Recapped my Macintosh Plus - not working altough correct voltages +5 -12 and 12V at the external floppy port

[Paulo Gago Camara]

Hi!

I'm a newbie.

I did a complete overhaul on my Macintosh Plus, including complete disassembly, cleaning, total analog board recap (kit from console5), floppy drive cleaning, lubrication and new eject gear.

Also retro bright mouse, keyboard and case. It looks like new, but....

When I switch it on I only get a short sound (not the chime but like its the start of the chime) and no image nor floppy activity although it has a floppy disk in it.

The drive motor does not spin, nor the heads try to move.

I measured the voltages at the floppy port, and they are all spot on +5, +12 and -12 at the correct pins.

Any ideas what might be the problem or pointer on what should I troubleshoot next ?

Thanks.

Regards,

Paulo

 

[davewongillies]

I suggest having a read through The Dead Mac Scrolls

 

[Paulo Gago Camara]

I suggest having a read through The Dead Mac Scrolls

Thanks for the reference. Didn't know this guide. I'll see if it can help.

 

[Paulo Gago Camara]

[***UPDATED] to reflect that the voltages are correct after applying De-Ox on the J4 to Logic Board Cable.

Hi!

I reflowed the connector on the Logic Board, as it was also presenting some cracks, but it didn't solve the problem.

My Mac passed the page 21 test on the "The Dead Mac Srolls", but on the page 22 test I got 32 ohms across CR5 instead of the 52/53 ohms indicated on page 22.

Removed the J4 connector cleaned it and tested for continuity and it passed.

When I power it on I get the same behaviour: no chime, dark screen, no strange noises, nothing.

when I checked the voltages again, I got +12 and -12 and 5V - * All OK *.

I found that the resistance between J4 connector pins 10 (+12 v) and 9 or 7 (both Ground) is as low as 30 ohms, triggering the continuity test beep on my multimeter. Is this normal? It's close to short....

Any pointer on what I should check next?

Thanks,
--
PGC

 

[macbard]

Have you checked the diodes? Have a look at page 63 here: https://vintageapple.org/macbooks/pdf/Macintosh_Repair_&_Upgrade_Secrets_1990.pdf

 

[Paulo Gago Camara]

Have you checked the diodes? Have a look at page 63 here: https://vintageapple.org/macbooks/pdf/Macintosh_Repair_&_Upgrade_Secrets_1990.pdf

Hi! Thanks for the reference.

I'll check it, but since after deoxing the J4 cable and connecters I got 5V adjusting half way of the potentiometer and +12 / -12 are also well inside the normal range, I think those diodes are good.

I'll keep posting my results.

 

[Paulo Gago Camara]

Hi,

After all, I was getting video, but the brightness potentiometer was on the low setting... my bad... :-\

When it turns on, the voltages at the FDD port are -12,14V +12,10 V and 5,01 V.

There are no strange noises or hissing. It's completely silent.

I don't get the turn on chime, neither the FDD seeks or rotates, although it has a startup disk inside.

I get a stable and sharp video but only with the desktop pattern.

There's no happy or sad mac icon, neither mouse pointer, nothing....

I think this suggests it's a Logic Board issue, right?

The dead mac scrolls book doesn't have this scenario.

Any help?

Best regards,
--
PGC

 

[se30]

I would double check the recap work. Check to make sure that there are no damaged traces around caps that were replaced. Check for proper polarity placement on your caps as well.

If you eject the disk and reboot do you get a '?' floppy icon then?

> I found that the resistance between J4 connector pins 10 (+12 v) and 9 or 7 (both Ground) is as low as 30 ohms

That is suspiciously low resistance more reason to check your recap work. I would also inspect the board closely for any solder blobs that found their way where they shouldn't be. If you haven't yet, give the board a thorough cleaning.

 

[Paulo Gago Camara]

I would double check the recap work. Check to make sure that there are no damaged traces around caps that were replaced. Check for proper polarity placement on your caps as well.

If you eject the disk and reboot do you get a '?' floppy icon then?

> I found that the resistance between J4 connector pins 10 (+12 v) and 9 or 7 (both Ground) is as low as 30 ohms

That is suspiciously low resistance more reason to check your recap work. I would also inspect the board closely for any solder blobs that found their way where they shouldn't be. If you haven't yet, give the board a thorough cleaning.

Hi!

Checked and double checked. The display is as stable and as sharp as it can be and no strange noises. Voltages stable at 5.00 V, 12.11 V and -12.10 V at external FDD port.

Disk ejected, same result. No solder bolbs, everything clean and shinny.

I've checked the clock signal at CPU pin 15 and got the results shown on the attached files.

I don't have a working machine to compare waveforms, does any one can confirm if the readings I got are normal?

Thanks!

