Macintosh LCII failure

[indibil]

Hi, I recently got an LCII that wouldn't boot. I recapped the power supply, and after that, the LCII powered on, but there was no chime, and the screen was just a blank image.

After that, I recapped the motherboard (just the electrolytic capacitors), but nothing changed. I've tried changing the RAM, the VRAM, removing the hard drive, the floppy drive... and nothing works. If, after turning it on and seeing the blank screen, I quickly turn it off and on again, it doesn't even show the blank screen anymore. I have to turn it off for a few seconds and then turn it on for it to display anything.

Is this a known problem? Does anyone have any idea what could be wrong? The motherboard doesn't seem to have any capacitor damage. I've cleaned everything thoroughly to rule it out, and it still doesn't work.

 

[phunguss]

It is hard to tell with your pic, it is a little out of focus. Take a couple more close up shots of the capacitor farm on the bottom left and the upper left where it looks cloudy.

 

[indibil]

I did another test. I was testing it with a dead battery (0.5V), and I tested it with a new battery (3.5V), and with both I get the same result, but if I remove the battery, I hear the chime of death. I put any battery back in and I don't hear it. The screen is always blank. Even removing the VRAM shows a blank screen.

 

[iigs123]

Is the PSU putting out the right voltages?

 

[indibil]

I am attaching photos that I was able to take yesterday.

As for the PSU, I have tested both the repaired one and the one I use in a fully operational LC. With both, the result was the same.

 

[phunguss]

I am attaching photos that I was able to take yesterday.

As for the PSU, I have tested both the repaired one and the one I use in a fully operational LC. With both, the result was the same.View attachment 26075View attachment 26076View attachment 26077View attachment 26078

Based on these photos, I am going to suggest a thorough cleaning. Completely remove the motherboard and soak it in IPA and gently scrub with a toothbrush. No solder point on the board should be orange or brown, as lead does not rust. It is corrosion from something, most likely capacitor electrolyte.

This look of everything being 'wet' is residue from something (capacitor electrolyte or solder flux). If you take a cotton swab and dip it in IPA and drag across these surfaces, does the cotton swab come out yellow? If yes, it needs a thorough cleaning.

Compare the pins on this chip. The ones in the center do not look the same as the ones on the outer edge. They should all appear similar. It may be possible cold solder joints. Again, more orange/yellow/brown residue, it needs to be cleaned.

This corrosion on the three pin transistor is due to capacitor leakage. the capacitor is not on straight, which makes me believe this board needs a full recap.

Things should not appear this brown and wet/sticky looking.

Thorough cleaning, then reinstall and test. If it is not better, then a full board recap is due. But that is just my opinion.

 

[iigs123]

is the capacitor by UA10, C22 I think, the correct type?
Why not get a cap kit from somewhere like Console5 and redo everything? here is a guide:

Macintosh LC II (Performa 400) - Recap-a-Mac

With 17 surface mount electrolytic capacitors that need replacing, you’ve really gotta love your Mac LC II if you want to keep it...

recapamac.com.au

 

[phunguss]

Here is the cap kit from Console 5 for LC II / 400. $7 is pretty cheap.

 

[indibil]

Based on these photos, I am going to suggest a thorough cleaning. Completely remove the motherboard and soak it in IPA and gently scrub with a toothbrush. No solder point on the board should be orange or brown, as lead does not rust. It is corrosion from something, most likely capacitor electrolyte.
View attachment 26079
This look of everything being 'wet' is residue from something (capacitor electrolyte or solder flux). If you take a cotton swab and dip it in IPA and drag across these surfaces, does the cotton swab come out yellow? If yes, it needs a thorough cleaning.
View attachment 26080
Compare the pins on this chip. The ones in the center do not look the same as the ones on the outer edge. They should all appear similar. It may be possible cold solder joints. Again, more orange/yellow/brown residue, it needs to be cleaned.
View attachment 26081
This corrosion on the three pin transistor is due to capacitor leakage. the capacitor is not on straight, which makes me believe this board needs a full recap.
View attachment 26082
Things should not appear this brown and wet/sticky looking.
View attachment 26083

Thorough cleaning, then reinstall and test. If it is not better, then a full board recap is due. But that is just my opinion.

Okay, I'm going to do a thorough cleaning. I've already done a little, but it doesn't seem to be enough.

As I mentioned in the first post, I've already recapped all the electrolytic capacitors, both on the PSU and the motherboard. That's why they're bent.

