Macintosh Classic II blank screen after recap

well Mitch, there is an eaten via or trace some where its usually in the area where the onboard ram is soldered on.

all it takes is one broke eaten trace. look closely.

I agree with Uniserver, I recapped my Classic II that I found in the trash, and now it boots up but no audio but that's fine for me for now. When I have the chance I'll try to fix the audio.

But look over your work, you might have to solder a cap or two and exam the area. Also checked if you shorted something out around the cap.

It is an Enhanced Audio revision Logic board. I checked the traces around the caps and found no breaks. I also ran a diode meter through the ceramic caps at the bottom, and found two that are shorted to ground. These are C18 and C40. They are both connected to the ground plane at the one side. I don't know if they're supposed to be like that or they are really shorted.

Does the Classic II even has any onboard RAM? Any ideas where the traces are most likely eaten?

know this is obvious, but did you give the board a good wash

I had similar problem on a SE30. removed all old capps, washed, recapped, washed again and when powered up ...zip

after 2 days with a magnifying glass could not find anything wrong .was going to give up

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so with nothing to loose I washed it again with toothbrush and alcohol .

lo and behold  she powered up perfect. I don't know if it was some electrelite or a tiny solder ball..........but it worked

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might be worth a try

My board is an early "prototype" Classic II, where it has 4 EPROM chips on sockets instead of ROM chips, and has if I remember correctly it has 4MB on the motherboard above the RAM SIM Sockets - 4 X 441000 chips (4bit x 1mb).

The caps should (not always but they do) go to ground.

You might want to get a set of traditional ROM chips for your Classic II, Elfen. Eventually, one way or another, those EPROM chips will degrade. In another 10 years they will probably be useless, if EPROM chips from the 80's are any indication.

I've removed all the "new" caps to inspect the traces under a magnifying glass. I checked almost all of them for continuity and found no broken traces. I was a bit sloppy when removing old caps, so I scratched the board one or two times near the caps, but even these nearby traces are intact.

I also checked other traces and found nothing visible broken or eaten away. As I said before, this board has no leakage damage.

Perhaps something else? I really want to get this board working, since the Classic II Enhanced rev. boards are rare.

I've snapped some pictures of my board. Perhaps could somebody see better where should I do more checks.

wow that board looks nice and clean.

I've soldered the new caps, but it is still dead as a dodo. I probed a using an oscilloscope around the board, but found no activity, just voltages sitting there. Only the oscillators seem to be running...

After about 15 minutes, only the CPU and the VLSI chip got a bit warm, other chips were cold. The power supply looks okay, as I get 5.00V and 11,92V.

So far I am in a dead end, and don't know where else to check. The traces look all good, even on the bottom side.

I also own a SE/30, can I swap the logic boards with Classic to see if the Classic's II Analog Board works?

Nope. Brightness circuits on Classics are different.

If the CPU or databus was dead, you would still get a checkerboard as the video generation is done purely in logic.

If you get a black screen then you have analog board issues. Or serious logic board failure.

If the RESET line is stuck low, you wont get anything either.

I figured that. SE/30 has manual brightness adjustment.

I borrowed another Classic II from a friend and swapped logic boards. My analog board is fine, as I booted it up with friend's logic board. So my logic board is clearly completely dead, as it also won't start in his Classic II. It also shows blank screen.

The only thing I can imagine is that I fried the logic board with ESD when I recaped it or it was already too far gone even before a recap.

RESET line... hmmm, if I only knew where to check it...

Ok, I got the 68030 pinout and traced the reset line. It is being pulled low.

maybe cap goo leaked under the reset switch causing a short, you do have four caps right there next to it.

have you immersed the board in hot water, and scrubbed it with a brush and soap?  then give it a hot rinse… then a good blast off with the air compressor…  it looks clean but looks can be deciving.

i'v had STRAY CAP GOO  cause me many issues in the past...

also looking at your pictures again.. looks like some of the cap pads look to be partially lifted.. you better check continuity from the pad to the trace and the nearest connection.

also maybe post current pictures of your board right now… with the caps on.

my most favorite tool that i use to scrape traces is this… 

hakko desoldering heater cleaner, of all things...

Thanks. The board was super clean to begin with no visible goo damage. There was very slight leakage under some of the caps when lifted, but no corrosion. I cleaned now the board about 3 times, the last time I left it in isopropyl alcohol overnight and then dried it. None of the pads are lifted, I've checked the continuity a few times to nearby traces, and it they're all good.

So far, I've traced the reset line from the CPU to the two VLSI chips, a 341S0851 chip near the CPU, to a SCSI controller and to sound chip. It gets pulled to 0.19V. I've tried pulling it up via a 1K resistor to a 5V VCC, but it didn't change a thing.

