Assembling El Cheapo Oxycheq O2 analyzer

crab · Feb 25, 2005

To anyone who has assembled this unit using the panel meter with surface mounted resistors... I am having a really fun time trying to connect the leads from the pot to the nearly microscopic contacts where I removed the R3 resistor from the board. I understand that older models of the meter had a larger top mount resistor that could be snipped off-- I wish I had one of those, it sounds much easier to solder to the leads to.

I am open to any tips/suggestions. I will be emailing Oxycheq with the question as well, but I don't expect to get a reply until next week.

Thanks!

DA Aquamaster · Feb 26, 2005

The R3 resistor is really tiny and the contacts are quite close together so heating the contact directly won't work and will potentially cause solder to bridge the gap between the two contacts.

Instead apply solder to the exposed portion of the lead - just enough to coat it. Then hold the lead to the contact and apply heat to the lead. When the solder on the lead melts the solder on the contact should also be soft and the lead should slide right into the hole in the contact with the solder on the lead being sufficient to seal the joint between the two (it's a case of less solder being a far better way to go) then just remove the heat and hold the lead in place a few seconds until the solder hardens.

Once done, inspect things to ensure there is still a space between the two contacts. If not, a little very careful picking with the tip of a #11 exacto knife blade or in more extreme cases a bit of heat with the clean tip of the soldering iron and a little suction from a solder removal bulb should clean it up.

crab · Feb 26, 2005

I tried a variation of the method you suggested, but there is no visible hole at the top (or bottom for that matter) contact point for R3. There is a nice small bead of lead remaining at the bottom of where R3 was formerly placed and I can actually get a good connection to that point. The problem is that there is no visible hole or contact pad for where the top of R3 was. Making matters worse, I have mucked up the board coating around the area where the contact should be by heating it with the iron and now there seems to be no hope of making a connection there. If there is supposed to be a hole where this surface mount R3 was placed, if I could locate it, I suppose I might be able to get the lead fixed there, but, if not, I might be scr*wed and will have to buy a new meter. Lucky me!

bedmund · Feb 26, 2005

I had a hard time with the first one I built too using the "newer" panel. I ended up locating one of the older PM128's and using that - they're out there, but a little hard to find. I've since built one with the PM128A panel doing basically what DA advised. In the Oxy Hacker Companion, Vance suggests using two soldering irons like pincers on the R3 and then lifting it off the board.

Good luck!

-Bill

~ edit: that is if you end up needing to get a new panel and starting over again. Sorry for the confusion.

crab · Feb 26, 2005

that is if you end up needing to get a new panel and starting over again.

This is looking more and more like what I will have to do.

DA Aquamaster · Feb 26, 2005

It's not as bad as it sounds. I don't remember the price of a PM128A, but I remember it was pretty cheap - maybe $20?

crab · Feb 26, 2005

DA Aquamaster:
It's not as bad as it sounds. I don't remember the price of a PM128A, but I remember it was pretty cheap - maybe $20?

I actually got the one I ruined for less than $11 including shipping. It's more about the principle than the price...

spyder · Feb 27, 2005

It's been a while since I put mine together so I'm a little fuzzy but I do remember making a run to Radio Shack for a new iron with a fine point and not a lot of watts. If I remember right I think I did what DA suggested but just soldered it to the pad and didn't worry about the hole. Put a drop of solder on the wire, just touched it to the pad, then applied heat. Not to offend but does your iron have a fine enough point? Initially I pulled out my old trusty iron and quickly determined it was not going to be fine enough and probably too hot. The biggest problem I had was carving up the box. A dremel tool and a steady hand seemed to be the ticket. It does work great when complete and well worth the effort.

crab · Feb 27, 2005

spyder:
Not to offend but does your iron have a fine enough point? Initially I pulled out my old trusty iron and quickly determined it was not going to be fine enough and probably too hot. The biggest problem I had was carving up the box. A dremel tool and a steady hand seemed to be the ticket. It does work great when complete and well worth the effort.

None taken... My iron does leave alot to be desired. If I'm going to go through the trouble of getting a new board, I might as well spring for a new iron with a fine point and lower temp.

Actually, carving up the box seems like a distant pleasant memory since my battle with the panel meter commenced-- a Dremel tool was perfect for the application.

DA Aquamaster · Feb 28, 2005

Yes, when I did mine I invested in a new iron with a very fine tip (and high and low settings) as well as a solder removal bulb since the board on the panel meter was a lot smaller than the electronics I had done before.

Assembling El Cheapo Oxycheq O2 analyzer

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crab

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DA Aquamaster

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crab

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bedmund

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crab

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DA Aquamaster

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spyder

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