[Lavalamp]

I have just finished my M3, and it's not working. I'm not getting any sound at all from it.

I can solder, follow diagrams and recognise components, but otherwise my knowledge is pretty rudimentary. Please bear that in mind if you are kind enough to respond.

My first query is that my power supply is a steady 24v. Once it is connected to the amp, it drops to 2.4v. That's the reading I get from the v+ and v- pads on the PCB.

Is this normal? If not, does it give me a pointer as to where the fault lies?

 

[amb]

Did you mix up the N and P channel MOSFETs?

BTW, your statement "not getting any sound" has me a little worried that you had connected headphones to the amp before you followed any of the initial setup procedures...

 

[Nisbeth]

Quote:

Originally Posted by Lavalamp My first query is that my power supply is a steady 24v. Once it is connected to the amp, it drops to 2.4v. That's the reading I get from the v+ and v- pads on the PCB. Is this normal? If not, does it give me a pointer as to where the fault lies?

No it's not normal. It sounds like you have a short circuit somewhere. Check you soldering work on the underside for bridges and recheck that all the components are in their correct positions. Once that is done (and any mistakes rectified), the proceed to follow the setup instructions on AMB's website

/U.

 

[Lavalamp]

Quote:

Originally Posted by amb Did you mix up the N and P channel MOSFETs? BTW, your statement "not getting any sound" has me a little worried that you had connected headphones to the amp before you followed any of the initial setup procedures...

My set up procedures seemed OK for the left and ground channel. I couldn't get a reading for the right channel, but I have a very dodgy DMM, and thought that could be the problem. I tried the amp with very cheap headphones thinking that if it's been powered up during set up, I can't do too much more damage by trying it with a source and headphones.

Last night I discovered that I had the mosfets round the wrong way in the right channel. I have rectified that problem, but the fault seems to remain.

I'll have a good look at my wiring and joints tonight.

 

[amb]

Measure your MOSFETs between the drain and source pins ('+' probe on the drain pin and '-' probe on the source pin for the N-channel, reverse it for the P-channel) with your meter set to resistance (low ohms) mode. You may get a brief reading due to the rail capacitor charge, but it should settle to "infinite" reading. If you read anything less than "infinite" then the MOSFET is probably blown (internally short circuited).

 

[Lavalamp]

Quote:

Originally Posted by amb Measure your MOSFETs between the drain and source pins ('+' probe on the drain pin and '-' probe on the source pin for the N-channel, reverse it for the P-channel) with your meter set to resistance (low ohms) mode. You may get a brief reading due to the rail capacitor charge, but it should settle to "infinite" reading. If you read anything less than "infinite" then the MOSFET is probably blown (internally short circuited).

Sorry AMB, I'm having difficulty locating the drain and source pin. One mosfet is a 24, the other is a 34. Is the 24 the N-channel, or vice versa?

By reference to the schematic, which is the drain pin? What other components is it connected to? Same query for the source pin.

Thanks for your patience!!

 

[amb]

Lavalamp, go to the International Rectifier website ( http://www.irf.com ), look up the MOSFETS IRFZ24N and IRF9Z34N. The datasheets for each of these will tell you which is N-channel and which is P-channel, and how to identify which pin is what. Then, correlate that to the M³ schematic and PCB layout diagrams you should be able to see where each of the pins connect to.

I could've given you an easier answer but I hope this exercise would help you learn.

 

[Lavalamp]

Quote:

Originally Posted by amb Lavalamp, go to the International Rectifier website ( http://www.irf.com ) I could've given you an easier answer but I hope this exercise would help you learn.

Much obliged. I'd rather be taught to fish than given a fish!!

 

[Lavalamp]

My mosfets for the right channel look good, as I'm getting an infinite reading.

I'm going through the set up instructions again.

Step 2 is fine, and there are no shorts according to this test.

Step 6 is a little strange. As I said earlier, my power supply drops from 24v to 2.4v once connected to the amp. My power led doesn't light. Perhaps this is due to such low voltage? All other steps in step 6 are fine in the sense that I'm getting 0.5v between pins 4 and 7, which is 2v less than the 2.4v power at V+ and V-. Voltage from pins 4 and 7 to IG is half of 0.5v.

For step 7, where it says to measure DC voltage across R5g, am I simpy to put the DMM probes on either end of R5? I'm doing this, and I can't seem to get any reading at all.

Again, I'm very grateful for your patience and assistence.

 

[amb]

Lavalamp, your power supply shouldn't drop to such a low voltage when connected to the amp. Until that is corrected the rest of the setup procedure is not useful.

What power supply are you using? Please provide some details about how it is configured. Also, what's the power-up sequence? Do you connect the power supply output to the amp board before turning on the power, or vice versa? How much rail capacitance do you have on the M³ board (the sum of all the C7 capacitors)?

 

[Lavalamp]

My power supply is a tread set for 24v. I'm the following torroidal tranformer:

http://www.altronics.com.au/index.as...=item&id=M5012

It is wired up in series.

I have the power supply in a separate case. It connects to the amplifier by way of about 2m of cable. The v- goes straight to the PCB, the V+ goes to an on/off switch first, and then the PCB. I am using this switch to switch power on and off.

I have a total of 9 x 330uf capacitors for C7.

 

[amb]

I think the inrush current to charge the C7s is causing your TREAD's LM317 to shut down. rjkdivin was having a similar problem, except his was a STEPS and his LM317 was blowing up. I suggest you try keeping the switch on, and with the power supply already connected to the amp, plug in the AC. If this works, then you should change to switch the AC on the primary side of the transformer.

 

[Lavalamp]

Thanks AMB. I just tried that with no luck. I'm still getting only 2.4v.

 

[thrice]

I had a similar problem with an M3. It turned out to be a bad Q5.

 

[amb]

Looks like something is drawing too much current. Are your BIAS trimpots installed in the proper orientation, and rotated fully-counterclockwize before you apply power?

I think at this point maybe posting a few clear pictures of the M³ board (both sides) and the power supply might help.