 PC To Calculator Link
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Sulaiman
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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
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I think you should meter the voltage across C4 - now.
If I read the datasheet for MAX232 correctly
C4 is used as a reservoir for the internally generated -10V at pin 6
So C4 positive side should go to 0V/Ground, negative side to pin 6.
Your circuit diagram, your pcb AND the original article all have
C4 positive to pin 6
which I believe is wrong.
I've never used a MAX-anything so I'm just going by the datasheet.
If the voltage across C4 is 'wrong' then put a NEW one in.
This incorrect polarity will draw excess current from the supply
via the regulator and MAX232 invertor.
It will also lead to C4 leaking or exploding.
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evilgecko
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Registered Member #288
Joined: Mon Mar 06 2006, 07:52AM
Location: Palmerston North
Posts: 32
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Your dead right sulaiman, voltage across C4 was 6.25V in the wrong direction. I'm surprized to find that is already hasn't gone CATO. I'm astounded how you managed to pick that small mistake up but I am also grateful for it! It would be bad if I sold a few and then they started popping and failing. That might explain why I get the transmission error as well.
Changing it around now.
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Sulaiman
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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
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per my post above;
"If the voltage across C4 is 'wrong' then put a NEW one in."
The surface structure of your C4 has been irreversibly altered
mainly resulting in lower capacitance, possibly higher leakage.
The original reverse polarity probably wouldn't result in explosion due to limited power 'pumped' by the MAX-xxx
but I think it could have leaked or vented.
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