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| Clicking Macintosh Plus |
Posted by: j2theLj on 2023-01-10 06:15:47
I have a Macintosh Plus with a constant clicking sound when it powers on. What could this be? I’ve reflowed the solder joints of the connectors on the analog board and also on the logic board. I’ve also checked the fuse on the power cable between the boards. The analog board has not been recapped yet…but does anyone recognise this as something else?
The sound seems to come from the analog board but not from the speaker.
Thankful for suggestions! |
Posted by: desertrout on 2023-01-11 13:37:52
Clicking could be caused by any number / combination of failed components. First order of business is to recap then reassess. JDW's recapping walkthrough is very useful (just note that if your board is the international (240V) version, some of the caps will be different):
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Posted by: LaPorta on 2023-01-11 13:41:11
If the clicking sound goes away when you insert a disk and it's read...then that is totally normal. A ticking sound from the AB when you first turn it on before the drive starts to work is normal. |
Posted by: desertrout on 2023-01-12 13:12:53
Ah good point to clarify --- is the system posting? I assumed the machine was not turning on and the clicking was the typical crowbar sound... |
Posted by: j2theLj on 2023-01-13 04:10:42
Thanks, yes I should have clarified - it is not posting and not seeking floppy. Only sign of life is the constant clicking from the AB. |
Posted by: LaPorta on 2023-01-13 04:49:57
Then yes, definitely an issue and good to proceed as per @desertrout . |
Posted by: bibilit on 2023-01-13 05:28:27
Optoisolator ?? common issue. |
Posted by: j2theLj on 2023-01-14 11:39:54
Optoisolator ?? common issue. Is that the light bulb looking components? |
Posted by: Iesca on 2023-01-14 17:39:54
The "light bulbs" are neon lamps used for surge suppression. They are supposed to light up if/when redirecting excess current. I'm not sure if anyone's figured out their specs for replacement, but they're unlikely to be the cause of your symptoms.
The optoisolator is a small, 6-pin DIP package on the analogue board, the small IC-looking component labelled "U3", and located at the bottom left of the analogue board (if facing the top), next to the brightness knob. It is a not-uncommon failure point in the Mac Plus and earlier. (Here is the wikipedia page on optoisolators if you're curious what it does.)
Whether it is the definitive source of your problems is hard to know, as many things can lead to your symptoms. The clicking you describe is likely the "flupping" sound (as described by Larry Pina in Macintosh Repair and Upgrade Secrets) of the power supply repeatedly attempting to start and then resetting when it hits a failure condition.
U3 should be cheap to replace, so it's worth a shot and may resolve your issues. If it does not, I suggest taking a look at the previously mentioned book, as well its follow-up, The Dead Mac Scrolls, which is a diagnostic manual for old Macs, with a list of symptoms and their likely remedies, without any extra fluff or explanations.
The original part number is "4N35". Philips made an equivalent version with part number "ECG 3041". If you're unable to find this on ebay or from a reseller, you can try searching for a 6-pin, 2500 Volt optoisolator. |
Posted by: j2theLj on 2023-01-15 12:04:56
The "light bulbs" are neon lamps used for surge suppression. They are supposed to light up if/when redirecting excess current. I'm not sure if anyone's figured out their specs for replacement, but they're unlikely to be the cause of your symptoms.
The optoisolator is a small, 6-pin DIP package on the analogue board, the small IC-looking component labelled "U3", and located at the bottom left of the analogue board (if facing the top), next to the brightness knob. It is a not-uncommon failure point in the Mac Plus and earlier. (Here is the wikipedia page on optoisolators if you're curious what it does.)
Whether it is the definitive source of your problems is hard to know, as many things can lead to your symptoms. The clicking you describe is likely the "flupping" sound (as described by Larry Pina in Macintosh Repair and Upgrade Secrets) of the power supply repeatedly attempting to start and then resetting when it hits a failure condition.
U3 should be cheap to replace, so it's worth a shot and may resolve your issues. If it does not, I suggest taking a look at the previously mentioned book, as well its follow-up, The Dead Mac Scrolls, which is a diagnostic manual for old Macs, with a list of symptoms and their likely remedies, without any extra fluff or explanations.
The original part number is "4N35". Philips made an equivalent version with part number "ECG 3041". If you're unable to find this on ebay or from a reseller, you can try searching for a 6-pin, 2500 Volt optoisolator. Many thanks for this, I’ll be sure to look into it. It definitely sounds like something is trying to start so this might very well be the issue. |
Posted by: Iesca on 2023-01-15 14:18:59
You're very welcome! And as it turns out, 4N35's are still manufactured today, so you should have no problem finding a replacement, should you go that route. |
Posted by: j2theLj on 2023-01-16 04:24:21
You're very welcome! And as it turns out, 4N35's are still manufactured today, so you should have no problem finding a replacement, should you go that route. Excellent, thanks! |
Posted by: jsilcox on 2024-11-12 14:49:38
Had this exact problem and noticed that C39 was physically damaged. Replacing it fixed the problem completely. Probably not the only failure mechanism, but at least the one that I experienced. |
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