orion 2150 power supply op amps

[Perry Babin]

I thought you stated that the rail voltage was steady after you checked across the emitters? Did I misunderstand?

 

[Nutcase21]

i'm sorry, it isn't. maybe it was the way i worded it. i get the proper rail voltage but only when the led is lit, and that's only for a second or two.

 

[Perry Babin]

When the 6488 was out of the circuit, did the voltage (measured across the emitters, not to ground) fade?

 

[Nutcase21]

yes it did

 

[Perry Babin]

Re-check with the 6488 out of the circuit after the LED fades. Do you still have a drive signal on pins 9 and 10 of the 494?

Do you still have 12v on the collectors of the NPN power supply driver transistors?

 

[Nutcase21]

after the led goes out I have 4.4 volts on pins 9 and 10 of the 494 but zero frequency. The collectors of the npn drivers fall to 3.7 volts approximately.

 

[Perry Babin]

If you set you meter to AC voltage and measure where you can no longer measure frequency on pins 9 and 10, what is the AC voltage?

Is the amp drawing excessive current from the 12v power supply?

 

[Nutcase21]

amp draw isn't excessive, it peaks at around 1.6amps before the led dies out and it stabilizes at ~0.2amps

weird thing i just noticed is that when i have the meter on dc voltage and i'm testing for frequency on pins 9 and 10 it shows 0hz and like 4.4vdc. now when i try it with the meter on ac voltage like you say i get 20.6khz on both pins 9 and 10 and ~4.6vac

 

[Perry Babin]

There is a large resistor between the 6488 and 7815 regulator, and the transformer. What resistance do you read across that resistor?

 

[Nutcase21]

68.01 ohms

 

[Perry Babin]

Black probe on ground... What is the DC voltage on each end of that resistor initially (when the amp is producing full rail voltage and then when the supply has shut down? That will be 4 voltage readings.

 

[Nutcase21]

After the supply has shut down its12.468vdc on the end closest to the positive power cable and 3.7285vdc on the other end. When the led is first lit it's 12.4 689 DC on the positive cable end and 3.733vdc on the other. I should ask, is this with the 6488 out still or back in?

 

[Perry Babin]

Out.

 

[Nutcase21]

My previous post has the correct measurements Then.

 

[Perry Babin]

I think I have one of these somewhere. I'll need to find it and try something. I may not get back to this until tomorrow.

 

[Nutcase21]

Figure anything out perry?

 

[Perry Babin]

Not sure.

If you measure the resistance from the emitter of the driver transistors to ground, what do you read?

 

[Nutcase21]

Odd, I get 7.6 ohms on 1 side of the supply and 99.6 on the other.

 

[Perry Babin]

You may have replaced one of the 100 ohm resistors with a 10 ohm. Confirm that you have at least one 100 ohm resistor on the side reading low. If you do, the Zener diode on that side is leaky.

 

[Nutcase21]

I do have one there, I replaced all the gate and pull down resistors on both sides of the supply. Didn't replace the diodes though I did test them. Must have missed it. I'm gonna pull it and check out of the circuit.