Jump to content

Macintosh Classic still suffer from simasimac after recapping the logic board


Recommended Posts

I recently recapped the logic board of Macintosh Classic (the simasimac has appeared before recapping, but has gone better). I have to turn on and off several times until it boots up (most of the times it's easier to boot the machine after it has been turned on for so long). All the voltage appeared to be normal.

Most of the similar case that I've found happened in Macintosh SE/30, and I'm not sure if the troubleshooting I've read here is valid for Macintosh Classic https://jeromevernet.pagesperso-orange.fr/SE 30/Repair Mac.html#Books. This is the only similar problem with the same model that I've found: https://discussions.apple.com/thread/7919401

 

Could it be possibly caused of bad crystal in Y1? Should I try recapping the A/B even though the voltage seems to be normal?

 

This is the history of repair:

- Replaced the CRT with Macintosh Plus

- Replaced the sticky rubber with viton in Quantum HD.

- Recapped the analog board

- Replaced the 2N3904 transistor on the video board

 

IMG_8978.JPG

 

IMG_8673.JPG

 

IMG_8660.JPG

Edited by fatlobster
Link to post
Share on other sites
  • 68kMLA Supporter

Was C3 replaced? That still looks to be an original cap.

 

The logic board photo is not high resolution enough to make it out, but perhaps some of the ICs need a further clean?

 

If you press reset when you get the simasimac, what happens?

Link to post
Share on other sites

When recapping my Classic I found that the pads for caps C5, C6, C8 and C9, while appearing cosmetically fine, had all lifted slightly and reduced the continuity to the lines they attach to. My pet theory is that the proximity to the power connector leads to thermal wear on these parts of the board. If you used the slightly haphazard "desolder a bit, lift the old cap a bit, desolder a bit more" removal method with a soldering iron then you will likely have exacerbated this issue. SMT pads are ultra-fragile and you should always check their connections before fitting new caps. 

 

A thorough cleaning should help with troubleshooting; your board looks a little greasy to me. 

Link to post
Share on other sites
  • 68kMLA Supporter
Posted (edited)

Too late to edit my post, I didn't click the image to view the full version - so now I can see where the problem might be. I can tell C3 has been replaced.

 

There is crud around the Sound chip - this needs sorting. The sound chip is essential to the start process, if anything is shorted around there it's not good news.

 

I would hazard a guess that this board will be a lot more reliable after a full clean.

 

As @PowerMac_G4 is suggesting, check the continuity of the caps you've replaced too.

Edited by joshc
Link to post
Share on other sites
Posted (edited)

I really thank you to everyone, I'm feeling grateful to have this community ever existed. I have attached a photograph after re-cleaning it with IPA. It works good so far (boot with no delay, previously the delay is slightly noticeable) – but I'm not sure in the next morning it will boot up as normal. Will keep everyone posted.

 

21 hours ago, joshc said:

Was C3 replaced? That still looks to be an original cap.

 

The logic board photo is not high resolution enough to make it out, but perhaps some of the ICs need a further clean?

 

If you press reset when you get the simasimac, what happens?

20 hours ago, joshc said:

Too late to edit my post, I didn't click the image to view the full version - so now I can see where the problem might be. I can tell C3 has been replaced.

 

There is crud around the Sound chip - this needs sorting. The sound chip is essential to the start process, if anything is shorted around there it's not good news.

 

I would hazard a guess that this board will be a lot more reliable after a full clean.

 

As @PowerMac_G4 is suggesting, check the continuity of the caps you've replaced too.

 

I think further cleaning will do the work. The reset button works when it boots, but in this case it does nothing. Hmm sound chip, that's what I never thought of before (as I thought a sound is just a sound) – I will check on that.

 

21 hours ago, dochilli said:

Did you clean the board with water and IPA?

 

 

Only with IPA, perhaps I was being too gentle cleaning the board. I haven't tried to clean with water as I'm afraid it will create damage.

 

20 hours ago, PowerMac_G4 said:

When recapping my Classic I found that the pads for caps C5, C6, C8 and C9, while appearing cosmetically fine, had all lifted slightly and reduced the continuity to the lines they attach to. My pet theory is that the proximity to the power connector leads to thermal wear on these parts of the board. If you used the slightly haphazard "desolder a bit, lift the old cap a bit, desolder a bit more" removal method with a soldering iron then you will likely have exacerbated this issue. SMT pads are ultra-fragile and you should always check their connections before fitting new caps. 

 

A thorough cleaning should help with troubleshooting; your board looks a little greasy to me. 

 

When I removed the old cap, I twisted and pulled it off very gently. It does leave its leg on top of the caps, so I have to deal desoldering the leg with desoldering wick. I can see a point that thorough cleaning should help, as I just realised I don't really clean the flux residue.

 

DSCF0633.JPG

Edited by fatlobster
Link to post
Share on other sites
  • 68kMLA Supporter
19 hours ago, fatlobster said:

Hmm sound chip, that's what I never thought of before (as I thought a sound is just a sound) – I will check on that.

