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Macintosh All-In-One Disaster

I've been forwarded to this forum for advice on a Mac Plus All in One I acquired recently. I've been told from the picture of your motherboard, it's definitely a Mac Plus, was likely a 512k once, but it's been upgraded.
When I first tested it it would operate properly for about 5 - 10 minutes, then just rapidly begin turning on/off on/off constantly (beeping every time).
I had changed all 3 RIFA caps and the unit worked great for about an hour. But I must say, when I first turned it on after replacing those caps, it did not boot up immediately. It turned on/off like before but much faster. After about a minute it came to life and didn't happen again. Then an hour later the screen turned off, and the floppy drive began constantly spinning. I then replaced all the caps on the analog board, but it made no difference. Still no screen boot, floppy spins on it's own and no beep. Also a "crackling" noise from the flyback.
This unit had extensive battery damage on it's frame, but both boards were safe. I cleaned both boards, reseated some chips, reflowed many of the joints on the power board (not all),cleaned the mess as well as I could (not pictured), still no change. Monitor tube will not boot, but neither will the computer board, only the drive starts spinning on it's own. Here are some pictures. Be warned some of these pictures were before the clean up.
I don't have any battery installed, if that makes a difference.
This is my first Mac, so I'm a newbie here as far as repairing these goes. I've repaired many vintage game consoles but this is an entirely different beast.
 

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desertrout

Well-known member
My first thought is a bad ground --- it looks from the images that the analog board ground wire point were severely rusted (and possibly the other ground points at bottom edge and the front edge of the analog board, depending on where the rust is) and still look pretty rusty in what looks like the post-recap photo... Those all really ought to be cleaned down to bare metal.

But also - did you only replace the RIFA's? Have you replaced the other electrolytic capacitors on the analog board? It's a bit of an old saw, but they really ought to be replaced if they haven't been. I can't say though if they're a cause of these symptoms. Someone else here might have a more definitive answer. However, it's good practice to troubleshoot with a known-good baseline, and that would include good grounding and good caps.
 
Thank you, yes I started by replacing all 3 RIFA capacitors. That's when it sprung to life and ran well for about an hour. Then I turned it off and on a few times, all was still good. But then it happened. I turned it on and I heard no beep. Monitor wasn't on, but I heard a spinning noise. It was the floppy disc drive (I've never used it). Drive constantly spins when I turn the unit on. So, I then replaced every single electrolytic capacitor on the analog board (had ordered a complete kit from Console5). Still no change though, same issues. I'll work on those ground points now with a wire brush, I only focused on the ground point in the back where you put the screw. I didn't even bother much with the points around the analog board, I'll work on those too for they are pretty rusty.
 
Brought all rusty grounds to bare metal.

Removed the old solder joints from all cables running from the analog board (J1, J2, J4).

Did the same to the flyback.

No change. Floppy drive is spinning, tube is not turning on, crackle sound from flyback.

I looked up the troubleshooting for a bad flyback (dark brown glue, you can see sparks through the enclosure in dark) but mine has none of those symptoms.

Could the monitor tube just be blown? But then, what would that have to do with the spinning floppy drive? There is no "beep" when I turn it on, so does that mean the computer is not turning on? The monitor wouldn't normally boot up anyway without the computer board attached, am I correct?

Here's a short video clip taken a few days ago before I did this work, but nothing has changed so it might be helpful:

 

bdurbrow

Well-known member
That crackle indicates to me that the flyback has had it's insulation on the windings break down, and is arcing internally. This will do several things. First you won't be getting proper high-voltage to the anode of the CRT; so even if everything else was working properly you wouldn't get an image. Second, that arcing generates a whole bunch of electromagnetic interference (both radiated and conducted into the power rails), so it's possible that it's the primary cause of the logic board symptoms.

Do you have a bench power supply with two outputs? If so, you might try hooking up the power supply to provide +12 and +5 volts to the logic board and bringing up the board and floppy drive without the analog board connected (or on) to see if the drive still spins. If you have a set of headphones handy, you might try connecting them to the sound jack on the logic board to see if it beeps (watch out; it's probably going to be very loud in the headphones!)
 
No, I do not have a bench power supply. I don't know if this will be of any help, but I tested the voltage coming out of the external floppy disc connector with my multimeter and it comes up as 6.2 volts. It's been years since I've used a multimeter, so I attached a picture (just in case my settings are wrong!). The voltage adjustment knob on the side of the mac doesn't seem to change that reading in any way. I tested the headphone jack too and there is no "beep" coming from it.
 