So I guess one of the chips must be the problematic. Also when measuring the reset line to the ground, it looks like it is charging a capacitor, as the resistance goes up. It is about 300 ohms at the start.

EDIT:

I rememmbered that I originally soldered wrong capacitor to the C15, as insetad of 1uF 50V, I've used 10uF 16V. Perhaps this fried something? Also all the tantalums are new and checked with capacitance and ESR meter so they are all within spec.

also if you popped the roms out make sure they went back in right.

u22 - 341-0257

u23 - 341-0261

Roms are in correct places... I've pulled them a few times and the pins are like brand new.

Also found out if I leave the board long enought powered off, when turned on, the reset line will jump to a 3.2V for a second and then drop to 0.2V..

carefully check out these links ok?

https://68kmla.org/forums/index.php?/topic/22873-macintosh-classic-ii-raster-but-no-sound-or-arrow-pointer/

https://68kmla.org/forums/index.php?/topic/22339-simasimac-on-recapped-classic-ii/page-2?hl=u14

I was looking at the hot air gun on my desk for some time now. And I figured, prehaps is the sound IC dead, as I soldered the wrong capacitor. So I took it off. The problem however, presisted.

Then I pulled the U10 (EGRET, 341S0851) and now the reset line isn't stuck anymore.

Finally some progress!!!

The monitor turns on now and I get a checkerboard pattern.

yes,  and if you have a junk LC-II laying around you could borrow parts.  EGRET etc

also stupid question… when you test the board,do you do it with the case on?

sometimes those Reset interrupt fingers can cause you issue.

I have a dead LC III logic board with major battery leakage. I'll swap the EGRET.

What this EGRET even does? ADB and stuff? Should the board boot to the insert disk icon without this chip?

I tested the board with the case removed. Sometimes I tested it without even the board in the computer, held just by piece of cloth agains the bottom rails.

EDIT: Found a list of what Egret and other chips do. Also there is a list of a computers using SWIM chip, that sometimes goes in the Mac Portables.

http://www.mess.org/mess/driver_info/mac_technical_notes

i have good news,  i have a dead screen classic (enhanced sound) II here, i took off the EGRET and like 4 legs fell off of it.. it was rotted out.

cleaned up all the pads, and soldered on a EGRET from a dead LC-III and it works now… the only problem now is the sound is dead… 

so i guess i will work on that.   darn cap goo!.

I swapped the EGRET with the one from the LC III, but I have the same error. The reset line gets pulled low and nothing happens.

So perhaps is also this EGRET chip dead, but I suspect a problem somewhere else.

what error?

you can remove the ASC chip,  that controls reset..

also remove U1 U2 cap goo ooooozes in those and rots em up.

also it has no vram… it uses ram… looks like U14 ram chip can go bad(from cap goo).  good news is the ram chips on the same LC3 Donor board are the same.

Thanks. I'll do that. ASC chip is which one? Hmm, would the bad ram cause blank screen error?

To clear what I've written before: the EGRET chip is not the culprit, as when I swapped it with the one from LCIII, it didn't help at all (I got blank screen). However without the EGRET, I get checkerboard.

Hope that clears it.

I'll post results.

oh the sound chip is U4

I removed the U1, U2 and U4. Also removed the U14 RAM chip. There is no cap goo damage. See the attached pic how clean the traces are

Still the reset line gets stuck on and I get blank screen.

I believe that something connected to the U10 Egret chip must be shorted as without the Egret chip it shows the checkerboard.

Any status with this? Looks like fallen had found a troubled spot under q1. And under the rp on the flip side of the board.

Sorry that is u1 not q1, But looks like there might be some cap goo crust under U2 chip, might want to also look at.

Seems like with these classic ii's. Short out the sound, the whole thing is dead, and that I think is because the sound dac just like in the se30 controls system reset as well.

I am returning to this board after 2 months, the situation is the same.

I've pulled all the small chips, U1,U2,U3,U4,U5,U6,U7,U10,U11,U12,U15, but it will only display checkerboard wihtout U10 present (Egret). Others don't make any difference in operation. I also did the RC1, RC2, RC3 - no difference.

Underneath the chips, all the traces are intact, as this is probably the cleanest old Mac logic board I've ever seen (in the start, there were no leaking capacitors).

Is possible that the other Egret chip is also dead? The other one was pulled from a dead LC III board.

Ok, I've swapped the Egret from another Classic II (Rev. 1) board, but it didn't help at all. The Egret chip was definitely okay, as it works okay on the other board.

Also when I tried the working board with the Egret chip removed, it was completely dead, the exact opposite of what the broken one does, as the broken one does checkerboard without the Egret.