 

If I remember correctly, in the Classic the sound chip (for some reason best known to Apple) also monitors the power supply rails and issues the reset to the CPU to turn it on when the voltages are stable.  This is certainly true for the SE, anyway, and the Classic is heavily based on the SE.  So it's entirely possible for sound dodginess to bring the whole machine down.

 

I'd agree that your next steps here are a thorough clean.  Using a cleaner based on distilled water or deionised water is fine, you just have to make sure you dry it properly afterwards.  There are actually plenty of specialist PCB cleaners based on water.  If you wash with IPA after your water wash, and wash thoroughly with IPA, the IPA will actually dissolve the water and help it evaporate; A water+IPA solution is much more prone to evaporate than just water on its own, because chemistry, so it will dry faster and better.

Link to post
Share on other sites
  • 68kMLA Supporter
20 hours ago, fatlobster said:

I can see a point that thorough cleaning should help, as I just realised I don't really clean the flux residue.


Flux on its own shouldn't do harm, but best to clean it all up, as per cheesestraws' great advice. The problem comes from electrolytic leakage which causes shorts in the circuit.

 

20 hours ago, fatlobster said:

Hmm sound chip, that's what I never thought of before (as I thought a sound is just a sound) – I will check on that.


That would be logical - but on these boards (and many other Macs of this era), the sound chip, as @cheesestraws has mentioned, is involved in the RESET circuit so it's a crucial part of the start sequence.

 

Page 9 of the Bomarc schematics for the Classic shows how this works, you can get that here: https://archive.org/details/Macintosh68kSchematics if you want to see which pins to check continuity on.

Link to post
Share on other sites
Posted (edited)
On 3/14/2021 at 9:40 PM, cheesestraws said:

 

If I remember correctly, in the Classic the sound chip (for some reason best known to Apple) also monitors the power supply rails and issues the reset to the CPU to turn it on when the voltages are stable.  This is certainly true for the SE, anyway, and the Classic is heavily based on the SE.  So it's entirely possible for sound dodginess to bring the whole machine down.

 

I'd agree that your next steps here are a thorough clean.  Using a cleaner based on distilled water or deionised water is fine, you just have to make sure you dry it properly afterwards.  There are actually plenty of specialist PCB cleaners based on water.  If you wash with IPA after your water wash, and wash thoroughly with IPA, the IPA will actually dissolve the water and help it evaporate; A water+IPA solution is much more prone to evaporate than just water on its own, because chemistry, so it will dry faster and better.

On 3/14/2021 at 10:14 PM, joshc said:


Flux on its own shouldn't do harm, but best to clean it all up, as per cheesestraws' great advice. The problem comes from electrolytic leakage which causes shorts in the circuit.

 


That would be logical - but on these boards (and many other Macs of this era), the sound chip, as @cheesestraws has mentioned, is involved in the RESET circuit so it's a crucial part of the start sequence.

 

Page 9 of the Bomarc schematics for the Classic shows how this works, you can get that here: https://archive.org/details/Macintosh68kSchematics if you want to see which pins to check continuity on.

 

The previous re-cleaning job is not enough, the simasimac has reappeared.

I decided to do another re-cleaning job to the board thoroughly as everyone have suggests, this time with distilled water+IPA.

I noticed that there are a lot of white residues (I assume it's aluminum) that can't be seen with naked eyes until it dries. I guess these are the root of the problems.

 

One thing that I noticed when I tried powering on again with cold boot in the second I turn it off: simasimac appeared briefly. I assume that the CRT still have the power to immediately show the simasimac during its first boot.

 

Question

Does simasimac is normally appear during its first boot (as it won't be seen because it happened very quick?

And I encountered another form of simasimac that I've never seen before anywhere (something like a glitch - happened when I turn on the mac just right after I switched it off), is this something that I should worry in the future?

 

IMG_9026.JPG

IMG_9021.JPG

IMG_9020.JPG

Edited by fatlobster
Link to post
Share on other sites

That board is really dirty. I would bath it in warm water and soap and scrub it with a soft toothbrush. Take care of Y1! Take the ROM chip off before the bath. Afterwards you can use IPA to clean and dry the board. I use my kitchen oven set to 50-60 degree C for half an hour for drying. Put the ROM back in the orientation like seen in your pictures.

 

My Compacts show the same behavior, like shown in your videos.

 

Edited by dochilli
Link to post
Share on other sites
21 hours ago, fatlobster said:

IMG_9026.JPG

 

Is this the current state of your board‽ If so, this is definitely the source of your trouble. 

 

If I'm totally honest you may have to completely remove the caps you have installed in order to thoroughly clean this machine and get it working properly. It's going to take some fairly intense cleaning to get this board looking the way it should. You probably shouldn't have powered the board up with it looking like this. 

Edited by PowerMac_G4
typo correction
Link to post
Share on other sites
  • 68kMLA Supporter

The board needs properly cleaning. Soapy, warm water, with a tooth brush - you can be fairly vigorous with this but use common sense, as mentioned some components are a little fragile like Y1. IPA soak afterwards to displace the water. Leave it enough time to dry, either using the oven trick, hot air gun, or leaving it to air dry for a few days at least...

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...