Another IIci ROM hack

[Trash80toHP_Mini]

Have you tested the Power Cord you were using when the IIci "Stopped Working?" That's one of the nastiest failures and one that often goes untested. It's a pain to unhook one at the plug end, so it often goes untested and the computer end is plugged right into the test PSU w/o testing. One of my IDE<->USB2/SATA adapters came with a bad power cable and I figured the whole thing was bad, when I returned it . . .

. . . they tested it and found the noob boob for me . . . :I

 

[Dennis Nedry]

It's probably the capacitors on the 'dead' IIci board. I bet they were ready to go and you've been using it more than usual. The soft power circuit is fairly simple, totally separate from any ROM-related stuff, and a schematic can be found on Gamba's site:

As you can see, even if you blew up the processor, the soft power would still kick on the power supply, so the problem is somewhere on this schematic, most likely the electrolytic capacitors. I'm actually surprised if ANY IIci still works with stock capacitors after this long. None of mine did.

 

[dougg3]

Got the Quadra 700 to boot into Finder in MESS this weekend after a few months of hitting my head against various aspects, but there's always more work to do

Cool! And as for how you did the ASC stuff, awesome! I started looking at the Sound Manager drivers a little bit, but the MESS code was so much simpler to follow. I think I found an interesting string resource in the System file describing the ASC driver, I might have to pull that one out if I can find it again.

I think it died from too much awesomeness.

Haha, good point! That has to be what happened

Have you tested the Power Cord you were using when the IIci "Stopped Working?" That's one of the nastiest failures and one that often goes untested. It's a pain to unhook one at the plug end, so it often goes untested and the computer end is plugged right into the test PSU w/o testing. One of my IDE<->USB2/SATA adapters came with a bad power cable and I figured the whole thing was bad, when I returned it . . .. . . they tested it and found the noob boob for me . . . :I

Thanks for the suggestion jt! Unfortunately that same power cord booted the other IIci fine. Oh man that would be annoying to discover that the power cord was the problem all along

As you can see, even if you blew up the processor, the soft power would still kick on the power supply, so the problem is somewhere on this schematic, most likely the electrolytic capacitors. I'm actually surprised if ANY IIci still works with stock capacitors after this long. None of mine did.

Yeah, it was pretty surprising it was still working. I haven't checked to see if there are leaking caps but there must be. In fact I think this machine was having some kind of weird problem where soft power down would result in an immediate reboot, but that problem mysteriously disappeared. I'll take a look at it later, thank you for the info!

Do you happen to have any ideas on repairing a IIci power supply? My other machine has an Astec power supply that bit the dust, so they are both sharing this GE one. I saw the diode fix and haven't been able to try it, but the "flip a power strip off and on" trick wouldn't work for me and I'm not getting a 5V trickle voltage out of it at all.

 

[olePigeon]

My IIci worked fine for the past few years. I didn't even think to check for leaky caps until recently. I then recapped my IIci. Still works great. Now all I need is a Quadra 700 power supply to replace the one in my IIci. I don't think the original power supply has enough power to run my accelerator.

 

[dougg3]

LOL, I definitely need to re-cap and clean that "bad" logic board. I noticed the board is filthy near the soft power circuit (underneath the power supply), some from dust and some from leaky caps. I blew compressed air all over the soft power circuit and the IIci is alive again. OK for a temporary fix but I will re-cap and clean it soon.

Thanks again for the info Dennis Nedry! When you said that it would still at least start the power supply if I had blown the CPU for example, that made me feel a lot better!

 

[Dennis Nedry]

No problem Doug! I've never found any exact science with power supplies. If you find clues on the web, definitely try those first. Otherwise if you're really lucky you might find a big chunk out of something or a bulged out capacitor, but most of the time there won't be a visible sign. In that case, I guess I'd start by pulling out a voltmeter and trying to trace back from the trickle line until I found some juice.

I have fixed a couple of IIsi power supplies that had two smallish electrolytics that went bad with no visible signs. They shorted the trickle to ground I believe. When poking around, it helps to think about, what should this voltage be at this point, and what would make it wrong. Is there a series resistor behind this point, if so, test both sides of it. If it's good on one side and not the other, poke around the bad side for things that could be shorting it. Just basic experimentation like that, unsolder things, test if possible, solder on similar parts if you can't test, etc. Knowledge to gain and not much to lose.

You can even take a pretty good bet a lot of times and unsolder all of the capacitors one by one, testing for a short. If they don't test as shorted, maybe they're blown open, but that's not usually likely to make a power supply totally dead.

Heck, try plugging AC into the power supply just out on its own and feeding it external +5V to pin 9, ground to 5, 6, or 7, defeating the purpose of the trickle voltage. Whatever happens or doesn't happen could give you some clues. Maybe it's just the trickle, maybe it's deeper if it still doesn't wake up.

 

[dougg3]

Thanks for all the info Dennis Nedry! I tried your last suggestion since it didn't involve any case opening and...whoa...

So I applied +5V from my bench PSU to the /PFW pin (9) (and connected the grounds together), as you suggested.

