Classic II – won't start after cleaning

[joshc]

So that’s all it was? Working fine with the logic board that wasn’t working now?

I’ve never come across a Classic analog board that didn’t have very leaky caps - I think they were a lot lower quality than the ones used on Plus/SE analog boards. The Classic and Classic II were low cost machines and the analog board design shows it.

 

[blindowl]

Ok, I understand the importance of re-capping the AB, but I won't do that now. The problem seems to be related to the LB (see post #19).

Back to my original question. Any theories on what kind of short or damage could be causing the problems I described? Guessing, a short on an address line (for example) wouldn't stop the computer from starting. Maybe something on the +12 V rail (guessing again)? Where do I start troubleshooting in such case? According to Bomarc's schematics, C5 appears to be part of the +12 V circuit. I will re-solder that cap. And I now see that C14 (connected to U2, which is providing +8 V, right? Don't know what parts of the circuit are using +8 V?) is not attached straight and seems loose (cathode might not be grounded properly), I will re-solder it too. Any other cap I should focus on? Most others appear to be parts of the audio circuit. Please let me know if my theories are completely wrong!

 

[blindowl]

According to this post +8 V is only used by the DFAC chip: Classic II Logic Board +8V rail

Which @joshc mentioned is involved in the machine's startup. So I have to look into that.

 

[blindowl]

Re-soldering C14 did not help.

If the RESET line was stuck, how would the machine then behave when powered on (fan, HDD, CRT)?

 

[joshc]

Are the AB voltages strong with the other LB?

 

[blindowl]

Are the AB voltages strong with the other LB?

Don’t I have time to swap boards at the moment, but just before my cleaning of the faulty board they were at 11,98/5,02.

 

[AwkwardPotato]

If the reset line was stuck low and the power supply was functioning normally, you'd hear the fan running, but the screen would be blank/displaying the initial state of the VRAM (checkerboard, jailbars, etc). No audio either. Typical EGRET issues definitely won't cause instability on the power supply's outputs.

I almost wonder if a solder blob was left on the board during recapping, and cleaning dislodged it such that it's now shorting out a couple of pins somewhere? Might be a bit of a stretch. Also check that you have the ROMs installed in their sockets the correct way around.

 

[blindowl]

If the reset line was stuck low and the power supply was functioning normally, you'd hear the fan running, but the screen would be blank/displaying the initial state of the VRAM (checkerboard, jailbars, etc). No audio either. Typical EGRET issues definitely won't cause instability on the power supply's outputs.

Thanks for the clarification!

I almost wonder if a solder blob was left on the board during recapping, and cleaning dislodged it such that it's now shorting out a couple of pins somewhere? Might be a bit of a stretch. Also check that you have the ROMs installed in their sockets the correct way around.

Yeah ROM's are seated correclty. I actually forgot to put them back after the cleaning so my first thought was that it was an easy fix and just put them back, but unfortunately it wasn't that easy..

Previously I also discovered that some pins on the CPU were bent and perhaps touching. But that wasn't the solution either. I just hope all components are still working and not being fried...

 

[chiptripper]

I’m concerned that you soaked the board in vinegar overnight. I don’t use vinegar as a board cleaner at all. It has some conductivity, and if it isn’t washed away super well it can get trapped under ICs and rot vias, corrode ROM leads, crawl down traces, and so on.

I imagine a little on a toothbrush is OK, but a vinegar soak scares me.

 

[blindowl]

I’m concerned that you soaked the board in vinegar overnight. I don’t use vinegar as a board cleaner at all. It has some conductivity, and if it isn’t washed away super well it can get trapped under ICs and rot vias, corrode ROM leads, crawl down traces, and so on.

I imagine a little on a toothbrush is OK, but a vinegar soak scares me.

Yeah, maybe you're right.. I haven't had any issues with vinegar before, but this time I have obviously damaged things.

Just discovered this, anyone knows what its suppose to connect to, and its value?

