Apple II 699-0133 Astec Model AA13585

[Chevy2]

I have an Apple II PSU that just makes a ticking noise like it's turning off and on and the computer wont boot. Caps seem ok, but I know how that goes. Any ideas on where to start checking components?

[PeteS in CA]

Re: Apple II 699-0133 Astec Model AA13585

I mean no disrespect, but that sucker is ancient! IOW, the chances that some or all of the O/P capacitors are dried out is very high. I'd recap the thing out of hand. Thing is, even Nichicon PW or UCC LXZ series may be too good. So maybe find some Nichicon PS series or UCC LXV series parts.

I'll have to post more later, but I'd suggest testing it with a resistive load to see if the P/S works or there is a problem with the computer main board.

[BigTroll]

Re: Apple II 699-0133 Astec Model AA13585

on one of my macintosh LC power supplies it was ticking over and over, one thing you can try is to put the psu infront of a small space heater for about 5-10 minutes then put back in system and try starting, This worked on my LC however once cold it would do the same thing until I replaced most the caps.

[PeteS in CA]

Re: Apple II 699-0133 Astec Model AA13585

The Apple II P/S is a very basic, 43W IIRC, self-oscillating discontinuous flyback design. That ticking sound probably means it is continually trying to start and either there is a short which is tripping current limit or it isn't regulating and tripping the OVP crowbar (which shorts out the +5V, tripping the current limit).

So check both the P/S and the computer main board for shorts. If one or more of the O/P caps was dried out, that could have messed up the regulation. Once the +5V gets high enough, regulation comes from the TL431 (or TL430), a reference plus an amplifier that is used as a comparator shutting off the switch transistor every cycle.

I would suggest making a resistive load of .6-.8A on the +5V and .1-.2A on the +12V rather than trying to test the P/S connected to the computer board.

Also, it's not utterly impossible that the big I/P electrolytic capacitor (datecode "8827", meaning 27th week of 1988?) could be bad as well.

[Chevy2]

Re: Apple II 699-0133 Astec Model AA13585

The Apple II P/S is a very basic, 43W IIRC, self-oscillating discontinuous flyback design. That ticking sound probably means it is continually trying to start and either there is a short which is tripping current limit or it isn't regulating and tripping the OVP crowbar (which shorts out the +5V, tripping the current limit).

So check both the P/S and the computer main board for shorts. If one or more of the O/P caps was dried out, that could have messed up the regulation. Once the +5V gets high enough, regulation comes from the TL431 (or TL430), a reference plus an amplifier that is used as a comparator shutting off the switch transistor every cycle.

I would suggest making a resistive load of .6-.8A on the +5V and .1-.2A on the +12V rather than trying to test the P/S connected to the computer board.

Also, it's not utterly impossible that the big I/P electrolytic capacitor (datecode "8827", meaning 27th week of 1988?) could be bad as well.

Fixed it. It was a 220uf cap at C12. Replaced it and it's working fine. Thanks for all the help!

[kc8adu]

Re: Apple II 699-0133 Astec Model AA13585

may as well replace all.those caps are way beyond their expected life and they dont owe you anything.
btw i have industrial customers still running these systems on critical to their business machines.
its surprising just how many of these i get in that have been running since new and just now gave up!