Macintosh II Astec AAI3780 Repair

[egrath]

Hi,
my Macintosh II seems to be dead in the water, power supply isn't starting up, even when using the jumpstart method of supplying 5 V between the white pin and ground. So my assumption is that the PSU itself has some issues. Are there any known issues with the Astec AAI3780 power supply which i could check? In a first inspection i didn't saw any obvious issues (fuse is OK, no leaked or cracked caps). Any hints on how to start the analysis?

 

[joshc]

Got any photos of your Mac II logic board? Would be good to rule it out first. I've never had a bad Mac II power supply so far (not saying it doesn't happen, but I think its more likely a logic board thing).

 

[egrath]

Yes can take them, but isn't it a clear indication that the PSU has some issues when even jumpstarting the PSU does not work?

 

[egrath]

 

[egrath]

Now that i've taken Photos at high resolution and taking a look at it, some of the caps really seem to have leaked a little bit. Especially C14, C17 and C18 already have damaged the traces as far as i see. Thought at first that it was some nasty dust when i took a look.

 

[3lectr1cPPC]

Yeah those caps are completely toasted. I'm not at all surprised you're having power issues. You're definitely going to need to recap that board and give it a very good cleaning before you're going to see any life out of it. The traces around the caps also look pretty bad, you're probably going to have several breaks.

 

[joshc]

Any Mac II with electrolytics needs recapping, and was probably due for it about 10 years ago, at least.

You need to replace those capacitors and replace the two original batteries before attempting to power this on. I can see some possibly bad traces as well that need repair.

 

[egrath]

Thanks for all your help, he's alive since a few minutes

Cleaned up the entire board, repaired some eaten away traces and replaced all caps with solid tantalum one's. Also the Battery holders have been replaced by new ones which let me replace the 1/2 AA batteries should they run out of juice. While the iron was hot i also took the chance and replaced the Fan in the PSU with a Noctua branded which is way quieter than the original one and also has more airflow/hour.

One more question: Can i use 8 x 4 MiB sticks for a total of 32 MiB? I think of purchasing these ones:

PurpleRAM 16MB (4MB x 4) 30-pin DRAM SIMM kit by Siliconinsider on Tindie

PurpleRAM 16MB (4MB x 4) 30-pin non-parity DRAM SIMM kit

www.tindie.com

Materials used:

2 x https://www.digikey.com/en/products/detail/6S-1-2AA/6S-1-2AA-ND/2077833 (they almost fit perfectly, one side of the connectors needs to be bent carefully and on the two sides where they touch you need to grind away a half mm each with sand paper)
1 x https://noctua.at/en/products/fan/nf-a8-flx (cut away the connector from the original fan and solder it on the noctua wires. You don't need to connect the yellow wire, it's the RPM sense signal)

 

[LaPorta]

What exactly did you have to do with the fan? You mean the connector for the fan has to be transferred to work with the header inside the PSU?

 

[egrath]

Yes exactly. The original PSU fan has a 2-pin connector, the Noctua a 3-pin one. The 3-pin one does not fit onto the corresponding header on the PSU circuit board. I built a little 3-to-2-pin adaptor from the additional parts in the Noctua box (extension cables, ...) and the original fan, just in case i have to replace the fan at some point in the future:


In the picture above, the part right to the shrink wrap came from the original fan, the parts on the left side of it were a 3 pin extension cable that came with the noctua and was stripped from it's third wire and then soldered together.

 

[joshc]

Nice work. I'm so pleased to see another Mac II ressurected, and it gives me hope for the others out there still waiting to be repaired as it again shows that it tends to be broken traces/bad capacitors that cause problems in these machines, not the power supply. No doubt the Noctua makes it much more usable too -- Mac IIs are a bit like a wind tunnel with their original fan.

I think with Mac II memory, 4MB or larger SIMMs must be PAL SIMMs. Garret's Workshop sell Mac II compatible RAM: https://www.ebay.com/itm/GW4194A-4x...r-Macintosh-II-and-IIx-16-MB-kit/255445473759

 

[LaPorta]

Thanks very much. I may install one of these in my IIfx.

 

[egrath]

Now after i have put back everything into the case, i found out that i still have some issues ... eventually someone has a hint on how to fix these:

1. With power disconnected from the PSU, the batteries are drained at extreme rates. Both are drained from 3.6 to 0.2 V in about 24 hours. Both got hand warm during this period (warmer than the environment around).
2. When the device is being shut down from within the operating system, it does not power off automatically. Also powering off with either the keyboard or main switch does not work, need to completely disconnect from the power outlet.
3. The device only works with either 4 or 8 pieces of 100 ns 256 KByte SIMMs installed. Putting in 1 MByte SIMMs from another working Mac SE/30 results in the Chime of Death. As far as my research turned out, only 4 MB simms should be problematic and need to be PAL ones.
4. Does anyone know what cap C9 is for (the one next to the RAM sockets on board edge side). In my board this was originally unpopulated ... in every picture of the Rev B board i found, it's populated.