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Macintosh Plus chirping/clicking from speaker


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Hi all! Before I start, I am quite the beginner and I thought this would be an easy fix, turns out it wasn't, so please bear with me :lol:

 

I picked up a non-working Macintosh Plus 1MB after a friend send me a link to it - the seller described it as "not powering up" and that was about it. Thinking it would just be a cracked solder joint somewhere I bought it.

It's been anything but that, and someone's been in it before me.

 

There's a lot of metalwork corrosion (not caused by the battery it looks like) and some battery corrosion to the switch (which I fixed), power contacts, and the back of the analogue board ever so slightly (all traces are OK). Keyboard connector is corroded too but I'll sort that later.

 

The main issue I have with it now is that it just chirps like a bird from the speaker and does little else, with or without the logic board attached. We spent a few hours comparing my analogue board to my friend's 512K board and nothing seems to be out of the ordinary - the diodes are maybe 2-3 ohms out at best but that's about it. I also reflowed the solder on the interconnect pins on both boards. After getting nowhere it looks like it maybe an issue with the logic board.

 

With my multimeter I get no continuity between +12v/-12v and ground. However, +5v shows 107ohms. That to me sounds like a short?

 

I checked that at the very least the 68000 is connected to VCC and ground, and it is. We've scoured through the Dead Mac Scrolls and all kinds of other docs,I just want to make sure that what we've done is the right way to go and what could be on the board to short out. I've (hopefully) attached a video of it chirping. If anyone has any ideas, please let me know! Thank you!

 

(tl;dr - mac plus chirps like a bird, checked analogue board and seems good, possible 5v short on motherboard, what do?)

Edited by cleanycloth
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That sounds to me like the power side is crowbarring - the 5V line is over voltage, i.e. above 5.45 or so. First thing I would do is turn down the voltage pot (all the way clockwise, if I remember correctly), and see if that changes anything. Check your voltages on the floppy port, adjust accordingly.

If it's not a high 5V, then there are other potential causes - @bibilit's suggestion is one (the 4N35 at U3 on the analog board) though I haven't seen any socketed 4N35's, also there's an SCR that can die ... some other stuff as well. Is this a North America or International version? No matter what the cause is, it's fixable, so take heart. That's the nice thing about the early compact AB's.

 

Some helpful resources:

http://www.maccaps.com/MacCaps/DIY_Information_files/Classic Mac Repair Notes .pdf

http://www.maccaps.com/MacCaps/Repair_books_files/Macintosh Repair and Upgrade Secrets.pdf

 

Edited by desertrout
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Ah yeah, should've said - it's an international version, hello from the UK! This machine is also a bit unusual - it has a 512K front but a 1MB rear shell, board, and it's had a 4MB upgrade in its time. The resistor was already cut.

 

Spotted the opto, mine isn't in a socket and I don't have any spares but I'll keep that in mind. I turned my voltage pot clockwise to match the resistance value of my friend's board (diagnosing things over Twitter DMs is not easy haha) from over 300ohm to about 211. I'll try turning it down further and see what happens. (edit: turned it all the way down, same thing. I'll give this another go tomorrow and try and measure the voltage again)

 

I tried measuring the voltage across the internal floppy connector (don't have any thin probes at hand to stick through the external port) but I don't think my multimeter updates fast enough - it was jumping about and maxed out at 1v at best. It's a Lidl special, perhaps it's time to invest in a better unit! :p

 

We had checked that first PDF, albeit an older version, but the second one looks very useful too, thank you!

Edited by cleanycloth
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Hello from Canada! God Save The Queen etc.

 

The second PDF is a classic repair manual, but is a bit dated and doesn't cover more recent issues with these old machines. However it does provide a lot of useful insight and may help narrow down the issue.

 

At this point, I'd say it's time to check all resistors, they do fail often. Of course, there's always the possibility - some would say likelihood - that some of the capacitors are bad, even if they don't look bad.  Many here will advise that you simply replace all of the electrolytic capacitors, and I also do that now as a first step.