I heard a relay click and the fan started spinning slower than usual. I measured the outputs and they were jumping wildly from where they are supposed to be (12V was jumping between 6 to 8 V, -12V was jumping between -6V to -8V, and 5V was jumping between 0 and 4V). It was drawing about 30 mA from my bench supply.

Then, I removed my bench supply and started playing around looking at the pins. I checked the +5V trickle pin (10), and the +5V trickle was there again! I didn't bother checking before I had started playing around with it though, so it's possible the trickle was already there, but I know at one point a while ago it was completely gone. So I tried telling the power supply to turn itself on by shorting /PFW and the +5V trickle, and it did the same thing it does with external power -- slow fan and too-low voltages.

Anyway, naturally after seeing that, I put the power supply into my other IIci, and suddenly, IT WORKS!

WTF is going on here? Did applying external power "fix" the +5V trickle temporarily or something? Did I accidentally make a loose solder joint good again by moving it around? Why does jump-starting the power supply like I did not allow the voltages to go all the way up? This is confusing and exciting because both my power supplies work again! Thanks for the awesome suggestions! I still have no idea what is going on here...haha

 

[olePigeon]

The computer gods are pleased with your work, and rewarded you with a working power supply. )

 

[Bunsen]

Woah. Having finally taken the time to read and comprehend this thread properly, all I can say is -

What an epic adventure - and by the sound of it, this is just the beginning. dougg3, and everyone involved, take a bow.

 

[Bunsen]

So, to check that I'm up to speed-

I gather that the barrier to using the ROM slot as storage or general-purpose expansion is the absence of any write lines?

Also, Trash, it's worth bearing in mind that a USB *Device* port/chipset/stack and a USB *Host* port are not the same thing. The one on a computer is a host, the one on a disk is a device. There is a protocol that can do both, called USB On The Go (OTG) - but in general, an IC that acts as a device will not be able to mount (host) another device. Pardon me if I'm pointing out the bleedin' obvious here, but from your earlier posts, you seemed to be making that confusion.

Meanwhile, this tidbit caught my eye, and perhaps warrants further investigation:

How the Classic's ROM disk image is implemented

and ROM Disk driver.

Sure, still read-only, but perhaps a convenient, OS-friendly way of making use of spare ROM capacity?

*cough* SD card?

One small suggestion for the programming board- USB to RS232 or TTL cables are readily available, cheap, and infinitely useful for further hackery, so, in order to keep the custom board as simple (ergo, cheap) as possible, why not have TTL or serial headers on the board, and let the end user buy a USB converter? Some of us will no doubt have one lying about, and others (like me) have been meaning to get one anyway.

That also leaves the door open for maniacs who might want to program their ROM from a Mac serial port

 

[Dennis Nedry]

I'm glad to hear that your power supply is working. Have you tested the voltages on the logic board with this power supply running? You can test +5 and +12 easily in the hard drive power connector. I'm a little bit concerned that the voltages were unstable.

 

[techknight]

Well if your voltages are "bouncing" that means the power supply is cycling, which means there is an overload on one of the rails somewhere. Unplug the power supply from the mainboard, measure each rail point to ground in ohms. take a note of the measurements. Go to a good board, do the same thing. what you will likely find is one or more of the rails is reading lower resistance = leakage/short somewhere. have to track it down.

 

[dougg3]

The computer gods are pleased with your work, and rewarded you with a working power supply. )

That's about the only explanation that makes any sense! ;-)

What an epic adventure - and by the sound of it, this is just the beginning. dougg3, and everyone involved, take a bow.

Thank Bunsen! I still appreciate all the info/feedback/help everyone has given me on this project, it has been a TON of fun even through the few minor roadblocks I keep running into! It's also helping me get into hardware stuff which has always been fascinating to me.

I gather that the barrier to using the ROM slot as storage or general-purpose expansion is the absence of any write lines?

Exactly -- I suppose we could tie into a write enable line somewhere (maybe?) and get read/write capabilities, but I don't know where to look for that or if it's even feasible -- maybe someone with more hardware knowledge would know?

How the Classic's ROM disk image is implemented

and ROM Disk driver.

Sure, still read-only, but perhaps a convenient, OS-friendly way of making use of spare ROM capacity?

*cough* SD card?

As long as a microcontroller/FPGA or something could translate between ROM requests and SD card accesses, but the fast timing there would probably cause problems. BMOW probably knows more about this stuff and I'm suspecting that the image of what's stored on the SD card would have to be loaded into RAM that's connected to the IIci's SIMM pins--I don't think it could read off the SD card in real time fast enough (at least that's my first guess).

One small suggestion for the programming board- USB to RS232 or TTL cables are readily available, cheap, and infinitely useful for further hackery, so, in order to keep the custom board as simple (ergo, cheap) as possible, why not have TTL or serial headers on the board, and let the end user buy a USB converter? Some of us will no doubt have one lying about, and others (like me) have been meaning to get one anyway.
That also leaves the door open for maniacs who might want to program their ROM from a Mac serial port

Good idea! It also makes the board design easier for me Since I'm going to be using a 5V microcontroller, it would be easier if I use a 5V serial port instead of 3.3V. Is that going to cause a problem? I think a lot of those types of cables are designed for 3.3V if I'm not mistaken.

