1. No, no chimes at all
2. I haven't checked out the reset yet. I'm working through Voltages, Clocks, Reset next.
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Restoring my IIcx
- Thread starter rodders
- Start date
2. I haven't checked out the reset yet. I'm working through Voltages, Clocks, Reset next.
I do get a thump through the speaker when I switch on but I suppose the sound chips could have a problem. I have hooked up the Apple Colour Monitor that came with it but I don't know if it works. There is nothing on the screen but that could be because its faulty or out of adjustment. I need to make up a cable so I can hook up to my GBS-C.
Well, all that means is that the audio amplifier has powered up. It doesn't require the CPU to be running or anything digital to be happening at all.
Checked voltages all over the board and I'm getting 5.02v everywhere. I had a few problems checking the clocks as my scope was coming up with som weird values. However, setting the ranges appropriately and calculating manually all 4 clocks seem about right. The problem seems to be noise on the voltage rails with regular spikes which were causing the scope to report the frequency of the spikes rather than the clock.
I need to find the source of the noise. It could just be my cheap ATX PSU, or the interface board that I made introducing noise. The noise seems consistent across 5v 12v and -12v so i suspect the psu as its probably using group regulation. Some large electrolytics in the right place could fix it.
I need to find the source of the noise. It could just be my cheap ATX PSU, or the interface board that I made introducing noise. The noise seems consistent across 5v 12v and -12v so i suspect the psu as its probably using group regulation. Some large electrolytics in the right place could fix it.
Checked reset values at various points, all were high (inactive).
The spikes in the DC voltages are coming from the cheap PSU I used. The scope shows spikes at 22kHz of about 2V p-p. I'm guessing this is seriously going to mess up the clocks which could explain why its not booting up. I've dug out an old ATX PSU which seems to have much cleaner voltages so I'll try hooking it up to see if I can at least get a chime.
The spikes in the DC voltages are coming from the cheap PSU I used. The scope shows spikes at 22kHz of about 2V p-p. I'm guessing this is seriously going to mess up the clocks which could explain why its not booting up. I've dug out an old ATX PSU which seems to have much cleaner voltages so I'll try hooking it up to see if I can at least get a chime.
This is what 5V looks like on the cheap PSU:
that can't be good.
I've tried another, PSU with much cleaner voltages. The clock signals look much better but still no chime, its just not booting.
I've checked a few address and data lines but there's nothing happening.
The main chips do warm up a bit but nothing is hot.
Assuming that the CPU is actually OK, what would prevent it from starting up?
Any advice on where to look next would be appreciated. I'm not familiar with these machines so not sure what the boot sequence is or if there is any POST information anywhere.
that can't be good.
I've tried another, PSU with much cleaner voltages. The clock signals look much better but still no chime, its just not booting.
I've checked a few address and data lines but there's nothing happening.
The main chips do warm up a bit but nothing is hot.
Assuming that the CPU is actually OK, what would prevent it from starting up?
Any advice on where to look next would be appreciated. I'm not familiar with these machines so not sure what the boot sequence is or if there is any POST information anywhere.
To continue with testing I've lashed up an alternative PSU with a cleaner output.
After much cleaning, examining and testing I established that the ROM select line was not being activated.
This line goes through jumper W1 which disables the ROMs when a SIMMROM is used. By removing the jumper I found that the ROM Select was indeed being pulled low by the GLU chip so there has to be a fault with the ROMs, clamping it high.
I removed the ROMs one at a time in the sequence HH, MH, ML and LL and tested ROMSEL each time (with the W1 jumper back in place). It was only after removing the last one (LL) that I saw ROMSEL being pulled low. It therefore looked like it was LL that was the problem. However, on reading the ROMs using my TL866 I verified LL, ML and HH but MH was all FFs. That was never going to work!
So I obtained some sockets and W27C512 chips, fitted the sockets, burned the set of ROMs and voila! A sad Mac chime (no RAM fitted). With RAM back in I got a Happy Mac and it booted to the floppy screen. With a floppy inserted it proceeded to boot into MacOS 6.0.8 so my floppy refurbishment has succeeded too! Whoopee!
Feeling I was on a roll I had another look at my refurbished PSU. The output was still noisy but what the heck, give it a go.
After reassembling it and dropping it into place the machine boots up like a good 'un.
I may try swapping in the old ROMs to see which ones are bad but that's for another day when I have nothing better to do.
After much cleaning, examining and testing I established that the ROM select line was not being activated.
This line goes through jumper W1 which disables the ROMs when a SIMMROM is used. By removing the jumper I found that the ROM Select was indeed being pulled low by the GLU chip so there has to be a fault with the ROMs, clamping it high.
I removed the ROMs one at a time in the sequence HH, MH, ML and LL and tested ROMSEL each time (with the W1 jumper back in place). It was only after removing the last one (LL) that I saw ROMSEL being pulled low. It therefore looked like it was LL that was the problem. However, on reading the ROMs using my TL866 I verified LL, ML and HH but MH was all FFs. That was never going to work!
So I obtained some sockets and W27C512 chips, fitted the sockets, burned the set of ROMs and voila! A sad Mac chime (no RAM fitted). With RAM back in I got a Happy Mac and it booted to the floppy screen. With a floppy inserted it proceeded to boot into MacOS 6.0.8 so my floppy refurbishment has succeeded too! Whoopee!
Feeling I was on a roll I had another look at my refurbished PSU. The output was still noisy but what the heck, give it a go.
After reassembling it and dropping it into place the machine boots up like a good 'un.
I may try swapping in the old ROMs to see which ones are bad but that's for another day when I have nothing better to do.
Good stuff! :-D
Oh well done, you've tied this up nicely. It's great when things come together after putting in so much work.
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