continuing lowrider problems

[rmfroyd]

I need a Christmas Miracle....

Had problems with the first board I bought.  They all started with IC5, specifically the Voltages at pin 8 and pin 14.  I would measure the voltage at pin 14 and it would be correct.  Measure at pin 13, correct, go back and measure at pin 14  and voltage was down about 5 volts. Went through about 10 %$^&in IC's same result.  Bought new ones, same result.

Put myself in a time out for a couple weeks, and I bought a new board.  Populated it, and I am still having problems at pin 8 and pin 14.  Brand new IC's.  This time the voltage is fluctating on both pins between 5 and 6 on pin 14 and between 1.5 and .003 on pin 8.  All new IC's, all resistors check out, reflowed solder eleventyhundred times....

I have built over 100 boards and I have never failed this badly.  Is there a chance it is a bad batch of PCB's?  Has anyone built one in the last 6 months that has worked?

Thanks for taking the time.

[madbean]

What end result are you hearing? No octave down, I suspect? Have you tried swapping your LM324 into IC1 and checking voltages there? Would be one way to help eliminate issues with the IC itself. You've bought several LM324, it seems. Where did you get them?

[rmfroyd]

Thanks for getting back to me, MB.  I havn't hooked it up to my test box to see how it sounds, I just wanted to check the voltages first.

The first batch of LM324s were from tayda.  The last 2 batches(12) have been from Digi-key.

Voltages are dead nuts on IC1, IC2, IC3 and IC4.  IC5 is fine except for Pin 8 and pin 14. Since those voltages are off, it in turn mucks up the voltages on IC6 and IC7.

I don't remember off the top of my head, I hope to get to it this weekend, But Q1's gate voltage wasn't dropping down to 4.6, it was similar to the drain and source voltages.  The MPF102's I sourced from Small Bear.

Thanks again for your help.

[madbean]

Thanks for getting back to me, MB.  I havn't hooked it up to my test box to see how it sounds, I just wanted to check the voltages first.

The first batch of LM324s were from tayda.  The last 2 batches(12) have been from Digi-key.

Voltages are dead nuts on IC1, IC2, IC3 and IC4.  IC5 is fine except for Pin 8 and pin 14. Since those voltages are off, it in turn mucks up the voltages on IC6 and IC7.

I don't remember off the top of my head, I hope to get to it this weekend, But Q1's gate voltage wasn't dropping down to 4.6, it was similar to the drain and source voltages.  The MPF102's I sourced from Small Bear.

Thanks again for your help.

Well I always suspect any active device from Tayda, but given your other batch is from DK then let's just rule out an IC issue. Take a listen this weekend to see what you are hearing. If needed, I'll pull mine out and re-check my voltages. It's possible there could be some voltage fluctuations normally there due to the diode recitfiers. But, it also doesn't seem quite right, either.

[rmfroyd]

Thanks, will do.

[madbean]

Also, I don't rule out anything when it comes to debugging so a PCB manufacturing error is possible. It's rare but it happens. Generally I catch anything obvious since I put eyes on every board I get. But, while you are at it, take a really close look at the pads around the LM324 on the bottom of the board. Look for any sort of hair trace under the soldermask connecting things that should not be connected.

[rmfroyd]

Ok.  I will do that.

I have triple checked everything on both boards so I know it isn't component placement error, to the point I may be able to populate a board from memory....lol.

[rmfroyd]

As far as I can tell there isn't anything wrong with the board itself, I couldn't find and errant traces.

Also, Voltages at the gate of q2 and q3 are wildly fluctuating.

I will plug it in later, right now I am trying to balance pedal time with in-law time.....