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Apple /// restoration

ravuya

Active member
I’ve tested suspect sockets before by doing a continuity test on the multimeter from the leg of the chip to the socket’s solder joints on the other side of the board.

You can’t press too hard, or you may force the chip’s leg temporarily into the socket and get a false reading, but it generally gives a decent report of whether you’re getting clean contact or not. Any lack of continuity, or an unusually large resistance/voltage drop shown if it beeps would be enough for me to bin the socket. My Amiga 2500 had a corroded CPU socket that only showed up once the plastic had been broken around the pin during removal, but it was enough to sever the 68k’s d8 pin from the data bus.

It does suck to do a lot of these since you have to crane your neck around the board to look side to side. I usually put the board between two big books in order to hold it vertical.
 

pball52998

Well-known member
When you say "flat" do you mean low/no voltage or just a flat waveform?

Can you check what voltage you see on each side of R48?
No waveform, thankfully everything is keeping a good voltage. (For the most part..) List of all the R / Q in that line according to the osciliscope.

R52 - 1v increase on each side. no wave form.
R91 - 5v on left, nothing on right, no wave
R90 - 5v on left, nearly 12v on right(?) no wave
R48 - 5v on left, nearly 12v on right(?) no wave
R51 - 1v increase on both sides, no wave
R49 - 5v on left, 5v on right, no wave

Now these seem a little.. off.. but that's what the osciliscope showed. I can test them with a multimeter later if anyone wants to see that.

Tested Q10/Q11 too.

2/3 legs on both of those get a solid 5-6v increase on scope, no wave.
 

davidg5678

Well-known member
Have you confirmed that this new oscilloscope is working and will show any waveforms? Perhaps you should try probing a logic board from a compact Mac (specifically its oscillator crystal) just to make sure that the measurements you are taking from the Apple III are valid.

Is this the model you are using? https://jyetech.com/dso-150-shell-oscilloscope/

If the DSO 150 oscilloscope's max bandwidth is only 200KHz, To the best of my knowledge, this oscilloscope isn't fast enough to take many useful measurements from the Apple III, which I think runs at 1.8MHz (an order of magnitude faster.)
1669477906722.png

I saw this video pop up a few days ago which reviews a similar style inexpensive oscilloscope, but I believe this product is far more sophisticated, with a 120MHz bandwidth in contrast to 200Khz. I haven't had the chance to watch the video yet, but it might be worth taking a look at:

 

pball52998

Well-known member
Have you confirmed that this new oscilloscope is working and will show any waveforms? Perhaps you should try probing a logic board from a compact Mac (specifically its oscillator crystal) just to make sure that the measurements you are taking from the Apple III are valid.
I tried it on my c64 and it's able to see things on the 6502 at least. Tried on the crystal in there too.. nothing on it. Someone stated earlier it might not produce a signal though when it's probed. But not sure.

I've considered returning and buying a Hantek 6022BE



It seems well rated. I might bite the bullet as I have several other machines that would benefit from a better scope in general.

Got the dso138/150 at the recommendation for a cheaper one earlier in the thread.

I do agree though, might be a little low for anything useful with the iii.

Might return it and see what else I can do.

Edit: Watching the video, it actually looks like a really good scope. Surprising. Might buy that and see what I can get.
 
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AwkwardPotato

Well-known member
If you're interested in playing with electronics you may want to look at a used analog o-scope; for the same $60-70 you can find a 20/50MHz Tektronix scope for instance (occasionally 100MHz) with more channels and far greater usability.
 

davidg5678

Well-known member
I've considered returning and buying a Hantek 6022BE
Generally, I've read it's best to have an oscilloscope with a rating at least 5x faster than what you'll need it for. This means that the 20MHz 6022BE would only really be useful for computers up to 4MHz. Similarly, if you get an oscilloscope that's rated for 100MHz max bandwidth, then you can use it for up to around 20MHz computers (this would be suitable around the speed of the 16MHz Mac SE/30.)

