trying to identify this component

[Chris_D]

Hello All,
I'm Chris from Belgium and I'm mostly a newbie concerning electronics.
However I'm trying to repair an old device (lightmeter) and I need to identify an electronic component, which I think is a tiny ceramic capacitor, with unknown specifications.
It is about a 10th of an inch, like a grain of wheat or something, it is brown/yellowish of colour and it has a tiny white (or grey?) stripe on it.
Is there something who can help me out?
Thanks in advance!
Regards.

[gbaddeley]

Do you have a schematic, or tried tracing it out yourself? I’m not sure why a light meter would have tiny caps in it.

[Chris_D]

Hi Glenn,
No unfortunately I don't have any schematics. But this is part of the circuit that goes to an additional lamp, to be able to read the values in low light situations. Basically, the lightmeter (Pentax spotmeter V) seems to be a kind of old ampere meter with a needle and with a cds lightcell reading the light and converting it into current. But I had also the same insight of you. And because I do know from guitar pedals that there is something as a 'decoupling' and'bypass' (not sure which one of the two this is)capacitor, I wonder if this could be the same. It is put between the positive lead wire coming from the lamp switch and going straight to the light bulb. And my guess is that it perhaps serves to turn on the lamp without affecting the current of the meter, could that be possible?

[gbaddeley]

If it’s only a series element in the light bulb scale illumination circuit, it may be a PTC or resistor to keep the brightness constant as the battery drains down. Just a thought.

[Chris_D]

Hello Glenn,
It's possible. It has most certainly something to do with keeping the current on the same level.
I've fiddled a bit with the contact, and now the light bulb gives a very faint light. Taken out of the circuit it shines very bright, so it isn't the light bulb or the contact, that's for sure. Anyway, it could be a resistor, but I have never seen something similar. But I guess it must have some color code. because on the picture, you can see another similar one, being red, with a black horizontal stripe.This one is yellowish with a white stripe.

[golden_labels]

Have you tried gently rubbing off the line with alcohol? Not necessarily isopropyl alcohol, ethanol would do too. It looks as if someone hidden the component markings with a marker. Removing that with a cotton swab might provide more clues. Just don’t rush it and check what you can see after each few rubs: if there are any markings underneath, they may get removed too if that’s done too quickly.

[Chris_D]

Hi,
Ok, that's a thought. As far I can see, there is nothing underneath, but I can try.

[Chris_D]

Ok, I removed it a little, but I don't have the impression that there is something underneath. But maybe it is just a sign to indicate polarity of something, for the people who need to assemble this?

[Gyro]

As a general rule, I don't remove anything that I can't identify - and may not be able to find a replacement for. Try to measure it in circuit, or by disconnecting leads of adjacent known components.

I'm wondering if that part, and the red one next to it, might be thermistors for temperature compensation [Edit: and/or, as gbaddeley suggests, battery voltage compensation].

[Chris_D]

Yes, I agree, it is still not disconnected by the way.

[Chris_D]

I have only a very rudimentary multimeter, and I'm terribly bad with it
...but...I put the meter on 2000 Ohm, and it dropped in number until it stayed on 178 Ohm.
Does that mean that this is 178 Ohm resistor?

[Nusa]

Do you have a year of manufacture for the device? Or at least an estimate of its age?

[Terry Bites]

?? https://www.pentaxforums.com/forums/125-flashes-lighting-studio/389200-honeywell-pentax-1-21-spotmeter-diy-replace-mercurys-battery-regulator.html

[Chris_D]

Do you have a year of manufacture for the device? Or at least an estimate of its age?

I think approx.50 years

[Chris_D]

?? https://www.pentaxforums.com/forums/125-flashes-lighting-studio/389200-honeywell-pentax-1-21-spotmeter-diy-replace-mercurys-battery-regulator.html

This is the predecessor model of the Pentax V, and this device had still two batteries in it: one for low light reading, and one for bright light reading. It was 9V and 1.3 volt mercury. The spotmeter V has already 3x 1.5 alkaline batteries. I have the schematics of the earlier one by the way, but it doesn't seem to be the same.As far as I can tell.

[Chris_D]

If it’s only a series element in the light bulb scale illumination circuit, it may be a PTC or resistor to keep the brightness constant as the battery drains down. Just a thought.

Glenn, I think your hypothesis according the thermistors may be correct. The Pentax manual says the device can perform in situations from minus 20 degrees to 50 degrees Celsius. So I was wondering: how could the device know this? So: could the little brown element be for instance a NTC-thermistor? I got a reading from my multimeter of 178 Ohm, but the thermistor can of course be broken? And do you know (or anyone here at the forum) how to identify the value of a thermistor, because they also seem to have color bands?

[tooki]

Have you tried gently rubbing off the line with alcohol? Not necessarily isopropyl alcohol, ethanol would do too. It looks as if someone hidden the component markings with a marker. Removing that with a cotton swab might provide more clues. Just don’t rush it and check what you can see after each few rubs: if there are any markings underneath, they may get removed too if that’s done too quickly.

I think that’s almost certainly not the case. I suspect the colors are the component markings. They probably follow standard color code, most likely with the base color being the most significant digit and the stripe being the least significant. But they might also be non-numeric, i.e. arbitrarily assigned to a few values or parameters.

Unfortunately I don’t know what these particular components are, so I can’t give any concrete clues.

[Chris_D]

Yes, it is a mystery for the moment. Maybe it is an ordinary resistor, but very oddly shaped. I will try to make a reading of it with my multimeter while 'warming' the component with my hand (probably finger, because it is so tiny) and see of it reacts like a thermistor would do apparently.