IIsi HDD getting 5V but not 12V - I think - advice?

[IIsiGuy]

Glad I found this board. Hope someone point me in a useful direction to get a recently liberated Mac IIsi up and running.

Long story short: There may be multiple problems, but number one is the hard drive is not getting 12V of the 12V/5V needed for it to work. After a SCSI drive swapped in still didn't spin up, I measured the voltages and 5V to GND OK, but not OK is 12V to GND. Even measured directly in the logic board socket (without the cable adapting it to the molex-type on the drive).

So swapped the PSU (unbelievable how easy these early machines are -no tools needed!) - but it made no difference.

It had been booting OK from the floppy drive, but that just started grinding and not reading. Another thing to clean or swap.

Dust has been blown off the logic board but it still seems kind of grimy in places. Although not electronically experienced, a logical approach generally isolates problems for me - but if this is a PCB repair problem, it's beyond my tool-kit. Anything else I'll try.

Hey the IIsi listed at $3770 according to everymac - after only 20 years I expect it still can be made to work well… And I'm looking forward to using Cricket Graph as MS products no longer support patterned fills.

Thanks.

 

[spiceyokooko]

Have you checked and replaced the PRAM battery? That's the first thing I'd look at doing.

I had a similar 'type' problem when recently trying to resurrect a IIfx. The hard disk wasn't spinning up even though I knew the HD was good. I tested the PSU voltages and they were fine.

On inspecting the logic board I noticed a shorted circuit with a break in it, a drop of solder later and a reassemble and the HD spun up and booted fine.

If your swopped in PSU is known to be good and the swopped in HD is also known to be good, and you've replaced the PRAM battery with a new one - I'd be looking at the logic board for possible circuit breaks.

The fact the machine boots from floppy but there's not enough juice to spin up the HD does rather point to the PRAM battery for me.

 

[Bunsen]

Do you have an external SCSI drive or case? It may be worth seeing if the machine will boot from that, at least to narrow down a plan of attack. Disconnect the internal drive, or move it into the external case.

 

[bibilit]

I have got two of them and both boot without any Pram battery.

I also think you have a logic board issue.

try to wash the board and let it dry for a couple of days, maybe this will sort your issue, the floppy is also getting power from the board, so maybe the issue is related.

 

[zuiko21]

Certainly, the floppy is the other major +12 V consumer... I'd try to fully disconnect the floppy (including the flat cable!) and check whether the +12V rail operates again. Check also the external floppy connector, there's a +12 V line that could be shorted.

 

[uniserver]

hopefully my ADD is not kicking in again, but is it possible this replacement PSU could also have the same issue?

 

[trag]

I think washing the board is a good idea. There could be a short from 12V to ground or to 5V caused by capacitor leakage on the board. Worse, would be an internal short in one of the bypass caps on the 12V plane.

But if the short was 0 resistance, I don't think the power supply would start up. If there is a short, it is probably somewhat resistive.

I would start by disconnecting the power supply and the disk drives and then check the resistance between 12V and ground and between 12V and 5V using an ohmmeter.

 

[IIsiGuy]

Wow. Thanks for the great suggestions.

It's going to take me a while to work through them. My (un-inventoried) vintage Mac parts stash is at another location - and the IIsi PSUs are there too. Know I have more floppy drives. There possibly might even be another logic board to try.

But if there isn't one - for me liquids+electronics is not a familiar mix. Any links to proper board washing and drying? (Seems to be very different methods mentioned online.)

Thinking that the power supply from an ATA/USB drive adapter (same molex) would power the drive in the case, but will wait until the floppy drive is replaced so can run utilities.

As far as external booting, think I still have a SCSI case for an HDD, also dimly recall making a Zip disc with a bootable System 7 on it, so can try that too.

Do these models boot from an external CD? Pretty sure I can find an OS 7.6 CD to put into an Apple CD-300.

Battery is new.

Couldn't try the no-floppy drive suggestion without the PSUs here, but did some ohm-metering (though I can't interpret). Disclaimer: it's a cheap beat up meter with fat probes generally used for battery checks. Done with PSU and drives removed.

HDD Power Pins (believe 1 12V, 2&3 GND, 4 5V)

1-2 or 1-3 brief 0 ohm, then either readings from 0.5 M ohm up to 2 ohm

1-4 1.8 M ohm

2-3 0 ohms (ground ground)

2-4 or 3-4 0.4 K ohm, and slowly rising

Thanks very much for the support.

 

[trag]

HDD Power Pins (believe 1 12V, 2&3 GND, 4 5V)

1-2 or 1-3 brief 0 ohm, then either readings from 0.5 M ohm up to 2 ohm

1-4 1.8 M ohm

2-3 0 ohms (ground ground)

2-4 or 3-4 0.4 K ohm, and slowly rising

Thanks very much for the support.

The readings with a low resistance and then increasing, are caused by the bypass capacitors doing their job in reverse. When you first start taking a reading, current flows into the capacitors (because capacitors store charge) and the current flow looks like a low resistance to the ohmmeter. Eventually, it should level off and give you an actual reading of the resistance.

Was the 1-2 or 1-3 reading .5 M ohm up to 2 M ohm? Or "up to 2 ohm" as you wrote? If it only rises to 2 ohms, then there's definitely a short there somewhere, as 12V through 2 ohms would cause 6 amps to flow, which the power supply cannot supply. But if that was a typo, and it's really 2 M ohms, then no problem.

The 2-4 and 3-4 readings are fine. Most good motherboard I've checked show about 500 ohms of resistance, so .4 K ohms is right in the ball park. Even switched off, all the transistors have a little bit of leakage, and it adds up.