 

If the resistors are all good, and you said the diodes check out (don't forget CR20 and CR21), and if the caps are good, then you're likely looking at U3 - if the opto is bad, you might read high voltages on pin... 3? I think? There will be a difference there between your board and your mate's board - and potentially Q10, Q11, and Q12. If it's Q12... well, actually being in the UK you might be alright since replacement SCR's seem to be more available over there.

 

Anyway, like I said, whatever the issue actually is, it's fixable. Even if you just replace everything on the switching side of the board haha.

 

PS - check voltages at the external floppy port, it's easy, less risk of accidental shorts. I use a paper clip or an old clipped capacitor leg (one of the thicker ones)... I think both of those PDF's explain the procedure.

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Hi everyone!
 

I decided to have another go at reading the voltages on the board. This time though I fired it up and I could hear a fizzing sound (like gently cooking bacon) that I've not heard from it before so I quickly shut it back down.
 

I took it outside (yes, I'm a wuss haha) and turned it on again. The fizzing was still there and in fact was slightly worse.
 

There are no funny smells coming from the machine. The sound seems to be coming from the analogue board but I'm far too scared to boot it up again in case I damage anything. This was with the logic board connected so I hope I haven't damaged anything.
 

What should I do?

 

EDIT: I powered on the analogue board without the logic board connected. The clicking/chirping was much faster and there was no more fizzing, just a quiet buzz. I know these analogue boards reset over and over when there's no load on it so that's fine. Maybe it's a logic board issue?

Edited by cleanycloth
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Yeah, I thought that was about right since my friend's 512K clicks quickly like mine with the LB out.

 

I'm just hoping I'm not damaging the CRT or anything with it fizzing like that. It's certainly possible that the Rifas are on their way out and it's causing it - one of them is cracked - and I'm using a smart socket (manually!) to turn the machine on and off without having to go anywhere near it with the cover off.

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I can't seem to edit my last post and I don't like double posting, but here we go:

 

So I gathered up the confidence to take the analogue board mostly out (it's been off all day, I think I managed to discharge the CRT properly - no pops or anything but I definitely touched something under the cap). I've still got the anode cable attached as I'm not sure how to get that off yet.

 

After the fizzing incident nothing on either boards look damaged - no obviously leaking caps, no holes in chips, no burn marks, nada. If I can get the cap off I'll try and take pictures of the boards to see if any of you find anything I'm missing. I have checked U3 with a friend's and so far it seems OK (checking with the diode and resistance settings), but he's going to check one last thing on it tomorrow. I slightly mangled it getting it out so I might just replace it anyway, to be honest.

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A sizzling sound suggests to me a bad ground. Did you have the AB out of the machine before that started happening? If so, ensure that the AB's grounding wire is attached to the chassis, and that the grounding plate is in place and secured with both screws.

 

The other possibility in all this is a bad flyback... pictures could help, but ultimately this is a process of elimination.

 

PS: RIFA's just look like that after a while, doesn't necessarily mean their about to fail. However, as with the electrolytics, it advisable to replace them as a matter of course.

 

 

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I didn't even think to check that, and you might be right. The LB is not grounding to the chassis very well due to some substantial metalwork corrosion (and the other side that's clean isn't making great contact either). The ground planes on the AB are corroded from the battery, it seems to be making /some/ contact but it might not be good enough so I've tried to scrape away the corrosion and get better contact. I'll also see if I can get the LB to have better contact too.

 

The AB has been in the machine the whole time until I took it apart last night after the whole incident occurred. The corrosion is pretty bad around that area (as above) so I've cleaned that up a fair bit and I'm going to drop the screws into some vinegar to clean those up.

