II+ power supply voltage checking

3 posts / 0 new
Last post
Offline
Last seen: 1 week 4 days ago
Joined: Sep 26 2019 - 16:46
Posts: 11
II+ power supply voltage checking

I'm trying to get an Apple II+ clone fully working (it boots up like it should, but there's no response from the keyboard -something I'm looking into, suspecting the keyboard itself needing repair). However, there are some other things worth considering like the power supply output. With the computer switched on I measure these voltages:

 

- 12.009 V
+ 11.480 V

+ 4.998 V
- 5.033 V

 

My concern is the +12V line. Is it too low? if it is, what action will likely remedy this?

 

Another thing: there's a 0.5pf trimmer capacitor near the 14.31818 MHz crystal oscillator (bottom left hand side of the motherboard) -what's it for? The two other trimmers on the board are for adjusting the video output level and color trim, but I have no idea what this one is for.

Offline
Last seen: 6 hours 3 min ago
Joined: Aug 18 2017 - 16:53
Posts: 70
Fuji wrote:My concern is the

Fuji wrote:

My concern is the +12V line. Is it too low? if it is, what action will likely remedy this?

It is a bit low but normally this isn't an issue. Are there any disk drives? If not, add one or two and use them. Some power supplys will raise the voltage when in use.

 

Regards

Ralf

 

Offline
Last seen: 1 week 4 days ago
Joined: Sep 26 2019 - 16:46
Posts: 11
I just checked with the hard

I just checked with the hard drive attached. It goes down to +11.010 when booting but returns to around the same as before (+11.50) when stopped by pressing reset (my keyboard isn't working at the moment except for reset).

Log in or register to post comments