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| Macintosh Plus (M0001AP) boot chime loop |
Posted by: macintoshpleasework on 2019-08-26 07:29:56
I have recently acquired a Macintosh Plus 1Mb. Unfortunately, after switching the machine on I hear the normal boot chime but it repeats endlessly and the screen remains blank.
Any help on diagnosing this would be fantastic.
Thanks in advance
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Posted by: bibilit on 2019-08-26 07:35:19
Pluses are notorious for having flaky solder joints in the Analog board, you can start there.
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Posted by: macintoshpleasework on 2020-04-26 10:01:11
Thanks for your reply on this. Finally getting around to having a look at the machine.
After taking off the analog board, it looks in pretty good shape to me. Are there any areas that I should focus on?
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Posted by: bibilit on 2020-04-26 10:11:25
If the boot chime repeats endlessly, more an issue with voltage outputs.
Probably not stable, you can check outputs at the external floppy drive connector.
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Posted by: macintoshpleasework on 2020-04-26 13:37:45
Thanks for the response.
I checked the output at the external floppy (as detailed here https://www.classic-computers.org.nz/blog/2015-05-14-mac-plus-checkerboard.htm ) and I got a stable 12.3 V on pins 7,8 and 5 V on pin 6.
Does this point the finger at the logic board (SIMM possibly)?
Thanks
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Posted by: macintoshpleasework on 2020-05-01 07:47:28
Just to update on this: Removing, cleaning, and reseating the RAM had no effect on the boot chime loop. Voltages are still stable at the Floppy output.
Any ideas much appreciated.
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Posted by: dochilli on 2020-05-01 10:54:36
Perhaps a stuck reset switch?
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Posted by: dochilli on 2020-05-01 10:56:01
Check the voltages with an osciloskop!
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Posted by: The MAC MANIAC! on 2020-05-02 13:55:11
It's not Analog related... And if its passing POST it may be the Logic board. Have you inspected the restart and interrupt buttons? Try using them, or inspecting to make sure they are not stuck.
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Posted by: macintoshpleasework on 2020-05-02 14:34:18
Thanks for your responses.
dochilli - No access to an oscilloscope, unfortunately.
Regarding the buttons, pressing the interrupt has no effect on the repeated bong. The reset button stops the bongs during the press, but they restart as soon I let go of the button.
Thanks
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Posted by: IlikeTech on 2020-05-02 18:21:13
It might also be something related to the reset circuit. I would take a look at the schematics.
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Posted by: Joe on 2020-05-03 20:40:07
Check the 12V overvoltage trip circuit. If the 12V rail exceeds 12V and a bit, a zener diode fires a thyristor that shortens the 12V rail to ground, the power supply shuts down momentarily, autorecovers, only to shutdown again, ad infinitum. You can sometimes hear this as a continous tick-tick sound upon power-on as the high-voltage circuit comes and goes too.
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Posted by: elemenoh on 2020-05-04 10:40:58
I've had this happen to multiple Plus's. All it took to resolve was spraying down the connector at J1 with contact cleaner and they worked well long after.
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Posted by: macintoshpleasework on 2020-05-04 13:28:26
Check the 12V overvoltage trip circuit. If the 12V rail exceeds 12V and a bit, a zener diode fires a thyristor that shortens the 12V rail to ground, the power supply shuts down momentarily, autorecovers, only to shutdown again, ad infinitum. You can sometimes hear this as a continous tick-tick sound upon power-on as the high-voltage circuit comes and goes too. The sound I am hearing is not a ticking, just a the bong over and over again.
I've had this happen to multiple Plus's. All it took to resolve was spraying down the connector at J1 with contact cleaner and they worked well long after. I have reflowed J1 with fresh solder and cleaned the contacts. Still the same issue.
The issue seems similar to that mentioned here - where 'The problems was the two ROMs on the logic board and the JFET Q5 on the vertical sweep.'
https://www.eevblog.com/forum/repair/macintosh-plus/
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Posted by: elemenoh on 2020-05-04 15:29:43
I have reflowed J1 with fresh solder and cleaned the contacts. Still the same issue. Not the joints, spray the pins and interior of the receptacle.
oops didn't read the whole reply 🙂
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Posted by: macintoshpleasework on 2020-05-08 01:27:14
Still no luck with the Mac Plus - bong, bong, bong. I have gone over the AB again, reflowing everything that looks suspect. Voltages still look good at the floppy port.
I don't really have the kit to go poking around on the LB, but this may be what is necessary for this machine.
There are a couple of the previous posts that point to the RESET circuitry (http://www.vcfed.org/forum/showthread.php?64106-Mac-SE-Checkerboard-pattern-after-cleaning-battery-leak/page2 , https://www.eevblog.com/forum/repair/macintosh-plus/), but not sure where to start with that.
Any ideas welcome!
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Posted by: macintoshpleasework on 2020-06-15 17:59:21
To update on this problem:
It seems like it was the ROM.
Not having my own EEPROM programmer, I built one with an Arduino following this great tutorial (see youtube link below).
Reading the ROMs revealed som flipped bits on the 3420342a LO-ROM.
Using the ROM images found here (https://www.nightfallcrew.com/25/04/2014/macintosh-plus-sad-face-repair/) I reprogrammed the offending ROM onto a new pin-out compatible W27C512-45Z chip (https://www.digikey.co.uk/product-detail/en/winbond-electronics/W27C512-45Z/W27C512-45Z-ND/1133334)
Putting this new ROM in the Mac resulted in only a single bong, and then to my amazement, the 'no boot disk found' floppy symbol.
I don't have a boot disk available, but I do have a Prodrive40 harddrive. Plugging this in and turning on prior to boot doesn't result in any progress passed the 'no boot disk' symbol - so maybe no operating system is actually installed on it. Any tips on diagnosing this further would be great, or if someone has an easy way I can get hold of a boot floppy?
Thanks in advance!
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Posted by: dochilli on 2020-06-15 20:12:59
That is not so easy because the Plus has a 800 KB floppydrive. You can not use a modern PC oder Mac to write these floppy. What you need is a Mac that is able to read 1.44 MB disks (perhaps a SE/30). Then you can download images for a boot disk from the internet (if you can connect to the net with the SE, write it on a 1.44 MB disk and from this disk you can write it to a 800k disk. There are some articles in the net how you can do this with old PC or MAC. Here are some links that may help you:
http://spt0010a.sport.uni-oldenburg.de/bycmac/index-Dateien/Page661.htm
Where do you live? Perhaps I can send you a bootable Disk.
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Posted by: macintoshpleasework on 2020-06-15 22:47:25
Thanks for your reply.
Yes, it seems like making my own boot disk wouldn't be possible since the Plus is the only machine I have (besides a PowerMac G4).
I'm in the UK at the moment.
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