 

The anode cap is pretty stiff so I'm not sure how I should go about taking the anode off without damaging it. I also managed to get U3 back into shape and into the socket again so that's fine :P

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So after some sanding and measuring of my optoisolator again, it turns out the opto might be faulty. Between pin 6 and 4, my friend's working machine measures 4.5MOhm whereas mine reads about 600Kohm, so it's looking like that's shot (it read as low as 50Kohm at one point). I've been looking around to find a replacement part on here and I've come across two, either the 4N35 or the CNY75GB. The 4N35 is easier to get, is that a good choice?

 

Think I'll pick up some new Y caps for the board as well while I'm at it. Ground seems to be much better now as well, so that's a start. I can't see anything else wrong with the analogue board so if it isn't the opto I've got no idea (besides possibly the flyback as you mentioned)...

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4N35 is the replacement part for the North American board, and appears to be the same for the International version. So, yes, it's a good choice. :)

 

If the issue isn't resolved with the 4N35, at least you've eliminated it from the list. But it's a pretty common failure point, so fingers crossed.

 

Getting the anode cap out is tricky at first, but becomes easier with practice. Sometimes you need to get a flat-head screwdriver or something in there to gently push one side in enough so it can clear the hole, then it just lifts out. Persevere with it (gently) - it would be a good idea to get the AB out so that you can properly assess (and address) the corrosion damage. There are probably some decent take-apart videos out YT that will give you a good sense of how to approach it.

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Quick little update - I ordered the 4N35, thanks for the clarification. I managed to get the anode cap off too - I thought you could squeeze the cap and pop it off but you're right - I slipped a screwdriver in there and geeeeently pushed on one side and then lifted it out.

 

I checked over the analogue board and corrosion is minimal. The legs of the power switch (and presumably the internals before I flushed it with contact cleaner) are pretty badly corroded. The ground plane and a few traces have been attacked but they all test absolutely fine, and to make sure I sanded down the contacts ever so gently on the grounding areas to make better contact. I popped some of the screws into vinegar to clean those up.

 

Analogue board is OK too, the solder on the board looks a bit dull but there's no signs of damaged traces, in fact the underside of the board looks pretty much perfect. There's some corrosion on the hooks that hold the board against the chassis (and where the back cover screws through) so I'll need to sort that out.

 

All of the components on both boards look absolutely fine. As a precaution though, I've ordered capacitors to replace the ones on the analogue board, except for the 25v3.9uf non-polarised one which I wasn't able to find from RS so I've left that one for now. The parts should arrive tomorrow (well, today since it's nearly 1am, oops).

 

I've taken some pics of the boards below. You can see the damage to the analogue board on the centre left and bottom but I have tested all of those traces and they make perfect contact. U3 is missing because I've taken it out ready for replacement. I also tried cleaning the motherboard but my toothbrushes need replacing so they just kinda moved crap around rather than getting rid of it.

 

On an unrelated note, I had a look at the floppy drive and since half of this machine was originally a Mac 512K, it's got a 400K Sony floppy drive in it so that's pretty neat! I've got no idea if it works since I can't test it yet.

 

EDIT: Actually, I just found the sticker for the original model number for the front of the machine. It's "M0001" and if I'm not mistaken, that's a Macintosh 128K? This thing seems to have had an upgrade from a 128K board and rear housing to a Plus 1MB...!

 

IMG_5475.JPG

IMG_5476.JPG

IMG_5477.JPG

IMG_5478.JPG

Edited by cleanycloth
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Thanks for sharing the pics. Yeah, the model number would suggest a 128k, though someone else here would be in a better position to confirm that. Interesting that they would upgrade the AB but not the floppy drive?

 

Overall everything looks pretty good! I was expecting more damage based on what you were saying earlier. You say those traces on the bottom part of the AB ring out, so that's great.

