- Joined: 12 Feb 2022
- Posts: 3
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low voltage on 7805 chip
 Posted: Fri Feb 18, 2022 1:18 pm
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Hi I picked up a master system 1 but when I try to switch it on I only get a black screen. Im using a cheap ebay power supply but it works fine with my master system 2.
If I put my meter on the power supply barrel it show 8.69v but I only get 7.72v on the In leg of the 7805 & 4.7v on the out leg on the master sytem 1.
Is the problem likely to be the psu, the 7805 chip, both or a fault I should look for elsewhere?
is 4.7v too far below the normal 5v for the unit to operate?
Any advice appreciated thanks
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- Joined: 25 Feb 2013
- Posts: 384
- Location: Osaka
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Posted: Fri Feb 18, 2022 2:20 pm
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As long as it gets more than 7V it should output 5V. A properly working 7805 won't go as low as 4.7V. I would replace it.
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