Author Topic: cpc 464 short circuit  (Read 621 times)

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Offline retro_4_ever

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cpc 464 short circuit
« on: 12:52, 15 March 21 »
hi, i'm looking at a Z70200 (big board) it appears to have a short from the 5 volt rail to ground- i removed the power jack and the single electrolytic cap to rule them out then realized that the line from power jack to tape connector pin 3 is ok. its from the output (pin1 onward) i have gone through all the chips thinking that i would see some difference in resistance on there power lines on a defective one but they all show about 16 ohms . there doesn't appear to be any open circuit resisters. cpu and gate are in sockets so they are removed.. any suggestions or am i missing something ? mark .

Offline Bryce

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Re: cpc 464 short circuit
« Reply #1 on: 13:02, 15 March 21 »
If it's a straight short circuit, something must be getting pretty hot? Are you sure the voltage drop isn't because the PSU can't provide enough current?


Bryce.

Offline retro_4_ever

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Re: cpc 464 short circuit
« Reply #2 on: 13:39, 15 March 21 »
i thought it wise not to power it again until the short is gone, I have another motherboard of the same model that i am using for comparisons . i was using a good supply when it was originally powered it up.
the 5 volt line to ground of the ram chips etc all show next to no resistance (16 ohms) this cant be correct ?



mark

Offline Bryce

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Re: cpc 464 short circuit
« Reply #3 on: 14:09, 15 March 21 »
Check the ceramic capacitors, that the legs of any them aren't shorted. 16ohms sounds touching (oxidised) wires.


Bryce.