New project: Allen Engine analyzers, restoration?

[3175375]

I’m with @MoPar~Man on this. Ensure that ALL power forms are as documented.
I will try to print out the schematic screen shots that you provided, but I may not get to it until tomorrow.

 

[HWYCRZR]

Power to to the board is +15.2 and -14.9v which the spec is +15 -15 coming out of the power supply. Signal seems pretty stable. Not sure how to detect ripple unless you mean an unstable signal. Peak to peak is 200-400mV so minimal movement. Zooming way in on the signal is pretty solid.
I need to keep going downstream. TP101 is the recommended first test point, which is not giving me the 1VppAC I need. So my first section to dissect.

 

[3175375]

Power to to the board is +15.2 and -14.9v which the spec is +15 -15 coming out of the power supply. Signal seems pretty stable. Not sure how to detect ripple unless you mean an unstable signal. Peak to peak is 200-400mV so minimal movement. Zooming way in on the signal is pretty solid.
I need to keep going downstream. TP101 is the recommended first test point, which is not giving me the 1VppAC I need. So my first section to dissect.

View attachment 707245View attachment 707246

Are there other power forms that are derived from those two?

I have seen circuits that require lesser voltage and very low current and the design just used a divider network to make the reference voltage.

 

[HWYCRZR]

Are there other power forms that are derived from those two?

I have seen circuits that require lesser voltage and very low current and the design just used a divider network to make the reference voltage.

So, mistakenly measured the output from the board to the CO and HC zero knobs. I went back to my pencil sketches of the circuit and found the input from the transformer. Input to the board is 54.4Vpp and 54.4Vpp from each side of the transformer. Now to find out what it is supposed to input. But makes sense 1/2 of 110 ac? It is very steady.

 

[HWYCRZR]

Another tidbit on the power supply I found deeper in the manual. The question I have, is the 51-54v combined should be around 110v. So is it really an issue if I am only getting 102-108VAC? I need to re-read and absorb the information below. Sorry for my thinking out loud.

 

[HWYCRZR]

These little bad boys here are not the rectifiers that reduce the power supply to +-15V for the board. I think I need to check these out. I think I can check them like a diode. My little copper wire is pointing to them. Kind of small compared to the capacitors next door.

 

[MoPar~Man]

Diodes are not normally used as voltage reducers (unless it's a zener diode). The voltage drop across a diode is only going to be .5 to 1.5 volts. If those 1000 uf caps are across a power bus then they're there to take out any ripple or noise on the bus.

Do these boards have edge-card connectors? If they are, pop them off and use a pink pencil eraser and rub them good and hard across the fingers to clean them up.

Your power lines (+/- 15 volts) look clean, but is the power supply loaded? Are all boards hooked up?

What year was this thing made?

 

[HWYCRZR]

Instead of the +-15V on each side of the rectifiers I am getting +25 and -23V. Checking the diodes (still in the circuit so maybe influenced by the capacitors). I am getting about 2.5-7V in one direction and about 0.5 volts in the other direction.
I probably should check after the resistors , but likely ok as I am getting close to the 15V coming out of the board. So for now I am going to call my power supply good. The two big main capacitors C401 and C402 are not shorting out as I am only getting 420mV through them (23-25V on the other side) and they are 25V so seem to be working.

 

[HWYCRZR]

Diodes are not normally used as voltage reducers. The voltage drop across a diode is only going to be .5 to 1.5 volts. If those 1000 uf caps are across a power bus then they're there to take out any ripple or noise on the bus.

Do these boards have edge-card connectors? If they are, pop them off and use a pink pencil eraser and rub them good and hard across the fingers to clean them up.

Yes the main connector, but have already cleaned them with electrical terminal cleaner and a toothbrush. But based on my last measurements the board is getting full power. I need to work my way towards why my LED’s that flash through the chopper disk are not powering on, as that controls the signal to the gauges. Working my way through.

