Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

[Audioguru]

The 1N4740 zener diode will work well if it is not connected backwards. Measure that it has 10V across it.
The driver and output transistors voltages are messed up. Disconnect and bypass them to see if the U2 opamp works properly like this:

 

[bushtech]

Pretty sure D13 connected correctly:



But I'm seeing 30 V between it and Q3
Thanks for that Audioguru. Will get on it

 

[bushtech]

Lifted the anode leg of D9 and a leg each on R12 and C6. Measuring the voltage on cathode leg of D9 = 5.2V

Voltage between R6/C12 and pin 6 of U2 = 35V. Voltage does not change when adjusting voltage on panel pot or RV2
Sigh!

 

[Audioguru]

I cannot see where pin 7 (the positive power supply pin) of U3 connects to. It should connect as shown on my schematic.

If pin 7 of U3 is about 30V (is it?) then the added 10V zener diode is not destroyed then since the output of U3 is only 5.2V it is in current regulate mode and lights the LED. It should be in the current regulate mode only if the setting on the current setting pot is less than the load current.

My last sketch showed R6/C12 disconnected from the project's output (because maybe the driver and output transistors are messed up) and R6/C12 are connected temporarily to the output pin 6 of U2 as a test. Also, with the driver and output transistors disconnected from U2, what voltages are on their pins (to see if one transistor is backwards or is shorted)?

 

[bushtech]

Audioguru, I feel so bad about wasting your time with this. My apologies.

Pin 7 of U3 involves Di3 where I used paulv's connection and track breaks:

Not sure how all that connects with pin 7

Pin 7 of U3 is sitting at approx 40V!

Apologies I now understand how to connect R12/C6 and pin 6 of U2. But which pot do I have to adjust to see if output goes from 0 to 30 V

Do I need to check the voltages on BD139 and the 2 2n3055's? ie with above disconnects

 

[Audioguru]

You have too many threads about this miserable power supply and have a Chinese kit with none of its parts numbered and made from the original defective circuit and some changes made by Paul on his blog.

Paul's schematic (with skinny wires that are hard to see) shows the 10V zener diode the same as mine, powering Q3 and R3 but maybe his wiring changes are wrong.

The Chinese pcb has the pots marked A and V. Which one of them adjusts the voltage?

 

[bushtech]

This is the only thread I have about this power supply. What other threads are there?

The only numbered one I have found kindly done by paulv:


Ok, so now I know you are talking about the front panel voltage pot .

With the disconnect/connects done output voltage sits at around 40V and turning the voltage pot makes no difference.

Voltage on BD139:
e: 38.9V
c: 40.4V
b: 39.4V

Voltages on 2N3055:
Q4
b: 38.8V
e: 38.4V
C: 40.3

and Q5 the same

 

[bushtech]

Readings on the opamps:
These readings taken with the disconnects/connects still in place
U1:
1. 1.2V
2. 5.6V
3. 5.6V
4. 0V
5. 0.6V
6. 11.2V
7. 41V
8. 0V

U2:
1. 0.4V
2. 3.7V
3. 37.4V
4. 4.4V
5. 4.5V
6. 4.8V
7. 41V
8. 0V

U3(overheating)
1. 3.6V
2. 16V
3. 11.3V
4. 4.3V
5. 3.6V
6. 41V
7. 41V
8. 0V

I hope this shows up something
Where can I start investigating?

 

[Audioguru]

Some voltages are wrong. The 0V black lead of the meter should connect to the negative wire of C1. Are your opamps TLE2141?

1) U1 voltages are correct.
2) Pin 3 of U2 is wrong. It connects to P1 so it should go from 0V to +11.2V as P1 is turned up. Maybe pin 3 is shorted to something or maybe U2 has been destroyed. See if the variable voltage is normal when U2 is removed.
3) Pin 4 of U2 is wrong. It wrongly connects to -5.6V on the original kit and I think also on the Chinese kit. I did not look at what it connects to on Paul's schematic. Mine has it connected to 0V.
4) Pin 6 of U2 is wrong. It should go from 0V to about +32V as P1 is turned. I think U2 is destroyed by something wrong at or with the driver transistor.
5) Pin 6 of U3 is much too high. Since its pin 2 voltage is higher than its pin 3 voltage then its output voltage should be near 0V. Maybe it is a defective or fake opamp.
Pin 4 of U3 is too high and is the wrong polarity. It is -1.3V on my schematic. Maybe the fault in U3 causes its pin 4 to be wrong, measure pin 4 with the opamp removed.

