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.