See here: https://www.eetimes.com/choosing-an-oscilloscope-with-the-right-bandwidth/
or here: https://blogs.keysight.com/blogs/tech/bench.entry.html/2020/08/25/tips_on_how_to_selec-2q2u.html

As the DSO150 is only rated for 200KHz ( its only really useful for 40Khz --which is only 2x the highest frequency a human can hear), I think this means that its measurements are better suited for things other than computers such as sound waves or 60Hz frequencies.

I would recommend getting a faster product than the Hantek 6022BE. A faster ~100MHz oscilloscope will be useful in diagnosing more vintage computers than just the slowest ones.
 

pball52998

Well-known member
Generally, I've read it's best to have an oscilloscope with a rating at least 5x faster than what you'll need it for. This means that the 20MHz 6022BE would only really be useful for computers up to 4MHz. Similarly, if you get an oscilloscope that's rated for 100MHz max bandwidth, then you can use it for up to around 20MHz computers (this would be suitable around the speed of the 16MHz Mac SE/30.)

See here: https://www.eetimes.com/choosing-an-oscilloscope-with-the-right-bandwidth/
or here: https://blogs.keysight.com/blogs/tech/bench.entry.html/2020/08/25/tips_on_how_to_selec-2q2u.html

As the DSO150 is only rated for 200KHz ( its only really useful for 40Khz --which is only 2x the highest frequency a human can hear), I think this means that its measurements are better suited for things other than computers such as sound waves or 60Hz frequencies.

I would recommend getting a faster product than the Hantek 6022BE. A faster ~100MHz oscilloscope will be useful in diagnosing more vintage computers than just the slowest ones.
I'll try out the ZEEWEII DSO1511G from ali $50 shipped with "black friday" deal.

Watching the video seems to do 14mhz (which I need for timing tshooting) really well as per adrian.

And if it really is 120 then it'll do well as you said for something like the se/30.

Posts might be a little slower as I get more parts in to troubleshoot/get things down.

But I should start soldering back the keyboard soon. I've just been lazy and haven't gotten that far yet.

About 15 or 20 of my switches are dead with absolutely no continuity, no life, no anything. I can get these off ebay at least to replace these.

A few are spotty at best. Will probably replace those too.

I really appreciate everyone giving advice here. A bit overwhelming going through alone and happy to see such a supportive community to bring these machines back.

Again thank you for everyone with the help so far. Sorry for any ignorance!
 

SuperSVGA

Well-known member
No waveform, thankfully everything is keeping a good voltage. (For the most part..) List of all the R / Q in that line according to the osciliscope.

R52 - 1v increase on each side. no wave form.
R91 - 5v on left, nothing on right, no wave
R90 - 5v on left, nearly 12v on right(?) no wave
R48 - 5v on left, nearly 12v on right(?) no wave
R51 - 1v increase on both sides, no wave
R49 - 5v on left, 5v on right, no wave

Now these seem a little.. off.. but that's what the osciliscope showed. I can test them with a multimeter later if anyone wants to see that.

Tested Q10/Q11 too.

2/3 legs on both of those get a solid 5-6v increase on scope, no wave.

Most of those look fine. Looks like you're getting a good supply voltage and the voltage divider resistors are working fine.

I think the tricky part is there's both an earth/shield ground and a signal ground, so if you're referencing earth ground you might not see 0V on the signal ground.

clock3.png

If possible, see if you can measure R51 and R52 with the signal ground on the other side of the resistors as the reference.


Have you tried checking the signal with the 74S86 removed? It's possible that's pulling the clock signal low.
If you still don't get any clock with that removed, my guess is either the crystal or one/both of the transistors. If you have some 2N3906s you can swap those in.
 

pball52998

Well-known member
Have you tried checking the signal with the 74S86 removed? It's possible that's pulling the clock signal low.
Traded in my oscilloscope to try and get a 120mhz one to see if I can get something more accurate/better in general.

