Hi,

Hoping for some help identifying these 3 components that are poorly circled in the attached picture.

The device is from a 1982 Yamaha motorcycle and part of the Computer Monitoring System. They work in conjunction with the quad op-amp on the right side of the picture and the op-amp is misbehaving so I am trying to determine what these devices are. They do have a resistance value, two of which appear to be about 158K in circuit testing, the other is close to 1950 ohms, but once again in circuit measurement so may not be accurate. The resistance values are not sensitive to freeze spray so I think I have ruled out some type of thermistor.

I am most interested in the middle one, which appears to be in parallel with another 170K resistor of which the two are sourced by a 170K resistor with a 5V supply. The Vout is used as a reference voltage on the op-amp non-inverting pin and calculates with those values to be about 1.6 volts, but I am getting a reading close to 4.3 volts. The inverting side of the op-amp is switched between 0 and 5 volts, at which time the op-amp output pin should switch low, which it does not.

And just to add, that top one on the board with the funky looking solder on the left side is not unique, I am seeing that on several samples of this CCA.

Thanks in advance for any feedback

 

https://www.njr.com/semicon/PDF/NJM2902_E.pdf
if you track the ic pinout to PCB el.-s you may be able to guess

 

if you track the ic pinout to PCB el.-s you may be able to guess

Thanks for the input, I have done that and already had the data sheet for the quad op-amp. The issue is trying to determine just how the reference voltage is set and what value should be on the op-amp non inverting pin. If I don't know what the components are, then I can't determine the correct voltage value.

 

Well kind of a duh moment but I just realized that what I said about them having a resistive value is not true, since the particular one (middle) that I am interested in I can follow the etch and verify it is in parallel with an actual resistor - so I can further state I don't have a clue what they are since the parallel resistor has no value marked on it.

 

Hard to tell from the picture but if you scratch off the coating, are there any markings on said components?

 

? if it's a glass housing it may mean they are some kind of diodes ?varactors? but all the www found smd varactors are in opaque housing
?? protective small power schottkies (so one can see a blown one ?? by color change ??)

 

Hard to tell from the picture but if you scratch off the coating, are there any markings on said components?

No markings to be seen, the only parts on the CCA that are marked are the transistors and op-amp. Perhaps removing one from the CCA could be helpful - at least I could check it for resistance and capacitance as a stand alone component.

? if it's a glass housing it may mean they are some kind of diodes ?varactors? but all the www found smd varactors are in opaque housing
?? protective small power schottkies (so one can see a blown one ?? by color change ??)

A protective device is a good thought - I need to look again but I might be seeing some delay present at that op-amp input at power up.