Thursday, January 27, 2022

RATS!! Now I'll Never Know.....

 Well, things are the workbench were going well with the Heathkit THD Analyzer, until the other night. I'd soldered two leads onto the circuit board pads that the photocell solders to, and this allowed me keep my Ohmmeter attached while I played with the position of the cell. This let me get a feel for how the cell picks up the light from the bulb, and how to position the cell. Having the shield cap off while playing likes this makes the resistance value of the cell go all over the place from room lighting, but at least I can see how moving the cell  up/down, right/left, in/out affects the reading, and could help me find the sweet spot where the cell should be.

The reading on the meter indicates 56,000 Ohms for this cell. The target is 28,000 to 32,000 Ohms, so it's wee bit off.

I moved the bulb as much as possible, and positioned the cell every which way to get a feel for it, and no matter how much I try, I cannot get it below 42,000 Ohms. The little foil reflectors I was paying with were required to even get it down that far. Now granted, I'm assuming this thing did work at one time, so what's changed?

I pulled the bulb out to examine it more closely, which revealed nothing. And then when I was putting the bulb back in, the "padded" tweezers I was using slipped, and TWANG!, the bulb goes sailing off to Where The Wild 10mm's Live......Buh-BYE!

The offending tool: 

Yes, some colorful language was used....

The replacement bulbs I'd ordered last week came in the day after, so all was not lost. These are small bulbs:

One thing I immediately noticed after I put the "replacement" bulb in place, is that the filament is about one-third the size of the OEM bulb:

And of course, it made no difference. I've checked all the voltages in the lamp driver circuit, and they're very close to what the schematic says they should be, indicating the the current flowing through the bulb is in the correct range, meaning the brightness of the bulb is probably correct. The other identical lamp driver circuit also has voltages that match the schematic, so it looks like things are working properly.

The other side with the four photocells adjusted just fine. The target resistance was not-too-difficult to get set, and adjusting them went about how I expected it should go. This leaves the one photocell as the last thing that's suspect. Looks like I'll have to go photocell shopping.....


Had about 6" of snow on Tuesday, and the Ariens took about 20 minutes from start to finish. It fired right up, and 6" of snow just disappeared. All I had to do was walk behind it and guide it, and I had to use a higher speed to keep the maw full, as it seemed to throw the snow better the more you stuffed into it. Too bad I didn't have it the last two winters!




20 comments:

  1. You will find that bulb some day when you hear a real tiny crunch sound under your foot.....

    ReplyDelete
    Replies
    1. ROFLMFAO!!!!

      You are, of course, exactly correct...

      Delete
  2. What Phil said, except it will happen only when you are not wearing shoes.

    Thanks for the snowblower report. We're possibly getting some on Saturday here in North Central Florida. Or just ice. Brrrr.

    ReplyDelete
    Replies
    1. I rarely go down there without shoes on. It's a work area, like the garage, and proper footwear is encouraged.

      Yeah, the new snowblower is working great!

      Delete
  3. Glad your snow blower is working as you hoped. I also hope you get a lot more use this winter - we need the water.

    ReplyDelete
    Replies
    1. Yup....been too dry here. I'll bet Horsetooth is noticeably lower this Summer.

      Delete
  4. It's just shy of 1000 in Philly and a quarter inch of the snow that NOAA said would begin around 1500 is already on the ground.

    As the tailor said, "Twill be what it twill be."

    The tiny bit of electronic knowledge that I have tells me that what you do is way beyond my skills and I am in awe.

    ReplyDelete
    Replies
    1. We're supposed to get hit late next week, but it's still too far out to get an accurate forecast.

      Delete
  5. I swear, if I ever build a house, there will be a 'dedicated' work room with white walls, a white floor, and the floor inclined to the center of the room! Sigh... Good luck with the photocell hunt!

    ReplyDelete
    Replies
    1. Exactly!

      There's a zillion photocells on eBay, now I just have to figure out which one I need...

      Delete
  6. The photocell is probably hiding in a mechanical assembly for a control so that it will crunch when you are adjusting the control after fully assembling the unit. Either that, or Phil was right about stepping on it.

    ReplyDelete
    Replies
    1. I shook the chassis pretty well just in case it fell inside, but nope.

      It went sailing pretty far!

      Delete
  7. If it is like the short medical scissors I lost a few days ago, it will be at the bottom of some box.

    Glad all was not lost, except for some snow.
    You all be safe and God bless, drjim.

    ReplyDelete
    Replies
    1. HAH! Yeah, I've pawed my way through many boxes of stuff to find something I knew I had. One of the projects on my list is to get some bins so I can sort my parts out.

      Delete
  8. Looks like tape on the tweezers. Might try using heatshrink, but consider forming the grasping sections first. Might need a bit of heat to deal with the temper first. Sometimes multiple layers of 'shrink are required to get the shape/size needed, and you can indent grasping grooves while it is still warm.

    Sometimes it works better to start with hemostats, to get more strength and control.

    ReplyDelete
    Replies
    1. Yep, just some blue painter's tape. Didn't think about heat shrink, but I will next time!

      I prefer tweezers for this, as I've crushed small parts with hemostats.

      Delete
  9. Hopefully it will be possible to ID the photocell and track down the response curve. And if the cover is on, no one's to know that maybe there are two of them in parallel.

    ReplyDelete
    Replies
    1. There's not much info on the part they used. It has a Heathkit part number, 9-70, and a listed resistance of "100k". They put enough light on it to drop it to 30k when it's in the right position, so I'm guessing "100k" is either the dark resistance or the "10 Lux" resistance. I'll go through my 1960's and 70's Allied Radio catalogs and see what I can find. Clairostat used to be huge in photocells.

      Delete
  10. Brrrrr. Snow here on Thursday, our Old Enemy knows no bounds.

    Like your tech, even though I don't understand it. Still mining Doge, I hope?

    ReplyDelete
    Replies
    1. We're supposed to get some more starting Tuesday afternoon (cue the Moody's!) going through the evening. Lord knows we need the soil moisture....

      The tech is really Olde Skool, like I grew up with, so it's kind of fun using modern techniques and equipment to troubleshoot it.

      Son has his mining rig set up here, and is cranking away.....

      Delete

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