I was looking at what I'm supposed to get (c64 wise) and it just wasn't up there it seems/measuring well

First thing I will do and get back when I get my new one though 🙂

Next part of the project will probably be just soldering back keycaps (boring I know) till I can get a better scope that can actually see mhz clock signals vs hz/khz.

Probably clean and get rust off other 2 floppy drives too. Order belt etc. All the boring things!

Looking forward to trying it though!
 

SuperSVGA

Well-known member
I did some more experimenting, and I think you should check C23. I was able to replicate what you're measuring in the clock section by removing C23 from the circuit.
 

pball52998

Well-known member
I did some more experimenting, and I think you should check C23. I was able to replicate what you're measuring in the clock section by removing C23 from the circuit.
Still waiting for my oscilloscope to come in the mail.. soon! I hope..!

By checking for C23, what are you specifically looking for? Signal? Voltage? mhz? Etc

I know you said you were able to replicate it. If I may ask, how?
 

SuperSVGA

Well-known member
By checking for C23, what are you specifically looking for? Signal? Voltage? mhz? Etc
If possible, remove it from the board and test it with the capacitance setting on a multimeter if you have that available. Or just replace it if possible.

I know you said you were able to replicate it. If I may ask, how?
I just put together the main clock circuit since it's not too complex:
IMG_0378.jpeg
You can also see a similar effect in a circuit simulator, but this isn't a perfect representation. Delete the capacitor and reset the simulation, and watch as the clock output flattens around 1V.
 

pball52998

Well-known member
If possible, remove it from the board and test it with the capacitance setting on a multimeter if you have that available. Or just replace it if possible.
Don't have any replacements, but will buy if needed!

Unfortunately my multimeter, fluke 23 doesn't have a capacitance option it seems..

1670376223370.png

Seems they're decently cheap. 120 of them from amazon for $8 https://www.amazon.com/mxuteuk-Mult...uf&qid=1670376375&sprefix=1uf+,aps,317&sr=8-3

I know amazons not desired but I have gift cards there and shipping anywhere for anyone else is at least $5-7, and that seems like a waste for 10 cents worth of parts.

you can check that the capacitors in the oscillator aren't dead-shorted (0 ohms) with an in-circuit resistance check on your multimeter.
I did check this however, c73 tested because it's right beside it.

C23: 623 (no k or m)
C73: 184.5 (no k or m)

Will also check resistors soon if still wanted.

I'm almost hesitant to desolder items before seeing with a more powerful scope, but if the previous scope showed enough evidence I'll start ordering caps/resistors and seeing where I can go.

My mind is still confused on which ones to order though/where to start since unfortunately I don't have a lot of these items. I will buy them though! (As seen through this thread lol)
 

pball52998

Well-known member
Again too easily convinced after reading again, and wanting to work on this thing since it's sitting on my dining room table in pieces!
To test the resistors, you will need to desolder and lift one leg of each out of the board before doing the multimeter check. If all of those test fine you're left with either the crystal or one of the two transistors.
I desoldered one leg per transistor in that line (R49,51,48,90,91) but either these resistors are glued to the board or years of dust and grime has caused this board to stick them to the board.

Unless I force them off the board to try and get a leg out I don't feel too comfortable ripping the legs out. If I really need to rip the leg out I will but as follows for resistance:

R49: 46.8
R51: 74.4
R48: 180.2
R90: 700
R91: 670
R52: 49

Will leave desoldered for a few days in case anyone wants me to test/rip out if really needed.

This oscilloscope can't get here fast enough

On another note, my monitor /// went kaput...

Plugged in my c64 and 5150 to see if I could get any response, it would flash the screen and immediately go blank. Tried turning every button and messing with it in what seems every combination, but nothing.

I have a monitor ii coming that I hope doesn't get damaged, and another crt. Along with flatscreens that take composite. Just another thing to add to the pile to repair.
 

AwkwardPotato

Well-known member
For the time being, I think you're right for not pulling the legs out of the board. If the resistors don't want to come up it's because the through-holes haven't been entirely cleared of solder (the resistors aren't glued), and forcing them up would damage the board.

