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help for a Classic II recap

Classicman

Member
Hi all!

I'm trying to bring back to life my Mac Classic II (with logic board rev B).
Briefly my story: (Sorry for my bad english!)
I buy this Mac Classic II on the internet which initially worked without problems but only the sound did not work.
One day I go to turn it back on and nothing ... bad news: checkerboard on video (normal brightness on video)!
I gradually managed to recover all the capacitors to replace on the logic board.
So I have installed all ceramic capacitors but only the three 47 microfarads I was forced to put them electrolytic smd.
Now, when I go to boot it up with the recapped logic board, I get the typical checkerboard screen (now very low brightness) and no boot chime but fan spin and the hard drive run. Rarely large vertical lines appear in place of the checkerboard, always with low brightness.
Making attempts with the recapped logic board and keeping it on with the on-screen chessboard, I suddenly hear the Classic II start-up sound! and the screen starts up at the right brightness and arrives at the floppy disk screen with flashing question mark (I had unplugged the hard drive).
Incredulous and happy, I wait a few minutes and the question mark continues to flash smoothly. So I turn off the Classic II, plug in the hard drive power connector, turn it on and ... nothing more ... the usual low brightness chessboard. And nothing… is not wanted to boot again.
I've checked with a multimeter the 12 and 5 volts on the hard drive connector and the results are 11.84 and 4.95. Are these values okay? I think so...
Now my thoughts are on the analog board. Should I recap that too? Can you explain to me this one strange unique correct boot of my Mac with the amazing sound working?

Thanks you all that can help me!
 

Johnnya101

Well-known member
Definitely recap the analog board. The 11.84 seems a little bit low. Sounds like it may be straining when the hard drive is connected from bad caps? Wouldn't hurt at least...

There's a chance you may be able to adjust the voltage pot on the analog board to try and turn up the voltage, however I would recommend holding off until the caps are replaced. It worked when new in that position, so it should be okay.
 

bibilit

Well-known member
Voltages are OK, the 12 volt rail can be low as far as the 5 volt rail is between 4.85 and 4.95 volts.

have you a way to connect the hard drive to any external psu for a test while leaving the Molex from the AB not connected ? (for a test)
 

Classicman

Member
OK, first thank you a lot for all the replies!
To bibilit: yeah, I have tested it in this way... but nothing... the same problem...
Probably, for reasons of bad voltages or other due to bad capacitors, the analog board is unable to power and then start the logic board of the Mac Classic II.
I have to recap my analog board... hoping that's the problem!
 

Classicman

Member
Hi guys! here I am again!
I finally found the time to recap the analog board of my beloved Mac Classic II. The work was performed in a workmanlike manner and the voltages were calibrated with the dedicated trimmer: 12.25 volts and 5.15 volts. Unfortunately, the Mac at the first start after the recap did not start ... it started after 5/6 attempts leaving it on for a short time with the checkerboard on the screen ... Once the Classic II started it works without any problem! now works Mac audio too !!!!!! I tried to turn it off after a few minutes of use and it immediately restarted with the sound working. It gave me the satisfaction of working for 20/25 minutes! But once it was turned off and left off for 20 minutes it didn't want to start again and... believe me... I'm very sad and a little angry!
I am sure that the problem is related to the recapped logic board and not to the recapped analog board ... My logic board is revision B, can any of you tell me if I need to check some bad tracks on the logic board? Do I have to check anything else in particular ??
Please help me I'm freaking out...!
Thanks a lot!!!
 

Jamieson

Well-known member
Did you clean the logic board? The caps you replaced where probably leaking and there could be conductive gunk in there.

Also double check your solder joints, especially on the 47uF caps since they are SMT electolytics which can be tricky to solder.
 

Classicman

Member
Finally I have repaired my beloved Mac Classic II !!!
I found some "suspicious" solder under the rom and ram sockets. I re-soldered them and I re-soldered a smd 47uF electrolytic capacitor. After, a nice total "bath" in isopropylic alcohol.
Now it WORKS PERFECTLY at EVERY START !!!
THANK YOU ALL FRIENDS !!! 
 

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Jamieson

Well-known member
Nice! If you still have a hard drive in there I recommend replacing it with a Blue SCSI. HUGE upgrade! Wonderfully quiet and speedy!
 

Classicman

Member
Thanks Jamieson!! ;) actually Blue SCSI is a great upgrade and convenience for us old Macintosh enthusiast users. I'll think about it!
 

cheesestraws

Well-known member
Nice! If you still have a hard drive in there I recommend replacing it with a Blue SCSI. HUGE upgrade! Wonderfully quiet and speedy!
Thanks Jamieson!! ;) actually Blue SCSI is a great upgrade and convenience for us old Macintosh enthusiast users. I'll think about it!