 

[joshc]

Vinegar should be ok, generally. A vinegar soak is not uncommon and is good for getting rust off boards.

A missing C102 may not be helping matters. I don't have a Classic II board so I don't know its value.

The most common causes of problems on these boards are dirty Egret legs, cap goo/corrosion/crud on the ICs near caps. The Apple sound chip (DFAC) needs to be clean for successful start.

 

[AwkwardPotato]

Based on its location I'm assuming C102 is the decoupling cap for one/both of the 74LS245s on the flip side of the board. Most likely 0.1uF, 10V or more, 0603 case size, exact value really isn't critical. It being missing might be enough to cause minor system instability but it's definitely not related to the analog board clicking.

Will this analog board boot the Classic II's motherboard with the HDD disconnected from power? Grasping at straws here, but I wonder if the difference in current draw between the Classic I and II motherboards is enough to push a likely-marginal analog board over the edge and start ticking.

 

[rikerjoe]

Yeah, maybe you're right.. I haven't had any issues with vinegar before, but this time I have obviously damaged things.

Just discovered this, anyone knows what its suppose to connect to, and its value?

View attachment 51182

Here is a pic of my Classic II board showing C102, which is marked as A4 = 10 nF


On my board it is connected to +5V and ground. Hope that helps!

 

[joshc]

but I wonder if the difference in current draw between the Classic I and II motherboards is enough to push a likely-marginal analog board over the edge and start ticking.

This is why I still think recapping the analog board should be done first.

 

[blindowl]

Here is a pic of my Classic II board showing C102, which is marked as A4 = 10 nF
View attachment 51191

On my board it is connected to +5V and ground. Hope that helps!

Thank you for checking! Now I know what to replace it with.

 

[blindowl]

Well, would you look at that, it's alive again! Removed, cleaned and re-soldered the Egret chip, plus two caps that were accidentally moved from the heat of the hot air gun. At first boot, same issue as before, just a tick-tick-tick sound from the speaker so I turned it of immediately. Then I though I should let it run for some time to see what will happen. Again, tick-tick-tick from the speaker but suddently it came to life.

So now back to the initial issue.

 

[blindowl]

Picking up from last week. This machine has two issues:

• Sometimes, not often, but sometimes, the screen will stay black on power-on.

or

• Black bars like here:

Even though the voltage rails were very stable and a very clean analog board with no leaky caps (at least to the eye) – I have now re-capped the analog board too. But both issues remain. Voltages are stable at 5.10 V and 12.24 V.

Before the whole LB cleaning mishap, the Mac had the exact same issues. I got it working for a few times after swapping out the RAM modules. But not anymore. I'm now running it with the onboard RAM only to rule out bad memory sticks.

As seen in the picture, bar 3, 4, 7, 8, 11, 12, 15, 16 looks clean, and the rest are garbled. What does that mean? If I repeatedly power off and on the computer the other bars can get garbled too, but normally it looks like in the picture.

As previously mentioned in this thread I have removed and cleaned the Egret chip. I have now also cleaned and re-soldered the RAM chips (without removing them).

This computer has had these exact two issues since I got it. Both before and after re-capping the LB and AB.

I'm curious if bar 1, 2, 5, 6, 9, 10, 13, 14 being garbled points to any specific RAM address and maybe a specific RAM chip being bad?

 

[imactheknife]

I had bars like that, replaced onboard ram.. cant say 100% it solved it as i did some other stuff, but sure it was part of problem on one of my classic ii boards

 

[Fred1212]

On early Macs ROM chips could cause vertical stripe problem, clean and reseat ROMs!. I'd also be suspicious of the onboard RAM chip.

 

[blindowl]

I had bars like that, replaced onboard ram.. cant say 100% it solved it as i did some other stuff, but sure it was part of problem on one of my classic ii boards

Interesting! Maybe I should start with removing and clean the chips (which is a pain..), and eventually replace them.