i also tested the resistance of each. one was a direct short and the other had some resistance although very little. after further thought i do remember one channel having about 360mv at the drain of q1 and the other channel had about 4mv at the drain of q1. the channel that had 4mv is also the one that had the zener that is a complete short and the other had the zener with a little resistance to it. so what would cause these zeners to go bad? is my higher input voltage affecting them? i am using 9.1v zeners
fligti91 said:
Nothing, as long as you dont fiddle with the input RCA's🙂
Did you check your boards against the pic's I posted earlier? The best you can do, is to check every connection one by one. It seems like you have all the components on the wrong side of the PCB.
🙂
steenoe said:
We just returned to the castle, after a nice cup of coffee served by Steenoe and the Mrs. Oe. 😎
I talked this over with Steenoe, as I had the pleasure of having Mike (Fligti91) on Skype Friday night.
Conclusion: either wrong value potentiometers, or dead Zeners.
Magura 🙂
ok before we all get to excited. what is the voltage supposed to be at the gate of q2? one channel ran for about 3 minutes until i turned it off. heat was being produced on the heat sink🙂 .
but on the other channel the 9240 had a small spark come out of it and no that channel is dead. probable causes? heat rise to fast on that one 9240?
so the zeners were shorted. mr. pass thank you for the idea to run without them, is there a recommended zener for my application that would work better than the last 2?
but on the other channel the 9240 had a small spark come out of it and no that channel is dead. probable causes? heat rise to fast on that one 9240?
so the zeners were shorted. mr. pass thank you for the idea to run without them, is there a recommended zener for my application that would work better than the last 2?
forgot to note that the 9240 that blew did not blow right away. it took about a minute or so before it went.
fligti91 said:
They're there to protect the gate of Q1 from static discharge at the input. You can certainly run without them, just make sure you ground yourself and input cable before you plug it in. The one listed in the article is fine.
I'm not sure about the voltage for Q2, before you turn everything on again, check for continuity between the metal tab on the fet (drain) and your heatsink, I know you've done it, but double-check. You shouldn't get any continuity. And of course make sure the fet is physically tight and snug to the sink.
Congrats on partially getting it working, you're almost there, victory will be sweet!!! I think I might even re-populate my zen boards for some re-exploration!!
-john
ok the original article states that the gate of q2 should be regulated by q3 to @4volts.
im getting in the 30's??? why is that
im getting in the 30's??? why is that
after looking at your picture i see that it seems my mpsa92's are backwards. hmm, i guess i had them right in the beginning. the original article shows the emitter going to main power and collector to gate. mine are the other way around
Hold your horses.....
Before you start turning anything around, take a look at the channel that works.
You say you have 30V at the gate of Q1, that's all good and fine, as the voltage is dependent of the position of the potentiometer.
If you adjust the voltage on the drain of Q2 to be approx. half of your supply voltage, I bet you the voltage on the gate of Q1 will drop to something more reasonable.
Magura 🙂
Before you start turning anything around, take a look at the channel that works.
You say you have 30V at the gate of Q1, that's all good and fine, as the voltage is dependent of the position of the potentiometer.
If you adjust the voltage on the drain of Q2 to be approx. half of your supply voltage, I bet you the voltage on the gate of Q1 will drop to something more reasonable.
Magura 🙂
no q1 has almost exactly 4 volts on it but q2 had in mid 30's. after looking at the circuit diagram and the mpsa92 pinouts i confirmed the mpsa92's are backwards.
i have the collector going to main power
i have the collector going to main power
fligti91 said:
Most likely this happened due to over heating.
When you fire it up, measure the voltage on the drain of Q2, and adjust it to half of your supply voltage.
If the circuit does not share the load equal between Q1 and Q2, the P-channel fet (Q2) will give in, being the weakest link.
Magura 🙂
fligti91 said:
I dare to assume we are talking about the channel that still runs.
The voltage on the gate of Q2 is not an issue.
Try power it up, and adjust it as I described above, you will most likely find that it works.
Magura 🙂
- Status
- Not open for further replies.