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davidg5678

Well-known member
No, I do not have a bench power supply. I don't know if this will be of any help, but I tested the voltage coming out of the external floppy disc connector with my multimeter and it comes up as 6.2 volts. It's been years since I've used a multimeter, so I attached a picture (just in case my settings are wrong!). The voltage adjustment knob on the side of the mac doesn't seem to change that reading in any way. I tested the headphone jack too and there is no "beep" coming from it.
From what I can see in the photos you attached, the logic board just looks a bit dirty, but the analog board looks like it may have sustained more damage. The voltage reading you took provides some valuable information. I'm unsure whether you measured the voltage coming from the +5V rail or the +12v rail, but either way, a reading of 6.2 volts is really far away from what the Macintosh needs to operate correctly. If the +12V rail is running at 6.2V, I think that this would be an indication that something has gone really wrong with the analog board. Perhaps a component there has failed or shorted out? Other members here who are more familiar with analog boards will likely be able to provide further insight.

To address your multimeter question: this variety of multimeter has a manual voltage range selector. This means it requires you to manually pick a rough estimate of what voltage level the computer is operating at. If you were probing voltages directly from 120V mains, I think the 200V setting would be a good choice for the range. As for Macintosh computers, at least on the digital side (which is where the floppy drive connects), the max voltage is supposed to be +12V or so. Therefore, the 20V range would also work for taking this kind of reading with the multimeter. Using 200 isn't strictly wrong, but I believe that the decimal place will line up better if you switch your dial to 20V.

Here is a link to a classic mac repair guide. It is a little on the older side, and I'm not certain if anything in here applies to your specific issue, but maybe reading over it could provide you with some helpful information. There is a section that covers taking voltage measurements from the floppy port, which may or may not be of interest.

Best of luck getting your computer working again!
 
Yes, that picture of the logic board was when I first removed it. It's very clean at this point. I also cleaned all removable chips and ram. Analog board was filthy too, but has been cleaned, joints resoldered, and all electrolytic capacitors replaced. It ran for an hour (after just changing the 3 RIFA caps). I was reading through that guide, and I think I might have read that somewhere that some Macs will not boot up without a battery. I don't have a battery in this unit (hard to find). Could it be something as simple as a missing battery? But then, why did it run perfectly for an hour after I changed only the RIFA caps, with no battery installed? When I put the multimeter on 20v I get 3.11 volts, which is probably too low am I correct? The voltage adjustment screw does nothing at all to change that. That rail is supposed to be 5v, I'm following this video here (timestamped at 17:57):
 
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joshc

Well-known member
Firstly, congrats on acquiring a Plus and welcome to the forum.

The main thing to bear in mind, is that the early Mac analog boards (well, all of them, really), were designed to a cost and were never that good. Even when new, they exhibited problems caused by overheating and a generally poor design. So component failure is not uncommon at all, especially at this age as well.

This problem isn't to do with the battery, it will run fine without one. As davidg said, if the voltages are that off, there is something quite wrong with the analog board. Finding exactly what is causing the low voltages might be a bit tricky (I am no expert at diagnosing analog boards, just offering my experience of dealing with ABs that don't provide the right voltages).

Did you replace every capacitor, including the bipolar 3.9uf 100V capacitor at C1?

At this point, I'd be testing other components on the board to try to find the fault - there could be a bad diode or optocoupler causing this.

You may find the notes here useful, it explains how the circuitry for each voltage rail works: https://vintageapple.org/gamba2/images/plus_analog.PDF

What are your readings for +12V and 5V?
 
I'm getting 7.44 on the 12v line (using the multimeter settings davidg5678 recommended, "black 20" on the multimeter dial). If I put the dial on the "red 200" setting I get 6.2 on the 5v line and 15.6 on the 12v line. Just like before, the voltage dial does nothing to change it. Sorry, I'm still learning how to properly use a multimeter.
No, I did not change the bipolar 3.9uf 100V capacitor at C1 (wasn't included in the kit from Console5!). Can someone point me to where I can purchase one for a reasonable price? eBay has it for nearly $25 for a single capacitor! And it's "new old stock". I think I'd prefer just "new".
 
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desertrout

Well-known member
It's great to see you diving into the troubleshooting / repair process - well done! And keep going. :)

'Black 20' or 'Black 200' on the right side of you DMM is where you want it set, as you're measuring DC voltages. 'Red' on the right side your DMM is for AC voltages, so won't give you the proper reading on this board (unless you're measuring mains voltage at the switch and transformer).