 

[se30]

Just did a quick search and this discussion while discussing a lot of what you have already covered mentions that the PRAM battery could be an issue. I quickly reviewed the schematics for the plus and I got no clarity on the CLK signal at pin 15. Perhaps someone else can answer that one?

 

[Paulo Gago Camara]

Just did a quick search and this discussion while discussing a lot of what you have already covered mentions that the PRAM battery could be an issue. I quickly reviewed the schematics for the plus and I got no clarity on the CLK signal at pin 15. Perhaps someone else can answer that one?

Hi!

Thanks for the reference.

I think Macintosh Pluses don't have a PRAM. I'm booting it without an RTC battery, as I don't have one and these machines operate normally without one.

I'll buy new Logic Board capacitors and change them in order to rule out that those might be the problem.

I'll post the result here.

 

[Douglas]

Since you've checked the voltages and they seem fine, it might be worth taking a closer look at the floppy drive itself. Maybe double-check the connections and make sure everything's snug?

 

[Paulo Gago Camara]

Since you've checked the voltages and they seem fine, it might be worth taking a closer look at the floppy drive itself. Maybe double-check the connections and make sure everything's snug?

Thanks for the suggestion. I've checked FDD connections and they're fine. Also tried to turn it on without the FDD connected, I think It should at least show an error message and the mouse pointer, right?

 

[Paulo Gago Camara]

Major update: Macintosh Plus is working fine!

After all it was ok since the beginning. The problem was that since there was no startup bong, and the 4Mb RAM testing takes some seconds, I disconnected it before it ended the RAM test, to prevent "further damage".

After troubleshooting and probing *** allot *** , seeing a video of a similar machine booting prompted me to try and wait some seconds after turning it on, although it didn't sound the startup bong.

Surprise, it started booting from the FDD normally.

The real problem is on the internal speaker. It seems dead. Probing it with the multimeter reads open circuit, instead ~65 ohms. Connecting an headphone to the speakers jack, I ear the bong, So the sound circuitry is working fine.

Just need to replace the internal speaker, which is annoying because I'll have to disconnect and remove the whole analog board again.

Thanks for the help.

 

[MacOfAllTrades]

Nice work!!
Yeah check the connector and the speaker wire connections to its connector. These sometimes go and the wire or the metal connector pin gets separated or loose etc. Or just a bad speaker is of course possible.

Tough one losing all that time to a ram test but hey - you learned a ton and got a working plus!!! How do you like the keyboard? Mine’s a Mitsumi (not an alps) and my keys are stiff as bricks. But I enjoy the beauty of its silent operation (esp. with an SD SCSI solution like blue scsi!)

 

[Paulo Gago Camara]

Nice work!!
Yeah check the connector and the speaker wire connections to its connector. These sometimes go and the wire or the metal connector pin gets separated or loose etc. Or just a bad speaker is of course possible.

Tough one losing all that time to a ram test but hey - you learned a ton and got a working plus!!! How do you like the keyboard? Mine’s a Mitsumi (not an alps) and my keys are stiff as bricks. But I enjoy the beauty of its silent operation (esp. with an SD SCSI solution like blue scsi!)

Thanks! I'm really proud of it.

The speaker was dead. I replaced it with another one from a dead analog board and it's fully working now.

I definitely learned a ton about these machines, I even studied the Logic Board schematics. I'm able to repair any Macintosh Plus.

I'm currently restoring an external SC20 hard drive, which has a Quantum Prodrive ELS 80MB SCSI hard disk inside that has the sticky head problem. I'm gonna try to replace the rubber which involves disassembling the hard drive heads and platter.

I've also ordered the BlueScsi2 to load it up with all the software goodies this Mac deserves.

Don't know if my keyboard is a Mitsumi, but the keys are soft and have a beautiful sound.

I even managed to restore to fully working order the original set of Apple System Disks.

Cleaned them up with Isopropyl alcohol and a cotton stick.

They're in perfect condition.

As you can see from the photos my machine looks and works like brand new!

Repairs done:

• Full disassembly
• Full dust and dirt clean up
• Full retro bright immersed in water in a transparent plastic tin with hydrogen peroxide 18%
• Logic board solder reflow at the connector
• Full analog board inspection and solder reflow where solder joints cracked
• Full analog board recap with the kit from Console 5
• RIFA caps replaced by brand new ones bought on local store
• FDD cleanup and lubed
• FDD eject motor gear replaced by new one (the original one was fully degraded in little bits and pieces)
• Full keyboard disassembly and cleanup
• Full keyboard retro bright using the same method described above
• Full mouse disassembly and cleanup
• Full mouse retro bright using the same method described above
• Original diskettes restored to full working order using isopropyl alcohol
• Speaker replaced
• Screen height and width adjusted
• Voltages checked and adjusted to original specs
• 4.5V Battery installed (adapter kit from amazon)

I'll post back with the results of the hard drive repair.