BlueSCSI is badly-designed hardware which massively overloads the microcontroller. If you go and look at the datasheet for whatever STM32 is on the one you're using, you'll note that the "absolute maximum" sink current for the GPIO pins is something like 25 mA (it varies depending on the processor), and that it's only able to sink 120mA to ground. Note that the absolute maximum rating in datasheets is the point at which damage is likely to start. The SCSI spec requires 40something mA per wire. I did the maths before and worst-case, it's overloading the absolute maximum sink capability of the chip by something like five or six times!

Which is kinda bad.

They have unfortunately been told this loads of times by multiple people, and have reacted... very badly to it. So at this point they know they're selling defective hardware but keep doing it, which is a bit unfortunate and suggests a slightly dubious approach to engineering ethics.

There are better options out there.
 

Classicman

Member
Thanks a lot cheesestraws for all your technical informations. Can you recommend me a valid and non-destructive alternative?
 

cheesestraws

Well-known member
To be clear, the BlueSCSI isn't likely to kill anything else on the SCSI chain, it just seems at risk of cooking itself. So if you are willing to treat them as essentially disposable and use them on short SCSI chains then they'll do that. They might just stop doing it at short notice. :)

Mostly I have a mix of scsi2sds from itead and Inertial both. Boards from both suppliers have been totally reliable. I tend to mount the itead ones in compacts, because they're a physically smaller board. I have so far a single ZuluSCSI, and so far that's been decent too: easier to set up than the scsi2sds. MacSD is more expensive and probably not what I'd suggest for a compact: I like mine a lot, but the extra features it has are really aimed at newer machines using CD-ROM software, so mine tends to live with PowerPC machines.

In the interests of fairness, I'd also say that I think there are some incoming BlueSCSI derivatives that do have the correct line drivers. I'm not going to touch them personally, because the BlueSCSI people have burned all the trust they're going to get from me, but people who are less jaded or more experimental might find those a good option.

Those are the non-Blue ones I've used. As far as I can see, they're all solid hardware-wise, though I am at best an amateur at hardware, so if someone with serious hardware knowledge comes in and tells me I'm wrong, good.
 

Classicman

Member
Thanks again, friends! With your technical explanation, you were very clear.
Now I have clear ideas if I should buy one of these modern SCSI "adapters". ;)
 

Jamieson

Well-known member
Interesting info on BlueSCSI and GPIOs directly connected to the SCSI bus. Agreed some external buffering is probably a better option if the GPIO pin is struggling to pull the line low against the SCSI terminations.
 

Jamieson

Well-known member
Sorry I derailed a thread on a Classic II boot/power problem.

Speaking of which... I have a similar problem on my Classic II. When power has been off for more than a minute, it fails to boot. I get the death chimes and I can see some minor flicker in the screen. Cycle the power (or press reset) and it boots right up. Recapped analog board and logic board. No other issues exept for this boot fail at cold power up. +5V and +12V rails measure just fine.

I figure it's got to be related to the analog board switching power supply. Any suggestions for what else to look at there?

edit: when I recapped the analog board I replaced only some of the caps as recommended by recapamac. These are mostly the output caps of the switching supply. I did not replace the two high voltage main caps on the input to the switcher. Those caps look OK visually.
 
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CC_333

Well-known member
I did not replace the two high voltage main caps on the input to the switcher. Those caps look OK visually.
Try removing them to check underneath. Usually, I've noticed that some capacitors used on analog boards don't always show visible signs of leakage until you remove them, as the electrolyte pools underneath it instead of spreading around.

I have a similar problem on my Classic II. When power has been off for more than a minute, it fails to boot. I get the death chimes and I can see some minor flicker in the screen. Cycle the power (or press reset) and it boots right up. Recapped analog board and logic board. No other issues exept for this boot fail at cold power up. +5V and +12V rails measure just fine.
I've had that kind of problem too, of course with a Classic (seems to be some kind of test that most serious collectors must encounter at least once), except mine kind of had this weird pulsating bulge move vertically up or down the screen, and it would hang at the checkerboard pattern as the voltages gradually ramped up. Eventually, it would bong, the drives would wake up, and the on-screen distortions would subside.

Oddly, recapping never really fixed it; had to get another analog board instead.

I think there's an opto-isolator (or some such) that tends to go bad and cause fluctuating voltages, which manifests in various ways (this has been mentioned before, I'm sure). Allegedly replacing it would've fixed my board, but at that point, I just wanted the stupid computer to work!

c
 
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