 

[indibil]

is the capacitor by UA10, C22 I think, the correct type?
Why not get a cap kit from somewhere like Console5 and redo everything? here is a guide:

Macintosh LC II (Performa 400) - Recap-a-Mac

With 17 surface mount electrolytic capacitors that need replacing, you’ve really gotta love your Mac LC II if you want to keep it...

recapamac.com.au

1uF, like the original.

 

[indibil]

Hello again.

I've thoroughly cleaned the motherboard. It looks much better now, with no traces of acid.

The PSU is supplying +5.2V, +12.3V, and -5.1V when connected to the motherboard and powered on.

It's still the same, just a white screen and no chime. It won't boot.

Could it be the oscillators? Could you tell me where on the motherboard I could check them? I recently got a simple oscilloscope that I could try.

Thanks.

 

[phunguss]

First photo, top right is part Y1, looks like the old mac classic oscillator. Photo 3 looks like two obvious oscillators. I donr’t have schematics, but maybe someone can point those out.

 

[indibil]

Hi.

I have some news .

Since I couldn't get it to work, I cleaned it with a product that has helped me revive old circuits many times, both in consoles and computers. I applied a little, spread it with a brush, and left it for a few days.

Yesterday afternoon I connected the LCII, turned it on, and "chang"!!! It turned on and works perfectly!!!

Just one detail, and I didn't have time to check the voltages, but after a few power-ups, the chime started cutting out at the end, and the last few power-ups, the chime didn't work at all. But the LCII kept starting up and working without any problems, with sound.

Could it be that the PSU isn't providing enough power when it starts up, as it heats up? I don't think it's a motherboard issue because once it's on, the sound works.

 

[indibil]

I'm updating my previous post, as I didn't have much time yesterday and wasn't fully aware of everything.

Today I tried a "modern" PSU with an adapter. And the sound problem persists.

When I power it on from cold, I have a chime and sound, but as it warms up, the sound gradually disappears until after a while there's no sound at all. If I let it cool down, the sound seems to return.

Could UB10 be damaged? I tried pressing it firmly on the power-up to rule out a cold solder joint, but I still have no sound.

If I have sound when it's cold, it shouldn't be a damaged trace, right?

 

[phunguss]

I tried pressing it firmly on the power-up to rule out a cold solder joint, but I still have no sound.

If I have sound when it's cold, it shouldn't be a damaged trace, right?

It is likely a cold solder joint. With thermal expansion, the connection gets broken. Lead free solder is usually the culprit, but I think these models pre-dated the lead free movement. Either way, you may need to reflow some solder joints with some leaded solder.

 

[indibil]

I've checked the solder joints and the traces, and everything's still the same. When I turn it on from cold, I hear the "bing" sound, and then when I play a game (Lemmings), the sound gradually distorts and loses volume...

Insufficient power supply? Which pin on UB10 can I measure the voltage on? What value should I read?

 

[David Cook]

If you want to further narrow down the location of the sound issues, put some headphones on or use an external speaker. If the problem persists, it exists prior to that portion of the sound circuit.

 

[indibil]

If you want to further narrow down the location of the sound issues, put some headphones on or use an external speaker. If the problem persists, it exists prior to that portion of the sound circuit.

Yes, I already tried that, it sounds the same through headphones as through the speaker. Could it be a UB10?

 

[David Cook]

Do you have an oscilloscope? I would measure this point in the circuit and see if the amplitude declines. You might be able to catch this with a voltmeter in peak measurement mode which you reset between playing a sound. Basically, if the voltage levels declines (when you play the beep sound in the control panel over time) at this point, the problem is earlier in the circuit. Or, if the voltage level is about the same but you can hear the speaker volume decline, it is after this point in the circuit.

 

[indibil]

Do you have an oscilloscope? I would measure this point in the circuit and see if the amplitude declines. You might be able to catch this with a voltmeter in peak measurement mode which you reset between playing a sound. Basically, if the voltage levels declines (when you play the beep sound in the control panel over time) at this point, the problem is earlier in the circuit. Or, if the voltage level is about the same but you can hear the speaker volume decline, it is after this point in the circuit.

View attachment 26397

Thanks for the suggestion.

I have a small oscilloscope that I haven't used yet. I connected it to C104 (it's on the back, ceramic) and, as you said, the amplitude has been decreasing. I've attached some videos.

So, where do you suggest the problem might be?