 7 different ways relating to current draw, DC offset, Thermal conditions present, or inaccuracies between input and output from the power amp stages.

Checking the speaker system/cables with an ohms meter will give you a quick test to see if there is a problem there with a short circuit. Try another speaker connected to the amp may also help you to eliminate that end of it.

Otherwise, most probably when audio from the mic is amplified, there is an electronic fault is producing a DC voltage in the output stage,and firing the protection circuit. This problem is often caused by failing solder or cracked/dry solder joints in and about the output stage. This is where I would start to look for problems. Happy to talk to you further about the problem.

regards
robotek

Posted on Dec 04, 2008

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  • Master
  • 734 Answers

Sound condenser/filter might be faulty due to which it resets at higher volume.....get them repaired

Posted on Dec 04, 2008

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  • Master
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If an amp protection circuit kicks in at volume level changes, the problem is usually in the pre-amp stage. What is happening here is that there is DC voltage being presented to the output stage. That is detected by the protection circuitry and is causing the shutdown. Normally, these amps are designed as cap coupled to filter out any lingering or transistional DC from stage to stage. If the coupling cap has shorted or is leaky, this type of symptom can occur.

Any service shop that works on audio gear should be able to trace this problem with a scope and resolve it quickly and cheaply. Expect a parts cost in the $10-$15 range.

Dan

Posted on Dec 04, 2008

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Sir, did you try to check your settings of your device?

CHARCOIS

Posted on Dec 03, 2008

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If the unit goes in protection mode when you lower the volume down test the boards with controls and remote sensor. Let me have more details on the problem.

Posted on Dec 03, 2008

  • Ginko
    Ginko Dec 03, 2008

    Usually amps fail when you pump up the volume , not when you lower it down.
    When amps fail at a certain point when turnig volume up , that is usually for a shorted speaker wire.

    In your case:

    If this just happened and it is the first time, unplug power cord for ten or twenty minutes, test a different AC socket, in case the one you are using is not well grounded.

    If amp fails at a low volume in general, then it can be any internal problem or faulty component, the board must be taken out and tested.

    If the active speaker fails when you lower down the volume, always at same point, that means that the amp is not stable at that determined ohm level, this because of a faulty component, usually one of the ICs that do the same job of Valves/transistors on the old amps in the amp final.

    If the problem does not goes by leaving the unit unplugged, or using a different socket, the active speaker must be taken apart, and speaker wiring and amp onboard component tested.

  • Ginko
    Ginko Dec 03, 2008

    If the fault only happens when using an external mic, then either the mic is shorted, or there is a fault on the mic wirings, usually the connector wiring.

    Test a different mic first.


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The most common cause is a short circuit somewhere - something even as simple as loose speaker wiring could cause a short, triggering the Protect message.

You will need to determine if there is a possible short somewhere, so I recommend you start by firstly turning power OFF, disconnecting all speaker wires, then turn unit back ON.

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Page 13

Speaker Connection Precautions

(North American and Taiwan models) You can connect speakers with an impedance of between 6 and 16 ohms. If you use speakers with a lower impedance, and use the amplifier at high volume levels for a long period of time, the built-in amp protection circuit may be activated.

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The STANDBY indicator flashes red


The protection circuit has been activated. Remove the power cord from the wall outlet immediately.

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Overloads can be from excessive periods of high output or marginally low impedance loading by the speakers; and shorts would be wiring issues or a speaker blowing up.


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If the amp comes back on after cooling, you're lucky. They only have so many self-protection cycles in their lives so continuously resetting or cycling their power without addressing the cause can do more harm than good.


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Keep me posted.
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The unit may be experiencing an overload caused by a short circuit, internally or externally. Try disconnecting all the speakers, then turning up the volume. If nothing happens, connect one speaker at a time and turn up the volume to see if you get more sound. You may have a speaker that has shorted internally and this will help you discover the bad one. However, if when you have all the speakers disconnected, and the unit still goes into protection mode with the volume up, then there is a problem with the unit itself.

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the system protect is usually displayed when a condition of short or shorting is occurring in the speaker wiring or the voice coil of any of your speakers.... thte circuit of you reciever is trying to protect itself and you from a very costly repair,,,so it you have another set of speakers try to use them and see if the condition still exists and if it does the problem is in the output section of the receiver,,,and if the protect no longer exists you have fixed your problem,,,good luck

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