I'm glad to hear that your power supply is working. Have you tested the voltages on the logic board with this power supply running? You can test +5 and +12 easily in the hard drive power connector. I'm a little bit concerned that the voltages were unstable.

Me too I just did that...thanks for the idea.

+5V reads as 5.10 V

+12V reads as 11.89 V

-12V reads as -12.18 V

Those seem ok...maybe the IIci power supply doesn't like to be started without a load connected to it?

Well if your voltages are "bouncing" that means the power supply is cycling, which means there is an overload on one of the rails somewhere. Unplug the power supply from the mainboard, measure each rail point to ground in ohms. take a note of the measurements. Go to a good board, do the same thing. what you will likely find is one or more of the rails is reading lower resistance = leakage/short somewhere. have to track it down.

Thanks for the info techknight! The weird thing is that the power supply was doing that outside of the computer with no motherboard connected to it. With a motherboard connected to it, it behaves fine. Could starting the power supply with no load cause it to choke like that and keep cycling?

SIMM Update:

The second SIMM I have been having trouble with is now functional. It had nothing to do with the solder paste -- again, it was a case of nearby SIMM contacts getting shorted to each other. Possibly this time by me scraping the contacts with my probe as I was testing continuity. Something is different about the SIMM contacts than last time -- maybe they didn't coat them with solder in the revision 1 SIMMs? I'm thinking I can solve a lot of this by sucking off the solder with my desoldering gun and maybe some wick (although the wick is expensive!) Anyway, like I said earlier, I still think I will switch back to using ordinary solder and cutting out the bottoms of the sockets just to be safe. So anyway, it's coming along and I will soon be able to start selling them once I'm comfortable with them! (With the problems I've been having I want to make sure they will be reliable before I sell to anyone).

 

[Trash80toHP_Mini]

How about just gluing the "bottoms" back in as spacers once you're done soldering? :?:

Also, Trash, it's worth bearing in mind that a USB . . .

Thanks for the primer . . . I've deliberately avoided loading the USB Spec into my noggin' as yet . . .

. . . it's already bogged down with hardware hackin' mania. :

p.s. We really need a USB<->Classic/NuBus Architecture Brainstorming Thread . . .

p.p.s. I really miss the maniac . . . :'(

 

[olePigeon]

With the ability to make custom boot ROMs, does that make a USB NuBUS card more likely? Or is it an architectural barrier between the NuBUS design and sending USB data over it?

 

[Trash80toHP_Mini]

It's more a question of driver obsolescence under any NuBus Architecture OS, only PCI Architecture 'Books & Macs have the firmware/drivers available to handle USB 1 under OS9, so all 68k and, all or almost every 603e Mac or their owners are/were just SOL. Why would Apple retrofit older machines to do current tech (ancient tech by now) when they only wanted to sell new PCI Boxen? [?]

A SCSI<->USB adapter is entirely possible, as SCSI is a general purpose interface, an open standard (which Apple botched with full documentation available as is USB. However one would need to do it for kicks and have some serious development chops to grab for the BRASS RING of NuBus Architecture Hackery. [V]

 

[techknight]

yes it will cycle with no load because you dont have a load to keep the regulation circuitry in check. Without a load, the power supply tries to compensate and increase the voltage to +12v and +5v etc. It overshoots (no load) so the power supply drops off to bring it back down. falls under 12v, and itll overshoot again. cycle repeats.

 

[Trash80toHP_Mini]

Still going strong at 16 pages of AWESOME! Way to go doug! :approve:

 

[PowerPup]

Awesome work Doug. Makes me wish I had grabbed a Mac II from my dad while I had the chance.

At this rate there should be 20 pages by Christmas! :lol:

 

[dougg3]

How about just gluing the "bottoms" back in as spacers once you're done soldering? :?:

The thing is, when I break out the bottom it shatters into multiple pieces. Maybe if I can cut it out intact...not sure though.

With the ability to make custom boot ROMs, does that make a USB NuBUS card more likely? Or is it an architectural barrier between the NuBUS design and sending USB data over it?

I don't think the custom boot ROM really changes anything as far as USB goes -- like jt said, it's mostly about the software drivers. Theoretically one could create a printer/modem port to USB adapter (although it would be much slower than SCSI--I like the SCSI idea too).

yes it will cycle with no load because you dont have a load to keep the regulation circuitry in check. Without a load, the power supply tries to compensate and increase the voltage to +12v and +5v etc. It overshoots (no load) so the power supply drops off to bring it back down. falls under 12v, and itll overshoot again. cycle repeats.

Gotcha, thanks! That makes perfect sense...looks like everything is OK on my power supply for now!

Still going strong at 16 pages of AWESOME! Way to go doug! :approve:

Awesome work Doug. Makes me wish I had grabbed a Mac II from my dad while I had the chance.
At this rate there should be 20 pages by Christmas! :lol:

Haha, no kidding!!! Thanks! (If it makes you feel any better, I'm pretty sure the original II doesn't have a soldered ROM SIMM socket -- but there are holes to add one)