Interesting Voltage across 5300UF capacitor at D-15

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juanoshea's picture
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Interesting Voltage across 5300UF capacitor at D-15
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It was a great feeling to connect my PEM to the unpopulated mainboard and not have a fire start, or a vortex to hell appear. However, eventhough the build guide did warn me to expect Roughly +10 Volts at 5300UF capacitor 14V does seem a bit high. 

 

Should I be worried?

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Joined: Apr 1 2020 - 16:46
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Don't worry ...

.... transformers without any load are known to produce much higher voltages than under load conditions. 

 

My build has 9.95V on this capacitor with all ICs in (running).  With only the video section populated it was 10.93V. Did not take numbers with no ICs.

 

I'd think your best route would be to check for the +5V to be OK and then turn off, populate all TTL ICs  (none of the expensive Signetics shift regs and char gen yet) and check again. Then check the +12V and the -5V, -12V regulators. Not the prescribed sequence, but I'd think the safest way if in any doubt.

 

The LM323 is a great IC design and it will protect itself from self destructing and it can easily handle the +14V you see. 

 

But  it needs a heat sink. Don't forget this.

 

Bernie

 

 

 

 

 

 

juanoshea's picture
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thumbnail_IMG_1598.jpg

 

All good now - I've populated the Video Section and got what I expected. Unfortunately my only monitor is far too modern and I will have to find something which can grab the signal from the board without jumping. To be continued.....

 

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