Lynx LMX4 Micro Mixer power fault

[Graeme]

Hi there! Hope someone can help.

I have this cute little mixer I use to plug guitars through from time to time. I usually use it with a 9v power supply. The other night I tried to use it with a PP3 battery. After several attempts with different batteries I could not get it to work.

I opened it up and did a few multimeter tests to see that the power is reaching the circuit board. It is doing that fine, both with the power supply and battery.

What would the obvious ideas be for what has gone wrong? There don't seem to be many components at all. Here's the circuit:

Thanks in anticipation...

 

[duke37]

I assume that the components with the prison bars are electrolytic capacitors but the values are absurd. Possibly 4.7M is 4.7µF.

The amplifier and electrolytics are polarity sensitive and will be damaged if the battery is connected the wrong way round. Did you do this?

 

[Graeme]

Thank you for your reply.

I found the circuit online so I can't vouch for its correctness. What puzzled me is there doesn't seem to be a battery or power symbol.

Regarding your question, it s a PP3 9V battery so it only goes in one way. Same with the 9V power connector which only goes one way. Its wired however it came from the factory and its worked for two years like that on the power connector. It did work with the battery originally.

So I have to conclude that either a component in the power circuit has failed or a connection has gone dry.

 

[Graeme]

Oops...just spotted the power symbol now - but nothing about the battery / power connector arrangement. I guess its a switched jack.

Lol - also four channel 1's...

 

[duke37]

The first thing to do to find the fault, is to get the DC voltages right, it will not work if it they are wrong. Get the details of the IC to see what the voltages should be. When measuring, make sure that you do not short two pins together.

 

[davenn]

Oops...just spotted the power symbol now - but nothing about the battery / power connector arrangement. I guess its a switched jack.

Lol - also four channel 1's...

look at the top right side of the circuit there's the power connection, it indicates the polarity
no its NOT a switched jack there is a power switch there and its linked to the volume control

you PP3 9V battery may not have enough current capability for this circuit
( assuming you havent already damaged the circuit as Duke suggested??)

Dave

 

[Graeme]

Hi Dave,

Thanks for getting back to me. I Have a few 9V batteries here which I have tested. The voltages are all good and they are the type recommended by the manufacturer. The device still works perfectly with transformer power. Its just with the battery it doesn't work now.

Regarding the idea of a switched jack, I think I was a bit confusing. I didn't mean the jack on the diagram is switched. There is only the indication that its the DC input there. I suspect the jack itself on the device is switched so that the battery is disconnected when the power supply is plugged in. I will look at that closely and perhaps post some pics. I will have to carefully take it to pieces again.

Thanks for the help in the meantime.

 

[Graeme]

Hi All,

Well, I made up a connector that allows me to connect the PP3 battery to the DC input socket rather than use the normal battery connector. The unit works fine like that so it can't be the battery not having enough juice or the circuit being damaged.

Why I thought the power jack might be switched is that when one plugs in the DC power supply it should cut out the battery from the circuit. The unit needs to get power from either not both. I do have some little switched sockets of this type.

So I will try and see if the power socket is switched. I will post my results when I know them.

Be well.