 

[MoPar~Man]

In your photo showing 2 yellow arrows on pins 8 and 16. There is a center-tapped transformer (T301) with pin 10 going to ground. The output is coming off pins 8 and 9. Measure the voltage across pins 8 and 9. Use a regular volt meter for that, set to AC volts. Using a scope to measure that is tricky unless you use both probes and set the input to differential. The other side of that transformer is connected to a component called a "chopper". Don't know what that is. I don't know where the power is coming from to that transformer (ie what is the primary side and what is the secondary side). IR source is a resistor, so it's a heater of some sort. R310 is a 12-watt resistor. So this is fairly high current. Pins 8 and 9 are probably going to be the input to the transformer, the output is going to the heater IR source and is going other places as well through pins 2/4/6 and 3 other pins that are covered by your yellow arrow. They're using 3 pins each because of the high current probably.

Is T301 a large or small transformer?

I look at this again, I think ac power (of unknown voltage) is coming from somewhere to T301 through the 6 pins (3+3) to power the heater and the transformer, high or moderately high current. The output of the transformer is on pins 8 and 9, center tapped to ground. I can't tell from the schematic where those pins are going (electrically).

 

[HWYCRZR]

In your photo showing 2 yellow arrows on pins 8 and 16. There is a center-tapped transformer (T301) with pin 10 going to ground. The output is coming off pins 8 and 9. Measure the voltage across pins 8 and 9. Use a regular volt meter for that, set to AC volts. Using a scope to measure that is tricky unless you use both probes and set the input to differential. The other side of that transformer is connected to a component called a "chopper". Don't know what that is. I don't know where the power is coming from to that transformer (ie what is the primary side and what is the secondary side). IR source is a resistor, so it's a heater of some sort. R310 is a 12-watt resistor. So this is fairly high current. Pins 8 and 9 are probably going to be the input to the transformer, the output is going to the heater IR source and is going other places as well through pins 2/4/6 and 3 other pins that are covered by your yellow arrow. They're using 3 pins each because of the high current probably.

Is T301 a large or small transformer?

I look at this again, I think ac power (of unknown voltage) is coming from somewhere to T301 through the 6 pins (3+3) to power the heater and the transformer, high or moderately high current. The output of the transformer is on pins 8 and 9, center tapped to ground. I can't tell from the schematic where those pins are going (electrically).

All the heat elements work fine. The IR source around 1000 degrees. The chopper is just a fast rotating disk that switches the “view” of the reference chamber and the CO HC chamber to compare and translate to voltage. The transformer is fairly small and at pins 8 and 9 which are actually the output of the transformer measure 19.65 volts AC with the regular Voltage Meter. The he transformer is fed by pins 3 and 4 which is full 110 AC. Power going into the board is around 20 volts and the rectifiers on the board are converting it to close to +-15 volts in which most of the board tests properly until I get to TP 101 which is the pre amplifier. Circuit in which I am getting a garbage or limited voltage. Orange pointer.

 

[HWYCRZR]

When I go to TP (test port) 101 I am supposed to have a nice ac wave of 1 V. All I have is noise. This line bounces around.

 

[HWYCRZR]

Thanks @MoPar~Man for your advice so far. Pretty certain my power supply is not my issue. Now I am focusing on circuit 101 as it was the recommended first test. As stated before the test port TP101 is supposed to be 1VppACc but am getting a garbage reading. I tracked back to the amplifier that feeds the circuit A101 and verified that it was working correctly. 14.93V feeding the amplifier and converting it down to around 3.3V to amp pin6 which feeds the circuit for TP101. However once it comes through the capacitor (C104). The signal is garbage. That side of the capacitor is the same voltage that is supposed to feed TP101 at 1V but is only giving 75mVppAC.
So thinking C104 capacitor 10/15 may be the first issue. I want to see if I can test it in circuit before I pull it out. I will have to do some reading on how to test a dual capacitor.

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