ThinkJet battery pack

ThinkJet battery pack

Postby glefebvre » Tue Dec 27, 2022 8:55 pm

Hello,

My ThinkJet battery pack is no long charging. I looks like one of the resistors has failed. The larger resistor in the middle of the circuit board have broken in two. I looks like a yellow, black, gold, gold resistor.

Would someone be so kind as to check their battery pack and let me know if that those are correct colors for that resistor.

Thank you,

Gary
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Re: ThinkJet battery pack

Postby Garth » Tue Dec 27, 2022 11:20 pm

Mine died about 35 years ago, and I'm sure I don't still have it.  After that, I powered the printer with a separate power supply I made, and never went back to any sort of battery pack.  For a resistor, yellow, black, gold, gold would be 4.0Ω, which is not a standard value.  4.7Ω (with violet instead of black) would be, but I doubt there would be a series resistor that high, unless it's only for charging and a diode would bypass it when powering the printer.
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Re: ThinkJet battery pack

Postby glefebvre » Wed Dec 28, 2022 6:22 pm

Thanks for the info.

I've attached an image with the resistor in question. Please have a look and let me know what you think the colors are.

Thank you,

Gary
Attachments
DSC02451 copy.jpg
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Re: ThinkJet battery pack

Postby Garth » Wed Dec 28, 2022 8:54 pm

Hmmm... For that second band in particular, it's any body's guess as to what color that was before it was burned.  If you can trace out the circuit, I expect we can figure out something that would work, even if it doesn't match the original exactly.  It's not terribly critical that things be exact.  In the short time between when my battery pack went south and when I made the power supply, I actually ran the printer on a 9V battery.  :!:   It would only print something like six pages though before the battery would be too low to supply the needed current.  It cost me fifty cents to make the power supply, as I had everything I needed except a particular diode, and the diode was fifty cents. :mrgreen:
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Re: ThinkJet battery pack

Postby glefebvre » Wed Dec 28, 2022 9:28 pm

Here are two images of the circuit board.

1st image with all resistors and the 2nd is the circuit board filled over with the traced.

Hope this will help.
Attachments
DSC00137 copy.jpg
DSC00138 copy.jpg
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Re: ThinkJet battery pack

Postby glefebvre » Thu Jan 19, 2023 5:40 pm

Last night I replaced the broken resistor with 4.7 ohms one and replaced the batteries. Charged the pack overnight and test this morning. I now have a battery pack that is working and I can now my
ThinkJet again.

I followed these instructions.

https://www.hpmuseum.org/cgi-sys/cgiwra ... i?read=563
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Re: ThinkJet battery pack

Postby Garth » Thu Jan 19, 2023 6:58 pm

That's good to hear.  After you posted last time, I meant to get back to this after catching up on some other things, then I forgot.
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