Macintosh IIsi, Recapped, quite chime, no display.

[BullyFreeBear]

I had recently gotten a Macintosh IIsi that didn't have any signs of life. I've gone through it and recapped a fair amount of the power supply and tested the voltages, I was getting a solid +12.3 +5.4 -12.3. The machine powered up but no display or chime, I thought nothing more then it just being bad capacitors on the logic board so I ordered new tantalum capacitors and installed them. To my surprise the machine chimed very quietly but it chimed, so I went to plug in an monitor just to be greeted with no display so I tried the one that came with it and still the same thing. So I checked my work, cleaned the board and resoldered some chips that looked rather sad but still nothing. So I started trouble shooting to the best that I could without much knowledge of the machine and started taking parts off to see it what would could be wrong and found that the machine would only chime when then hard drive power cable was plugged in. Im at a loss at why the machine would only chime with the hard drives power cable connected.

If anyone could point me in the correct direction that would be great.

EDIT: I should add that the hard drive power cable is connected to the hard drive with the SCSI connecter disconnected.

 

[JDW]

I don't own a IIsi, nor have I worked on one, so I can't tell you from personal experience what it might be. However, I think it would be helpful to others with IIsi experience if you could post clear, hi-rez photos of your motherboard. That might help others come along and identify problem areas.

Your mention of a "quiet" chime indicates there still may be audio issues too, although I don't know how low the volume defaults to on a IIsi. And if you can't see anything on a display, it's not possible for you to try and boost the volume via the Sound control panel.

 

[BullyFreeBear]

A little bit of an update. I got the computer to display video, the monitors video adapter was dirty. But now I’m stuck with the flashing floppy disc icon, when I put in a good system disc it just spits it out and gives me an X on the screen. Ive tried using a ZIP disc with an entire Mac classic II system backup and it didn’t even attempt to read, it acted as if it wasn’t even there.

Now I’ve noticed some dark blue corrosion on the AM85C80-8JC and on the 26LS30 and from what I can tell on the schematic that chip being bad or not connected to the board would maybe give me the same problem. Going back to when the Mac boots I see that it resets once with a bunch of purple garbage on the screen then it boots into the flashing “?” on the floppy disc, now from what I can tell it only does it from a hard boot.

Last thing that I still don’t understand is how I get a Crunchy Bong from the machine when I plug in the hard drive power cable into the hard drive, but then when I unplug it, it will go silent.

I have attached some pictures of the board when you can see my rough resoldering of most of the chips with nasty solder.

I’ll retake the pictures in some better lighting if necessary.

 

[JDW]

I assume that 5.4v you measured from the power supply was with the PSU disconnected and in the no-load state, correct? If so, what is your loaded state? Do you measure something more along the lines of 5.0v when the power supply is driving the motherboard and with the computer on? Because if you get 5.4v at the motherboard, that seems rather high to me.

When you plug and unplug the hard drive, I assume you do both with the machine powered off, correct? If so, you seem to be saying that powering the hard drive is making your audio crackle. If so, can you record that audio with your iPhone and upload that audio file? And can you check the audio with headphones to see if it is only your speaker? If you get the crackle with headphones too, that means it is something affecting all audio, not only your speaker. And in that case, you should check voltage at the hard drive connector to see if you are getting a rock solid 5v and 12v or not. Of course, if you only have a hand-held meter, it may not show voltage dips like an oscilloscope would. My concern here is that power may be unstable.

When you say "good System disk," what System, specifically? Apparently, the IIsi requires System 6.0.6 or higher, so if you have that or a 6.0.8 disk, that would be good to try. System 7.0.1 will also work. You can use 7.1 without any special System Enabler. If you have a FloppyEMU, that would be the fast-track to trying many different OS's quickly. You just want to make sure whatever System Disk you use is truly a non-corrupted disk that will indeed work on any IIsi.

 

[BullyFreeBear]

THE MACHINE IS HEALING.

There’s still almost no audio, but to answer you’re question I’m not getting just a crackle at the speaker but I’m getting a crunchy bong and with headphone I am getting perfect audio with no crunch so I’m guessing either the speaker needs to be looked at or the amplifier need to be fully looked over again.

The +5.4 was from the hard drive cable as the psu looks like it’s connected almost directly to it, loaded it’s around 5.2. I should take a scope to look at the voltage because I don’t fully trust the psu just quite yet.

The hard drive does not show up making me believe that the hard drive is bad or needs to be fixed, I’ve read that there is a piece of rubber that goes hard in them that stops the heads from moving and that quite a few people have been able to fix it. But good news is my ZIP drive is visible.

 

[croissantking]

The sound issue might just be a bad connection to the internal speaker. The design the IIsi uses - sprung contacts under the logic board - is notorious for being flaky. Try inspecting and cleaning the contacts as well as the pads on the logic board which press against them.