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Color Classic woes- recapped but no power

TrueNorthStrong

TrueNorthStrong

6502
Hi,

Looking to get some additional input on repairing a color (colour...) classic Macintosh. 

Here's the tests and procedures, in order, that I have done so far:

Pulled motherboard to check power supply functionality- OK

Washed motherboard and reinserted for a basic check- FAIL

Removed rear housing and checked A/B board for leaking caps- OK

Replaced motherboard caps and checked functionality- FAIL

Double checked replacement caps- OK (AFAIK...)

Tried the "remove and insert mobo" trick- FAIL

Checked for the continuity points between the ADB chip and external ADB pins / mobo edge connector- OK

Checked for continuity on the nearby via by the ADB clock- OK

Essentially, I checked all results Google pulled up on the color classic and related repair attempts that had been documented online. There was one here posted about a year ago, but that thread seems to have never been resolved and I'd rather not necro-post it. 

I purchased this Mac to give a go at repairing a compact Mac by my own hands. I've fixed up ones in the past, but have always sent the soldering jobs to others. Seems I'm in a bit over my head now. The recapping went without a hitch, as far as I can tell. They're more or less flat, there's no shorts, no lifted pads, and polarity has been triple checked. 

With the board removed, the power supply starts up well. No whining caps, no delays; sounds brand new.

If anyone has some experience in repairing these machines, I'd greatly appreciate it. I'd really hate to give up and just cheat my way to a functional machine with a replacement board. 

Thanks in advance. 

 
Have you recapped the Analog board as well or only the logic board ?
If you haven't done the analog board yet, it has to be recapped as well, the capacitors are over 20 years old and degraded.

It's normal behavior for a color classic that it powers on without the logic board installed.

If the analog board is recapped then the fault is often on the logic board or the housing's contacts where it slides in.
Clean the copper contacts are the back of the logic board with IPA.

The housing's contacts are difficult to clean. I poor IPA on the copper contacts of the logic board and then slide it into the case for a few times. The rubbing of the contacts will clean the connections after a few times.
Of course do this with the power unplugged.

Do you have a spare logic board from another CC to test ?

Is the Pram battery good as without one a CC won't start.

 
The whole point of my test without the logic board installed was to check that the analog board was at least partially functional. It seems to me that, while it hasn't been recapped, I should be able to at least get it running with whats there. If there are screen issues, I'll get to those fixes later. Right now, I'd trying to get the soft boot going. 

I haven't cleaned the contacts, so I'll aim to try that out in the next day or two. To be sure, I'll just dismantle it and properly clean the edge connector inside. 

I have ran this both with and without a brand new PRAM battery, but a fellow with solid knowledge of these machines has told me that no PRAM battery is necessary for it to start. 

no spare boards at the moment. I will, but not for a few weeks. 

 
TrueNorthStrong said:
The whole point of my test without the logic board installed was to check that the analog board was at least partially functional. It seems to me that, while it hasn't been recapped, I should be able to at least get it running with whats there.

I have ran this both with and without a brand new PRAM battery, but a fellow with solid knowledge of these machines has told me that no PRAM battery is necessary for it to start. 
Click to expand...

There are different revisions of the CC logic board. Some power on without a Pram battery, others don't. I have tested it with my 2x CC machines and they don't power on without Pram battery. 

Ok there's some life in your analog board, but have you checked the voltages to the logic board ?

If they are not within tolerance, it will never power on with the logic board installed.

 
Last edited by a moderator:
nvdeynde said:
There are different revisions of the CC logic board. Some power on without a Pram battery, others don't. I have tested it with my 2x CC machines and they don't power on without Pram battery. 

Ok there's some life in your analog board, but have you checked the voltages to the logic board ?

If they are not within tolerance, it will never power on with the logic board installed.
Click to expand...
I have not, where is the best point to check the voltage to the board? 

MJ313 said:
Might be worth checking this thread below as it has some good info (trace by Y1):

https://www.thinkclassic.org/viewtopic.php?id=537
Click to expand...
I checked that when checking continuity on the ADB chip. It checks out.

mraroid said:
Hi...

