Right Channel Not Working - BOSOZ Question

[lgreen]

Hi, on my BoSoz, the right channel is somehow not working. I did this on a perfboard. Traced it out vs. the schematic and I think I have it right. Then I "forgot" about the schematic and created a schematic from the board stand-alone, and this also looks right. the pins on the IRF 610's look like they are oriented correctly too. Its kind of killing me why it doesn't work.

Here are the symptoms- it doesn't draw power from the power supply, voltage at the drain is 59.5 volts when it should be 30 volts. voltage at the gate is 0.0 volts, voltage at the source is negative 3.3 volts.

Measured the mosfets, none have shorts across any pins. Obviously the problem is something with the drain part, right, as no current is flowing through the 750 ohm drain resistors? But I've been over it a hundred times. Would not bug everyone if I hadn't been. The 750 ohm resistors are not shorted out, they measure 750 ohms; the 221 ohm resistor to v+ measures 220 ohms. The polarity of the cap is correct.

??

[eLarson]

I'm assuming that you are talking about the amplifying portion of the circuit and not the voltage stabilizing part. (That seems to be right if you see about 60V... presumably you see -60 V at the other rail.)

Does one half of the diff-pair work or are both MOSFETs (not) doing the same thing?

[Alain Dupont]

lgreen,

Could you provide us with some measures on the schematic...

And perhaps some pictures of your design...

Regards.

Alain.

[lgreen]

Here is the drawing I came up with based on the circ board that is built but not working, if you want to see the board, that will be posted later.

The full volume controls are not shown but Ive got them arranged just like the article, on another board. Anyway it should work with or without the output pots I would think. And I tried it 1st with them connected and get the same problems.

[Alain Dupont]

lgreen,

Well, at first sight your schematic is good.

Could you replace the 2 IRF610, to verify if there could be the pb...

Or verify

PS: I join the pins of the IRF 610

Regards.

Alain.

[lgreen]

Yeah, I looked at that pinout 20 times last night to make sure I had it right. I'll try new IRF 610's to see if the problem is that the 610's are not working. Dont see how that could be though, but i'm running out of options.

Any other ideas?

[wuffwaff]

Hi Igreen,

looking at the voltages your circuit is working. The wrong voltages are caused by not enough bias.
Vgate is OK
Vgs is OK
bias should be (-3.3V -60V) / 1500 = 38mA

looking at Vdrain it is 1/750 = 1.33mA

Are you really really shure that the source resistors are 1500 ohms (750 + 750) and not 56,7V / 0,00133A = 42k????

If they are 1500 Ohms then 38mA must be running somewhere else, look for connections to ground.

good luck!

William

[lgreen]

Thanks everyone for looking at this.

Turns out William was kind of right. I had triple checked my component values and my wiring it turns out everything was correct....except that I had installed a 100K resistor where the 22.1 ohm V- resistor should have been, and installed the 22.1 at the input. So I measured all the right values, but two were in the wrong place which was tough to pick up on my point to point veloboard. If I could read resistor codes it would have been easier. I re-swapped them and it works fine. Thank you all for your help, this was driving me nuts! Now to finish the project.

[Alain Dupont]

lgreen,

Something that could help you...