If you review the cap list from JDW's video, you'll see a suitable modern replacement for C1... a film cap like this will work: https://www.digikey.ca/en/products/detail/panasonic-electronic-components/ECW-F2395JA/1635194

Echoing @joshc, the 4N35 at U3 *could* be a factor here as they are known to go bad and will cause voltage-related issues. Not that I advocate a 'parts cannon' approach, for the few cents it costs it's just worth doing imo. The zener diode at CR18 can also cause low voltages.

However, beyond all of this, the 'sizzling' sound from your flyback does not bode well, and the flyback itself may be kaput (even though it looks like it's in good condition). It would be helpful if you had another, known-good flyback to swap in there... but I understand that may not be the case. Perhaps you know someone with a compact Mac (SE/30 and earlier) that would be willing to let you swap the flyback for testing purposes?
 
Thank you, I was unaware he had listed a parts list. I see the replacement part you listed (ECW-F2395JA), but when I put JDW's part number into DigiKey's search bar I get this replacement capacitor:

ECW-F2395JB

But they both have the same item description, so I suppose it doesn't matter which I choose?

As per your suggestion, I might as well change out 4N35 at U3 while I'm at it. I searched on Digikey for it, is this the correct one?:

OPTOISO 3.55KV TRANS W/BASE 6DIP

No, I do not have access to another flyback for testing. But I live in the USA and if after changing out that cap and chip above, if there are no results, I'd gladly send the board out to anyone here who would like to make some extra money.
 

desertrout

Well-known member
Yes to both.

Yeah, at some point you have to decide what your tolerance / comfort level is for chasing the fix... often-time the issues are actually multiple and the rabbit hole can get quite deep.
 

davidg5678

Well-known member
A question for analog board experts: What happens if you remove the flyback from the PCB for troubleshooting? Will the PSU still function normally without a flyback present? Maybe this could be a way to test if the voltages on the logic board return to normal without a flyback.
 
I purchased the ECW-F2395JB and the 4N35 from DigiKey but I had forgotten to add the Zener Diode (1N5349BRLG) to my cart before checking out. It has since been shipped and I'll receive them next week. Instead of ordering a .45 cent Zener Diode at DigiKey:


and have to pay $5 shipping, are these from Amazon the same Zener Diode that I need (it's missing the "RLG" at the end of the part number)?:


For roughly the same price (I get free shipping via Amazon), I could get 10. Not that I need 10 of course, but if anyone else here needs one, let me know and I'll ship one out to you free in a first class envelope. Of course, I might as well install the 2 items I ordered first from DigiKey to see if it fixes the problem. If not I'll order the Zener Diode(s).
 
I replaced the capacitor at C1, no change. Felt like giving up at that point. Then I replaced the 4N35 at U3...and it came to life! I'm also getting the proper voltages on both the 5v and 12v lines, and the floppy drive is back to normal. I want to thank all of you for your help during this stressful ordeal. I hear the floppy drives tend to go bad with age (eject seize up, broken gears), so I don't even plan on using it. I just ordered a Floppy Emu Model C Bundle from BMOW and a keyboard cable for the M0110 keyboard which I need.
 

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psa425

New member
Happy to find this thread, I have a Mac Plus with similar issues. I'm getting roughly 50-60% normal voltage on the 5v and 12v. I replaced the fly back and now have raster, patterns on the screen but no bong or boot. I see a new 4N35 at U3 might help, specs for 4N35 say it has 3.55kv output. I have some extra CNY17-3 from some Classic II repairs which is similar 6 pin Optoisolator but specs say 5.00kv output. Can the CNY17-3 be used in place of a 4N35 noted in thread above or would the voltage difference cause some serious issues?


Edit: The analog board has been fully recapped. Have tried with two working logic boards as well.
 
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desertrout

Well-known member
Then I replaced the 4N35 at U3...and it came to life! I'm also getting the proper voltages on both the 5v and 12v lines, and the floppy drive is back to normal. I want to thank all of you for your help during this stressful ordeal. I hear the floppy drives tend to go bad with age (eject seize up, broken gears), so I don't even plan on using it. I just ordered a Floppy Emu Model C Bundle from BMOW and a keyboard cable for the M0110 keyboard which I need.
Ah, that's fantastic to hear! I'm glad the issue appears to solved. Congrats. :)

FloppyEMU is a good call. While I personally enjoy using classic storage or networking to move data around, the FloppyEMU is amazing if you just want to get to it (and on lots of different machines too)

Can the CNY17-3 be used in place of a 4N35
It would seem so as they appear to have very similar characteristics and the same pinout. It's a pretty generic part. But personally for the price and the availability (should be able to get one at your local electronics supply, provided you have one), I would put a 4N35 in there to remove any doubts.
 
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