New project: Allen Engine analyzers, restoration?

[HWYCRZR]

For those interested in how these old exhaust analyzers work I will post a PDF of the service manual whereas the first section explains how the HC and CO levels are transmitted into electrical signals.
For those that were helping me, this is a different manual than what I was using, but seems to have more of the proper voltages (page 40 has the A101 circuit.) If you recall I was only getting 3.35V out of pin 6 of the A101 amplifier. In this document I should be getting 5V. To get the full picture I think I need to use both service manuals.
Below is the service manual that I have not been using that maybe I need to read. I may be able to boost the signal to A101 to get the 5 V, but still concerned about the "floating" signal at TP101.

 

[HWYCRZR]

This is the manual I have been using. It has the overall larger schematics. Although the schematics for both look very much the same. Just one goes into further depth in other areas.

More reading to do this weekend when I get back

 

[3175375]

It appears that the circuit has LM741 op amps. Maybe you can get a magnifying glass and look more carefully at the markings. LM741s are extremely common and inexpensive.

 

[MoPar~Man]

In this case A101 is labelled as RC15560N (see post 98) which is almost certainly a Raytheon part number, which I'm pretty sure would cross to a 1456 (ie LM1456) which is just a "hi performance" version of a 741. But that isin't the issue here, I'm sure that chip is fine. The input to this circuit comes from a polycrystalline lead selenide photo detector, which are sensitive to 1 um - 4 um wavelength (far infrared).

There's a small AC motor that drives a wheel with a window on the end of a tube contraption with a heater acting as the IR source, the light gets bounced down a pair of tubes, air pumps pull ambient air into one tube and tailpipe air into the second tube, the chopper wheel causes the IR beam to pass alternating through each tube, the photo detector will generate a signal that should resemble a square wave if the air in the tubes have a different concentration of I guess CO2 or HC. Without actually having either actual combustion gas flowing through one of the tubes, or a sample gas from a test cylinder source, you're not going to see a difference between the tubes. But if the wheel interupts the IR light then I guess you will see a signal. So this all depends of the contacts between the photo detector and the op-amp A101 is good, if the heater is working and generating IR light, if the detector is working and has a clean window, and all relavent reflector surfaces and optics are clean.

 

[HWYCRZR]

I am back working on this again. I made a quick YouTube video to better show what is going on. I am still at a loss why I am only getting 3 volts out of pin 6 on A101 when I should be at 6. Adjusting the pre amp is not changing the voltage.

 

[MoPar~Man]

The voltage on the op-amp output (pin 6) is somewhat irrelavent because it's being fed through a capacitor to the next stage so it is effectively at zero volts plus what-ever signal is appearing at the input (pin-3). Your test point TP101 is on the other side of this capacitor. What are you seeing on the scope on pin 3 when the input sensor apparatus is functioning (ie heater on, ac motor spinning) ? You should see an amplified version of that signal at TP101.

 

[HWYCRZR]

Pin 3 of A101 is 2.79V every thing running and warm. TP101 is jumping around but only around 100mv max.
On another note I am not seeing any voltage throughput on the photo detector (signal sync)on the sample side. Will get deeper on the next post.

Here are my readings at pin 3 and TP101

Pin3 A101

Pin TP101

 

[HWYCRZR]

More on the photo transistor on the reference side. Circut 302 This is probably reflecting my reading on TP101. If the photo transistor is not telling the A101 circuit that it should measure the reference side is that why I am may be getting an erratic signal? sample side is working (301) but am not getting power through the photo transistor on 302.
I am not sure what is first in the circuit but am not getting my 30V at TP302 (signal sync)
But maybe an additional issue.

 

[HWYCRZR]

Not 100% sure on my Photo transistor. Within Circut the resistance measures the same between the one that is allowing voltage to pass through (sample sync) and the one that has minimal voltage output. Not sure how to test. Could it be an alignment problem? I think the LED’s are working correctly as they are in series with one another and measuring voltage fine at the end of the circuit (P301)
Q301 is giving a voltage reading, but Q302 is not. I will try cleaning and alignment first. If that doesn’t work I will need to learn more about photo transistors and how to size them as original parts are not available. Not quit sure what TIL66 means, could it be the spec?