68kMLA Classic Interface

This is a version of the 68kMLA forums for viewing on your favorite old mac. Visitors on modern platforms may prefer the main site.

Click here to select a new forum.
Trying to bring a Performa 450 back to life
Posted by: Ajediday on 2022-02-24 15:37:50
I picked up a Performa 450 off ebay, no video, no sound. First thing I did was recap the motherboard and power supply. There was a little bit of leakage with one cap that I noticed on the motherboard (C20), cleaned that up. Still no joy, started to check voltages on the power supply (Astec 16251), with the power supply disconnected, all voltages look good. When hooked up to the computer, 5 and 12 volts are fine. The -5 is showing up at -2.4. My first thought is the voltage regulator (AN79N05) might be bad. Would that be a good place to start or is there something else I should be looking at to bring this back to life? Thank you.
Posted by: joshc on 2022-02-24 16:04:34
First off, are you trying with a good 3.6V PRAM battery? Some of these machines require a good one to start.

-5V is not needed for video/sound to work as far as I know, it's used for serial.
Posted by: Ajediday on 2022-02-24 16:19:59
First off, are you trying with a good 3.6V PRAM battery? Some of these machines require a good one to start.

-5V is not needed for video/sound to work as far as I know, it's used for serial.
Using a new battery, also tested battery before using.
Posted by: joshc on 2022-02-24 16:22:25
Got any high-res/close-up pics of the logic board?
Posted by: Ajediday on 2022-02-24 16:33:19
The discolor near C20 is kapton tape I used to protect the area I cleaned up
IMG_2793.JPG
Posted by: joshc on 2022-02-24 17:06:41
Have you checked continuity of the caps? Some of them look quite blobby (too much solder).

I can see cap goo/leakage under/around the legs of the DFAC (sound chip):
1645751097748.png

What's this at the corner of the Egret chip, dirt or something else?

1645751137231.png

Egret is essential for startup, it has to be very clean.

Has the whole board been soaked in IPA (isopropyl alcohol) and scrubbed?
Posted by: Ajediday on 2022-02-25 01:13:49
I didn't soak it (limited amount of 91% ipa on hand), but went over it with a small brush, moving area to area, and you spotted something I missed. That was a crumb next to the chip 🙂
Posted by: Ajediday on 2022-02-25 03:31:53
Also to follow up, any recommendations on how long to let it soak?
Posted by: joshc on 2022-02-25 04:36:24
I don't usually soak for very long, your board isn't very dirty so I think the scrubbing around DFAC and Egret are what I'd focus on.
Posted by: moldy on 2022-02-25 05:05:43
Egret is essential for startup, it has to be very clean.
I support this view, had exact same problems with some cap goo stuck under EGRET. Had to desolder, clean and solder again.
Posted by: Ajediday on 2022-02-25 06:30:15
Recleaned both areas, no change. Looked at both with microscope, one side of the egret didn't look right. Went over the pads with a soldering iron, just to reflow each pin. We have sound, we have video. Thank you for the help in narrowing this down.
Posted by: joshc on 2022-02-25 16:09:03
Nice!
Posted by: volvo242gt on 2022-02-25 16:22:03
Nice work. Now, another LCIII comes back to life...
1