SE FDHD no power

[ishbooisland]

Hi all,
First post here. I have an SE FDHD that I got for 35 bucks off of a person on Craig's list. I got it about a year ago, and up until this morning it has worked fine every time I turned it on. When I got it I first checked for any leaking capacitors, and removed the old battery that was luckily not damaged. Recently I put together a DIY wifi232 and got it online, but after shutting down yesterday, now I can't get the computer to come on at all. When I hit the switch, nothing happens at all, no fan, no sound, no CRT. I took off the analog board, and removed the power supply to see if any power was coming from it at all. The voltages looked good except the -12V which was reading as around -10 V. Since it seems like there is power coming from the PSU to some extent, I'm planning on buying the capacitors to recap the analog board, despite no leakage. What are your thoughts on the -10V? Should I also recap the PSU? I believe it's the Astec PSU, so maybe more worth it to just upgrade to a modern PSU? Ebay has the Sony models for about 50, could be another route. I'm just a little surprised that it died so suddenly, none of the CRT flickering or dim issues, or random shut downs have happened prior to this. Thanks for any input

 

[ishbooisland]

Today I put everything back in the case and turned it on, nothing still. Went I went to turn the power button off, I heard a quick beep. Intrigued, I powered it on again and it came on! I shut it down, and now when powering it back on it took a few seconds before actually doing anything. Any ideas? I feel like maybe it is in fact the power supply

 

[bdurbrow]

Sounds like the PSU has gone funky. It's possible that it's no longer capable of carrying load; yet when unloaded does come up to voltage (or at least, does on everything except that -12v output).

If the main logic board is nonfunctional (or even removed) turning it on should result in the fan running. I wouldn't expect the CRT to get high-voltage without a horizontal video sync signal (which comes from the logic board via the power supply cable); as the flyback transformer wouldn't be getting any pulses. If this was a model with an internal HDD; it should spin up without the logic board (even though it wouldn't do anything else; except perhaps unpark the heads and do a tracking calibration).

So, yeah - my suspicion would be on the power supply. Capacitors (or even just one that's in a particularly critical spot) could be at fault; and probably are where I'd start. However, if that doesn't help; it could well be any other component, or a cracked solder joint or trace on the PSU board.

 

[bigmessowires]

Went I went to turn the power button off, I heard a quick beep.

My first thought upon hearing this was a power switch problem. Cruddy corroded switch contacts. What happens if you try wiggling the switch, or flipping it from 0 to 1 slowly and gently?

 

[ishbooisland]

Yeah I thought it was odd that nothing would come on at all. It does still have the original 20 Mb hdd, it wasn’t spinning up either. My knowledge of electrical components is scarce, but don’t capacitors get “charged up” so to speak? Wonder if the delay sometimes is a capacitor failing to charge fast enough. I’m going to try wiggling the power switch and see what happens, will report back.

 

[ishbooisland]

So I tried turning it on, and it’s dead again lol. I did try wiggling the switch, tapping it, on and off slowly, no difference. What is did notice though is that if I hold the switch in the middle and just go back and forth, I can hear a little electrical crack when I pass the point of contact, so it sounds like the switch is doing what it should. Going to order the parts to recap the analog board and probably the modern PSU, thanks for the tips and info.

 

[bdurbrow]

Yes, they do get charged up, but (depending on the capacitor and what it’s being used for) this takes between nanoseconds (for a small ceramic capacitor used as a high-frequency bypass on a single chip’s power leads) to milliseconds (for a typical electrolytic used as a bulk power reserve).

Note that capacitors used in signal applications would have charge times that are dependent on the signal being passed thru them.

 

[krishnadraws]

It sounds like the PSU needs a recap. I proactively did this on a Mac SE FDHD I purchased from Craigslist two years ago (for the princely sum of $30!). JDW's excellent guide on YT walked me through the whole thing, and in his video description, he has the complete parts list you'll need.

 

[ishbooisland]

Yep, those are the videos I’m using for the analog board recap as well. Love the pre made lists.