[Lavalamp]

Trim pots seem in the right orientation. I turned full counter-clockwise and heard a definited "click".

I'll try and post some pictures shortly.

Thanks.

 

[Lavalamp]

Photos posted:

http://au.pg.photos.yahoo.com/ph/lav...bum?.dir=/3927

All suggestions gratefully accepted.

 

[amb]

Quote:

Originally Posted by Lavalamp Photos posted: http://au.pg.photos.yahoo.com/ph/lav...bum?.dir=/3927

I just had a look, even though the photo caption indicates that the originals are high-resolution, yahoo would only display a much smaller version which doesn't provide enough detail. How does one access the original, full resolution versions?

 

[Lavalamp]

Many thanks to AMB for looking at my photos.

I had misread the circuit diagram, and installed all my mosfets the wrong way round.

I have removed tham all, and tested them. They were all ok on the test.

I installed them correctly, and went through the set up procedure flawlessly.

I left the amp switched on. I could feel the heatsinks warming up.

When I came back, the heatsinks had cooled right down, and I can only get 0.7v between pins 4 and 7 of all opamps.

I started the set up procedure again. I don't seem to have any shorts.

I just tried re-adjusting the trimpots, but can't seem to get any readings across r5 and r9.

Any suggestions?

I did power up the mosfets in the wrong position, but they test ok, and set up perfectly the first time.

 

[amb]

Quote:

Originally Posted by Lavalamp I left the amp switched on. I could feel the heatsinks warming up. When I came back, the heatsinks had cooled right down, and I can only get 0.7v between pins 4 and 7 of all opamps.

At this point, did you check the voltage across V+ and V-? Was your M³ LED still on?

If you look at the schematic you'll see that the MOSFETs get their power directly (after the D1 protection diode) from the PSU, whereas the opamps power rails are isolated after the capacitance multiplier. You need to determine whether your PSU is still putting out the proper voltage, or if the capacitance multiplier's pass transistors (Q5+, Q5-) have died.

 

[Lavalamp]

Quote:

Originally Posted by amb At this point, did you check the voltage across V+ and V-? Was your M³ LED still on? If you look at the schematic you'll see that the MOSFETs get their power directly (after the D1 protection diode) from the PSU, whereas the opamps power rails are isolated after the capacitance multiplier. You need to determine whether your PSU is still putting out the proper voltage, or if the capacitance multiplier's pass transistors (Q5+, Q5-) have died.

The power supply was still a rock steady 24v. The power led was on (in fact it takes a few minutes after switching off to die, which I presume is normal, granted all those capacitors!).

Looks like it could be Q5.

 

[amb]

Quote:

Originally Posted by Lavalamp The power supply was still a rock steady 24v. The power led was on (in fact it takes a few minutes after switching off to die, which I presume is normal, granted all those capacitors!). Looks like it could be Q5.

Yup, looks like either Q5+ or Q5- (or possibly both) went bad. These don't just die by themselves for no reason, so something must have caused them to operate beyond their ratings. Either the BIASOP was set too high, or the opamp(s) was oscillating, or there was an accidental short circuit (even a momentary one) on one of the opamp power supply rails.

You do have the correct value of C1 installed on each channel, right? Were the volume and bass boost pots were turned all the way down during initial setup (and warm up)? Are the Q5s brand-name, good quality 2N3904/3906 transistors? I've seen some no-name generics fail to meet the proper specs. Last but not least, be very careful during initial setup not to slip up with your meter test probes and short something out, and be sure the board is mechanically secure so that the bottom don't touch anything metallic that could cause shorts, etc.

 

[Lavalamp]

Quote:

Originally Posted by amb Yup, looks like either Q5+ or Q5- (or possibly both) went bad. These don't just die by themselves for no reason, so something must have caused them to operate beyond their ratings. Either the BIASOP was set too high, or the opamp(s) was oscillating, or there was an accidental short circuit (even a momentary one) on one of the opamp power supply rails. You do have the correct value of C1 installed on each channel, right? Were the volume and bass boost pots were turned all the way down during initial setup (and warm up)? Are the Q5s brand-name, good quality 2N3904/3906 transistors? I've seen some no-name generics fail to meet the proper specs. Last but not least, be very careful during initial setup not to slip up with your meter test probes and short something out, and be sure the board is mechanically secure so that the bottom don't touch anything metallic that could cause shorts, etc.

That makes alot of sense. I hadn't fixed my board to the case, and it did slip whilst powered up.

I have just replaced both Q5, and the set up went flawlessly. It is now warming up for the final test reading, but it looks like this story might have a happy ending. I'll report back.

 

[Lavalamp]

It's working, and sounds superb considering it has had no burn in.

I see what people mean about the bass boost. It is very nice!!

AMB, thank you very much for your assistence. I thought I would show my gratitude by coughing up and becoming a contributing member to this site.

I'm off to play some Steely Dan on vinyl.

 

[amb]

Quote:

Originally Posted by Lavalamp It's working, and sounds superb considering it has had no burn in.

Congratulations, enjoy the amp.

If you ever tear it apart again (for parts upgrades, whatever), be sure to let the C7 rail capacitors drain down completely before doing anything. This would help to prevent damage if something gets short circuited (even with the PSU disconnected).

 

[gstatton]

I would just like to say that i had the SAME problem with my M3....
amp ran fine through set-up, got audio out (amazing audio at that!) and then the MOSFET's went cold...and no voltage across the opamps.....i was very sad

then i read through this at work....realized i had generic Q5+/-....ran home, swapped 'um out....and i was getting good voltage again.....ran through setup and MOSFET's started heating up again!!!
i replaced with some generics that i had around, so most likely should order "brand-name" ones....
...but i would like to thank you guys for helping me as well!!!!
amb...great amp.....