Hi Valx,
No problem. Life happens to all of us all of the time.
Your measurements make sense. You have high bias but it works otherwise. It's hard to read, but Q109 looks like your bias transistor (the small one beside the driver transistors). Try to increase the resistance between its emitter and base. If you use a trimmer control you can adjust it and find the correct approximate value, then choose a fixed resistor close to that and install it in place. Make sure that Q109 has reasonable beta first and no leakage. You could measure the transistor on the other channel to see what the expected value is.
Across the emitter resistors, 3 to 5 mV difference could be a lot if the bias should be a couple mA. Probably 6 to 12 mA, and that isn't enough by itself to cause such high current and heating. So if that side is still getting hot, I question the readings across the emitter resistors, you measured each one - right?
Full power testing tends to swamp out bias issues as the load is drawing most of the power. What you are really testing is the inverter and bench power supply. You want to allow it to cool, then let it run in idle for a bit. Then check everything.
No problem. Life happens to all of us all of the time.
Your measurements make sense. You have high bias but it works otherwise. It's hard to read, but Q109 looks like your bias transistor (the small one beside the driver transistors). Try to increase the resistance between its emitter and base. If you use a trimmer control you can adjust it and find the correct approximate value, then choose a fixed resistor close to that and install it in place. Make sure that Q109 has reasonable beta first and no leakage. You could measure the transistor on the other channel to see what the expected value is.
Across the emitter resistors, 3 to 5 mV difference could be a lot if the bias should be a couple mA. Probably 6 to 12 mA, and that isn't enough by itself to cause such high current and heating. So if that side is still getting hot, I question the readings across the emitter resistors, you measured each one - right?
Full power testing tends to swamp out bias issues as the load is drawing most of the power. What you are really testing is the inverter and bench power supply. You want to allow it to cool, then let it run in idle for a bit. Then check everything.
Hello anatech 👋
Iddle test was from cold, then full power.
I didn't measured emitter resistors individually 🫣.
I didn't know who was driving who, would have been easy to desolder Q109 and Q209 and compare them with my cheap tester and tweak with the VR to find a good fixed value.
Now.... i explained to my friend the situation and he wanted to take the amp as it is, will see how long will last (he drives it hard all the time).
Meanwhile I am readind the Repair Tutorial from Mr. Babin, there is a lot to learn and i will know how to measure and what to ask you guys about a problem will encounter.
Iddle test was from cold, then full power.
I didn't measured emitter resistors individually 🫣.
I didn't know who was driving who, would have been easy to desolder Q109 and Q209 and compare them with my cheap tester and tweak with the VR to find a good fixed value.
Now.... i explained to my friend the situation and he wanted to take the amp as it is, will see how long will last (he drives it hard all the time).
Meanwhile I am readind the Repair Tutorial from Mr. Babin, there is a lot to learn and i will know how to measure and what to ask you guys about a problem will encounter.
Hi Valx,
Just run on idle to check, you can warm it up, no need for full power, then let it cool to see how stable it is. Full power tests are just to see that they continue to "hang together".
Okay, measure the voltage drop across each emitter resistor and record the values. You may find one pretty high.
Using the amp as-is is not intelligent. We know it has a fault already. It may fail in worse condition, and at the very \least run his electrical system too hard. In short, bad idea.
Just run on idle to check, you can warm it up, no need for full power, then let it cool to see how stable it is. Full power tests are just to see that they continue to "hang together".
Okay, measure the voltage drop across each emitter resistor and record the values. You may find one pretty high.
Using the amp as-is is not intelligent. We know it has a fault already. It may fail in worse condition, and at the very \least run his electrical system too hard. In short, bad idea.