JSR04, +12V, +5V (from the negative side)

[peranders]

JSR04 adjusted for +12 volts, LM431 = 6 V and gain of 2.
The negative side +5 volts, LM431 = 2.5 V, gain of 2

1.244 base-emitter T9 is way too much. You are not measuring between pin 6, IC7 and ground?

Max voltage base-emitter is 0.6-0.75 V

Are you getting approx 8-9 volts out? If yes, it's a sign of a dead or not working opamp.

Voltage:
Pin 7?
Between pin 2 and 3 and down to ground?
Pin 6?
Over R45 (should be 2.50 V if the LM431 is working.)?

Across R25? Should be approx. 1 volts)

Please notice also that the LM337 and LM317 don't have the same pinout so LM317 won't fit at location of IC2 or IC4. I might have forgot to tell you that.

[builder brad]

Hi P-A,

I am not sure how much of my original e-mail response you have seen, so I will include it here:


>Re the 12v positive ½ of the JSR 04
>
>I have 1.244 volts base emitter of T9
>The voltage drop across R11 is0.35volts
>
>The LM431 voltages are 3.89 volts between R31 and the IC and 0.96volts
>
>R33 = 1k
>R39 = 1k
>R31 = 2k2
>R43 = 1k5
>R45 = 1k
>
>R43 is not used, however P3 is still in the circuit.
>
>It is worth noting that the 12v supply was working with all of the
>above resistor values before I shorted the unstabilised raw voltage
>output with the regulated side ie. Output 12 with pins 9,10 and 11.
>
>Currently I have replaced a couple of the ICs as you suggested and have
>managed to get the led to light and get 8.6 volts out, although I am
>sure that some components still need replacing!
>
>Re the 5v positive ½ of the JSR 04 modified from the – output
>
>I am only getting 1.5 volts DC output from an input of 13.5 volts DC
>unregulated
>
>I have used the LM317 with careful re-working of the PCB to copy the +
>half of the board, and wonder whether this is the cause of the very low
>output voltage, presumably I require different values for R14 and R16?
>
>Thank you in advance of your help with this.

[builder brad]

The op-amp seems to be getting power and I am getting 8.6v output, so I will look to change the op-amp initially and see if this helps.

[peranders]

Have you measured the things I suggested? The opamp may not be dead.

[builder brad]

I have already replaced the op amp and can now confirm that the problem is not with the op amp. The only difference now is a slight reduction in the output voltage at 8.1 volts.

I will now measure the areas you requested

[builder brad]

OK..

I have now taken readings for the following

T9 output to pin 6 on the op amp voltage is 1.27v

the op amp pins have the follwing voltages

1. 4.04v
2. 4.09v
3. 3.91v
4. nc
5. 0.62v
6. 1.27v
7. 7.99v
8. 7.99v

the voltage over R45 is 0.97volts (this should be 1/2 of the target output voltage)

the voltage across R25 is 1.09volts

hope this helps

[peranders]

This may a symptom of too small values around LM431.

I may have missled you here because I have changed the values. See rather the newly upload schematics.

At startup and with a LM431 you must unsure that the LM431 has a _higher_ voltage than the feedback until the opamp gets active.

From readings now the inverting input has a higher voltage than the non-inverting. This will create a latchup or "lacthdown"

The easiest for you is to connect 2.2k in parallel to R31 just to check. If this was the problem you know that you have to change the ratio.

[builder brad]

!!!!!!!!!

you are right!

I now have 20v output with a 2.3k resistor in parallel with R31

I quickly checked the voltages around the op amp and have 19 volts supply with 10+ volts output.

FYI I also tested the PS with a 47 ohm 10watt resistor and observed a drop in the output to 16.5 volts

what do I now need to do?

Brad

[peranders]

How much voltage do you now have on pin 3? It should be 6 volts.

[builder brad]

pin 3 has 10v, which explains the 20 output, athough I am not sure what alternative resistor values will be needed for 12v. The value of r31 is currently 800 ohms

I have a similar "latching" problem with the 5v (from the -12 side) output, with less than 1.5 volts measured at the output. Is it worth trying a 2.3k resistor across r32 to see if this makes a difference to the output. r32 is currently 470 ohm.

[peranders]

If you load the 20 volts output, do you get a stable voltage? If yes, the regulator works but the reference is set wrong.

[builder brad]

Hi P-A, when I load a 47ohm resistor across the 20v output, this causes the voltage to drop to 16v which does not fluctuate

Brad

[peranders]

How about the voltage across R45? Is it 2.5 volts?

Pin 2 and 3, IC7? A couple of mV across the pins?

The output, pin 6, does it change anything?

[builder brad]

Hi P-A

Re The 12v + output section:

2.5v is drop is seen across r45

Pin 6 on ic7 measures 13.3v with no load and increases to 15.1 volts when the 47 ohm resistor is placed across the output

pins 2 and 3 have 0.5mv pd which increases to 630mv with that 47 ohm load.

[peranders]

The LM431 seems to work since you have 2.50 Volts between anode and ref but can you tell me which values you have around the LM431? You should have 6 volts so I'll suspect some error there in values.

Do you have 2.45-2.55 volts, probably 2.495-2.505V