 

You mention not being able to find a replacement for C1 - the modern replacement for that cap is of a different kind, a metallized polypropylene film capacitor (like this one: https://www.digikey.ca/en/products/detail/panasonic-electronic-components/ECW-F2395JB/248841?s=N4IgTCBcDaIAoDEwGYCcBWAtAOQCIgF0BfIA). In fact, if yours is the original 25V one you will want to replace it very soon - it's simply underpowered and it was common to uprate even back in the 80's.

 

If you haven't yet, I highly recommend watching @JDW's AB overview and recapping video (below) and taking a look at his replacement parts spreadsheet (noting of course this is for the North American boards, but PIna's Repair Secrets book I linked to above has parts lists in the appendices that show which parts are equivalent between the two): https://docs.google.com/spreadsheets/d/132RwzC8HM5ask-BdY_31txErOCwJDSkz099GY2XLpE0/edit?usp=sharing

 

Good news (in my mind) is that the flyback looks like it has low hours on it, so should be in good shape.

 

 

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tl;dr: Optoisolator was the issue, presuming wobbly screen sides is just bad caps?

 

Hey all!

 

The parts from RS arrived about an hour ago and I popped the machine back together with the new optoisolator. I was too impatient to recap the whole machine (and just in case the new part didn't work, I wanted to rule out one thing at a time) but I turned it on, and...

 

SHE BOOTS!

IMG_5489.thumb.jpg.fb9245c15fe589ef5a175965381df89b.jpg

(excuse the camerawork - it was fine on my phone screen until I hit capture, honest!)

Blinking question mark floppy icon and all! The only issue I have left is that the picture wobbles on the sides like a plate of jelly/jello. I have tested the grounds and everything is all 100% connected properly so I imagine that's just bad caps?

 

As for your replies, yep - the optoisolator is socketed really weirdly and it's just like pipes soldered into the holes in the board, and then it just pops on. One day I should probably replace it with a proper socket but for now it works just fine.

 

I wasn't able to get basically any axials but I've got radials with long leads so that should be fine.

 

I was absolutely /cacking/ myself (see: pooping) when turning it on so I'll leave this for a bit and then begin recapping it. But this is absolutely fantastic and thank you so much everyone for your help - I've learned quite a lot working on this Mac ^^

Edited by cleanycloth
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22 hours ago, cleanycloth said:

SHE BOOTS!

Excellent! Congratulations! It's a wonderful feeling. :)

 

Next step is to follow chapters 2, and 3 of Pina's Repair Secrets book (http://www.maccaps.com/MacCaps/Repair_books_files/Macintosh Repair and Upgrade Secrets.pdf) to establish your baseline. The screen issue very well may be the caps, but may also be that the voltage pot needs adjusting, still a poor grounding issue, the transistor at Q3...  But you're definitely in good shape.

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So I had to leave the project alone for a few days as some family stuff came up. Since then I've spent some time recapping the analogue board with fresh caps from RS just in case any were bad and would fix the wobbly CRT.

 

Unfortunately, we're now back to not starting up again. You can hear the high voltage for the CRT kick in (that little high pitch "fwip" noise) and that's all you get.

 

I checked the voltages and they are now way out of spec to an alarming degree - 5v is now down to about 2.9v and the 12 and -12 are screaming high at 18v and -18v respectively, this is with the logic board attached and the voltages measured through the external floppy drive connector. The only thing I have done to the board is replace the caps. The 400K floppy drive was thankfully not attached so that hasn't been potentially damaged.

 

I looked over the board multiple times, fixed a bad pad that had broken free from one of the new caps, checked continuity with every single capacitor pin I could find, and it's all clear. The caps are the right specs, they're all in the right way. I don't understand what's happened.

This is entirely a guess but could it be that I need to adjust the voltage pot to get the 5V back in line, which will then regulate the 12v correctly? Since there's no load coming from the board and that's not driving the CRT, that might explain the high 12v perhaps. I don't know.

 

I haven't looked through the books and stuff yet since as I say I've not had much time over the last few days, so my apologies if it's blindingly obvious :p

Edited by cleanycloth
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