F6 Illustrated Build Guide

[Yaho]

The earth wire can attach to the isolated meanwell chassis but not the korg chassis

that's what i will do, tomorrow. After looking at these things over 10 hours my eyes are watery.

thanks for all your help!

 

[2 picoDumbs]

Good

 

[2 picoDumbs]

that's what i will do, tomorrow. After looking at these things over 10 hours my eyes are watery.

thanks for all your help!

I know you confirmed this already but:
1) Meanwell 0V to Meanwell chassis should be open circuit
2) Meanwell Chassis to Korg Chassis should be open circuit

Then you can connect earth wire to Meanwell Chassis (not Korg chasis)

 

[tamra]

Did you turn down the bias pots, then re-bias after removing the bulb tester? You must do this and let it settle (get up to temprature)

Thank you for suggestion. I

Did you turn down the bias pots, then re-bias after removing the bulb tester? You must do this and let it settle (get up to temprature)

Thank you for suggestion. I will do it next time.

0.5 V is not 0.5 A

0.5V is around 1A

Bias to 0.5A, that is about 0.25V across the source resistors.

I see.I start from 0.25V.
The smoke come from R1 right channel.
I changed R1 this morning,then measured voltage at R2.
It was 0V.
Changed all caps. Vgs are 3.3V both.

 

[2 picoDumbs]

I am getting confused with the sequence of events

 

[2 picoDumbs]

If smoke was coming from the resistors and the mosfets no longer turn on even with 4.5V Vgs then most likely your mosfets, may now need replacing


Maybe explain your current situation better.

The question I have in my mind is why are the mosfets cooking with only around 4V at the gates.

 

[2 picoDumbs]

Could you take another photo of your board showing the burnt resistors

 

[2 picoDumbs]

Vgs 3.3 V may not be adequate.
Increase it to 4V

If the mosfets don't turn on with 4V Vgs then you need to replace the mosfets

 

[tamra]

I will change mosfets this evening,thank you.

 

[eddyvb]

Is this a 3W resistor? Looks small.

 

[2 picoDumbs]

Yeah.
I was thinking it looked like a 1 W.
Maybe CMF60

 

[tamra]

It's mills mra5, 5w.
I changed mosfets but nothing problem.
When I plug from bulb tester, bulb lights one second
Then all LED light up.
After 10seconds,LED turn off then bulb turn light again.
I'm checking every resistors but can't find any failure.

 

[2 picoDumbs]

What is the Value of Vgs across each mosfet when this happens?

 

[2 picoDumbs]

When I plug from bulb tester, bulb lights one second
Then all LED light up.
After 10seconds,LED turn off then bulb turn light again.
I'm checking every resistors but can't find any failure.

What can happen.

Eg
You have set your trimpots wrong, Vgs is too high

At start up
1) PSU Caps Charge - Bulb On
2) LEDs On - Bulb Off
3) C1, C2 Charge - Bulb Off
4) Mosfets turn On Really hard, - Bulb On
5) Supply rails drop in value due to voltage drop at bulb
6) Leds go out
7) Mosfets go off

 

[2 picoDumbs]

Measure Voltages at psu when light bulb tester is connected.

Please adjust trimpots to mid point.

 

[tamra]

When I turn on with bulb tester,
PSU have + - 25V.
But 5-10seconds later,PSU down to +,- 10V.

 

[2 picoDumbs]

Reset trimpots to middle position

Try again and measure Vgs of mosfets

 

[2 picoDumbs]

What is the voltage drop across the leds when they are on?

 

[meanie]

When I turn on with bulb tester,
PSU have + - 25V.
But 5-10seconds later,PSU down to +,- 10V.

What is the wattage of your bulb ?
Looks like its too low when the amp is trying to operates, therefore you got a huge drop in your secondary rails. 24-->10v

 

[tamra]

I have set trimpots at middle point.
LED voltage are 7.4v while led are on. After turn off LED,its 6.0V.
Vgs are 2.3V and 2.2V