Pentax V Spot Meter - no view finder illumination - help!

[RaphaelVazquez]

I have a Pentax V Spotmeter with its view finder illumination that does NOT work. Does anyone know if
the light bulb is available and if opening the unit can cause more harm?

Raphael

 

[MattKing]

Thread title tweaked - hope you learn what you need.

 

[Steve Goldstein]

Try Richard Ritter in Vermont USA about the bulb.

As with any piece of camera gear, opening it can certainly cause more harm if you don't know what you're doing or don't have the proper tools for the job.

 

[koraks]

Does anyone know if
the light bulb is available and if opening the unit can cause more harm?

IDK about the light bulb. As @Steve Goldstein points out it's of course possible to do damage if you start poking around inside the meter. On the other hand, if you're careful and systematic and take good notes + pictures, it's evidently possible to have a look inside without doing any harm.

How many versions of this meter exist, actually?
I suppose this may be relevant: https://www.instructables.com/Pentax-Spotmeter-V-Repair/
Note also the corrosion issues which is another possible cause for the failure of your unit.
Here's a pdf by someone who drafted a schematic of his unit: https://www.cameramanuals.org/flashes_meters/pentax_asahi_spotmeter_diagram.pdf
The link above doesn't mention any opamp, which prompted the question about versions. Not sure what you've got there.

Also, does it actually have a bulb for scale illumination, or does it use a nifty optical trick to channel light from the front of the meter onto the scale?

 

[Steve Goldstein]

There were at least two versions of the analog Pentax Spotmeter.

The earlier version required two different types of batteries, one of which was 9V, and corresponds to the PDF schematic @koraks linked on cameramanuals.org.

The later version, called Spotmeter V, used three G13 (same as LR44, A76, 357, and others) batteries in a single holder in the base/handle - this is the one shown in the instructables.com page.

These are the only two I've ever heard about, but I don't know if there were sub-versions.

The OP states he has the Spotmeter V. I'm pretty sure it used a real lightbulb for low-light scale illumination.

 

[koraks]

Thanks for adding that @Steve Goldstein , makes good sense!

I've not been able to find anything about the light bulb. If I were to hazard a guess, I'd suggest that the circled part is a bayonet bulb holder that might hold a small incandescent bulb:

The black & red wires it connects to seem to go to the big connector bar/button and also appear to be disjunct from the sensing circuitry, which would be consistent with a simple bulb.

 

[gordonrgw]

I took mine apart to clean, but haven't changed the bulb. Just to note the bulb itself when working is *very* faint, I originally thought mine was blown..

 

[Donald Qualls]

Another thing to note -- at least in mine (an older version) the bulb illuminates only the needle and its scale, and runs from the same (originally) PX25 cell that powers the meter's sensor. Unfortunately, the lithium/regulator conversion I bought for mine doesn't pass enough current through the regulator to operate the bulb. If/when I have time and resources to spare (after I retire?) I may look into installing regulators to run everything off the 9V booster battery, since the meter is plenty accurate enough in low light to make the dial illuminator worth having...

 

[Steve Goldstein]

Donal makes good points - the bulb is indeed very faint, illuminates only part of the scale, and is only visible in rather dim conditions. Make sure you check it in a darkened room.

 

[Richard T Ritter]

The area that you have the red circle is the needle movement,
As to the light bulb it is no longer made and is glued into the holder.
If the bulb was any brighter it would effect the reading the meter takes.
One thing to think about if you touch the main board just right you will short out a part that is no longer made. Meter will be dead.
Best thing to do is to track down Kodak's low light chart

 

[eli griggs]

I asked about solutions for a brighter bulb a few years ago, but i had very thick cataracts, now removed.

IMO, the most reasonable result of my inquiry was the suggestion that a tiny bulb used by miniature scale model trains was the correct replacement for the Pentax V meter.

I suggest you find the manufacturer nomenclature for the bulb, installed, and get online with a big model trains site.

Cheers