I am running out of ideas, I've already spent about 20 hours on this thing.

Only thing that might help are the schematics, but as for the most of the Macs they're unavailable.

In reviewing this, I read that the egret chip was swapped out several times with other egret chips with the same result. So unless everyone of those egret chip is bad, the problem is not there. It has to be elsewhere. So what's holding down the reset pin on the Classic II? I think the chips other than the Egret chips Uniserver is pointing too are the key, even if the chips are good, their traces and VIAs could be bad and cap goo shorting out traces as well. So start checking traces and VIAs as well around the 'usual suspects'.

It also good to dunk the board in a 3 to 2 parts mixture of distilled water (3) and ammonia (2), and slosh it around for a couple of minutes. This will eliminate what cap good is under the chips. If this liquid turns color (I noticed that it would turn green in many cases), that there was cap goo it eliminated. Then rinse out the board with distilled water and then high proof isopropyl alcohol (I use 70% or higher) Then dry the board with compressed air; if you don't have an air compressor, use a hand held hair dryer set to high air flow and high hot heat. DO NOT USE compressed air in a can.

I know that with an Apple II, if you flex the board back and forth slightly to loosen up chips that are in sockets, you start to break connecting traces at around where sockets are soldered to the trace.

Thanks,

The Egret is fine.

Well, I would be glad if there was any cap goo, but as I said, this board was very clean. And trust me with that, as I recapped at least 50 old Mac's boards, so when I find a clean one, I know it. I cleaned it with a mixture of degreaser and distilled water about 4 times, so I don't think that there is any goo left. Dried in oven at 80 deg. C for 1 hour after every cleaning. Also for the traces and vias, I doubt that there is one broken or shorted, but if it is, I don't think it is from cap goo. I have a feeling that this computer was retired early in its life, as the case is still snow white and the board was extremely clean. Possibly retired from an error that it troubles me now.

I lifted the reset leg from the Egret chip, so now the line stays high. Now it will sometimes boot to the checkerboard and sometimes not. I talked to my electronics friend and he said that if that chip is reseting itself, there must be a problem with something connected to this chip, also my logic says the same.

Before a recap, if I recall correctly, there was checkerboard at all times.

I have the classic II schematics,  but its the 4 rom chip variant. not the 2 rom chip verison.  I think they are pretty close though.

you can pm me if interested.

I finally made some progress. I managed to get the chime and white screen. It looks like there is a broken trace or perhaps a component that likes heat.

If I heat the board with the heatgun in the area underneath the Egret chip it will chime sometimes, sometimes it will do a jailbar pattern, sometimes it will do the checkerboard, and so on. I still have the reset pin lifted from the Egret, so I guess something must be wrong in this area. I checked it with the magnifying glass and removed the chokes for the ADB and audio, but I can't see any signs of anything broken...

eaten trace. 

It must be in a layer you can't see.

Yeah, however I thought that these boards are only 4 layer (bottom, ground, power and top plane)... If it is in a layer that I can't see, is it even possible to repair it somehow?

I also reflowed the capacitors on the bottom side, but it also did nothing. Also replaced the memory chips... It will chime when it is warm (not just under Egret, but also under sound ASIC area), but it freezes immediately after that, so if I reset it, it will do a chime of death and picture will still sometimes come, and sometimes won't after resets. Sometimes it will do a jailbar and sometimes a checkerboard. Also very commonly these two patterns are a bit scrambled, but not much, just pixels shifted a bit...

Any thoughts on that?

Not that this helps, but i registered because I recapped my classic II 2 years ago, when i pulled it out for use after working for 8 hrs or so i got the lines down the screen and no chime, so I ended up taking the board out and scrubbed it real good put it back in and its working fine, I must have missed some corrosion.

These guys arnt 4 layer, I believe they are 6 layer. But, the SE/30 its hard to tell if its 4 or 6, but they definitely run traces on the inner layers. But, its also possible it is a 4-layer, but they only use 1 layer for ground fill, and they use a 2nd layer for VCC traces, and regular traces. 

Only way to tell is take a sacrificial/battery acid board, strip it down to the bare PCB only, and grind/shave it off. one layer at a time, and document. 

is it even possible to repair it somehow?

Click to expand...

sure with a patch wire and the schematics.

uniserver said:

sure with a patch wire and the schematics.

Click to expand...

That def. seems like something someone would send to you rather than try themselves. On the other hand, maybe I'm just a wuss. I just prefer professionals fix my stuff, I love my compacts too much to risk them on my own repairs.

ill tell you guys what... i have seen some battery destroyed boards fixed by techknight. with traces/pads and VIA's complete shot... 

and wires ran all over like spaghetti that techknight fixed,  That man has some sickening patience.