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41CV won't turn on after reassembly. Did I kill it?
05-10-2019, 11:23 AM
Post: #4
RE: 41CV won't turn on after reassembly. Did I kill it?
(05-10-2019 04:54 AM)g8241CV Wrote:  Lots of more experienced people here (many great threads I researched before doing repairs on two 41's), but I would swap in known fresh batteries (1.5V) as your next step. Easy elimination of a variable for problem solving diagnostics, and you need them anyway to avoid the inevitable cell leaks from your weak existing cells. Then, before you try to close with your repaired post, suggest you try gentle cleaning of contacts (both sets, upper near batteries and lower for CPU PCB) with IPA, and use DeOxit. You're looking to eliminate a particulate contaminant on contacts that you may have missed in cleaning or dislodged during reassembly. While you're in there, suggest you use DeOxit on at least the bum key. Suggest you observe ESD precautions (e.g. use ESD strap).

Not sure what you mean by "shorting all the battery terminals" -- if this was really a short of all terminals, then no power to the calculator and that shorting may have reduced the cell voltage(s) below the operating threshold. You might post a close-up photo of the contacts since you had reason to be concerned.

Post back, don't give up too easily, there are lot's of other great threads on repairs to explore. It's a wonderful feeling when you bring a favorite calculator (CV for me) back to life.

Yeah, I ordered a dozen fresh N cells from Amazon just to rule that out. I've never seen a calculator run fine on low batteries, then refuse to turn on after they've been removed and reinserted, but I'm sure there's plenty of crazy things I haven't seen before. Worst-case scenario, I'll have a lifetime supply of batteries for my 19BII.

I'll probably give all the connectors a gentle scrub with some contact cleaner before I close it back up. Not sure I'd be able to use contact cleaner directly on the key, though, since the only access is a ~0.5 mm hole on the back of the PCB that I can get a couple of IPA-coated paintbrush bristles through. I'm definitely not going to pull all the heat stakes for one key that just requires slightly more force than the rest.

The battery terminal thing is often suggested with various models, in order to drain any stray charge in capacitors that might be holding the machine in some invalid (i.e. non-responsive) state. You just remove the batteries, then bridge the calculator's battery terminals with something conductive, like foil, or a coin.
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RE: 41CV won't turn on after reassembly. Did I kill it? - Dave Britten - 05-10-2019 11:23 AM

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