The bandwidth of your old scope was low enough that the measurements taken with it can be disregarded. Hopefully your new one will be more useful in troubleshooting the ///!
 

pball52998

Well-known member
For the time being, I think you're right for not pulling the legs out of the board. If the resistors don't want to come up it's because the through-holes haven't been entirely cleared of solder (the resistors aren't glued), and forcing them up would damage the board.
Tried again, got one up just fine (only tried one). Was being way too gentle/sensitive at first. Didn't pull or try to warp anything either, so no damage there. More flux, more wick, more time :) Needed to work more around the joint. From the previous post I just hadn't given enough time. Nothing was pulled/yanked though. Really trying my hardest to not damage this board.

Main things I've desoldered were just throw hole caps (analog boards/iisi psu) that I would cut and work around/easily fall right out, and those switches on the keyboard. Learning new techniques and what works as I go.

To be honest, I'll probably get them back, test everything with the new scope (here's to hoping it works better) and probably start a bit fresh of where I was near the beginning of troubleshooting this.

Back to square one entirely! Not a bad thing. Reinforces learning.
 
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SuperSVGA

Well-known member
Unfortunately my multimeter, fluke 23 doesn't have a capacitance option it seems..
You can do a basic test to see if it's working at the very least.
Remove the capacitor from the board and set your multimeter to test resistance. Short both ends of the capacitor, then test the resistance across it. It should very briefly show high resistance increasing then show overload or infinite resistance.
Remove the multimeter leads and then touch them back to the capacitor. It should still show overload or infinite resistance.
Short the capacitor again and repeat the measurement, and you should see behave like it did before, briefly showing high resistance before going to infinite.

Basically all you're doing here is using the small voltage that the multimeter uses to test resistance in order to charge up the capacitor. If the capacitor doesn't ever show infinite resistance or doesn't hold it when you disconnect and reconnect the leads, then it's likely not functioning.
 

ravuya

Active member
Cheapo hardware store multimeters often have a capacitance test. I think my Canadian Tire $8 special can do it.
 

pball52998

Well-known member
R49: 46.8
R51: 74.4
R48: 180.2
R90: 700
R91: 670
R52: 49
For anyone in the future.

R49: yellow, purple, black, gold, 47 ohms
R51: purple, green, black, gold, 75 ohms
R48: brown, silver, brown, gold 180 ohms
R90: brown, green, red, gold, 1.5k ohms
R91: brown, brown, red, gold 1.1k ohms
R51: yellow, purple, black, gold 47 ohms

Remeasured after taking each leg out for me fully everything stayed consistent but I got proper readings from

New:
R90: 1.5k
R91: 1.1k

All resistors are good!
Short both ends of the capacitor, then test the resistance across it.
Hate to ask more stupid questions. do you have a preferred way to do this? More than willing to do it.

Is it something like:
Took a resistor off the old psu, and hooked it to a test capacitor I had laying around. discharged it using alligator clips, then tested.

Unhook clips, Test in resistance mode, I then see what you said with very high then OL.

But on reconnect Iof probes I see it lower, then slowly go back to OL.

Not expected? Or doing it incorrectly?


I basically saw what they did and it worked like that for me.

Was going off this, if that's incorrect and needs another method I'll try on this capacitor before desoldering the tiny ones to the board and doing the wrong thing
 

SuperSVGA

Well-known member
Took a resistor off the old psu, and hooked it to a test capacitor I had laying around. discharged it using alligator clips, then tested.

Unhook clips, Test in resistance mode, I then see what you said with very high then OL.

But on reconnect Iof probes I see it lower, then slowly go back to OL.

Not expected? Or doing it incorrectly?
That sounds right, though it sounds as if your capacitor is draining a bit in between tests, which is probably normal to the spec of capacitor you used to test. It's not the most accurate test either, but it at least verifies basic functionality of the capacitor.
 
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