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

[bushtech]

Thanks Audioguru

The readings on the individual pins are measured with one probe connected to the negative of C1

 

[bushtech]

2N3055's disconnected and 10k resistor installed. BD139 disconnected. I then measured the voltages on the 3 desoldered leads as I'm very afraid of blowing my remaining new BD139.

Voltage on leads: ( Neg probe of DMM connected to C1)

E 40.2V
C 40.9V
B 0V

 

[Audioguru]

The 2N3055 transistors are disconnected from the output and from the emitter of the BD139 and the BD139 is removed. Then the BD139 emitter pcb pad has only R16 (1k) connected to the output that has the added 10k resistor to ground. Then the emitter pad of the BD139 should be 0V, not 40.2V. Whatever wrongly causes the emitter pad to be at 40.2V is blowing up the BD139.

The output of the project should also be at 0V by the added 10k resistor but maybe the output is wrongly shorted to a high positive voltage?

 

[bushtech]

Thanks Audioguru, something concrete to work on.
Days of power outages and internet outages, thanks to Zuma.

Been hunting down that 40V signal. I have found that the 40V runs from Emitter on BD139 through R16, down past R12/C6 (other side of R12/C6 about 14V) through D11, through C5 and to pin 7 of U2.

I have since replaced D11(1N4001) and the E of BD139 is now at 0V but C now at 40V and B at 39.8V.

Have no idea what is going on

 

[Audioguru]

D11 does not connect to +40V so how did it make the emitter pin of the BD139 at +40V? Maybe it had a solder whisker shorted to +40V. The collector of the BD139 is normally wired to +40V because it is an emitter follower.

Opamp U2 will not be connected to the missing BD139 so with its output temporarily connected to R6 and C12 (that have been disconnected from the output) then U2 has normal negative feedback and its output should smoothly follow the voltage control pot and go from 0V to about +30V. Since the output voltage of U2 (the base of the BD139) is too high then U2 is probably fried or its output is shorted to +40V.

 

[bushtech]

Thanks Audioguru
Currently R6/C12 reconnected and 10k resistor removed.
If pin 7 of U2 is pushing 40V it only has to traverse C5 to reach D11 and if D11 is not blocking 40V only has to get through R16 to reach emitter of BD139.

So the 40V at collector of BD139 is correct?
I would hate to replace U2 and fry another TLE2141- can you give me the relative voltages I should see on U2 that I need to get to before I can plug in another opamp

These are the voltages I am seeing with U2 removed:

I am seeing -0.0V on pins 1 to 8 with only pin 7 sitting at +40V+

 

[Audioguru]

The collector of the BD139, pin 7 of U2 and C5 should always have +40V on them.
I think the D11 shorted to +40V blew up things.
With the BD139 removed and R12 and C6 connected to the output pin 6 of U2 only pin 7 should have a voltage (+40V) on it and also pin 3 is its input which should smoothly go from 0V to +11.2V when the voltage pot P1 is turned.

The +40V on C5 can get to D11 only if the BD139 or the output transistors are shorted. I hope the Chinese pcb is correct.
Whose schematic are you looking at? Maybe the Chinese one that I do not have is wrong. I am looking at mine that is Rev 6 July '14.

I think you are ready to try a new TLE2141 opamp for U2 and when it works properly you can put R12 and C6 back to the project's output and install a new BD139 without the output transistors. Then when the bD139 works properly you can add the output transistors. If they work properly then you can adjust the offset voltage pot RV1 for 0.00V, calibrate for +30.00V and for 3.00A then you are finished this project.

 

[bushtech]

Thanks so much Audioguru. That sounds encouraging.
Yech!
BD139 and output transistors disconnected, R12/C6 connected I am getting 40V on pin7 of U2 BUT I am also getting 40V on pin6 of U2 and when turning pot pin3 goes from 0 to 4.8V.

So not quite there yet.

 

[bushtech]

Yep, building to Rev 6 July '14

 

[bushtech]

Situation:
BD139 disconnected
2 x 2N3055 disconnected
P1 pot turned half way
R12/C6 connected
10k link removed
U3 still getting hot
Black probe of DMM connected to neg of C1

U1

1 2V
2 5.6V
3 5.6V
4 0V
5 2.5V
6 11.2V
7 41V
8 0V

U2

1 0V
2 0V
3 3.8V
4 0V
5 0V
6 40.2V
7 41V
8 0V

U3

1 4V
2 3.2V
3 2.9V
4 3.8V
5 4V
6 4.3V
7 31V
8 0V

Problems I am aware of:
1. Pin 6 of U2 at 40V when it should be zero
2. Pin 4 of U3 not at -1.3V
3. U3 getting hot (Hoping that will be resolved by fixing point 1 and 2 above)

Due to a postal strike have not received my new 2N3055's.

 

[bushtech]

Oh, and led is lit

 

[bushtech]

Have I got Q3 the wrong way round:

Found a 9015 pinout here:
https://www.google.com/search?q=901...AhVLXRoKHf-6CbMQ9QEILDAB#imgrc=WBQTTNFfTyPUJM:

Don't know if it's correct but if it is the 9015 is E B C and the BC557 is C B E

 

[Audioguru]

Opamp U2 inverting input pin 2 is probably wrong at 0V because it is not being fed negative feedback through R12 and C6.
In the complete circuit, U2 gets negative feedback from the output but for this test there is no output. Since the BD139 and output transistors are removed then R12 and C6 should be temporarily connected from U2 inverting input pin 2 to U2 output pin 6.
But U2 non-inverting input pin 3 voltage is too low since it should be half of the output of U1. Your output of U1 is correct at 11.2V and with the voltage pot set halfway the input of U2 should be +5.6V.

Pin 2 of U3 should be at 0V since it connects to 0V with R21 (10K) in series with R7 (0.47 ohms) so either the TLE2141 is bad or there is a short on the pcb.

I use American transistors, not Oriental and not European. If you use the Oriental 9015 or the European BC557 then look at its pins on its datasheet.

 

[bushtech]

Have reversed the BC557 but have not noticed any change
Trying to hunt down the -1.3V.
Have replaced C2 and C3. Resistance on R2 and R3 checks out (in circuit readings)
Voltages across the following diodes:
2 x D7 = -3.9V
D5 = -0.72V
D6 = -0.72V

Is this what they should be?

 

[Audioguru]

Voltages across the following diodes:
2 x D7 = -3.9V
D5 = -0.72V
D6 = -0.72V

Is this what they should be?

No. The datasheet for the 1N4148 diode shows 0.65V when its current is 1.8mA. It is never as high as almost 2V even when its current is massive at 800mA.
I think your D7 diodes are connected backwards.
D5 and D6 have a correct forward voltage.

As a test remove U3 and replace the D7 diodes. They should produce close to -1.3V.

 

[bushtech]

Thanks for your endless patience Audioguru

Can we please sort out the 2x D7

Here is a photo (please excuse state of board but it's been busy)

Right hand leg of diodes connects to R3

Have I got them the wrong way round.? Not trusting myself anymore

 

[Audioguru]

Yes your D7 diodes are backwards. See the symbol on the pcb where one end of the diode box has a white bar? The diodes also have a bar (but it is black) on the cathode end.
The straight line in the schematic symbol of a diode is its cathode.

 

[bushtech]

Thanks Audioguru. me hangs head with bleeding forehead in shame

 

[bushtech]

Swung them around . Seeing -1.5V across them

 

[bushtech]

On your Rev 6 the bars on the diodes are on R3 side ?