Hello Everyone,
This is my first madbean build and need some debugging help on the egodriver circuit board.
I made a testing rig with built-in audio proble, and I have a DMM. OK...
First, I have not yet soldered on the PCB mounted pots and am not sure if this even needs to be done to correctly test the circuit board ??? However, I did solder the HP/LP switch into the board.
I am getting an input signal but no output signal with the audio probe. My dcV measurements at the IC are:
1-8.0 8-8.7
2-7.2 7-8.0
3-2.9 6-7.0
4-0 5-7.6
I think these values are incorrect but am not sure what to do or where to start at this point. My solder joints look good with no suspect under a magnifying glass.
Thanks for your help in advance!
You need some connection between pins 1 and 2 of the gain pot. Any value between a jumper and a 1M resistor tacked in temporarily. Otherwise the first stage is just an integrator and will latch up toward one of the rails. Also, check that Vbias is correct at the junction of R14 and R15. It should be sitting pretty close to 4.5vdc. I'm guessing it's OK since you're reading 2.9vdc at pin 3.
thanks for the reply oldhouse but I am still learning the ropes with all this. Where is the junction between R14-R15 located on the circuit board? Also, should I just solder in the gain pot to make sure the circuit is fully connected? is this why am having all the issues?
Another tidbit. When I switch on the clipping LEDs only one of them lights up. Any insight from this?
I really appreciate everyone's help here ;)
Measure the voltage (with respect to ground) at both ends of R15. One end should be 0v and the other about 4.5v. You can go ahead and solder in the gain pot, or you can temporarily solder in a jumper or resistor (any value up to 1meg) between pins 1 and 2, and yes, I believe this is a large contributor to your problems at this point. At least until we get further along with the troubleshooting, but hopefully it will just work after this. The one LED lighting up verifies the imbalance in the voltages around the IC.
OK. I soldered in the gain pot.
IC voltages are:
1-4.35 8-8.70
2-3.95 7-4.36
3-2.94 6-4.34
4-0.00 5-4.26
Voltage at R15 is 4.33
Does this all seam right? I am getting output now but there is a lot of squealing and cutting in/out but I do hear some overdrive otherwise. This could just be because nothing is mounted up/wired yet, not sure?
Am I good to go ???
Voltages look much better. The squealing could be grounding/unboxed condition, or more problems still. You're on the right track, though. Can you post pics?
Circuit is working ;D
I went ahead and soldered in the other pots (volume and tone) and hooked it up to the test rig and YES! Apparently all pots an switches must need to be hooked up for the circuit to test correctly?
It sounds great, especially the LED clipping. I played it for about an hour with the test rig. Now time to get it boxed up. I will post some pics o my first MB build soon.
Thank you very much oldhousescott for your help and patience with teaching a newb
Yes, all the pots and toggle switches need to be wired in for the circuit to work. Glad you got it working!
jacob