 

[IIsiGuy]

Very much appreciate the meter data interpretation. Yes 2 mega ohm - that was a typo. I think it may just be the meter, but in sequential measurements it rested at something as low as 0.5 M ohm or as high as 2 M ohm.

Next week I'll have a chance to pick up the external SCSI cases, replacement floppy drive, and another logic board that had been pulled from a IIsi that I'm told was retired for the sole reason of the usual speaker contact problem.

Thanks.

PS I'm fascinated by what kind of motherboard "wash" is recommended here. I see a range online from what appears to be organic solvent immersion (like dry cleaning), isopropanol (either 91% drugstore or 100% commercial) with a brush or cotton, distilled or deionized water, bathroom cleaners, dish soap and hot water (even in a dishwasher), followed by various drying methods.

 

[spiceyokooko]

I think a lot depends on why exactly you're doing a 'motherboard wash' in the first place. A lot here seem to favour the distilled water route followed by a dry with a hair dryer - personally I don't really see what that achieves apart from giving you a nice sparkling clean motherboard - perfect if you're mostly concerned about presentation.

I prefer the Isopropanol Alchohol (purest is best 99%+) route principally because I want the electrical contacts to be clean - I'm not that concerned about the overall appearance of the board and Iso is an excellent electrical contacts cleaner.

That's my view for what its worth - I'm sure others will have their own views and reasons for whatever route they favour.

 

[trag]

When the capacitors leak, they leak a sticky goo. Most of the washing recommendation is to remove that corrosive and (apparently) conductive goo.

So a pure distilled water wash probably wouldn't help, unless it was hot enough to dissolve the goo.

Detergents, solvents and hot dishwasher washing all serve the same purpose. Absent a careful study, it really boils down to which method you prefer. I like to use 91% alcohol and a soft bristle toothbrush, followed by distilled water, just because all the ingredients are easy to get, come is small(ish) bottles and aren't likely to make a big mess.

 

[IIsiGuy]

Thanks for all the advice, unfortunately it took longer than expected to pick up the replacement logic board.

Long story short, after replacing the board, the original hard drive still didn't spin up - but a replacement drive worked fine. Now up and running System 7. It also boots fine off a Zip 100 disk (external SCSI) that had a backup of the original 80MB drive on it.

So I'm of the very inexpert opinion that both the original drive and some board component(s) were problems - perhaps one electrically damaged the other?

If I get the time, might be curious to see if a wash rejuvenates the old board, etc. Also wondering if this setup (IIsi Sys 7) supports larger drives (maybe 0.5, 1, or 2 GB SCSI) which seem easier to find.

Thanks again. Very much appreciated.

 

[zuiko21]

SCSI drives up to 2 GB should work great. However, larger capacities aren't supported by all OS versions and machines, but you can always partition a big disk in several chunks just below 2 GB...

A few points to consider, just in case:

•Some drives (esp. server ones) can draw a lot of power, while the IIsi PSU is somewhat limited... check the amps needed for the +5 and +12 rails of the drive before purchasing -- it's indeed related to heat generation, something you want to be controlled inside a plastic IIsi... But, up to 2 GB this isn't likely to be an issue.

•For a Macintosh, best are 50-pin drives, but they're becoming somewhat rare. It's possible to use 68-pin and 80-pin (SCA) drives with a suitable adapter. With these wide-SCSI drives, sometimes you'll need to tinker with jumper settings in order to enable 8-bit (narrow) transfers, and/or disable the delayed startup. Some Ultra-320 drives do not support narrow transfers at all. But once again, this is more for larger disks.

•Unless you're lucky enough to find an Apple branded suitable drive, regular Apple formatting utilities will refuse to work on your disk... Use a third party formatter, or the patched version of HD SC Setup / Drive Setup.

 

[IIsiGuy]

I recall the 2GB volume limit, and the Apple ROM to format issue, but wasn't sure exactly where System 7 or the IIsi fit into that Apple timeline.

And thank you very, very much for the clear and specific SCSI drive and power tech tips. They'll be very useful going forward. (If I'm lucky it looks like I might be able to get a drive locally - untested - pulled years ago from an early Power Mac. I suppose it'd be 50pin somewhere from 500MB-2GB, unless it was an upgrade.)

It'll be nice to get a backup drive ready to swap in if the need arises...

 

[nvdeynde]

The only solution to get your IISi working again and running stable is to recap the logic board and the PSU.

I have already done this with most of my 68K Macs.

You will be surprised when you open the PSU and see the condition of the capacitors inside.

Good Luck,

Nico

 

[IIsiGuy]

The more I learn about vintage electronics, the more what you advise seems to be the best practice.

As yet I have zero direct experience with component level repair/PCBs. (Indirect experience? When a G4 MDD would no longer respond to my best troubleshooting, the only thing that worked was a PSU replacement for which I had to use a non-local "exchange for recapped unit" service.)

Not sure the best way to learn. All local electronic "repair" shops just replace things. I don't think they do any soldering. (And the most precise instrument currently in my collection is a 3 lb soldering gun...

 

[nvdeynde]

It's regrettably true that most electronic shops don't do these repairs anymore.

It's a time consuming job and you need a good soldering and de-soldering station to repair the boards, which is expensive, and of course you need the skill as well to work with them.

Next to soldering equipment, you also need a good DMM, an ESR meter to test the capacitors and a scope to trace other problems with the PCB.

However, there are several experts here on the Forum. With a bit of luck, there's someone near by that can do the repairs for you.

Take Care,

Nico

 

[onlyonemac]

My performa 475's hard drive spins up, but then down again before the mac can boot from it. It gets both 5 and 12 volt supplies, but still doesn't work.

Search "Can dead battery cause hard disk trouble?" on LC and Performa forum.