Do you have a schematic for the analog board?  Are you going to re cap it?

mraroid
Click to expand...
No schematic, but I've seen lots of resources online regarding recapping the board. I should do that, and with how often I've heard people saying I should, I'll probably just buckle down and do it soon. 

 
Here is a CC analog board cap list from another forum:

0.47uF 100v, 85c [x1]1uF 50v, 85c [x11]2.2uF 100v, 85c [x2]2.2uF 200v, 85c [x4]4.7uF 50v, 85c [x1]10uF 100v, 85c [x1]10uF 250v, 85c [x1]47uF 100v, 105c [x1]100uF 6.3v, 85c [x1]100uF 25v, 85c [x7]100uF 100v, 105c [x2]220uF 25v, 85c [x1]220uF 35v, 85c [x1]330uF 400v, 85c [x1]470uF 25v, 85c [x2]470uF 35v, 85c [x1]1000uF 10v, 105c [x1]1000uF 16v, 85c [x1]1000uF 16v, 105c [x1]1000uF 35v, 85c [x1]3300uF 16v, 85c [x1]3300uF 16v, 105c [x2]5600uF 10v, 105c [x2]Total Caps on Board: 47
Here is the link to the other forum:

https://www.thinkclassic.org/viewtopic.php?id=202

mraroid

 
also keep in mind sliding the logic board in the unit, puts a load on the power supply. if its weak, it wont hold the load. 

With the LB removed, its running unloaded. This can make a BIG difference if theres analog board issues. 

But... Given that, I tend to err on the side of the logic board being at fault here. Given that it has a track record for this very problem. 

 
Last edited by a moderator:
Yeah, I can't shake the feeling that it's something iffy on the motherboard. If there's some common issues I haven't already covered, I'm all ears. Otherwise, I'll be recapping that board in about a week, just to be sure

 
Will post pictures in a few hours. Washed with lightly warmed water and isopropyl. Scrubbed with a soft bristle toothbrush. That was done before the caps were removed, so I made sure to clean under the caps after I pulled them off.

 
Looks okay to me... Some stuff by some of the caps you replaced though, not sure if its the photo or what. Like a white film or layer of dust type thing. Either way, it probably would still turn on? So Im going to say AB. 

Now lets wait for the pros! lol

 
NIce photo TrueNorthSound....  Cleaning looks great!

Do you have any photos of your analog board?

mraroid

 
Johnnya101 said:
Looks okay to me... Some stuff by some of the caps you replaced though, not sure if its the photo or what. Like a white film or layer of dust type thing. Either way, it probably would still turn on? So Im going to say AB. 

Now lets wait for the pros! lol
Click to expand...
Yup, my thoughts exactly. It might be my first recap, but certainly not my first soldering job. That's some left over flux... I really ought to do a post-recap cleaning. It can't hurt, and I can leave it out to dry for a week since the analog board will be out for a week or two. 

agent_js03 said:
I was in a similar situation to you a year ago:

https://68kmla.org/forums/index.php?/topic/27905-macintosh-color-classic-repair-adventure/

I was never able to get soft power on to work. But I was able to hack it so that I could power it directly on using the switch. I guess that was good enough; I ended up selling it for more than twice what I paid for it.
Click to expand...
I did look into that thread, and made the wire bridge near the edge connector. Still a fail, so it's looking more and more like an analog board issue...

mraroid said:
NIce photo TrueNorthSound....  Cleaning looks great!

Do you have any photos of your analog board?

mraroid
Click to expand...
No photos yet, I didn't pull out the board on my days off. I might have time to do it after work, but I'm often too tired and just want to eat dinner + relax. I'll be able to pull it out within a week (I hope...)

With the responses, I'm really coming around to the idea that the power supply is functional under zero load, but simply can't hold any load due to some bad caps. Sounds like I'll have to make a trip down to the store, hopefully they stock nice nichicons. I'd rather not go cheap on it.

inb4 Digikey/mouser, but I'd rather have them immediately as opposed to waiting on shipping.

 
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