Connect a 10k resistor from the base of the driver transistor (nothing else is connector to its base during this test) and 0V then see if its emitter and the emitters of the output transistors also go to 0V.

 

[bushtech]

Audioguru: Thank you for your valuable comments. Busy working my way through them and checking stuff.
Opamps are TLE2141IPE4

 

[Audioguru]

Here is one reason that U3 gets hot:

 

[bushtech]

Thanks for the help Audioguru. Your insight into this just staggering. It took me a day to figure this out. Making that change has sorted the overheating U3, also switched off the led coming on when powering up. I am still working my way through your list of problems.
What i now want to sort out is breaking the connection between U3 pin4 and U2 pin4 without having to move the connection point of U2 pin 4, my previous bodge didn't work.

 

[Audioguru]

It is too bad that the Chinese companies copied the defective original circuit without testing it, and too bad that they did not number the parts on the pcb.

 

[bushtech]

Yeah, irritating, have to keep referring to paulv's numbered layout printout.
But making progress: Have now sorted pin 4 on U3 and U2 and think I have found an easy way to move D11 endpoint from R7 line to the line above.

Then we might start getting somewhere

 

[bushtech]

Have done a lot of checking and fixing. Led still coming on. OPamps getting warm but U3 not gettting as wickedly hot as previous bur still hot

U1 readings still the same so not reproduced
U2:
1. 0V
2. 0V
3. 3.6V
4. 0V
5. 0.1V
6. 19.3V
7. 41V
8. 0V

U3(overheating?)
1. 4.7V
2. 3.3V
3. 3V
4. 3.9V
5. 4.8V
6. 4.3V
7. 31.6V
8. 0V

I hope there is some improvement here, but sure there is still something wrong. Have got caps now so put a 0.1μf cap over base connection of big cap.

 

[bushtech]

Voltages: (V)
BD139
E 27
C 40
B 17

Q5 (2N3055)
B 27
E 39
C 40

Q4 (2N3055)
B 26
E 39
C 40

 

[bushtech]

Pin 4 of U3 goes to 0.3V when U3 removed
Voltage of pin 6 of U2 unchanged as Voltage pot turned. Output voltage constant at 41.6 V
Oh, and led on again.

 

[Audioguru]

U3 does not work properly because its negative power supply voltage of -1.3V on pin 4 is wrong and the -1.3V should not change when U3 is installed. Check or replace R2, R3, C2, C3, D5, D6 and both diodes making D7.

U2 has its pin 2 wrong at 0V when it should be the same voltage as pin 3.
You measured its pin 6 voltage at +19.3V but now you say its output does not change when the voltage pot is turned. Then its pin 3 voltage connected to the voltage pot should change. you say its output is now steady at +41.6V but was 19.3V earlier?

The emitter voltages of the output transistors cannot be higher than their base voltages and should be about 0.5V less when there is no load.
The emitter voltage of the BD139 also cannot be higher than its base voltage.
Either the pins of the transistors are mixed up or they are defective.

 

[bushtech]

Thank you Audioguru thank you.
The 19.3 V was measured on pin 6. The 41V measured on the power supplies outputs.
Thanks for the additional components to check on the -1.3V. That has been irritating me. Have checked 2xD7 already for polarity switching.
How easy is it to blow the BD139 and the @N3055's, have never felt them getting hot?

 

[Audioguru]

A blown transistor is either shorted or it has its parts disconnected (blown out). But your transistors have the emitter voltage higher than the base voltage which is impossible unless they are leaking current very badly collector to emitter or have their pins mixed up.
The power supply output was 41V because one or both output transistors are shorted from collector to emitter.